nts: save new server keys on start

If ntsdumpdir is specified and the server NTS keys are not reloaded from the file, save the generated keys on start instead of waiting for the first rotation or exit. This allows the keys to be shared with another server without having to use the dump command.
conf: free refclock strings on exit
2025-12-03 17:45:07 -05:00 · 2020-10-07 17:27:34 +02:00 · 2020-10-07 17:27:34 +02:00 · 2020-10-07 17:27:34 +02:00 · 2020-10-07 17:27:32 +02:00 · 2020-10-05 18:56:37 +02:00
160 changed files with 17258 additions and 3928 deletions
--- a/Makefile.in
+++ b/Makefile.in
@@ -21,44 +21,42 @@
 #
 # Makefile template

-SYSCONFDIR=@SYSCONFDIR@
-BINDIR=@BINDIR@
-SBINDIR=@SBINDIR@
-LOCALSTATEDIR=@LOCALSTATEDIR@
-CHRONYVARDIR=@CHRONYVARDIR@
+SYSCONFDIR = @SYSCONFDIR@
+BINDIR = @BINDIR@
+SBINDIR = @SBINDIR@
+LOCALSTATEDIR = @LOCALSTATEDIR@
+CHRONYVARDIR = @CHRONYVARDIR@
+DESTDIR =

 CC = @CC@
 CFLAGS = @CFLAGS@
 CPPFLAGS = @CPPFLAGS@
+LDFLAGS = @LDFLAGS@

-DESTDIR=
-
-HASH_OBJ = @HASH_OBJ@
+EXTRA_OBJS = @EXTRA_OBJS@

 OBJS = array.o cmdparse.o conf.o local.o logging.o main.o memory.o \
-       reference.o regress.o rtc.o samplefilt.o sched.o sources.o sourcestats.o stubs.o \
-       smooth.o sys.o sys_null.o tempcomp.o util.o $(HASH_OBJ)
+       reference.o regress.o rtc.o samplefilt.o sched.o socket.o sources.o sourcestats.o \
+       stubs.o smooth.o sys.o sys_null.o tempcomp.o util.o $(EXTRA_OBJS)

-EXTRA_OBJS=@EXTRA_OBJECTS@
+EXTRA_CLI_OBJS = @EXTRA_CLI_OBJS@

 CLI_OBJS = array.o client.o cmdparse.o getdate.o memory.o nameserv.o \
-           pktlength.o util.o $(HASH_OBJ)
+           pktlength.o socket.o util.o $(EXTRA_CLI_OBJS)

-ALL_OBJS = $(OBJS) $(EXTRA_OBJS) $(CLI_OBJS)
+ALL_OBJS = $(OBJS) $(CLI_OBJS)

-LDFLAGS = @LDFLAGS@
 LIBS = @LIBS@
-
-EXTRA_LIBS=@EXTRA_LIBS@
-EXTRA_CLI_LIBS=@EXTRA_CLI_LIBS@
+EXTRA_LIBS = @EXTRA_LIBS@
+EXTRA_CLI_LIBS = @EXTRA_CLI_LIBS@

 # Until we have a main procedure we can link, just build object files
 # to test compilation

 all : chronyd chronyc

-chronyd : $(OBJS) $(EXTRA_OBJS)
-	$(CC) $(CFLAGS) -o chronyd $(OBJS) $(EXTRA_OBJS) $(LDFLAGS) $(LIBS) $(EXTRA_LIBS)
+chronyd : $(OBJS)
+	$(CC) $(CFLAGS) -o chronyd $(OBJS) $(LDFLAGS) $(LIBS) $(EXTRA_LIBS)

 chronyc : $(CLI_OBJS)
 	$(CC) $(CFLAGS) -o chronyc $(CLI_OBJS) $(LDFLAGS) $(LIBS) $(EXTRA_CLI_LIBS)
@@ -70,6 +68,7 @@ distclean : clean
 	-rm -f Makefile config.h config.log

 clean :
+	$(MAKE) -C test/unit clean
 	-rm -f *.o *.s chronyc chronyd core.* *~
 	-rm -f *.gcda *.gcno
 	-rm -rf .deps
@@ -121,7 +120,7 @@ check : chronyd chronyc
 	cd test/system && ./run

 print-chronyd-objects :
-	@echo $(OBJS) $(EXTRA_OBJS)
+	@echo $(OBJS)

 Makefile : Makefile.in configure
 	@echo
@@ -135,4 +134,6 @@ Makefile : Makefile.in configure
 .deps/%.d: %.c | .deps
 	@$(CC) -MM $(CPPFLAGS) -MT '$(<:%.c=%.o) $@' $< -o $@

+ifndef NODEPS
 -include $(ALL_OBJS:%.o=.deps/%.d)
+endif
--- a/53
+++ b/53
@@ -1,3 +1,56 @@
+New in version 4.0
+==================
+
+Enhancements
+------------
+* Add support for Network Time Security (NTS) authentication
+* Add support for AES-CMAC keys (AES128, AES256) with Nettle
+* Add authselectmode directive to control selection of unauthenticated sources
+* Add binddevice, bindacqdevice, bindcmddevice directives
+* Add confdir directive to better support fragmented configuration
+* Add sourcedir directive and "reload sources" command to support dynamic
+  NTP sources specified in files
+* Add clockprecision directive
+* Add dscp directive to set Differentiated Services Code Point (DSCP)
+* Add -L option to limit log messages by severity
+* Add -p option to print whole configuration with included files
+* Add -U option to allow start under non-root user
+* Allow maxsamples to be set to 1 for faster update with -q/-Q option
+* Avoid replacing NTP sources with sources that have unreachable address
+* Improve pools to repeat name resolution to get "maxsources" sources
+* Improve source selection with trusted sources
+* Improve NTP loop test to prevent synchronisation to itself
+* Repeat iburst when NTP source is switched from offline state to online
+* Update clock synchronisation status and leap status more frequently
+* Update seccomp filter
+* Add "add pool" command
+* Add "reset sources" command to drop all measurements
+* Add authdata command to print details about NTP authentication
+* Add selectdata command to print details about source selection
+* Add -N option and sourcename command to print original names of sources
+* Add -a option to some commands to print also unresolved sources
+* Add -k, -p, -r options to clients command to select, limit, reset data
+
+Bug fixes
+---------
+* Don't set interface for NTP responses to allow asymmetric routing
+* Handle RTCs that don't support interrupts
+* Respond to command requests with correct address on multihomed hosts
+
+Removed features
+----------------
+* Drop support for RIPEMD keys (RMD128, RMD160, RMD256, RMD320)
+* Drop support for long (non-standard) MACs in NTPv4 packets (chrony 2.x
+  clients using non-MD5/SHA1 keys need to use option "version 3")
+* Drop support for line editing with GNU Readline
+
+New in version 3.5.1
+====================
+
+Security fixes
+--------------
+* Create new file when writing pidfile (CVE-2020-14367)
+
 New in version 3.5
 ==================

--- a/41
+++ b/41
@@ -29,9 +29,7 @@ What will chrony run on?

 The software is known to work on Linux, FreeBSD, NetBSD, macOS and
 Solaris.  Closely related systems may work too.  Any other system will
-likely require a porting exercise.  You would need to start from one
-of the existing system-specific drivers and look into the quirks of
-certain system calls and the kernel on your target system.
+likely require a porting exercise.

 How do I set it up?
 ===================
@@ -55,24 +53,20 @@ Where are new versions announced?
 =================================

 There is a low volume mailing list where new versions and other
-important news relating to chrony is announced.  You can join this list
+important news relating to chrony are announced.  You can join this list
 by sending mail with the subject "subscribe" to

 chrony-announce-request@chrony.tuxfamily.org

-These messages will be copied to chrony-users (see below).
-
 How can I get support for chrony?
-and where can I discuss new features, possible bugs etc?
-========================================================
+=================================

-There are 3 mailing lists relating to chrony.  chrony-announce was
-mentioned above.  chrony-users is a users' discussion list, e.g. for
-general questions and answers about using chrony.  chrony-dev is a more
-technical list, e.g. for discussing how new features should be
-implemented, exchange of information between developers etc.  To
-subscribe to either of these lists, send a message with the subject
-"subscribe" to
+There are two other mailing lists relating to chrony.  chrony-users is a
+discussion list for users, e.g. for questions about chrony configuration
+and bug reports.  chrony-dev is a more technical list for developers,
+e.g. for submitting patches and discussing how new features should be
+implemented.  To subscribe to either of these lists, send a message with
+the subject "subscribe" to

 chrony-users-request@chrony.tuxfamily.org
 or
@@ -80,12 +74,6 @@ chrony-dev-request@chrony.tuxfamily.org

 as applicable.

-When you are reporting a bug, please send us all the information you can.
-Unfortunately, chrony has proven to be one of those programs where it is very
-difficult to reproduce bugs in a different environment. So we may have to
-interact with you quite a lot to obtain enough extra logging and tracing to
-pin-point the problem in some cases. Please be patient and plan for this!
-
 License
 =======

@@ -100,18 +88,20 @@ Miroslav Lichvar <mlichvar@redhat.com>
 Acknowledgements
 ================

-In writing the chronyd program, extensive use has been made of RFC 1305
-and RFC 5905, written by David Mills. The source code of the NTP reference
-implementation has been used to check the details of the protocol.
+In writing the chronyd program, extensive use has been made of the NTPv3 (RFC
+1305) and NTPv4 (RFC 5905) specification.  The source code of the xntpd/ntpd
+implementation written by Dennis Fergusson, Lars Mathiesen, David Mills, and
+others, has been used to check the details of the protocol.

 The following people have provided patches and other major contributions
-to the program :
+to chrony:

 Lonnie Abelbeck <lonnie@abelbeck.com>
 Benny Lyne Amorsen <benny@amorsen.dk>
 Andrew Bishop <amb@gedanken.demon.co.uk>
 Vincent Blut <vincent.debian@free.fr>
 Stephan I. Boettcher <stephan@nevis1.columbia.edu>
+David Bohman <debohman@gmail.com>
 Goswin Brederlow <brederlo@informatik.uni-tuebingen.de>
 Leigh Brown <leigh@solinno.co.uk>
 Erik Bryer <ebryer@spots.ab.ca>
@@ -120,6 +110,7 @@ Bryan Christianson <bryan@whatroute.net>
 Juliusz Chroboczek <jch@pps.jussieu.fr>
 Christian Ehrhardt <christian.ehrhardt@canonical.com>
 Paul Elliott <pelliott@io.com>
+Robert Fairley <rfairley@redhat.com>
 Stefan R. Filipek <srfilipek@gmail.com>
 Mike Fleetwood <mike@rockover.demon.co.uk>
 Alexander Gretencord <arutha@gmx.de>
--- a/addressing.h
+++ b/addressing.h
@@ -30,16 +30,19 @@
 #include "sysincl.h"

 /* This type is used to represent an IPv4 address or IPv6 address.
+   Addresses which are not resolved yet can be represented with an ID.
   All parts are in HOST order, NOT network order. */

 #define IPADDR_UNSPEC 0
 #define IPADDR_INET4 1
 #define IPADDR_INET6 2
+#define IPADDR_ID 3

 typedef struct {
  union { 
    uint32_t in4;
    uint8_t in6[16];
+    uint32_t id;
  } addr;
  uint16_t family;
  uint16_t _pad;
@@ -47,8 +50,10 @@ typedef struct {

 typedef struct {
  IPAddr ip_addr;
-  unsigned short port;
-} NTP_Remote_Address;
+  uint16_t port;
+} IPSockAddr;
+
+typedef IPSockAddr NTP_Remote_Address;

 #define INVALID_IF_INDEX -1

--- a/addrfilt.c
+++ b/addrfilt.c
@@ -247,6 +247,8 @@ set_subnet_(ADF_AuthTable table,
          set_subnet(&table->base6, ip6, 4, 0, new_state, delete_children) == ADF_SUCCESS)
        return ADF_SUCCESS;
      break;
+    default:
+      break;
  }

  return ADF_BADSUBNET;
@@ -359,9 +361,9 @@ ADF_IsAllowed(ADF_AuthTable table,
    case IPADDR_INET6:
      split_ip6(ip_addr, ip6);
      return check_ip_in_node(&table->base6, ip6);
+    default:
+      return 0;
  }
-
-  return 0;
 }

 /* ================================================== */
--- a/candm.h
+++ b/candm.h
@@ -101,7 +101,14 @@
 #define REQ_ADD_PEER3 61
 #define REQ_SHUTDOWN 62
 #define REQ_ONOFFLINE 63
-#define N_REQUEST_TYPES 64
+#define REQ_ADD_SOURCE 64
+#define REQ_NTP_SOURCE_NAME 65
+#define REQ_RESET_SOURCES 66
+#define REQ_AUTH_DATA 67
+#define REQ_CLIENT_ACCESSES_BY_INDEX3 68
+#define REQ_SELECT_DATA 69
+#define REQ_RELOAD_SOURCES 70
+#define N_REQUEST_TYPES 71

 /* Structure used to exchange timespecs independent of time_t size */
 typedef struct {
@@ -245,6 +252,11 @@ typedef struct {
  int32_t EOR;
 } REQ_Ac_Check;

+/* Source types in NTP source requests */
+#define REQ_ADDSRC_SERVER 1
+#define REQ_ADDSRC_PEER 2
+#define REQ_ADDSRC_POOL 3
+
 /* Flags used in NTP source requests */
 #define REQ_ADDSRC_ONLINE 0x1
 #define REQ_ADDSRC_AUTOOFFLINE 0x2
@@ -255,9 +267,11 @@ typedef struct {
 #define REQ_ADDSRC_REQUIRE 0x40
 #define REQ_ADDSRC_INTERLEAVED 0x80
 #define REQ_ADDSRC_BURST 0x100
+#define REQ_ADDSRC_NTS 0x200

 typedef struct {
-  IPAddr ip_addr;
+  uint32_t type;
+  uint8_t name[256];
  uint32_t port;
  int32_t minpoll;
  int32_t maxpoll;
@@ -269,6 +283,7 @@ typedef struct {
  int32_t min_samples;
  int32_t max_samples;
  uint32_t authkey;
+  uint32_t nts_port;
  Float max_delay;
  Float max_delay_ratio;
  Float max_delay_dev_ratio;
@@ -309,6 +324,8 @@ typedef struct {
 typedef struct {
  uint32_t first_index;
  uint32_t n_clients;
+  uint32_t min_hits;
+  uint32_t reset;
  int32_t EOR;
 } REQ_ClientAccessesByIndex;

@@ -335,6 +352,21 @@ typedef struct {
  int32_t EOR;
 } REQ_NTPData;

+typedef struct {
+  IPAddr ip_addr;
+  int32_t EOR;
+} REQ_NTPSourceName;
+
+typedef struct {
+  IPAddr ip_addr;
+  int32_t EOR;
+} REQ_AuthData;
+
+typedef struct {
+  uint32_t index;
+  int32_t EOR;
+} REQ_SelectData;
+
 /* ================================================== */

 #define PKT_TYPE_CMD_REQUEST 1
@@ -373,7 +405,8 @@ typedef struct {
   Version 6 (no authentication) : changed format of client accesses by index
   (using new request/reply types) and manual timestamp, added new fields and
   flags to NTP source request and report, made length of manual list constant,
-   added new commands: ntpdata, refresh, serverstats, shutdown
+   added new commands: authdata, ntpdata, onoffline, refresh, reset,
+   selectdata, serverstats, shutdown, sourcename
 */

 #define PROTO_VERSION_NUMBER 6
@@ -387,8 +420,8 @@ typedef struct {
 #define PROTO_VERSION_PADDING 6

 /* The maximum length of padding in request packet, currently
-   defined by MANUAL_LIST */
-#define MAX_PADDING_LENGTH 396
+   defined by CLIENT_ACCESSES_BY_INDEX3 */
+#define MAX_PADDING_LENGTH 484

 /* ================================================== */

@@ -437,6 +470,9 @@ typedef struct {
    REQ_ReselectDistance reselect_distance;
    REQ_SmoothTime smoothtime;
    REQ_NTPData ntp_data;
+    REQ_NTPSourceName ntp_source_name;
+    REQ_AuthData auth_data;
+    REQ_SelectData select_data;
  } data; /* Command specific parameters */

  /* Padding used to prevent traffic amplification.  It only defines the
@@ -473,7 +509,12 @@ typedef struct {
 #define RPY_NTP_DATA 16
 #define RPY_MANUAL_TIMESTAMP2 17
 #define RPY_MANUAL_LIST2 18
-#define N_REPLY_TYPES 19
+#define RPY_NTP_SOURCE_NAME 19
+#define RPY_AUTH_DATA 20
+#define RPY_CLIENT_ACCESSES_BY_INDEX3 21
+#define RPY_SERVER_STATS2 22
+#define RPY_SELECT_DATA 23
+#define N_REPLY_TYPES 24

 /* Status codes */
 #define STT_SUCCESS 0
@@ -497,6 +538,7 @@ typedef struct {
 #define STT_INVALIDAF 17
 #define STT_BADPKTVERSION 18
 #define STT_BADPKTLENGTH 19
+#define STT_INVALIDNAME 21

 typedef struct {
  int32_t EOR;
@@ -511,17 +553,12 @@ typedef struct {
 #define RPY_SD_MD_PEER   1
 #define RPY_SD_MD_REF    2

-#define RPY_SD_ST_SYNC 0
-#define RPY_SD_ST_UNREACH 1
+#define RPY_SD_ST_SELECTED 0
+#define RPY_SD_ST_NONSELECTABLE 1
 #define RPY_SD_ST_FALSETICKER 2
 #define RPY_SD_ST_JITTERY 3
-#define RPY_SD_ST_CANDIDATE 4
-#define RPY_SD_ST_OUTLIER 5
-
-#define RPY_SD_FLAG_NOSELECT 0x1
-#define RPY_SD_FLAG_PREFER 0x2
-#define RPY_SD_FLAG_TRUST 0x4
-#define RPY_SD_FLAG_REQUIRE 0x8
+#define RPY_SD_ST_UNSELECTED 4
+#define RPY_SD_ST_SELECTABLE 5

 typedef struct {
  IPAddr ip_addr;
@@ -590,14 +627,17 @@ typedef struct {
 typedef struct {
  IPAddr ip;
  uint32_t ntp_hits;
+  uint32_t nke_hits;
  uint32_t cmd_hits;
  uint32_t ntp_drops;
+  uint32_t nke_drops;
  uint32_t cmd_drops;
  int8_t ntp_interval;
+  int8_t nke_interval;
  int8_t cmd_interval;
  int8_t ntp_timeout_interval;
-  int8_t pad;
  uint32_t last_ntp_hit_ago;
+  uint32_t last_nke_hit_ago;
  uint32_t last_cmd_hit_ago;
 } RPY_ClientAccesses_Client;

@@ -611,10 +651,13 @@ typedef struct {

 typedef struct {
  uint32_t ntp_hits;
+  uint32_t nke_hits;
  uint32_t cmd_hits;
  uint32_t ntp_drops;
+  uint32_t nke_drops;
  uint32_t cmd_drops;
  uint32_t log_drops;
+  uint32_t ntp_auth_hits;
  int32_t EOR;
 } RPY_ServerStats;

@@ -688,6 +731,50 @@ typedef struct {
  int32_t EOR;
 } RPY_NTPData;

+typedef struct {
+  uint8_t name[256];
+  int32_t EOR;
+} RPY_NTPSourceName;
+
+#define RPY_AD_MD_NONE 0
+#define RPY_AD_MD_SYMMETRIC 1
+#define RPY_AD_MD_NTS 2
+
+typedef struct {
+  uint16_t mode;
+  uint16_t key_type;
+  uint32_t key_id;
+  uint16_t key_length;
+  uint16_t ke_attempts;
+  uint32_t last_ke_ago;
+  uint16_t cookies;
+  uint16_t cookie_length;
+  uint16_t nak;
+  uint16_t pad;
+  int32_t EOR;
+} RPY_AuthData;
+
+#define RPY_SD_OPTION_NOSELECT 0x1
+#define RPY_SD_OPTION_PREFER 0x2
+#define RPY_SD_OPTION_TRUST 0x4
+#define RPY_SD_OPTION_REQUIRE 0x8
+
+typedef struct {
+  uint32_t ref_id;
+  IPAddr ip_addr;
+  uint8_t state_char;
+  uint8_t authentication;
+  uint8_t leap;
+  uint8_t pad;
+  uint16_t conf_options;
+  uint16_t eff_options;
+  uint32_t last_sample_ago;
+  Float score;
+  Float lo_limit;
+  Float hi_limit;
+  int32_t EOR;
+} RPY_SelectData;
+
 typedef struct {
  uint8_t version;
  uint8_t pkt_type;
@@ -717,6 +804,9 @@ typedef struct {
    RPY_Activity activity;
    RPY_Smoothing smoothing;
    RPY_NTPData ntp_data;
+    RPY_NTPSourceName ntp_source_name;
+    RPY_AuthData auth_data;
+    RPY_SelectData select_data;
  } data; /* Reply specific parameters */

 } CMD_Reply;
--- a/client.c
+++ b/client.c
--- a/clientlog.c
+++ b/clientlog.c
@@ -44,20 +44,17 @@
 #include "util.h"
 #include "logging.h"

+#define MAX_SERVICES 3
+
 typedef struct {
  IPAddr ip_addr;
-  uint32_t last_ntp_hit;
-  uint32_t last_cmd_hit;
-  uint32_t ntp_hits;
-  uint32_t cmd_hits;
-  uint16_t ntp_drops;
-  uint16_t cmd_drops;
-  uint16_t ntp_tokens;
-  uint16_t cmd_tokens;
-  int8_t ntp_rate;
-  int8_t cmd_rate;
+  uint32_t last_hit[MAX_SERVICES];
+  uint32_t hits[MAX_SERVICES];
+  uint16_t drops[MAX_SERVICES];
+  uint16_t tokens[MAX_SERVICES];
+  int8_t rate[MAX_SERVICES];
  int8_t ntp_timeout_rate;
-  uint8_t flags;
+  uint8_t drop_flags;
  NTP_int64 ntp_rx_ts;
  NTP_int64 ntp_tx_ts;
 } Record;
@@ -104,15 +101,12 @@ static uint32_t ts_offset;
 #define MIN_LIMIT_BURST 1
 #define MAX_LIMIT_BURST 255

-static uint16_t max_ntp_tokens;
-static uint16_t max_cmd_tokens;
-static uint16_t ntp_tokens_per_packet;
-static uint16_t cmd_tokens_per_packet;
+static uint16_t max_tokens[MAX_SERVICES];
+static uint16_t tokens_per_hit[MAX_SERVICES];

 /* Reduction of token rates to avoid overflow of 16-bit counters.  Negative
   shift is used for coarse limiting with intervals shorter than -TS_FRAC. */
-static int ntp_token_shift;
-static int cmd_token_shift;
+static int token_shift[MAX_SERVICES];

 /* Rates at which responses are randomly allowed (in log2) when the
   buckets don't have enough tokens.  This is necessary in order to
@@ -122,23 +116,18 @@ static int cmd_token_shift;
 #define MIN_LEAK_RATE 1
 #define MAX_LEAK_RATE 4

-static int ntp_leak_rate;
-static int cmd_leak_rate;
+static int leak_rate[MAX_SERVICES];

-/* Flag indicating whether the last response was dropped */
-#define FLAG_NTP_DROPPED 0x1
-
-/* NTP limit interval in log2 */
-static int ntp_limit_interval;
+/* Limit intervals in log2 */
+static int limit_interval[MAX_SERVICES];

 /* Flag indicating whether facility is turned on or not */
 static int active;

 /* Global statistics */
-static uint32_t total_ntp_hits;
-static uint32_t total_cmd_hits;
-static uint32_t total_ntp_drops;
-static uint32_t total_cmd_drops;
+static uint32_t total_hits[MAX_SERVICES];
+static uint32_t total_drops[MAX_SERVICES];
+static uint32_t total_ntp_auth_hits;
 static uint32_t total_record_drops;

 #define NSEC_PER_SEC 1000000000U
@@ -161,12 +150,28 @@ compare_ts(uint32_t x, uint32_t y)

 /* ================================================== */

+static int
+compare_total_hits(Record *x, Record *y)
+{
+  uint32_t x_hits, y_hits;
+  int i;
+
+  for (i = 0, x_hits = y_hits = 0; i < MAX_SERVICES; i++) {
+    x_hits += x->hits[i];
+    y_hits += y->hits[i];
+  }
+
+  return x_hits > y_hits ? 1 : -1;
+}
+
+/* ================================================== */
+
 static Record *
 get_record(IPAddr *ip)
 {
-  unsigned int first, i;
-  time_t last_hit, oldest_hit = 0;
+  uint32_t last_hit = 0, oldest_hit = 0;
  Record *record, *oldest_record;
+  unsigned int first, i, j;

  if (!active || (ip->family != IPADDR_INET4 && ip->family != IPADDR_INET6))
    return NULL;
@@ -184,12 +189,13 @@ get_record(IPAddr *ip)
      if (record->ip_addr.family == IPADDR_UNSPEC)
        break;

-      last_hit = compare_ts(record->last_ntp_hit, record->last_cmd_hit) > 0 ?
-                 record->last_ntp_hit : record->last_cmd_hit;
+      for (j = 0; j < MAX_SERVICES; j++) {
+        if (j == 0 || compare_ts(last_hit, record->last_hit[j]) < 0)
+          last_hit = record->last_hit[j];
+      }

      if (!oldest_record || compare_ts(oldest_hit, last_hit) > 0 ||
-          (oldest_hit == last_hit && record->ntp_hits + record->cmd_hits <
-           oldest_record->ntp_hits + oldest_record->cmd_hits)) {
+          (oldest_hit == last_hit && compare_total_hits(oldest_record, record) > 0)) {
        oldest_record = record;
        oldest_hit = last_hit;
      }
@@ -211,14 +217,18 @@ get_record(IPAddr *ip)
  }

  record->ip_addr = *ip;
-  record->last_ntp_hit = record->last_cmd_hit = INVALID_TS;
-  record->ntp_hits = record->cmd_hits = 0;
-  record->ntp_drops = record->cmd_drops = 0;
-  record->ntp_tokens = max_ntp_tokens;
-  record->cmd_tokens = max_cmd_tokens;
-  record->ntp_rate = record->cmd_rate = INVALID_RATE;
+  for (i = 0; i < MAX_SERVICES; i++)
+    record->last_hit[i] = INVALID_TS;
+  for (i = 0; i < MAX_SERVICES; i++)
+    record->hits[i] = 0;
+  for (i = 0; i < MAX_SERVICES; i++)
+    record->drops[i] = 0;
+  for (i = 0; i < MAX_SERVICES; i++)
+    record->tokens[i] = max_tokens[i];
+  for (i = 0; i < MAX_SERVICES; i++)
+    record->rate[i] = INVALID_RATE;
  record->ntp_timeout_rate = INVALID_RATE;
-  record->flags = 0;
+  record->drop_flags = 0;
  UTI_ZeroNtp64(&record->ntp_rx_ts);
  UTI_ZeroNtp64(&record->ntp_tx_ts);

@@ -306,31 +316,43 @@ set_bucket_params(int interval, int burst, uint16_t *max_tokens,
 void
 CLG_Initialise(void)
 {
-  int interval, burst, leak_rate;
+  int i, interval, burst, lrate;

-  max_ntp_tokens = max_cmd_tokens = 0;
-  ntp_tokens_per_packet = cmd_tokens_per_packet = 0;
-  ntp_token_shift = cmd_token_shift = 0;
-  ntp_leak_rate = cmd_leak_rate = 0;
-  ntp_limit_interval = MIN_LIMIT_INTERVAL;
+  for (i = 0; i < MAX_SERVICES; i++) {
+    max_tokens[i] = 0;
+    tokens_per_hit[i] = 0;
+    token_shift[i] = 0;
+    leak_rate[i] = 0;
+    limit_interval[i] = MIN_LIMIT_INTERVAL;

-  if (CNF_GetNTPRateLimit(&interval, &burst, &leak_rate)) {
-    set_bucket_params(interval, burst, &max_ntp_tokens, &ntp_tokens_per_packet,
-                      &ntp_token_shift);
-    ntp_leak_rate = CLAMP(MIN_LEAK_RATE, leak_rate, MAX_LEAK_RATE);
-    ntp_limit_interval = CLAMP(MIN_LIMIT_INTERVAL, interval, MAX_LIMIT_INTERVAL);
-  }
+    switch (i) {
+      case CLG_NTP:
+        if (!CNF_GetNTPRateLimit(&interval, &burst, &lrate))
+          continue;
+        break;
+      case CLG_NTSKE:
+        if (!CNF_GetNtsRateLimit(&interval, &burst, &lrate))
+          continue;
+        break;
+      case CLG_CMDMON:
+        if (!CNF_GetCommandRateLimit(&interval, &burst, &lrate))
+          continue;
+        break;
+      default:
+        assert(0);
+    }

-  if (CNF_GetCommandRateLimit(&interval, &burst, &leak_rate)) {
-    set_bucket_params(interval, burst, &max_cmd_tokens, &cmd_tokens_per_packet,
-                      &cmd_token_shift);
-    cmd_leak_rate = CLAMP(MIN_LEAK_RATE, leak_rate, MAX_LEAK_RATE);
+    set_bucket_params(interval, burst, &max_tokens[i], &tokens_per_hit[i], &token_shift[i]);
+    leak_rate[i] = CLAMP(MIN_LEAK_RATE, lrate, MAX_LEAK_RATE);
+    limit_interval[i] = CLAMP(MIN_LIMIT_INTERVAL, interval, MAX_LIMIT_INTERVAL);
  }

  active = !CNF_GetNoClientLog();
  if (!active) {
-    if (ntp_leak_rate || cmd_leak_rate)
-      LOG_FATAL("ratelimit cannot be used with noclientlog");
+    for (i = 0; i < MAX_SERVICES; i++) {
+      if (leak_rate[i] != 0)
+        LOG_FATAL("Rate limiting cannot be enabled with noclientlog");
+    }
    return;
  }

@@ -339,6 +361,7 @@ CLG_Initialise(void)
     table where two copies exist at the same time. */
  max_slots = CNF_GetClientLogLimit() / (sizeof (Record) * SLOT_SIZE * 3 / 2);
  max_slots = CLAMP(MIN_SLOTS, max_slots, MAX_SLOTS);
+  DEBUG_LOG("Max records %u", 1U << ((int)round(log(max_slots) / log(2)) + SLOT_BITS));

  slots = 0;
  records = NULL;
@@ -380,30 +403,33 @@ get_ts_from_timespec(struct timespec *ts)
 /* ================================================== */

 static void
-update_record(struct timespec *now, uint32_t *last_hit, uint32_t *hits,
-              uint16_t *tokens, uint32_t max_tokens, int token_shift, int8_t *rate)
+update_record(CLG_Service service, Record *record, struct timespec *now)
 {
-  uint32_t interval, now_ts, prev_hit, new_tokens;
-  int interval2;
+  uint32_t interval, now_ts, prev_hit, tokens;
+  int interval2, tshift, mtokens;
+  int8_t *rate;

  now_ts = get_ts_from_timespec(now);

-  prev_hit = *last_hit;
-  *last_hit = now_ts;
-  (*hits)++;
+  prev_hit = record->last_hit[service];
+  record->last_hit[service] = now_ts;
+  record->hits[service]++;

  interval = now_ts - prev_hit;

  if (prev_hit == INVALID_TS || (int32_t)interval < 0)
    return;

-  if (token_shift >= 0)
-    new_tokens = (now_ts >> token_shift) - (prev_hit >> token_shift);
-  else if (now_ts - prev_hit > max_tokens)
-    new_tokens = max_tokens;
+  tshift = token_shift[service];
+  mtokens = max_tokens[service];
+
+  if (tshift >= 0)
+    tokens = (now_ts >> tshift) - (prev_hit >> tshift);
+  else if (now_ts - prev_hit > mtokens)
+    tokens = mtokens;
  else
-    new_tokens = (now_ts - prev_hit) << -token_shift;
-  *tokens = MIN(*tokens + new_tokens, max_tokens);
+    tokens = (now_ts - prev_hit) << -tshift;
+  record->tokens[service] = MIN(record->tokens[service] + tokens, mtokens);

  /* Convert the interval to scaled and rounded log2 */
  if (interval) {
@@ -418,6 +444,11 @@ update_record(struct timespec *now, uint32_t *last_hit, uint32_t *hits,
    interval2 = -RATE_SCALE * (TS_FRAC + 1);
  }

+  /* For the NTP service, update one of the two rates depending on whether
+     the previous request of the client had a reply or it timed out */
+  rate = service == CLG_NTP && record->drop_flags & (1U << service) ?
+           &record->ntp_timeout_rate : &record->rate[service];
+
  /* Update the rate in a rough approximation of exponential moving average */
  if (*rate == INVALID_RATE) {
    *rate = -interval2;
@@ -457,50 +488,33 @@ CLG_GetClientIndex(IPAddr *client)

 /* ================================================== */

-int
-CLG_LogNTPAccess(IPAddr *client, struct timespec *now)
+static void
+check_service_number(CLG_Service service)
 {
-  Record *record;
-
-  total_ntp_hits++;
-
-  record = get_record(client);
-  if (record == NULL)
-    return -1;
-
-  /* Update one of the two rates depending on whether the previous request
-     of the client had a reply or it timed out */
-  update_record(now, &record->last_ntp_hit, &record->ntp_hits,
-                &record->ntp_tokens, max_ntp_tokens, ntp_token_shift,
-                record->flags & FLAG_NTP_DROPPED ?
-                &record->ntp_timeout_rate : &record->ntp_rate);
-
-  DEBUG_LOG("NTP hits %"PRIu32" rate %d trate %d tokens %d",
-            record->ntp_hits, record->ntp_rate, record->ntp_timeout_rate,
-            record->ntp_tokens);
-
-  return get_index(record);
+  assert(service >= 0 && service <= MAX_SERVICES);
 }

 /* ================================================== */

 int
-CLG_LogCommandAccess(IPAddr *client, struct timespec *now)
+CLG_LogServiceAccess(CLG_Service service, IPAddr *client, struct timespec *now)
 {
  Record *record;

-  total_cmd_hits++;
+  check_service_number(service);
+
+  total_hits[service]++;

  record = get_record(client);
  if (record == NULL)
    return -1;

-  update_record(now, &record->last_cmd_hit, &record->cmd_hits,
-                &record->cmd_tokens, max_cmd_tokens, cmd_token_shift,
-                &record->cmd_rate);
+  update_record(service, record, now);

-  DEBUG_LOG("Cmd hits %"PRIu32" rate %d tokens %d",
-            record->cmd_hits, record->cmd_rate, record->cmd_tokens);
+  DEBUG_LOG("service %d hits %"PRIu32" rate %d trate %d tokens %d",
+            (int)service, record->hits[service], record->rate[service],
+            service == CLG_NTP ? record->ntp_timeout_rate : INVALID_RATE,
+            record->tokens[service]);

  return get_index(record);
 }
@@ -530,71 +544,53 @@ limit_response_random(int leak_rate)
 /* ================================================== */

 int
-CLG_LimitNTPResponseRate(int index)
+CLG_LimitServiceRate(CLG_Service service, int index)
 {
  Record *record;
  int drop;

-  if (!ntp_tokens_per_packet)
+  check_service_number(service);
+
+  if (tokens_per_hit[service] == 0)
    return 0;

  record = ARR_GetElement(records, index);
-  record->flags &= ~FLAG_NTP_DROPPED;
+  record->drop_flags &= ~(1U << service);

-  if (record->ntp_tokens >= ntp_tokens_per_packet) {
-    record->ntp_tokens -= ntp_tokens_per_packet;
+  if (record->tokens[service] >= tokens_per_hit[service]) {
+    record->tokens[service] -= tokens_per_hit[service];
    return 0;
  }

-  drop = limit_response_random(ntp_leak_rate);
+  drop = limit_response_random(leak_rate[service]);

-  /* Poorly implemented clients may send new requests at even a higher rate
+  /* Poorly implemented NTP clients can send requests at a higher rate
     when they are not getting replies.  If the request rate seems to be more
     than twice as much as when replies are sent, give up on rate limiting to
     reduce the amount of traffic.  Invert the sense of the leak to respond to
     most of the requests, but still keep the estimated rate updated. */
-  if (record->ntp_timeout_rate != INVALID_RATE &&
-      record->ntp_timeout_rate > record->ntp_rate + RATE_SCALE)
+  if (service == CLG_NTP && record->ntp_timeout_rate != INVALID_RATE &&
+      record->ntp_timeout_rate > record->rate[service] + RATE_SCALE)
    drop = !drop;

  if (!drop) {
-    record->ntp_tokens = 0;
+    record->tokens[service] = 0;
    return 0;
  }

-  record->flags |= FLAG_NTP_DROPPED;
-  record->ntp_drops++;
-  total_ntp_drops++;
+  record->drop_flags |= 1U << service;
+  record->drops[service]++;
+  total_drops[service]++;

  return 1;
 }

 /* ================================================== */

-int
-CLG_LimitCommandResponseRate(int index)
+void
+CLG_LogAuthNtpRequest(void)
 {
-  Record *record;
-
-  if (!cmd_tokens_per_packet)
-    return 0;
-
-  record = ARR_GetElement(records, index);
-
-  if (record->cmd_tokens >= cmd_tokens_per_packet) {
-    record->cmd_tokens -= cmd_tokens_per_packet;
-    return 0;
-  }
-
-  if (!limit_response_random(cmd_leak_rate)) {
-    record->cmd_tokens = 0;
-    return 0;
-  }
-
-  record->cmd_drops++;
-  total_cmd_drops++;
-
-  return 1;
+  total_ntp_auth_hits++;
 }

 /* ================================================== */
@@ -614,7 +610,7 @@ void CLG_GetNtpTimestamps(int index, NTP_int64 **rx_ts, NTP_int64 **tx_ts)
 int
 CLG_GetNtpMinPoll(void)
 {
-  return ntp_limit_interval;
+  return limit_interval[CLG_NTP];
 }

 /* ================================================== */
@@ -653,10 +649,12 @@ static uint32_t get_last_ago(uint32_t x, uint32_t y)
 /* ================================================== */

 int
-CLG_GetClientAccessReportByIndex(int index, RPT_ClientAccessByIndex_Report *report, struct timespec *now)
+CLG_GetClientAccessReportByIndex(int index, int reset, uint32_t min_hits,
+                                 RPT_ClientAccessByIndex_Report *report, struct timespec *now)
 {
  Record *record;
  uint32_t now_ts;
+  int i, r;

  if (!active || index < 0 || index >= ARR_GetSize(records))
    return 0;
@@ -666,20 +664,44 @@ CLG_GetClientAccessReportByIndex(int index, RPT_ClientAccessByIndex_Report *repo
  if (record->ip_addr.family == IPADDR_UNSPEC)
    return 0;

-  now_ts = get_ts_from_timespec(now);
+  if (min_hits == 0) {
+    r = 1;
+  } else {
+    for (i = r = 0; i < MAX_SERVICES; i++) {
+      if (record->hits[i] >= min_hits) {
+        r = 1;
+        break;
+      }
+    }
+  }

-  report->ip_addr = record->ip_addr;
-  report->ntp_hits = record->ntp_hits;
-  report->cmd_hits = record->cmd_hits;
-  report->ntp_drops = record->ntp_drops;
-  report->cmd_drops = record->cmd_drops;
-  report->ntp_interval = get_interval(record->ntp_rate);
-  report->cmd_interval = get_interval(record->cmd_rate);
-  report->ntp_timeout_interval = get_interval(record->ntp_timeout_rate);
-  report->last_ntp_hit_ago = get_last_ago(now_ts, record->last_ntp_hit);
-  report->last_cmd_hit_ago = get_last_ago(now_ts, record->last_cmd_hit);
+  if (r) {
+    now_ts = get_ts_from_timespec(now);

-  return 1;
+    report->ip_addr = record->ip_addr;
+    report->ntp_hits = record->hits[CLG_NTP];
+    report->nke_hits = record->hits[CLG_NTSKE];
+    report->cmd_hits = record->hits[CLG_CMDMON];
+    report->ntp_drops = record->drops[CLG_NTP];
+    report->nke_drops = record->drops[CLG_NTSKE];
+    report->cmd_drops = record->drops[CLG_CMDMON];
+    report->ntp_interval = get_interval(record->rate[CLG_NTP]);
+    report->nke_interval = get_interval(record->rate[CLG_NTSKE]);
+    report->cmd_interval = get_interval(record->rate[CLG_CMDMON]);
+    report->ntp_timeout_interval = get_interval(record->ntp_timeout_rate);
+    report->last_ntp_hit_ago = get_last_ago(now_ts, record->last_hit[CLG_NTP]);
+    report->last_nke_hit_ago = get_last_ago(now_ts, record->last_hit[CLG_NTSKE]);
+    report->last_cmd_hit_ago = get_last_ago(now_ts, record->last_hit[CLG_CMDMON]);
+  }
+
+  if (reset) {
+    for (i = 0; i < MAX_SERVICES; i++) {
+      record->hits[i] = 0;
+      record->drops[i] = 0;
+    }
+  }
+
+  return r;
 }

 /* ================================================== */
@@ -687,9 +709,12 @@ CLG_GetClientAccessReportByIndex(int index, RPT_ClientAccessByIndex_Report *repo
 void
 CLG_GetServerStatsReport(RPT_ServerStatsReport *report)
 {
-  report->ntp_hits = total_ntp_hits;
-  report->cmd_hits = total_cmd_hits;
-  report->ntp_drops = total_ntp_drops;
-  report->cmd_drops = total_cmd_drops;
+  report->ntp_hits = total_hits[CLG_NTP];
+  report->nke_hits = total_hits[CLG_NTSKE];
+  report->cmd_hits = total_hits[CLG_CMDMON];
+  report->ntp_drops = total_drops[CLG_NTP];
+  report->nke_drops = total_drops[CLG_NTSKE];
+  report->cmd_drops = total_drops[CLG_CMDMON];
  report->log_drops = total_record_drops;
+  report->ntp_auth_hits = total_ntp_auth_hits;
 }
--- a/clientlog.h
+++ b/clientlog.h
@@ -31,20 +31,27 @@
 #include "sysincl.h"
 #include "reports.h"

+typedef enum {
+  CLG_NTP = 0,
+  CLG_NTSKE,
+  CLG_CMDMON,
+} CLG_Service;
+
 extern void CLG_Initialise(void);
 extern void CLG_Finalise(void);
 extern int CLG_GetClientIndex(IPAddr *client);
-extern int CLG_LogNTPAccess(IPAddr *client, struct timespec *now);
-extern int CLG_LogCommandAccess(IPAddr *client, struct timespec *now);
-extern int CLG_LimitNTPResponseRate(int index);
-extern int CLG_LimitCommandResponseRate(int index);
+extern int CLG_LogServiceAccess(CLG_Service service, IPAddr *client, struct timespec *now);
+extern int CLG_LimitServiceRate(CLG_Service service, int index);
+extern void CLG_LogAuthNtpRequest(void);
 extern void CLG_GetNtpTimestamps(int index, NTP_int64 **rx_ts, NTP_int64 **tx_ts);
 extern int CLG_GetNtpMinPoll(void);

 /* And some reporting functions, for use by chronyc. */

 extern int CLG_GetNumberOfIndices(void);
-extern int CLG_GetClientAccessReportByIndex(int index, RPT_ClientAccessByIndex_Report *report, struct timespec *now);
+extern int CLG_GetClientAccessReportByIndex(int index, int reset, uint32_t min_hits,
+                                            RPT_ClientAccessByIndex_Report *report,
+                                            struct timespec *now);
 extern void CLG_GetServerStatsReport(RPT_ServerStatsReport *report);

 #endif /* GOT_CLIENTLOG_H */
--- a/cmac.h
+++ b/cmac.h
@@ -0,0 +1,48 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2019
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for CMAC.
+
+  */
+
+#ifndef GOT_CMAC_H
+#define GOT_CMAC_H
+
+/* Avoid overlapping with the hash enumeration */
+typedef enum {
+  CMC_INVALID = 0,
+  CMC_AES128 = 13,
+  CMC_AES256 = 14,
+} CMC_Algorithm;
+
+typedef struct CMC_Instance_Record *CMC_Instance;
+
+extern int CMC_GetKeyLength(CMC_Algorithm algorithm);
+extern CMC_Instance CMC_CreateInstance(CMC_Algorithm algorithm, const unsigned char *key,
+                                       int length);
+extern int CMC_Hash(CMC_Instance inst, const void *in, int in_len,
+                    unsigned char *out, int out_len);
+extern void CMC_DestroyInstance(CMC_Instance inst);
+
+#endif
+
--- a/cmac_nettle.c
+++ b/cmac_nettle.c
@@ -0,0 +1,117 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2019
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Support for AES128 and AES256 CMAC in Nettle.
+
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include <nettle/cmac.h>
+
+#include "cmac.h"
+#include "memory.h"
+
+struct CMC_Instance_Record {
+  int key_length;
+  union {
+    struct cmac_aes128_ctx aes128;
+    struct cmac_aes256_ctx aes256;
+  } context;
+};
+
+/* ================================================== */
+
+int
+CMC_GetKeyLength(CMC_Algorithm algorithm)
+{
+  if (algorithm == CMC_AES128)
+    return AES128_KEY_SIZE;
+  else if (algorithm == CMC_AES256)
+    return AES256_KEY_SIZE;
+  return 0;
+}
+
+/* ================================================== */
+
+CMC_Instance
+CMC_CreateInstance(CMC_Algorithm algorithm, const unsigned char *key, int length)
+{
+  CMC_Instance inst;
+
+  if (length <= 0 || length != CMC_GetKeyLength(algorithm))
+    return NULL;
+
+  inst = MallocNew(struct CMC_Instance_Record);
+  inst->key_length = length;
+
+  switch (length) {
+    case AES128_KEY_SIZE:
+      cmac_aes128_set_key(&inst->context.aes128, key);
+      break;
+    case AES256_KEY_SIZE:
+      cmac_aes256_set_key(&inst->context.aes256, key);
+      break;
+    default:
+      assert(0);
+  }
+
+  return inst;
+}
+
+/* ================================================== */
+
+int
+CMC_Hash(CMC_Instance inst, const void *in, int in_len, unsigned char *out, int out_len)
+{
+  if (in_len < 0 || out_len < 0)
+    return 0;
+
+  if (out_len > CMAC128_DIGEST_SIZE)
+    out_len = CMAC128_DIGEST_SIZE;
+
+  switch (inst->key_length) {
+    case AES128_KEY_SIZE:
+      cmac_aes128_update(&inst->context.aes128, in_len, in);
+      cmac_aes128_digest(&inst->context.aes128, out_len, out);
+      break;
+    case AES256_KEY_SIZE:
+      cmac_aes256_update(&inst->context.aes256, in_len, in);
+      cmac_aes256_digest(&inst->context.aes256, out_len, out);
+      break;
+    default:
+      assert(0);
+  }
+
+  return out_len;
+}
+
+/* ================================================== */
+
+void
+CMC_DestroyInstance(CMC_Instance inst)
+{
+  Free(inst);
+}
--- a/cmdmon.c
+++ b/cmdmon.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2009-2016, 2018
+ * Copyright (C) Miroslav Lichvar  2009-2016, 2018-2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -38,11 +38,13 @@
 #include "ntp_sources.h"
 #include "ntp_core.h"
 #include "smooth.h"
+#include "socket.h"
 #include "sources.h"
 #include "sourcestats.h"
 #include "reference.h"
 #include "manual.h"
 #include "memory.h"
+#include "nts_ke_server.h"
 #include "local.h"
 #include "addrfilt.h"
 #include "conf.h"
@@ -53,21 +55,12 @@

 /* ================================================== */

-union sockaddr_all {
-  struct sockaddr_in in4;
-#ifdef FEAT_IPV6
-  struct sockaddr_in6 in6;
-#endif
-  struct sockaddr_un un;
-  struct sockaddr sa;
-};
+#define INVALID_SOCK_FD (-5)

 /* File descriptors for command and monitoring sockets */
 static int sock_fdu;
 static int sock_fd4;
-#ifdef FEAT_IPV6
 static int sock_fd6;
-#endif

 /* Flag indicating whether this module has been initialised or not */
 static int initialised = 0;
@@ -140,6 +133,13 @@ static const char permissions[] = {
  PERMIT_AUTH, /* ADD_PEER3 */
  PERMIT_AUTH, /* SHUTDOWN */
  PERMIT_AUTH, /* ONOFFLINE */
+  PERMIT_AUTH, /* ADD_SOURCE */
+  PERMIT_OPEN, /* NTP_SOURCE_NAME */
+  PERMIT_AUTH, /* RESET_SOURCES */
+  PERMIT_AUTH, /* AUTH_DATA */
+  PERMIT_AUTH, /* CLIENT_ACCESSES_BY_INDEX3 */
+  PERMIT_AUTH, /* SELECT_DATA */
+  PERMIT_AUTH, /* RELOAD_SOURCES */
 };

 /* ================================================== */
@@ -155,99 +155,45 @@ static void read_from_cmd_socket(int sock_fd, int event, void *anything);
 /* ================================================== */

 static int
-prepare_socket(int family, int port_number)
+open_socket(int family)
 {
-  int sock_fd;
-  socklen_t my_addr_len;
-  union sockaddr_all my_addr;
-  IPAddr bind_address;
-  int on_off = 1;
-
-  sock_fd = socket(family, SOCK_DGRAM, 0);
-  if (sock_fd < 0) {
-    LOG(LOGS_ERR, "Could not open %s command socket : %s",
-        UTI_SockaddrFamilyToString(family), strerror(errno));
-    return -1;
-  }
-
-  /* Close on exec */
-  UTI_FdSetCloexec(sock_fd);
-
-  if (family != AF_UNIX) {
-    /* Allow reuse of port number */
-    if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, (char *) &on_off, sizeof(on_off)) < 0) {
-      LOG(LOGS_ERR, "Could not set reuseaddr socket options");
-      /* Don't quit - we might survive anyway */
-    }
-
-#ifdef IP_FREEBIND
-    /* Allow binding to address that doesn't exist yet */
-    if (setsockopt(sock_fd, IPPROTO_IP, IP_FREEBIND, (char *)&on_off, sizeof(on_off)) < 0) {
-      LOG(LOGS_ERR, "Could not set free bind socket option");
-    }
-#endif
-
-#ifdef FEAT_IPV6
-    if (family == AF_INET6) {
-#ifdef IPV6_V6ONLY
-      /* Receive IPv6 packets only */
-      if (setsockopt(sock_fd, IPPROTO_IPV6, IPV6_V6ONLY, (char *)&on_off, sizeof(on_off)) < 0) {
-        LOG(LOGS_ERR, "Could not request IPV6_V6ONLY socket option");
-      }
-#endif
-    }
-#endif
-  }
-
-  memset(&my_addr, 0, sizeof (my_addr));
+  const char *local_path, *iface;
+  IPSockAddr local_addr;
+  int sock_fd, port;

  switch (family) {
-    case AF_INET:
-      my_addr_len = sizeof (my_addr.in4);
-      my_addr.in4.sin_family = family;
-      my_addr.in4.sin_port = htons((unsigned short)port_number);
+    case IPADDR_INET4:
+    case IPADDR_INET6:
+      port = CNF_GetCommandPort();
+      if (port == 0 || !SCK_IsIpFamilyEnabled(family))
+        return INVALID_SOCK_FD;

-      CNF_GetBindCommandAddress(IPADDR_INET4, &bind_address);
+      CNF_GetBindCommandAddress(family, &local_addr.ip_addr);
+      local_addr.port = port;
+      iface = CNF_GetBindCommandInterface();
+
+      sock_fd = SCK_OpenUdpSocket(NULL, &local_addr, iface, SCK_FLAG_RX_DEST_ADDR);
+      if (sock_fd < 0) {
+        LOG(LOGS_ERR, "Could not open command socket on %s",
+            UTI_IPSockAddrToString(&local_addr));
+        return INVALID_SOCK_FD;
+      }

-      if (bind_address.family == IPADDR_INET4)
-        my_addr.in4.sin_addr.s_addr = htonl(bind_address.addr.in4);
-      else
-        my_addr.in4.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
      break;
-#ifdef FEAT_IPV6
-    case AF_INET6:
-      my_addr_len = sizeof (my_addr.in6);
-      my_addr.in6.sin6_family = family;
-      my_addr.in6.sin6_port = htons((unsigned short)port_number);
+    case IPADDR_UNSPEC:
+      local_path = CNF_GetBindCommandPath();

-      CNF_GetBindCommandAddress(IPADDR_INET6, &bind_address);
+      sock_fd = SCK_OpenUnixDatagramSocket(NULL, local_path, 0);
+      if (sock_fd < 0) {
+        LOG(LOGS_ERR, "Could not open command socket on %s", local_path);
+        return INVALID_SOCK_FD;
+      }

-      if (bind_address.family == IPADDR_INET6)
-        memcpy(my_addr.in6.sin6_addr.s6_addr, bind_address.addr.in6,
-            sizeof (my_addr.in6.sin6_addr.s6_addr));
-      else
-        my_addr.in6.sin6_addr = in6addr_loopback;
-      break;
-#endif
-    case AF_UNIX:
-      my_addr_len = sizeof (my_addr.un);
-      my_addr.un.sun_family = family;
-      if (snprintf(my_addr.un.sun_path, sizeof (my_addr.un.sun_path), "%s",
-                   CNF_GetBindCommandPath()) >= sizeof (my_addr.un.sun_path))
-        LOG_FATAL("Unix socket path too long");
-      unlink(my_addr.un.sun_path);
      break;
    default:
      assert(0);
  }

-  if (bind(sock_fd, &my_addr.sa, my_addr_len) < 0) {
-    LOG(LOGS_ERR, "Could not bind %s command socket : %s",
-        UTI_SockaddrFamilyToString(family), strerror(errno));
-    close(sock_fd);
-    return -1;
-  }
-
  /* Register handler for read events on the socket */
  SCH_AddFileHandler(sock_fd, SCH_FILE_INPUT, read_from_cmd_socket, NULL);

@@ -290,39 +236,19 @@ do_size_checks(void)
 /* ================================================== */

 void
-CAM_Initialise(int family)
+CAM_Initialise(void)
 {
-  int port_number;
-
  assert(!initialised);
  assert(sizeof (permissions) / sizeof (permissions[0]) == N_REQUEST_TYPES);
  do_size_checks();

  initialised = 1;
-  sock_fdu = -1;
-  port_number = CNF_GetCommandPort();

-  if (port_number && (family == IPADDR_UNSPEC || family == IPADDR_INET4))
-    sock_fd4 = prepare_socket(AF_INET, port_number);
-  else
-    sock_fd4 = -1;
-#ifdef FEAT_IPV6
-  if (port_number && (family == IPADDR_UNSPEC || family == IPADDR_INET6))
-    sock_fd6 = prepare_socket(AF_INET6, port_number);
-  else
-    sock_fd6 = -1;
-#endif
-
-  if (port_number && sock_fd4 < 0
-#ifdef FEAT_IPV6
-      && sock_fd6 < 0
-#endif
-      ) {
-    LOG_FATAL("Could not open any command socket");
-  }
+  sock_fdu = INVALID_SOCK_FD;
+  sock_fd4 = open_socket(IPADDR_INET4);
+  sock_fd6 = open_socket(IPADDR_INET6);

  access_auth_table = ADF_CreateTable();
-
 }

 /* ================================================== */
@@ -330,24 +256,24 @@ CAM_Initialise(int family)
 void
 CAM_Finalise(void)
 {
-  if (sock_fdu >= 0) {
+  if (sock_fdu != INVALID_SOCK_FD) {
    SCH_RemoveFileHandler(sock_fdu);
-    close(sock_fdu);
-    unlink(CNF_GetBindCommandPath());
+    SCK_RemoveSocket(sock_fdu);
+    SCK_CloseSocket(sock_fdu);
+    sock_fdu = INVALID_SOCK_FD;
  }
-  sock_fdu = -1;
-  if (sock_fd4 >= 0) {
+
+  if (sock_fd4 != INVALID_SOCK_FD) {
    SCH_RemoveFileHandler(sock_fd4);
-    close(sock_fd4);
+    SCK_CloseSocket(sock_fd4);
+    sock_fd4 = INVALID_SOCK_FD;
  }
-  sock_fd4 = -1;
-#ifdef FEAT_IPV6
-  if (sock_fd6 >= 0) {
+
+  if (sock_fd6 != INVALID_SOCK_FD) {
    SCH_RemoveFileHandler(sock_fd6);
-    close(sock_fd6);
+    SCK_CloseSocket(sock_fd6);
+    sock_fd6 = INVALID_SOCK_FD;
  }
-  sock_fd6 = -1;
-#endif

  ADF_DestroyTable(access_auth_table);

@@ -361,51 +287,31 @@ CAM_OpenUnixSocket(void)
 {
  /* This is separated from CAM_Initialise() as it needs to be called when
     the process has already dropped the root privileges */
-  if (CNF_GetBindCommandPath()[0])
-    sock_fdu = prepare_socket(AF_UNIX, 0);
+  if (CNF_GetBindCommandPath())
+    sock_fdu = open_socket(IPADDR_UNSPEC);
 }

 /* ================================================== */

 static void
-transmit_reply(CMD_Reply *msg, union sockaddr_all *where_to)
+transmit_reply(int sock_fd, int request_length, SCK_Message *message)
 {
-  int status;
-  int tx_message_length;
-  int sock_fd;
-  socklen_t addrlen;
+  message->length = PKL_ReplyLength((CMD_Reply *)message->data);

-  switch (where_to->sa.sa_family) {
-    case AF_INET:
-      sock_fd = sock_fd4;
-      addrlen = sizeof (where_to->in4);
-      break;
-#ifdef FEAT_IPV6
-    case AF_INET6:
-      sock_fd = sock_fd6;
-      addrlen = sizeof (where_to->in6);
-      break;
-#endif
-    case AF_UNIX:
-      sock_fd = sock_fdu;
-      addrlen = sizeof (where_to->un);
-      break;
-    default:
-      assert(0);
-  }
-
-  tx_message_length = PKL_ReplyLength(msg);
-  status = sendto(sock_fd, (void *) msg, tx_message_length, 0,
-                  &where_to->sa, addrlen);
-
-  if (status < 0) {
-    DEBUG_LOG("Could not send to %s fd %d : %s",
-              UTI_SockaddrToString(&where_to->sa), sock_fd, strerror(errno));
+  if (request_length < message->length) {
+    DEBUG_LOG("Response longer than request req_len=%d res_len=%d",
+              request_length, message->length);
    return;
  }

-  DEBUG_LOG("Sent %d bytes to %s fd %d", status,
-            UTI_SockaddrToString(&where_to->sa), sock_fd);
+  /* Don't require responses to non-link-local addresses to use the same
+     interface */
+  if (message->addr_type == SCK_ADDR_IP &&
+      !SCK_IsLinkLocalIPAddress(&message->remote_addr.ip.ip_addr))
+    message->if_index = INVALID_IF_INDEX;
+
+  if (!SCK_SendMessage(sock_fd, message, 0))
+    return;
 }
  
 /* ================================================== */
@@ -414,6 +320,8 @@ static void
 handle_dump(CMD_Request *rx_message, CMD_Reply *tx_message)
 {
  SRC_DumpSources();
+  NSR_DumpAuthData();
+  NKS_DumpKeys();
 }

 /* ================================================== */
@@ -671,11 +579,8 @@ handle_source_data(CMD_Request *rx_message, CMD_Reply *tx_message)
    tx_message->data.source_data.stratum = htons(report.stratum);
    tx_message->data.source_data.poll    = htons(report.poll);
    switch (report.state) {
-      case RPT_SYNC:
-        tx_message->data.source_data.state   = htons(RPY_SD_ST_SYNC);
-        break;
-      case RPT_UNREACH:
-        tx_message->data.source_data.state   = htons(RPY_SD_ST_UNREACH);
+      case RPT_NONSELECTABLE:
+        tx_message->data.source_data.state   = htons(RPY_SD_ST_NONSELECTABLE);
        break;
      case RPT_FALSETICKER:
        tx_message->data.source_data.state   = htons(RPY_SD_ST_FALSETICKER);
@@ -683,11 +588,14 @@ handle_source_data(CMD_Request *rx_message, CMD_Reply *tx_message)
      case RPT_JITTERY:
        tx_message->data.source_data.state   = htons(RPY_SD_ST_JITTERY);
        break;
-      case RPT_CANDIDATE:
-        tx_message->data.source_data.state   = htons(RPY_SD_ST_CANDIDATE);
+      case RPT_SELECTABLE:
+        tx_message->data.source_data.state   = htons(RPY_SD_ST_SELECTABLE);
        break;
-      case RPT_OUTLIER:
-        tx_message->data.source_data.state   = htons(RPY_SD_ST_OUTLIER);
+      case RPT_UNSELECTED:
+        tx_message->data.source_data.state   = htons(RPY_SD_ST_UNSELECTED);
+        break;
+      case RPT_SELECTED:
+        tx_message->data.source_data.state   = htons(RPY_SD_ST_SELECTED);
        break;
    }
    switch (report.mode) {
@@ -701,11 +609,7 @@ handle_source_data(CMD_Request *rx_message, CMD_Reply *tx_message)
        tx_message->data.source_data.mode    = htons(RPY_SD_MD_REF);
        break;
    }
-    tx_message->data.source_data.flags =
-                  htons((report.sel_options & SRC_SELECT_PREFER ? RPY_SD_FLAG_PREFER : 0) |
-                        (report.sel_options & SRC_SELECT_NOSELECT ? RPY_SD_FLAG_NOSELECT : 0) |
-                        (report.sel_options & SRC_SELECT_TRUST ? RPY_SD_FLAG_TRUST : 0) |
-                        (report.sel_options & SRC_SELECT_REQUIRE ? RPY_SD_FLAG_REQUIRE : 0));
+    tx_message->data.source_data.flags = htons(0);
    tx_message->data.source_data.reachability = htons(report.reachability);
    tx_message->data.source_data.since_sample = htonl(report.latest_meas_ago);
    tx_message->data.source_data.orig_latest_meas = UTI_FloatHostToNetwork(report.orig_latest_meas);
@@ -722,6 +626,7 @@ static void
 handle_rekey(CMD_Request *rx_message, CMD_Reply *tx_message)
 {
  KEY_Reload();
+  NKS_ReloadKeys();
 }

 /* ================================================== */
@@ -783,14 +688,41 @@ handle_cmdaccheck(CMD_Request *rx_message, CMD_Reply *tx_message)
 /* ================================================== */

 static void
-handle_add_source(NTP_Source_Type type, CMD_Request *rx_message, CMD_Reply *tx_message)
+handle_add_source(CMD_Request *rx_message, CMD_Reply *tx_message)
 {
-  NTP_Remote_Address rem_addr;
+  NTP_Source_Type type;
  SourceParameters params;
  NSR_Status status;
+  char *name;
+  int pool, port;
  
-  UTI_IPNetworkToHost(&rx_message->data.ntp_source.ip_addr, &rem_addr.ip_addr);
-  rem_addr.port = (unsigned short)(ntohl(rx_message->data.ntp_source.port));
+  switch (ntohl(rx_message->data.ntp_source.type)) {
+    case REQ_ADDSRC_SERVER:
+      type = NTP_SERVER;
+      pool = 0;
+      break;
+    case REQ_ADDSRC_PEER:
+      type = NTP_PEER;
+      pool = 0;
+      break;
+    case REQ_ADDSRC_POOL:
+      type = NTP_SERVER;
+      pool = 1;
+      break;
+    default:
+      tx_message->status = htons(STT_INVALID);
+      return;
+  }
+
+  name = (char *)rx_message->data.ntp_source.name;
+
+  /* Make sure the name is terminated */
+  if (name[sizeof (rx_message->data.ntp_source.name) - 1] != '\0') {
+      tx_message->status = htons(STT_INVALIDNAME);
+      return;
+  }
+
+  port = ntohl(rx_message->data.ntp_source.port);
  params.minpoll = ntohl(rx_message->data.ntp_source.minpoll);
  params.maxpoll = ntohl(rx_message->data.ntp_source.maxpoll);
  params.presend_minpoll = ntohl(rx_message->data.ntp_source.presend_minpoll);
@@ -802,6 +734,7 @@ handle_add_source(NTP_Source_Type type, CMD_Request *rx_message, CMD_Reply *tx_m
  params.max_samples = ntohl(rx_message->data.ntp_source.max_samples);
  params.filter_length = ntohl(rx_message->data.ntp_source.filter_length);
  params.authkey = ntohl(rx_message->data.ntp_source.authkey);
+  params.nts_port = ntohl(rx_message->data.ntp_source.nts_port);
  params.max_delay = UTI_FloatNetworkToHost(rx_message->data.ntp_source.max_delay);
  params.max_delay_ratio =
    UTI_FloatNetworkToHost(rx_message->data.ntp_source.max_delay_ratio);
@@ -817,25 +750,31 @@ handle_add_source(NTP_Source_Type type, CMD_Request *rx_message, CMD_Reply *tx_m
  params.iburst = ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_IBURST ? 1 : 0;
  params.interleaved = ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_INTERLEAVED ? 1 : 0;
  params.burst = ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_BURST ? 1 : 0;
+  params.nts = ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_NTS ? 1 : 0;
  params.sel_options =
    (ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_PREFER ? SRC_SELECT_PREFER : 0) |
    (ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_NOSELECT ? SRC_SELECT_NOSELECT : 0) |
    (ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_TRUST ? SRC_SELECT_TRUST : 0) |
    (ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_REQUIRE ? SRC_SELECT_REQUIRE : 0);

-  status = NSR_AddSource(&rem_addr, type, &params);
+  status = NSR_AddSourceByName(name, port, pool, type, &params, NULL);
  switch (status) {
    case NSR_Success:
      break;
+    case NSR_UnresolvedName:
+      /* Try to resolve the name now */
+      NSR_ResolveSources();
+      break;
    case NSR_AlreadyInUse:
      tx_message->status = htons(STT_SOURCEALREADYKNOWN);
      break;
    case NSR_TooManySources:
      tx_message->status = htons(STT_TOOMANYSOURCES);
      break;
-    case NSR_InvalidAF:
-      tx_message->status = htons(STT_INVALIDAF);
+    case NSR_InvalidName:
+      tx_message->status = htons(STT_INVALIDNAME);
      break;
+    case NSR_InvalidAF:
    case NSR_NoSuchSource:
      assert(0);
      break;
@@ -847,13 +786,12 @@ handle_add_source(NTP_Source_Type type, CMD_Request *rx_message, CMD_Reply *tx_m
 static void
 handle_del_source(CMD_Request *rx_message, CMD_Reply *tx_message)
 {
-  NTP_Remote_Address rem_addr;
  NSR_Status status;
+  IPAddr ip_addr;
  
-  UTI_IPNetworkToHost(&rx_message->data.del_source.ip_addr, &rem_addr.ip_addr);
-  rem_addr.port = 0;
+  UTI_IPNetworkToHost(&rx_message->data.del_source.ip_addr, &ip_addr);
  
-  status = NSR_RemoveSource(&rem_addr);
+  status = NSR_RemoveSource(&ip_addr);
  switch (status) {
    case NSR_Success:
      break;
@@ -863,6 +801,8 @@ handle_del_source(CMD_Request *rx_message, CMD_Reply *tx_message)
    case NSR_TooManySources:
    case NSR_AlreadyInUse:
    case NSR_InvalidAF:
+    case NSR_InvalidName:
+    case NSR_UnresolvedName:
      assert(0);
      break;
  }
@@ -1065,7 +1005,7 @@ handle_client_accesses_by_index(CMD_Request *rx_message, CMD_Reply *tx_message)
  RPT_ClientAccessByIndex_Report report;
  RPY_ClientAccesses_Client *client;
  int n_indices;
-  uint32_t i, j, req_first_index, req_n_clients;
+  uint32_t i, j, req_first_index, req_n_clients, req_min_hits, req_reset;
  struct timespec now;

  SCH_GetLastEventTime(&now, NULL, NULL);
@@ -1074,6 +1014,8 @@ handle_client_accesses_by_index(CMD_Request *rx_message, CMD_Reply *tx_message)
  req_n_clients = ntohl(rx_message->data.client_accesses_by_index.n_clients);
  if (req_n_clients > MAX_CLIENT_ACCESSES)
    req_n_clients = MAX_CLIENT_ACCESSES;
+  req_min_hits = ntohl(rx_message->data.client_accesses_by_index.min_hits);
+  req_reset = ntohl(rx_message->data.client_accesses_by_index.reset);

  n_indices = CLG_GetNumberOfIndices();
  if (n_indices < 0) {
@@ -1081,24 +1023,28 @@ handle_client_accesses_by_index(CMD_Request *rx_message, CMD_Reply *tx_message)
    return;
  }

-  tx_message->reply = htons(RPY_CLIENT_ACCESSES_BY_INDEX2);
+  tx_message->reply = htons(RPY_CLIENT_ACCESSES_BY_INDEX3);
  tx_message->data.client_accesses_by_index.n_indices = htonl(n_indices);

  for (i = req_first_index, j = 0; i < (uint32_t)n_indices && j < req_n_clients; i++) {
-    if (!CLG_GetClientAccessReportByIndex(i, &report, &now))
+    if (!CLG_GetClientAccessReportByIndex(i, req_reset, req_min_hits, &report, &now))
      continue;

    client = &tx_message->data.client_accesses_by_index.clients[j++];

    UTI_IPHostToNetwork(&report.ip_addr, &client->ip);
    client->ntp_hits = htonl(report.ntp_hits);
+    client->nke_hits = htonl(report.nke_hits);
    client->cmd_hits = htonl(report.cmd_hits);
    client->ntp_drops = htonl(report.ntp_drops);
+    client->nke_drops = htonl(report.nke_drops);
    client->cmd_drops = htonl(report.cmd_drops);
    client->ntp_interval = report.ntp_interval;
+    client->nke_interval = report.nke_interval;
    client->cmd_interval = report.cmd_interval;
    client->ntp_timeout_interval = report.ntp_timeout_interval;
    client->last_ntp_hit_ago = htonl(report.last_ntp_hit_ago);
+    client->last_nke_hit_ago = htonl(report.last_nke_hit_ago);
    client->last_cmd_hit_ago = htonl(report.last_cmd_hit_ago);
  }

@@ -1200,12 +1146,15 @@ handle_server_stats(CMD_Request *rx_message, CMD_Reply *tx_message)
  RPT_ServerStatsReport report;

  CLG_GetServerStatsReport(&report);
-  tx_message->reply = htons(RPY_SERVER_STATS);
+  tx_message->reply = htons(RPY_SERVER_STATS2);
  tx_message->data.server_stats.ntp_hits = htonl(report.ntp_hits);
+  tx_message->data.server_stats.nke_hits = htonl(report.nke_hits);
  tx_message->data.server_stats.cmd_hits = htonl(report.cmd_hits);
  tx_message->data.server_stats.ntp_drops = htonl(report.ntp_drops);
+  tx_message->data.server_stats.nke_drops = htonl(report.nke_drops);
  tx_message->data.server_stats.cmd_drops = htonl(report.cmd_drops);
  tx_message->data.server_stats.log_drops = htonl(report.log_drops);
+  tx_message->data.server_stats.ntp_auth_hits = htonl(report.ntp_auth_hits);
 }

 /* ================================================== */
@@ -1261,98 +1210,217 @@ handle_shutdown(CMD_Request *rx_message, CMD_Reply *tx_message)
  SCH_QuitProgram();
 }

+/* ================================================== */
+
+static void
+handle_ntp_source_name(CMD_Request *rx_message, CMD_Reply *tx_message)
+{
+  IPAddr addr;
+  char *name;
+
+  UTI_IPNetworkToHost(&rx_message->data.ntp_source_name.ip_addr, &addr);
+  name = NSR_GetName(&addr);
+
+  if (!name) {
+    tx_message->status = htons(STT_NOSUCHSOURCE);
+    return;
+  }
+
+  tx_message->reply = htons(RPY_NTP_SOURCE_NAME);
+
+  /* Avoid compiler warning */
+  if (strlen(name) >= sizeof (tx_message->data.ntp_source_name.name))
+    memcpy(tx_message->data.ntp_source_name.name, name,
+           sizeof (tx_message->data.ntp_source_name.name));
+  else
+    strncpy((char *)tx_message->data.ntp_source_name.name, name,
+            sizeof (tx_message->data.ntp_source_name.name));
+}
+
+/* ================================================== */
+
+static void
+handle_reload_sources(CMD_Request *rx_message, CMD_Reply *tx_message)
+{
+  CNF_ReloadSources();
+}
+
+/* ================================================== */
+
+static void
+handle_reset_sources(CMD_Request *rx_message, CMD_Reply *tx_message)
+{
+  struct timespec cooked_now, now;
+
+  SRC_ResetSources();
+  SCH_GetLastEventTime(&cooked_now, NULL, &now);
+  LCL_NotifyExternalTimeStep(&now, &cooked_now, 0.0, 0.0);
+}
+
+/* ================================================== */
+
+static void
+handle_auth_data(CMD_Request *rx_message, CMD_Reply *tx_message)
+{
+  RPT_AuthReport report;
+  IPAddr ip_addr;
+
+  UTI_IPNetworkToHost(&rx_message->data.auth_data.ip_addr, &ip_addr);
+
+  if (!NSR_GetAuthReport(&ip_addr, &report)) {
+    tx_message->status = htons(STT_NOSUCHSOURCE);
+    return;
+  }
+
+  tx_message->reply = htons(RPY_AUTH_DATA);
+
+  switch (report.mode) {
+    case NTP_AUTH_NONE:
+      tx_message->data.auth_data.mode = htons(RPY_AD_MD_NONE);
+      break;
+    case NTP_AUTH_SYMMETRIC:
+      tx_message->data.auth_data.mode = htons(RPY_AD_MD_SYMMETRIC);
+      break;
+    case NTP_AUTH_NTS:
+      tx_message->data.auth_data.mode = htons(RPY_AD_MD_NTS);
+      break;
+    default:
+      break;
+  }
+
+  tx_message->data.auth_data.key_type = htons(report.key_type);
+  tx_message->data.auth_data.key_id = htonl(report.key_id);
+  tx_message->data.auth_data.key_length = htons(report.key_length);
+  tx_message->data.auth_data.ke_attempts = htons(report.ke_attempts);
+  tx_message->data.auth_data.last_ke_ago = htonl(report.last_ke_ago);
+  tx_message->data.auth_data.cookies = htons(report.cookies);
+  tx_message->data.auth_data.cookie_length = htons(report.cookie_length);
+  tx_message->data.auth_data.nak = htons(report.nak);
+}
+
+/* ================================================== */
+
+static uint16_t
+convert_select_options(int options)
+{
+  return (options & SRC_SELECT_PREFER ? RPY_SD_OPTION_PREFER : 0) |
+         (options & SRC_SELECT_NOSELECT ? RPY_SD_OPTION_NOSELECT : 0) |
+         (options & SRC_SELECT_TRUST ? RPY_SD_OPTION_TRUST : 0) |
+         (options & SRC_SELECT_REQUIRE ? RPY_SD_OPTION_REQUIRE : 0);
+}
+
+/* ================================================== */
+
+static void
+handle_select_data(CMD_Request *rx_message, CMD_Reply *tx_message)
+{
+  RPT_SelectReport report;
+
+  if (!SRC_GetSelectReport(ntohl(rx_message->data.select_data.index), &report)) {
+    tx_message->status = htons(STT_NOSUCHSOURCE);
+    return;
+  }
+
+  tx_message->reply = htons(RPY_SELECT_DATA);
+
+  tx_message->data.select_data.ref_id = htonl(report.ref_id);
+  UTI_IPHostToNetwork(&report.ip_addr, &tx_message->data.select_data.ip_addr);
+  tx_message->data.select_data.state_char = report.state_char;
+  tx_message->data.select_data.authentication = report.authentication;
+  tx_message->data.select_data.leap = report.leap;
+  tx_message->data.select_data.conf_options = htons(convert_select_options(report.conf_options));
+  tx_message->data.select_data.eff_options = htons(convert_select_options(report.eff_options));
+  tx_message->data.select_data.last_sample_ago = htonl(report.last_sample_ago);
+  tx_message->data.select_data.score = UTI_FloatHostToNetwork(report.score);
+  tx_message->data.select_data.hi_limit = UTI_FloatHostToNetwork(report.hi_limit);
+  tx_message->data.select_data.lo_limit = UTI_FloatHostToNetwork(report.lo_limit);
+}
+
 /* ================================================== */
 /* Read a packet and process it */

 static void
 read_from_cmd_socket(int sock_fd, int event, void *anything)
 {
+  SCK_Message *sck_message;
  CMD_Request rx_message;
  CMD_Reply tx_message;
-  int status, read_length, expected_length, rx_message_length;
+  IPAddr loopback_addr, remote_ip;
+  int read_length, expected_length;
  int localhost, allowed, log_index;
-  union sockaddr_all where_from;
-  socklen_t from_length;
-  IPAddr remote_ip;
-  unsigned short remote_port, rx_command;
+  uint16_t rx_command;
  struct timespec now, cooked_now;

-  rx_message_length = sizeof(rx_message);
-  from_length = sizeof(where_from);
-
-  status = recvfrom(sock_fd, (char *)&rx_message, rx_message_length, 0,
-                    &where_from.sa, &from_length);
-
-  if (status < 0) {
-    LOG(LOGS_WARN, "Error [%s] reading from control socket %d",
-        strerror(errno), sock_fd);
+  sck_message = SCK_ReceiveMessage(sock_fd, 0);
+  if (!sck_message)
    return;
-  }

-  if (from_length > sizeof (where_from) ||
-      from_length <= sizeof (where_from.sa.sa_family)) {
-    DEBUG_LOG("Read command packet without source address");
-    return;
-  }
-
-  read_length = status;
+  read_length = sck_message->length;

  /* Get current time cheaply */
  SCH_GetLastEventTime(&cooked_now, NULL, &now);

-  UTI_SockaddrToIPAndPort(&where_from.sa, &remote_ip, &remote_port);
+  /* Check if it's from localhost (127.0.0.1, ::1, or Unix domain),
+     or an authorised address */
+  switch (sck_message->addr_type) {
+    case SCK_ADDR_IP:
+      assert(sock_fd == sock_fd4 || sock_fd == sock_fd6);
+      remote_ip = sck_message->remote_addr.ip.ip_addr;
+      SCK_GetLoopbackIPAddress(remote_ip.family, &loopback_addr);
+      localhost = UTI_CompareIPs(&remote_ip, &loopback_addr, NULL) == 0;

-  /* Check if it's from localhost (127.0.0.1, ::1, or Unix domain) */
-  switch (remote_ip.family) {
-    case IPADDR_INET4:
-      assert(sock_fd == sock_fd4);
-      localhost = remote_ip.addr.in4 == INADDR_LOOPBACK;
-      break;
-#ifdef FEAT_IPV6
-    case IPADDR_INET6:
-      assert(sock_fd == sock_fd6);
-      localhost = !memcmp(remote_ip.addr.in6, &in6addr_loopback,
-                          sizeof (in6addr_loopback));
-      break;
-#endif
-    case IPADDR_UNSPEC:
-      /* This should be the Unix domain socket */
-      if (where_from.sa.sa_family != AF_UNIX)
+      if (!localhost && !ADF_IsAllowed(access_auth_table, &remote_ip)) {
+        DEBUG_LOG("Unauthorised host %s",
+                  UTI_IPSockAddrToString(&sck_message->remote_addr.ip));
        return;
+      }
+
+      assert(remote_ip.family != IPADDR_UNSPEC);
+
+      break;
+    case SCK_ADDR_UNIX:
      assert(sock_fd == sock_fdu);
+      remote_ip.family = IPADDR_UNSPEC;
      localhost = 1;
      break;
    default:
-      assert(0);
-  }
-
-  DEBUG_LOG("Received %d bytes from %s fd %d",
-            status, UTI_SockaddrToString(&where_from.sa), sock_fd);
-
-  if (!(localhost || ADF_IsAllowed(access_auth_table, &remote_ip))) {
-    /* The client is not allowed access, so don't waste any more time
-       on him.  Note that localhost is always allowed access
-       regardless of the defined access rules - otherwise, we could
-       shut ourselves out completely! */
-    return;
+      DEBUG_LOG("Unexpected address type");
+      return;
  }

  if (read_length < offsetof(CMD_Request, data) ||
      read_length < offsetof(CMD_Reply, data) ||
-      rx_message.pkt_type != PKT_TYPE_CMD_REQUEST ||
-      rx_message.res1 != 0 ||
-      rx_message.res2 != 0) {
-
+      read_length > sizeof (CMD_Request)) {
    /* We don't know how to process anything like this or an error reply
       would be larger than the request */
+    DEBUG_LOG("Unexpected length");
+    return;
+  }
+
+  memcpy(&rx_message, sck_message->data, read_length);
+
+  if (rx_message.pkt_type != PKT_TYPE_CMD_REQUEST ||
+      rx_message.res1 != 0 ||
+      rx_message.res2 != 0) {
    DEBUG_LOG("Command packet dropped");
    return;
  }

+  log_index = CLG_LogServiceAccess(CLG_CMDMON, &remote_ip, &cooked_now);
+
+  /* Don't reply to all requests from hosts other than localhost if the rate
+     is excessive */
+  if (!localhost && log_index >= 0 && CLG_LimitServiceRate(CLG_CMDMON, log_index)) {
+      DEBUG_LOG("Command packet discarded to limit response rate");
+      return;
+  }
+
  expected_length = PKL_CommandLength(&rx_message);
  rx_command = ntohs(rx_message.command);

  memset(&tx_message, 0, sizeof (tx_message));
+  sck_message->data = &tx_message;
+  sck_message->length = 0;

  tx_message.version = PROTO_VERSION_NUMBER;
  tx_message.pkt_type = PKT_TYPE_CMD_REPLY;
@@ -1367,7 +1435,7 @@ read_from_cmd_socket(int sock_fd, int event, void *anything)

    if (rx_message.version >= PROTO_VERSION_MISMATCH_COMPAT_SERVER) {
      tx_message.status = htons(STT_BADPKTVERSION);
-      transmit_reply(&tx_message, &where_from);
+      transmit_reply(sock_fd, read_length, sck_message);
    }
    return;
  }
@@ -1377,7 +1445,7 @@ read_from_cmd_socket(int sock_fd, int event, void *anything)
    DEBUG_LOG("Command packet has invalid command %d", rx_command);

    tx_message.status = htons(STT_INVALID);
-    transmit_reply(&tx_message, &where_from);
+    transmit_reply(sock_fd, read_length, sck_message);
    return;
  }

@@ -1386,21 +1454,12 @@ read_from_cmd_socket(int sock_fd, int event, void *anything)
              expected_length);

    tx_message.status = htons(STT_BADPKTLENGTH);
-    transmit_reply(&tx_message, &where_from);
+    transmit_reply(sock_fd, read_length, sck_message);
    return;
  }

  /* OK, we have a valid message.  Now dispatch on message type and process it. */

-  log_index = CLG_LogCommandAccess(&remote_ip, &cooked_now);
-
-  /* Don't reply to all requests from hosts other than localhost if the rate
-     is excessive */
-  if (!localhost && log_index >= 0 && CLG_LimitCommandResponseRate(log_index)) {
-      DEBUG_LOG("Command packet discarded to limit response rate");
-      return;
-  }
-
  if (rx_command >= N_REQUEST_TYPES) {
    /* This should be already handled */
    assert(0);
@@ -1408,7 +1467,7 @@ read_from_cmd_socket(int sock_fd, int event, void *anything)
    /* Check level of authority required to issue the command.  All commands
       from the Unix domain socket (which is accessible only by the root and
       chrony user/group) are allowed. */
-    if (where_from.sa.sa_family == AF_UNIX) {
+    if (remote_ip.family == IPADDR_UNSPEC) {
      assert(sock_fd == sock_fdu);
      allowed = 1;
    } else {
@@ -1547,12 +1606,8 @@ read_from_cmd_socket(int sock_fd, int event, void *anything)
          handle_cmdaccheck(&rx_message, &tx_message);
          break;

-        case REQ_ADD_SERVER3:
-          handle_add_source(NTP_SERVER, &rx_message, &tx_message);
-          break;
-
-        case REQ_ADD_PEER3:
-          handle_add_source(NTP_PEER, &rx_message, &tx_message);
+        case REQ_ADD_SOURCE:
+          handle_add_source(&rx_message, &tx_message);
          break;

        case REQ_DEL_SOURCE:
@@ -1599,7 +1654,7 @@ read_from_cmd_socket(int sock_fd, int event, void *anything)
          handle_cyclelogs(&rx_message, &tx_message);
          break;

-        case REQ_CLIENT_ACCESSES_BY_INDEX2:
+        case REQ_CLIENT_ACCESSES_BY_INDEX3:
          handle_client_accesses_by_index(&rx_message, &tx_message);
          break;

@@ -1655,6 +1710,26 @@ read_from_cmd_socket(int sock_fd, int event, void *anything)
          handle_onoffline(&rx_message, &tx_message);
          break;

+        case REQ_NTP_SOURCE_NAME:
+          handle_ntp_source_name(&rx_message, &tx_message);
+          break;
+
+        case REQ_RESET_SOURCES:
+          handle_reset_sources(&rx_message, &tx_message);
+          break;
+
+        case REQ_AUTH_DATA:
+          handle_auth_data(&rx_message, &tx_message);
+          break;
+
+        case REQ_SELECT_DATA:
+          handle_select_data(&rx_message, &tx_message);
+          break;
+
+        case REQ_RELOAD_SOURCES:
+          handle_reload_sources(&rx_message, &tx_message);
+          break;
+
        default:
          DEBUG_LOG("Unhandled command %d", rx_command);
          tx_message.status = htons(STT_FAILED);
@@ -1666,19 +1741,7 @@ read_from_cmd_socket(int sock_fd, int event, void *anything)
  }

  /* Transmit the response */
-  {
-    /* Include a simple way to lose one message in three to test resend */
-
-    static int do_it=1;
-
-    if (do_it) {
-      transmit_reply(&tx_message, &where_from);
-    }
-
-#if 0
-    do_it = ((do_it + 1) % 3);
-#endif
-  }
+  transmit_reply(sock_fd, read_length, sck_message);
 }

 /* ================================================== */
--- a/cmdmon.h
+++ b/cmdmon.h
@@ -29,7 +29,7 @@

 #include "addressing.h"

-extern void CAM_Initialise(int family);
+extern void CAM_Initialise(void);

 extern void CAM_Finalise(void);

--- a/cmdparse.c
+++ b/cmdparse.c
@@ -62,6 +62,8 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
  src->params.filter_length = 0;
  src->params.interleaved = 0;
  src->params.sel_options = 0;
+  src->params.nts = 0;
+  src->params.nts_port = SRC_DEFAULT_NTSPORT;
  src->params.authkey = INACTIVE_AUTHKEY;
  src->params.max_delay = SRC_DEFAULT_MAXDELAY;
  src->params.max_delay_ratio = SRC_DEFAULT_MAXDELAYRATIO;
@@ -140,11 +142,16 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
    } else if (!strcasecmp(cmd, "minstratum")) {
      if (sscanf(line, "%d%n", &src->params.min_stratum, &n) != 1)
        return 0;
+    } else if (!strcasecmp(cmd, "nts")) {
+      src->params.nts = 1;
+    } else if (!strcasecmp(cmd, "ntsport")) {
+      if (sscanf(line, "%d%n", &src->params.nts_port, &n) != 1)
+        return 0;
    } else if (!strcasecmp(cmd, "offset")) {
      if (sscanf(line, "%lf%n", &src->params.offset, &n) != 1)
        return 0;
    } else if (!strcasecmp(cmd, "port")) {
-      if (sscanf(line, "%hu%n", &src->port, &n) != 1)
+      if (sscanf(line, "%d%n", &src->port, &n) != 1)
        return 0;
    } else if (!strcasecmp(cmd, "polltarget")) {
      if (sscanf(line, "%d%n", &src->params.poll_target, &n) != 1)
@@ -261,7 +268,7 @@ CPS_SplitWord(char *line)
 /* ================================================== */

 int
-CPS_ParseKey(char *line, uint32_t *id, const char **hash, char **key)
+CPS_ParseKey(char *line, uint32_t *id, const char **type, char **key)
 {
  char *s1, *s2, *s3, *s4;

@@ -278,10 +285,10 @@ CPS_ParseKey(char *line, uint32_t *id, const char **hash, char **key)
    return 0;

  if (*s3) {
-    *hash = s2;
+    *type = s2;
    *key = s3;
  } else {
-    *hash = "MD5";
+    *type = "MD5";
    *key = s2;
  }

--- a/cmdparse.h
+++ b/cmdparse.h
@@ -32,7 +32,7 @@

 typedef struct {
  char *name;
-  unsigned short port;
+  int port;
  SourceParameters params;
 } CPS_NTP_Source;

@@ -49,6 +49,6 @@ extern void CPS_NormalizeLine(char *line);
 extern char *CPS_SplitWord(char *line);

 /* Parse a key from keyfile */
-extern int CPS_ParseKey(char *line, uint32_t *id, const char **hash, char **key);
+extern int CPS_ParseKey(char *line, uint32_t *id, const char **type, char **key);

 #endif /* GOT_CMDPARSE_H */
--- a/conf.c
+++ b/conf.c
--- a/conf.h
+++ b/conf.h
@@ -30,10 +30,13 @@

 #include "addressing.h"
 #include "reference.h"
+#include "sources.h"

 extern void CNF_Initialise(int restarted, int client_only);
 extern void CNF_Finalise(void);

+extern void CNF_EnablePrint(void);
+
 extern char *CNF_GetRtcDevice(void);

 extern void CNF_ReadFile(const char *filename);
@@ -46,6 +49,8 @@ extern void CNF_AddSources(void);
 extern void CNF_AddBroadcasts(void);
 extern void CNF_AddRefclocks(void);

+extern void CNF_ReloadSources(void);
+
 extern int CNF_GetAcquisitionPort(void);
 extern int CNF_GetNTPPort(void);
 extern char *CNF_GetDriftFile(void);
@@ -74,7 +79,11 @@ extern void CNF_GetFallbackDrifts(int *min, int *max);
 extern void CNF_GetBindAddress(int family, IPAddr *addr);
 extern void CNF_GetBindAcquisitionAddress(int family, IPAddr *addr);
 extern void CNF_GetBindCommandAddress(int family, IPAddr *addr);
+extern char *CNF_GetBindNtpInterface(void);
+extern char *CNF_GetBindAcquisitionInterface(void);
+extern char *CNF_GetBindCommandInterface(void);
 extern char *CNF_GetBindCommandPath(void);
+extern int CNF_GetNtpDscp(void);
 extern char *CNF_GetNtpSigndSocket(void);
 extern char *CNF_GetPidFile(void);
 extern REF_LeapMode CNF_GetLeapSecMode(void);
@@ -86,7 +95,9 @@ extern double CNF_GetMaxClockError(void);
 extern double CNF_GetMaxDrift(void);
 extern double CNF_GetCorrectionTimeRatio(void);
 extern double CNF_GetMaxSlewRate(void);
+extern double CNF_GetClockPrecision(void);

+extern SRC_AuthSelectMode CNF_GetAuthSelectMode(void);
 extern double CNF_GetMaxDistance(void);
 extern double CNF_GetMaxJitter(void);
 extern double CNF_GetReselectDistance(void);
@@ -101,6 +112,7 @@ extern int CNF_GetSchedPriority(void);
 extern int CNF_GetLockMemory(void);

 extern int CNF_GetNTPRateLimit(int *interval, int *burst, int *leak);
+extern int CNF_GetNtsRateLimit(int *interval, int *burst, int *leak);
 extern int CNF_GetCommandRateLimit(int *interval, int *burst, int *leak);
 extern void CNF_GetSmooth(double *max_freq, double *max_wander, int *leap_only);
 extern void CNF_GetTempComp(char **file, double *interval, char **point_file, double *T0, double *k0, double *k1, double *k2);
@@ -139,4 +151,17 @@ typedef struct {

 extern int CNF_GetHwTsInterface(unsigned int index, CNF_HwTsInterface **iface);

+extern char *CNF_GetNtsDumpDir(void);
+extern char *CNF_GetNtsNtpServer(void);
+extern char *CNF_GetNtsServerCertFile(void);
+extern char *CNF_GetNtsServerKeyFile(void);
+extern int CNF_GetNtsServerPort(void);
+extern int CNF_GetNtsServerProcesses(void);
+extern int CNF_GetNtsServerConnections(void);
+extern int CNF_GetNtsRefresh(void);
+extern int CNF_GetNtsRotate(void);
+extern char *CNF_GetNtsTrustedCertFile(void);
+extern int CNF_GetNoSystemCert(void);
+extern int CNF_GetNoCertTimeCheck(void);
+
 #endif /* GOT_CONF_H */
--- a/234
+++ b/234
@@ -5,7 +5,7 @@
 #
 # Copyright (C) Richard P. Curnow  1997-2003
 # Copyright (C) Bryan Christianson  2016
-# Copyright (C) Miroslav Lichvar  2009, 2012-2018
+# Copyright (C) Miroslav Lichvar  2009, 2012-2020
 # Copyright (C) Stefan R. Filipek  2019
 #
 # =======================================================================
@@ -55,6 +55,34 @@ test_code () {
  return $result
 }
 #}}}
+#{{{ test_executable
+test_executable () {
+  name=$1
+  executable=$2
+  options=$3
+
+  printf "%s" "Checking for $name : "
+
+  echo $executable $options >> config.log
+  $executable $options >> config.log 2>&1
+
+  if [ $? -eq 0 ]
+  then
+    echo "Yes"
+    result=0
+  else
+    echo "No"
+    result=1
+  fi
+  echo >> config.log
+  return $result
+}
+#}}}
+#{{{ pkg_config
+pkg_config () {
+  $PKG_CONFIG "$@" 2>> config.log
+}
+#}}}
 #{{{ usage
 usage () {
  cat <<EOF
@@ -80,15 +108,13 @@ for instance \`--prefix=$HOME'.

 For better control, use the options below.
  --disable-readline     Disable line editing support
-  --without-readline     Don't use GNU readline even if it is available
  --without-editline     Don't use editline even if it is available
-  --with-readline-includes=DIR Specify where readline include directory is
-  --with-readline-library=DIR Specify where readline lib directory is
-  --with-ncurses-library=DIR Specify where ncurses lib directory is
  --disable-sechash      Disable support for hashes other than MD5
  --without-nettle       Don't use nettle even if it is available
  --without-nss          Don't use NSS even if it is available
  --without-tomcrypt     Don't use libtomcrypt even if it is available
+  --disable-nts          Disable NTS support
+  --without-gnutls       Don't use gnutls even if it is available
  --disable-cmdmon       Disable command and monitoring support
  --disable-ntp          Disable NTP support
  --disable-refclock     Disable reference clock support
@@ -137,6 +163,11 @@ Some influential environment variables:
              headers in a nonstandard directory <include dir>
  LDFLAGS     linker flags, e.g. -L<lib dir> if you have libraries in a
              nonstandard directory <lib dir>
+  PKG_CONFIG  path to pkg-config utility
+  PKG_CONFIG_PATH
+              directories to add to pkg-config's search path
+  PKG_CONFIG_LIBDIR
+              path overriding pkg-config's built-in search path

 Use these variables to override the choices made by \`configure' or to help
 it to find libraries and programs with nonstandard names/locations.
@@ -154,13 +185,6 @@ add_def () {
  fi
 }
 #}}}
-#{{{ pkg_config
-pkg_config () {
-  type pkg-config > /dev/null 2> /dev/null || return 1
-
-  pkg-config $@ 2> /dev/null
-}
-#}}}
 #{{{ get_features
 get_features () {
  ff=1
@@ -186,23 +210,24 @@ OPERATINGSYSTEM=`uname -s`
 VERSION=`uname -r`
 MACHINE=`uname -m`

+LIBS=""
 EXTRA_LIBS=""
 EXTRA_CLI_LIBS=""
 EXTRA_OBJECTS=""
-EXTRA_DEFS=""
-SYSDEFS=""
+EXTRA_CLI_OBJECTS=""

 feat_debug=0
 feat_cmdmon=1
 feat_ntp=1
 feat_refclock=1
 feat_readline=1
-try_readline=1
 try_editline=1
 feat_sechash=1
 try_nettle=1
 try_nss=1
 try_tomcrypt=1
+feat_nts=1
+try_gnutls=1
 feat_rtc=1
 try_rtc=0
 feat_droproot=1
@@ -211,9 +236,6 @@ try_clockctl=0
 feat_scfilter=0
 try_seccomp=-1
 priv_ops=""
-readline_lib=""
-readline_inc=""
-ncurses_lib=""
 feat_ipv6=1
 feat_phc=1
 try_phc=0
@@ -244,21 +266,9 @@ do
    --disable-readline )
      feat_readline=0
    ;;
-    --without-readline )
-      try_readline=0
-    ;;
    --without-editline )
      try_editline=0
    ;;
-    --with-readline-library=* )
-      readline_lib=-L`echo $option | sed -e 's/^.*=//;'`
-    ;;
-    --with-readline-includes=* )
-      readline_inc=-I`echo $option | sed -e 's/^.*=//;'`
-    ;;
-    --with-ncurses-library=* )
-      ncurses_lib=-L`echo $option | sed -e 's/^.*=//;'`
-    ;;
    --prefix=* | --install_prefix=* )
      SETPREFIX=`echo $option | sed -e 's/[^=]*=//;'`
    ;;
@@ -373,6 +383,12 @@ do
    --without-tomcrypt )
      try_tomcrypt=0
    ;;
+    --disable-nts )
+      feat_nts=0
+    ;;
+    --without-gnutls )
+      try_gnutls=0
+    ;;
    --host-system=* )
      OPERATINGSYSTEM=`echo $option | sed -e 's/^.*=//;'`
    ;;
@@ -432,8 +448,7 @@ case $OPERATINGSYSTEM in
    ;;
    Darwin)
        EXTRA_OBJECTS="sys_macosx.o"
-        EXTRA_LIBS="-lresolv"
-        EXTRA_CLI_LIBS="-lresolv"
+        LIBS="$LIBS -lresolv"
        add_def MACOSX
        if [ $feat_droproot = "1" ]; then
          add_def FEAT_PRIVDROP
@@ -452,8 +467,7 @@ case $OPERATINGSYSTEM in
    ;;
    SunOS)
        EXTRA_OBJECTS="sys_generic.o sys_solaris.o sys_timex.o sys_posix.o"
-        EXTRA_LIBS="-lsocket -lnsl -lresolv"
-        EXTRA_CLI_LIBS="-lsocket -lnsl -lresolv"
+        LIBS="$LIBS -lsocket -lnsl -lresolv"
        try_setsched=1
        try_lockmem=1
        add_def SOLARIS
@@ -485,7 +499,7 @@ fi

 if [ $feat_ntp = "1" ]; then
  add_def FEAT_NTP
-  EXTRA_OBJECTS="$EXTRA_OBJECTS ntp_core.o ntp_io.o ntp_sources.o"
+  EXTRA_OBJECTS="$EXTRA_OBJECTS ntp_auth.o ntp_core.o ntp_ext.o ntp_io.o ntp_sources.o"
  if [ $feat_ntp_signd = "1" ]; then
    add_def FEAT_SIGND
    EXTRA_OBJECTS="$EXTRA_OBJECTS ntp_signd.o"
@@ -553,6 +567,16 @@ if [ "x$MYCC" = "xgcc" ] || [ "x$MYCC" = "xclang" ]; then
  MYCFLAGS="$MYCFLAGS -Wmissing-prototypes -Wall"
 fi

+if [ "x$PKG_CONFIG" = "x" ]; then
+  PKG_CONFIG=pkg-config
+fi
+
+if ! test_executable "pkg-config" $PKG_CONFIG --version; then
+  try_nettle=0
+  try_nss=0
+  try_gnutls=0
+fi
+
 if test_code '64-bit time_t' 'time.h' '' '' '
  char x[sizeof(time_t) > 4 ? 1 : -1] = {0};
  return x[0];'
@@ -592,11 +616,9 @@ then
 fi

 MATHCODE='return (int) pow(2.0, log(sqrt((double)argc)));'
-if test_code 'math' 'math.h' '' '' "$MATHCODE"; then
-  LIBS=""
-else
+if ! test_code 'math' 'math.h' '' '' "$MATHCODE"; then
  if test_code 'math in -lm' 'math.h' '' '-lm' "$MATHCODE"; then
-    LIBS="-lm"
+    LIBS="$LIBS -lm"
  else
    echo "error: could not compile/link a program which uses sqrt(), log(), pow()"
    exit 1
@@ -611,10 +633,11 @@ then
 fi

 if [ $feat_ipv6 = "1" ] && \
-  test_code 'IPv6 support' 'arpa/inet.h sys/socket.h netinet/in.h' '' "$EXTRA_LIBS" '
+  test_code 'IPv6 support' 'arpa/inet.h sys/socket.h netinet/in.h' '' "$LIBS" '
    struct sockaddr_in6 n;
    char p[100];
    n.sin6_addr = in6addr_any;
+    n.sin6_scope_id = 0;
    return !inet_ntop(AF_INET6, &n.sin6_addr.s6_addr, p, sizeof(p));'
 then
  add_def FEAT_IPV6
@@ -647,15 +670,16 @@ if [ $try_clock_gettime = "1" ]; then
  fi
 fi

-if test_code 'getaddrinfo()' 'sys/types.h sys/socket.h netdb.h' '' "$EXTRA_LIBS" \
+if test_code 'getaddrinfo()' 'sys/types.h sys/socket.h netdb.h' '' "$LIBS" \
  'return getaddrinfo(0, 0, 0, 0);'
 then
  add_def HAVE_GETADDRINFO
 fi

 if [ $feat_asyncdns = "1" ] && \
-  test_code 'pthread' 'pthread.h' '-pthread' '' \
-    'return (int)pthread_create((void *)1, NULL, (void *)1, NULL);'
+  test_code 'pthread' 'pthread.h' '-pthread' '' '
+    pthread_t thread;
+    return (int)pthread_create(&thread, NULL, (void *)1, NULL);'
 then
  add_def FEAT_ASYNCDNS
  add_def USE_PTHREAD_ASYNCDNS
@@ -665,22 +689,22 @@ fi

 if test_code 'arc4random_buf()' 'stdlib.h' '' '' 'arc4random_buf(NULL, 0);'; then
  add_def HAVE_ARC4RANDOM
-fi
-
-if test_code 'getrandom()' 'stdlib.h sys/random.h' '' '' \
-    'return getrandom(NULL, 256, 0);'; then
-  add_def HAVE_GETRANDOM
+else
+  if test_code 'getrandom()' 'stdlib.h sys/random.h' '' '' \
+      'return getrandom(NULL, 256, 0);'; then
+    add_def HAVE_GETRANDOM
+  fi
 fi

 RECVMMSG_CODE='
  struct mmsghdr hdr;
  return !recvmmsg(0, &hdr, 1, MSG_DONTWAIT, 0);'
 if [ $try_recvmmsg = "1" ]; then
-  if test_code 'recvmmsg()' 'sys/socket.h' '' "$EXTRA_LIBS" "$RECVMMSG_CODE"; then
+  if test_code 'recvmmsg()' 'sys/socket.h' '' "$LIBS" "$RECVMMSG_CODE"; then
    add_def HAVE_RECVMMSG
  else
    if test_code 'recvmmsg() with _GNU_SOURCE' 'sys/socket.h' '-D_GNU_SOURCE' \
-      "$EXTRA_LIBS" "$RECVMMSG_CODE"
+      "$LIBS" "$RECVMMSG_CODE"
    then
      add_def _GNU_SOURCE
      add_def HAVE_RECVMMSG
@@ -731,6 +755,7 @@ if [ "x$timepps_h" != "x" ] && \
    pps_handle_t h = 0;
    pps_info_t i;
    struct timespec ts;
+    ts.tv_sec = ts.tv_nsec = 0;
    return time_pps_fetch(h, PPS_TSFMT_TSPEC, &i, &ts);'
 then
  add_def FEAT_PPS
@@ -759,10 +784,12 @@ if [ $feat_scfilter = "1" ] && [ $try_seccomp = "1" ] && \
    'seccomp_init(SCMP_ACT_KILL);'
 then
  add_def FEAT_SCFILTER
-  # NAME2IPADDRESS shouldn't be enabled with other operations as the helper
-  # process works on one request at the time and the async resolver could
-  # block the main thread
-  priv_ops="NAME2IPADDRESS RELOADDNS"
+  if [ $feat_ntp = "1" ]; then
+    # NAME2IPADDRESS shouldn't be enabled together with a privops operation
+    # used by the main thread as the helper process works on one request at
+    # a time and the async resolver would block the main thread
+    priv_ops="NAME2IPADDRESS RELOADDNS"
+  fi
  EXTRA_LIBS="$EXTRA_LIBS -lseccomp"
 fi

@@ -817,6 +844,7 @@ if [ $try_lockmem = "1" ] && \
    'setrlimit(RLIMIT_MEMLOCK, ...)' \
    'sys/resource.h' '' '' '
     struct rlimit rlim;
+     rlim.rlim_max = rlim.rlim_cur = RLIM_INFINITY;
     setrlimit(RLIMIT_MEMLOCK, &rlim);'
 then
  add_def HAVE_SETRLIMIT_MEMLOCK
@@ -830,37 +858,11 @@ fi
 READLINE_LINK=""
 if [ $feat_readline = "1" ]; then
  if [ $try_editline = "1" ]; then
-    if test_code editline 'stdio.h editline/readline.h' \
-      "$readline_inc" "$readline_lib -ledit" \
+    if test_code editline 'stdio.h editline/readline.h' '' '-ledit' \
      'add_history(readline("prompt"));'
    then
      add_def FEAT_READLINE
-      add_def USE_EDITLINE
-      MYCPPFLAGS="$MYCPPFLAGS $readline_inc"
-      READLINE_LINK="$readline_lib -ledit"
-    fi
-  fi
-
-  if [ "x$READLINE_LINK" = "x" ] && [ $try_readline = "1" ]; then
-    if test_code readline 'stdio.h readline/readline.h readline/history.h' \
-      "$readline_inc" "$readline_lib -lreadline" \
-      'add_history(readline("prompt"));'
-    then
-      add_def FEAT_READLINE
-      MYCPPFLAGS="$MYCPPFLAGS $readline_inc"
-      READLINE_LINK="$readline_lib -lreadline"
-    fi
-  fi
-
-  if [ "x$READLINE_LINK" = "x" ] && [ $try_readline = "1" ]; then
-    if test_code 'readline with -lncurses' \
-      'stdio.h readline/readline.h readline/history.h' \
-      "$readline_inc" "$readline_lib $ncurses_lib -lreadline -lncurses" \
-      'add_history(readline("prompt"));'
-    then
-      add_def FEAT_READLINE
-      MYCPPFLAGS="$MYCPPFLAGS $readline_inc"
-      READLINE_LINK="$readline_lib $ncurses_lib -lreadline -lncurses"
+      READLINE_LINK="-ledit"
    fi
  fi

@@ -879,22 +881,28 @@ if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ]  && [ $try_nettle = "1" ];
  then
    HASH_OBJ="hash_nettle.o"
    HASH_LINK="$test_link"
-    LIBS="$LIBS $HASH_LINK"
    MYCPPFLAGS="$MYCPPFLAGS $test_cflags"
    add_def FEAT_SECHASH
+
+    if test_code 'CMAC in nettle' 'nettle/cmac.h' "$test_cflags" "$test_link" \
+      'cmac128_update(NULL, NULL, NULL, 0, NULL);'
+    then
+      add_def HAVE_CMAC
+      EXTRA_OBJECTS="$EXTRA_OBJECTS cmac_nettle.o"
+      EXTRA_CLI_OBJECTS="$EXTRA_CLI_OBJECTS cmac_nettle.o"
+    fi
  fi
 fi

 if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ]  && [ $try_nss = "1" ]; then
  test_cflags="`pkg_config --cflags nss`"
-  test_link="`pkg_config --libs-only-L nss` -lfreebl3"
+  test_link="`pkg_config --libs-only-L nss` -lfreebl3 -lnssutil3"
  if test_code 'NSS' 'nss.h hasht.h nsslowhash.h' \
    "$test_cflags" "$test_link" \
    'NSSLOWHASH_Begin(NSSLOWHASH_NewContext(NSSLOW_Init(), HASH_AlgSHA512));'
  then
    HASH_OBJ="hash_nss.o"
    HASH_LINK="$test_link"
-    LIBS="$LIBS $HASH_LINK"
    MYCPPFLAGS="$MYCPPFLAGS $test_cflags"
    add_def FEAT_SECHASH
  fi
@@ -906,12 +914,58 @@ if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ] && [ $try_tomcrypt = "1" ]
  then
    HASH_OBJ="hash_tomcrypt.o"
    HASH_LINK="-ltomcrypt"
-    LIBS="$LIBS $HASH_LINK"
    MYCPPFLAGS="$MYCPPFLAGS -I/usr/include/tomcrypt"
    add_def FEAT_SECHASH
  fi
 fi

+EXTRA_OBJECTS="$EXTRA_OBJECTS $HASH_OBJ"
+EXTRA_CLI_OBJECTS="$EXTRA_CLI_OBJECTS $HASH_OBJ"
+LIBS="$LIBS $HASH_LINK"
+
+if [ $feat_ntp = "1" ] && [ $feat_nts = "1" ] && [ $try_gnutls = "1" ]; then
+  test_cflags="`pkg_config --cflags gnutls`"
+  test_link="`pkg_config --libs gnutls`"
+  if test_code 'gnutls' 'gnutls/gnutls.h' \
+    "$test_cflags" "$test_link" '
+      return gnutls_init(NULL, 0) + GNUTLS_TLS1_3 +
+        gnutls_priority_init2(NULL, "", NULL, GNUTLS_PRIORITY_INIT_DEF_APPEND) +
+        gnutls_prf_rfc5705(NULL, 0, "", 0, "", 16, NULL);'
+  then
+    if test_code 'SIV in nettle' \
+      'nettle/siv-cmac.h' "" "$LIBS" \
+      'siv_cmac_aes128_set_key(NULL, NULL);'
+    then
+      EXTRA_OBJECTS="$EXTRA_OBJECTS siv_nettle.o"
+      add_def HAVE_SIV
+      add_def HAVE_NETTLE_SIV_CMAC
+    else
+      if test_code 'SIV in gnutls' 'gnutls/gnutls.h' \
+        "$test_cflags" "$test_link" '
+          return gnutls_aead_cipher_init(NULL, GNUTLS_CIPHER_AES_128_SIV, NULL);'
+      then
+        EXTRA_OBJECTS="$EXTRA_OBJECTS siv_gnutls.o"
+        add_def HAVE_SIV
+      else
+        if test_code 'AES128 in nettle' 'nettle/aes.h' '' "$LIBS" \
+          'aes128_set_encrypt_key(NULL, NULL);'
+        then
+          EXTRA_OBJECTS="$EXTRA_OBJECTS siv_nettle.o"
+          add_def HAVE_SIV
+        fi
+      fi
+    fi
+
+    if grep '#define HAVE_SIV' config.h > /dev/null; then
+      EXTRA_OBJECTS="$EXTRA_OBJECTS nts_ke_client.o nts_ke_server.o nts_ke_session.o"
+      EXTRA_OBJECTS="$EXTRA_OBJECTS nts_ntp_auth.o nts_ntp_client.o nts_ntp_server.o"
+      LIBS="$LIBS $test_link"
+      MYCPPFLAGS="$MYCPPFLAGS $test_cflags"
+      add_def FEAT_NTS
+    fi
+  fi
+fi
+
 if [ $use_pthread = "1" ]; then
  MYCFLAGS="$MYCFLAGS -pthread"
 fi
@@ -981,7 +1035,7 @@ add_def MAIL_PROGRAM "\"$mail_program\""

 common_features="`get_features SECHASH IPV6 DEBUG`"
 chronyc_features="`get_features READLINE`"
-chronyd_features="`get_features CMDMON NTP REFCLOCK RTC PRIVDROP SCFILTER SIGND ASYNCDNS`"
+chronyd_features="`get_features CMDMON NTP REFCLOCK RTC PRIVDROP SCFILTER SIGND ASYNCDNS NTS`"
 add_def CHRONYC_FEATURES "\"$chronyc_features $common_features\""
 add_def CHRONYD_FEATURES "\"$chronyd_features $common_features\""
 echo "Features : $chronyd_features $chronyc_features $common_features"
@@ -997,15 +1051,15 @@ add_def CHRONY_VERSION "\"${CHRONY_VERSION}\""
 for f in Makefile doc/Makefile test/unit/Makefile
 do
  echo Creating $f
-  sed -e "s%@EXTRA_OBJECTS@%${EXTRA_OBJECTS}%;\
+  sed -e "s%@EXTRA_OBJS@%${EXTRA_OBJECTS}%;\
+          s%@EXTRA_CLI_OBJS@%${EXTRA_CLI_OBJECTS}%;\
          s%@CC@%${MYCC}%;\
          s%@CFLAGS@%${MYCFLAGS}%;\
          s%@CPPFLAGS@%${MYCPPFLAGS}%;\
-          s%@LIBS@%${LIBS}%;\
          s%@LDFLAGS@%${MYLDFLAGS}%;\
+          s%@LIBS@%${LIBS}%;\
          s%@EXTRA_LIBS@%${EXTRA_LIBS}%;\
          s%@EXTRA_CLI_LIBS@%${EXTRA_CLI_LIBS}%;\
-          s%@HASH_OBJ@%${HASH_OBJ}%;\
          s%@SYSCONFDIR@%${SYSCONFDIR}%;\
          s%@BINDIR@%${BINDIR}%;\
          s%@SBINDIR@%${SBINDIR}%;\
--- a/doc/chrony.conf.adoc
+++ b/doc/chrony.conf.adoc
@@ -3,7 +3,7 @@
 // Copyright (C) Richard P. Curnow  1997-2003
 // Copyright (C) Stephen Wadeley  2016
 // Copyright (C) Bryan Christianson  2017
-// Copyright (C) Miroslav Lichvar  2009-2017
+// Copyright (C) Miroslav Lichvar  2009-2020
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of version 2 of the GNU General Public License as
@@ -32,12 +32,14 @@ chrony.conf - chronyd configuration file
 == DESCRIPTION

 This file configures the *chronyd* daemon. The compiled-in location is
-_@SYSCONFDIR@/chrony.conf_, but other locations can be specified on the
+_@SYSCONFDIR@/chrony.conf_. Other locations can be specified on the
 *chronyd* command line with the *-f* option.

 Each directive in the configuration file is placed on a separate line. The
-following sections describe each of the directives in turn. The directives can
-occur in any order in the file and they are not case-sensitive.
+following sections describe each of the directives in turn. The directives are
+not case-sensitive. Generally, the directives can occur in any order in the file
+and if a directive is specified multiple times, only the last one will be
+effective. Exceptions are noted in the descriptions.

 The configuration directives can also be specified directly on the *chronyd*
 command line. In this case each argument is parsed as a new line and the
@@ -61,9 +63,10 @@ source. The client-server relationship is strictly hierarchical: a client might
 synchronise its system time to that of the server, but the server's system time
 will never be influenced by that of a client.
 +
-The *server* directive is immediately followed by either the name of the
-server, or its IP address. The *server* directive supports the following
-options:
+This directive can be used multiple times to specify multiple servers.
+
+The directive is immediately followed by either the name of the
+server, or its IP address. It supports the following options:
 +
 *minpoll* _poll_:::
 This option specifies the minimum interval between requests sent to the server
@@ -82,13 +85,13 @@ interval should stay at or below 9 (512 seconds). The default is 10 (1024
 seconds), the minimum is -6 (1/64th of a second), and the maximum is 24 (6
 months).
 *iburst*:::
-With this option, the interval between the first four requests sent to the
-server will be 2 seconds or less instead of the interval specified by the
-*minpoll* option, which allows *chronyd* to make the first update of the clock
-shortly after start.
+With this option, *chronyd* will start with a burst of 4-8 requests in order to
+make the first update of the clock sooner. It will also repeat the burst every
+time the source is switched from the offline state to online with the
+<<chronyc.adoc#online,*online*>> command in *chronyc*.
 *burst*:::
-With this option, *chronyd* will shorten the interval between up to four
-requests to 2 seconds or less when it cannot get a good measurement from the
+With this option, *chronyd* will send a burst of up to 4 requests when it
+cannot get a good measurement from the
 server. The number of requests in the burst is limited by the current polling
 interval to keep the average interval at or above the minimum interval, i.e.
 the current interval needs to be at least two times longer than the minimum
@@ -96,7 +99,7 @@ interval in order to allow a burst with two requests.
 *key* _ID_:::
 The NTP protocol supports a message authentication code (MAC) to prevent
 computers having their system time upset by rogue packets being sent to them.
-The MAC is generated as a function of a password specified in the key file,
+The MAC is generated as a function of a key specified in the key file,
 which is specified by the <<keyfile,*keyfile*>> directive.
 +
 The *key* option specifies which key (with an ID in the range 1 through 2^32-1)
@@ -107,6 +110,12 @@ otherwise no relationship between the computers will be possible.
 If the server is running *ntpd* and the output size of the hash function used
 by the key is longer than 160 bits (e.g. SHA256), the *version* option needs to
 be set to 4 for compatibility.
+*nts*:::
+This option enables authentication using the Network Time Security (NTS)
+mechanism. Unlike with the *key* option, the server and client do not need to
+share a key in a key file. NTS has a Key Establishment (NTS-KE) protocol using
+the Transport Layer Security (TLS) protocol to get the keys and cookies
+required by NTS for authentication of NTP packets.
 *maxdelay* _delay_:::
 *chronyd* uses the network round-trip delay to the server to determine how
 accurate a particular measurement is likely to be. Long round-trip delays
@@ -194,14 +203,14 @@ authenticated source to be safely combined with unauthenticated sources in
 order to improve the accuracy of the clock. They can be selected and used for
 synchronisation only if they agree with the trusted and required source.
 *xleave*:::
-This option enables an interleaved mode which allows the server or the peer to
-send transmit timestamps captured after the actual transmission (e.g. when the
-server or the peer is running *chronyd* with software (kernel) or hardware
-timestamping). This can significantly improve the accuracy of the measurements.
+This option enables the interleaved mode of NTP. It enables the server to
+respond with more accurate transmit timestamps (e.g. kernel or hardware
+timestamps), which cannot be contained in the transmitted packet itself and
+need to refer to a previous packet instead. This can significantly improve the
+accuracy and stability of the measurements.
 +
 The interleaved mode is compatible with servers that support only the basic
-mode, but peers must both support and have enabled the interleaved mode,
-otherwise the synchronisation will work only in one direction. Note that even
+mode. Note that even
 servers that support the interleaved mode might respond in the basic mode as
 the interleaved mode requires the servers to keep some state for each client
 and the state might be dropped when there are too many clients (e.g.
@@ -221,6 +230,9 @@ intervals. The default is 8 and a useful range is from 6 to 60.
 This option allows the UDP port on which the server understands NTP requests to
 be specified. For normal servers this option should not be required (the
 default is 123, the standard NTP port).
+*ntsport* _port_:::
+This option specifies the TCP port on which the server is listening for NTS-KE
+connections when the *nts* option is enabled. The default is 4460.
 *presend* _poll_:::
 If the timing measurements being made by *chronyd* are the only network data
 passing between two computers, you might find that some measurements are badly
@@ -243,8 +255,8 @@ when the polling interval is 512 seconds or more, an extra NTP client packet
 will be sent to the server a short time (2 seconds) before making the actual
 measurement.
 +
-The *presend* option cannot be used in the *peer* directive. If it is used
-with the *xleave* option, *chronyd* will send two extra packets instead of one.
+If the *presend* option is used together with the *xleave* option, *chronyd*
+will send two extra packets instead of one.
 *minstratum* _stratum_:::
 When the synchronisation source is selected from available sources, sources
 with lower stratum are normally slightly preferred. This option can be used to
@@ -267,18 +279,22 @@ directive, except that it is used to specify a pool of NTP servers rather than
 a single NTP server. The pool name is expected to resolve to multiple addresses
 which might change over time.
 +
+This directive can be used multiple times to specify multiple pools.
+
 All options valid in the <<server,*server*>> directive can be used in this
 directive too. There is one option specific to the *pool* directive:
-*maxsources* sets the maximum number of sources that can be used from the pool,
-the default value is 4.
 +
-On start, when the pool name is resolved, *chronyd* will add up to 16 sources,
-one for each resolved address. When the number of sources from which at least
-one valid reply was received reaches the number specified by the *maxsources*
-option, the other sources will be removed. When a pool source is unreachable,
+*maxsources* _sources_:::
+This option sets the desired number of sources to be used from the pool.
+*chronyd* will repeatedly try to resolve the name until it gets this number of
+sources responding to requests. The default value is 4 and the maximum value is
+16.
+
+{blank}::
+When an NTP source is unreachable,
 marked as a falseticker, or has a distance larger than the limit set by the
 <<maxdistance,*maxdistance*>> directive, *chronyd* will try to replace the
-source with a newly resolved address from the pool.
+source with a newly resolved address of the name.
 +
 An example of the *pool* directive is
 +
@@ -295,6 +311,14 @@ is mainly useful when the NTP implementation of the peer (e.g. *ntpd*) supports
 ephemeral symmetric associations and does not need to be configured with an
 address of this host. *chronyd* does not support ephemeral associations.
 +
+This directive can be used multiple times to specify multiple peers.
+
+The following options of the *server* directive do not work in the *peer*
+directive: *iburst*, *burst*, *nts*, *presend*.
+
+When using the *xleave* option, both peers must support and have enabled the
+interleaved mode, otherwise the synchronisation will work in one direction
+only.
 When a key is specified by the *key* option to enable authentication, both
 peers must use the same key and the same key number.
 +
@@ -381,6 +405,8 @@ driver-specific parameter. The two parameters are followed by zero or more
 refclock options. Some drivers have special options, which can be appended to
 the driver-specific parameter using the *:* character.
 +
+This directive can be used multiple times to specify multiple reference clocks.
+
 There are four drivers included in *chronyd*:
 +
 *PPS*:::
@@ -396,7 +422,7 @@ By default, the PPS refclock uses assert events (rising edge) for
 synchronisation. With this option, it will use clear events (falling edge)
 instead.
 +
-:::
+{blank}:::
 Examples:
 +
 ----
@@ -415,7 +441,7 @@ supports the following option:
 This option specifies the permissions of the shared memory segment created by
 *chronyd*. They are specified as a numeric mode. The default value is 0600
 (read-write access for owner only).
-:::
+{blank}:::
 +
 Examples:
 +
@@ -469,7 +495,7 @@ value is 0.
 This option enables timestamping of clear events (falling edge) instead of
 assert events (rising edge) in the PPS mode. This may not work with some
 clocks.
-:::
+{blank}:::
 +
 Examples:
 +
@@ -479,7 +505,7 @@ refclock PHC /dev/ptp1:nocrossts poll 3 pps
 refclock PHC /dev/ptp2:extpps:pin=1 width 0.2 poll 2
 ----
 +
-::
+{blank}::
 The *refclock* directive supports the following options:
 +
 *poll* _poll_:::
@@ -593,12 +619,13 @@ behaviour, whereas the *settime* command allows samples of manually entered
 time to be provided.)

 [[acquisitionport]]*acquisitionport* _port_::
-By default, *chronyd* uses a separate client socket for each configured server
-and their source port is chosen arbitrarily by the operating system. However,
-you can use the *acquisitionport* directive to explicitly specify a port and
-use only one socket (per IPv4 or IPv6 address family) for all configured servers.
-This can be useful for getting through some firewalls. If set to 0, the source
-port of the socket will be chosen arbitrarily.
+By default, *chronyd* as an NTP client opens a new socket for each request with
+the source port chosen randomly by the operating system. The *acquisitionport*
+directive can be used to specify the source port and use only one socket (per
+IPv4 or IPv6 address family) for all configured servers. This can be useful for
+getting through some firewalls. It should not be used if not necessary as there
+is a small impact on security of the client. If set to 0, the source port of
+the permanent socket will be chosen randomly by the operating system.
 +
 It can be set to the same port as is used by the NTP server (which can be
 configured with the <<port,*port*>> directive) to use only one socket for all
@@ -614,14 +641,40 @@ This would change the source port used for client requests to UDP port 1123.
 You could then persuade the firewall administrator to open that port.

 [[bindacqaddress]]*bindacqaddress* _address_::
-The *bindacqaddress* directive sets the network interface to which
-*chronyd* will bind its NTP client sockets. The syntax is similar to the
-<<bindaddress,*bindaddress*>> and <<bindcmdaddress,*bindcmdaddress*>>
+The *bindacqaddress* directive specifies a local IP address to which
+*chronyd* will bind its NTP and NTS-KE client sockets. The syntax is similar to
+the <<bindaddress,*bindaddress*>> and <<bindcmdaddress,*bindcmdaddress*>>
 directives.
 +
 For each of the IPv4 and IPv6 protocols, only one *bindacqaddress* directive
 can be specified.

+[[bindacqdevice]]*bindacqdevice* _interface_::
+The *bindacqdevice* directive binds the client sockets to a network device
+specified by the interface name. This can be useful when the local address is
+dynamic, or to enable an NTP source specified with a link-local IPv6 address.
+This directive can specify only one interface and it is supported on Linux
+only.
+
+An example of the directive is:
+
+----
+bindacqdevice eth0
+----
+
+[[dscp]]*dscp* _point_::
+The *dscp* directive sets the Differentiated Services Code Point (DSCP) in
+transmitted NTP packets to the specified value. It can improve stability of NTP
+measurements in local networks where switches or routers are configured to
+prioritise forwarding of packets with specific DSCP values. The default value
+is 0 and the maximum value is 63.
+
+An example of the directive (setting the Expedited Forwarding class) is:
+
+----
+dscp 46
+----
+
 [[dumpdir]]*dumpdir* _directory_::
 To compute the rate of gain or loss of time, *chronyd* has to store a
 measurement history for each of the time sources it uses.
@@ -639,6 +692,8 @@ behaviour whilst it is not running). The *dumpdir* directive defines the
 directory where the measurement histories are saved when *chronyd* exits,
 or the <<chronyc.adoc#dump,*dump*>> command in *chronyc* is issued.
 +
+If the directory does not exist, it will be created automatically.
+
 An example of the directive is:
 +
 ----
@@ -655,6 +710,10 @@ The *maxsamples* directive sets the default maximum number of samples that
 individual sources in the <<server,*server*>> and <<refclock,*refclock*>>
 directives. The default value is 0, which disables the configurable limit. The
 useful range is 4 to 64.
+
+As a special case, setting *maxsamples* to 1 disables frequency tracking in
+order to make the sources immediately selectable with only one sample. This can
+be useful when *chronyd* is started with the *-q* or *-Q* option.

 [[minsamples]]*minsamples* _samples_::
 The *minsamples* directive sets the default minimum number of samples that
@@ -669,8 +728,130 @@ changes in the frequency and offset of the clock. The offsets in the
 <<chronyc.adoc#sourcestats,*sourcestats*>> reports (and the _tracking.log_ and
 _statistics.log_ files) may be smaller than the actual offsets.

+[[ntsdumpdir1]]*ntsdumpdir* _directory_::
+This directive specifies a directory for the client to save NTS cookies it
+received from the server in order to avoid making an NTS-KE request when
+*chronyd* is started again. The cookies are saved separately for each NTP
+source in files named by the IP address of the NTS-KE server (e.g.
+_1.2.3.4.nts_). By default, the client does not save the cookies.
+
+If the directory does not exist, it will be created automatically.
+
+An example of the directive is:
+
+----
+ntsdumpdir @CHRONYVARDIR@
+----
+
+This directory is used also by the <<ntsdumpdir2,NTS server>> to save keys.
+
+[[ntsrefresh]]*ntsrefresh* _interval_::
+This directive specifies the maximum interval between NTS-KE handshakes (in
+seconds) in order to refresh the keys authenticating NTP packets. The default
+value is 2419200 (4 weeks).
+
+[[ntstrustedcerts]]*ntstrustedcerts* _file_::
+This directive specifies a file containing certificates (in the PEM format) of
+trusted certificate authorities (CA) that should be used to verify certificates
+of NTS servers in addition to the system's default trusted CAs (if the
+*nosystemcert* directive is not present).
+
+[[nosystemcert]]*nosystemcert*::
+This directive disables the system's default trusted CAs.
+
+[[nocerttimecheck]]*nocerttimecheck* _limit_::
+This directive disables the checks of the activation and expiration times of
+certificates for the specified number of clock updates. It allows the NTS
+authentication mechanism to be used on computers which start with wrong time
+(e.g. due to not having an RTC or backup battery). Disabling the time checks
+has important security implications, e.g. if an NTP server was ever
+compromised, its certificate could be used in an attack after the expiration
+time. The default value is 0, which means the time checks are always enabled.
+
+An example of the directive is:
+
+----
+nocerttimecheck 1
+----
+
+This would disable the time checks until the clock is updated for the first
+time, assuming the first update corrects the clock and later checks can work
+with correct time.
+
 === Source selection

+[[authselectmode]]*authselectmode* _mode_::
+NTP sources can be specified with the *key* or *nts* option to enable
+authentication to limit the impact of man-in-the-middle attacks. The
+attackers can drop or delay NTP packets (up to the *maxdelay* and
+<<maxdistance,*maxdistance*>> limits), but they cannot modify the timestamps
+contained in the packets. The attack can cause only a limited slew or step, and
+also cause the clock to run faster or slower than real time (up to double of
+the <<maxdrift,*maxdrift*>> limit).
+
+When authentication is enabled for an NTP source, it is important to disable
+unauthenticated NTP sources which could be exploited in the attack, e.g. if
+they are not reachable only over a trusted network. Alternatively, the source
+selection can be configured with the *require* and *trust* options to
+synchronise to the unauthenticated sources only if they agree with the
+authenticated sources and might have a positive impact on the accuracy of the
+clock. Note that in this case the impact of the attack is higher. The attackers
+cannot cause an arbitrarily large step or slew, but they have more control over
+the frequency of the clock and can cause *chronyd* to report false information,
+e.g. a significantly smaller root delay and dispersion.
+
+This directive determines the default selection options for authenticated and
+unauthenticated sources in order to simplify the configuration with the
+configuration file and *chronyc* commands. It sets a policy for authentication.
+
+Sources specified with the *noselect* option are ignored (not counted as either
+authenticated or unauthenticated), and they always have only the selection
+options specified in the configuration.
+
+There are four modes:
+
+*require*:::
+Authentication is strictly required for NTP sources in this mode. If any
+unauthenticated NTP sources are specified, they will automatically get the
+*noselect* option to prevent them from being selected for synchronisation.
+*prefer*:::
+In this mode, authentication is optional and preferred. If it is enabled for at
+least one NTP source, all unauthenticated NTP sources will get the *noselect*
+option.
+*mix*:::
+In this mode, authentication is optional and synchronisation to a mix of
+authenticated and unauthenticated NTP sources is allowed. If both authenticated
+and unauthenticated NTP sources are specified, all authenticated NTP sources
+and reference clocks will get the *require* and *trust* options to prevent
+synchronisation to unauthenticated NTP sources if they do not agree with a
+majority of the authenticated sources and reference clocks. This is the default
+mode.
+*ignore*:::
+In this mode, authentication is ignored in the source selection. All sources
+will have only the selection options that were specified in the configuration
+file, or *chronyc* command. This was the behaviour of *chronyd* in versions
+before 4.0.
+{blank}::
+
+As an example, the following configuration using the default *mix* mode:
+
+----
+server foo.example.net nts
+server bar.example.net nts
+server baz.example.net
+refclock SHM 0
+----
+
+is equivalent to the following configuration using the *ignore* mode:
+
+----
+authselectmode ignore
+server foo.example.net nts require trust
+server bar.example.net nts require trust
+server baz.example.net
+refclock SHM 0 require trust
+----
+
 [[combinelimit]]*combinelimit* _limit_::
 When *chronyd* has multiple sources available for synchronisation, it has to
 select one source as the synchronisation source. The measured offsets and
@@ -737,6 +918,27 @@ distances are in milliseconds.

 === System clock

+[[clockprecision]]*clockprecision* _precision_::
+The *clockprecision* directive specifies the precision of the system clock (in
+seconds). It is used by *chronyd* to estimate the minimum noise in NTP
+measurements and randomise low-order bits of timestamps in NTP responses. By
+default, the precision is measured on start as the minimum time to read the
+clock.
+
+The measured value works well in most cases. However, it generally
+overestimates the precision and it can be sensitive to the CPU speed, which can
+change over time to save power. In some cases with a high-precision clocksource
+(e.g. the Time Stamp Counter of the CPU) and hardware timestamping, setting the
+precision on the server to a smaller value can improve stability of clients'
+NTP measurements. The server's precision is reported on clients by the
+<<chronyc.adoc#ntpdata,*ntpdata*>> command.
+
+An example setting the precision to 8 nanoseconds is:
+
+----
+clockprecision 8e-9
+----
+
 [[corrtimeratio]]*corrtimeratio* _ratio_::
 When *chronyd* is slewing the system clock to correct an offset, the rate at
 which it is slewing adds to the frequency error of the clock. On all supported
@@ -845,7 +1047,7 @@ clock will be off for a longer time. On Linux with the default
 No correction is applied to the clock for the leap second. The clock will be
 corrected later in normal operation when new measurements are made and the
 estimated offset includes the one second error.
-::
+{blank}::
 +
 When serving time to NTP clients that cannot be configured to correct their
 clocks for a leap second by slewing, or to clients that would correct at
@@ -854,7 +1056,7 @@ slightly different rates when it is necessary to keep them close together, the
 enable a server leap smear.
 +
 When smearing a leap second, the leap status is suppressed on the server and
-the served time is corrected slowly be slewing instead of stepping. The clients
+the served time is corrected slowly by slewing instead of stepping. The clients
 do not need any special configuration as they do not know there is any leap
 second and they follow the server time which eventually brings them back to
 UTC. Care must be taken to ensure they use only NTP servers which smear the
@@ -868,7 +1070,7 @@ A recommended configuration to enable a server leap smear is:
 ----
 leapsecmode slew
 maxslewrate 1000
-smoothtime 400 0.001 leaponly
+smoothtime 400 0.001024 leaponly
 ----
 +
 The first directive is necessary to disable the clock step which would reset
@@ -876,11 +1078,17 @@ the smoothing process. The second directive limits the slewing rate of the
 local clock to 1000 ppm, which improves the stability of the smoothing process
 when the local correction starts and ends. The third directive enables the
 server time smoothing process. It will start when the clock gets to 00:00:00
-UTC and it will take 17 hours 34 minutes to finish. The frequency offset will
-be changing by 0.001 ppm per second and will reach a maximum of 31.623 ppm. The
-*leaponly* option makes the duration of the leap smear constant and allows the
-clients to safely synchronise with multiple identically configured leap
-smearing servers.
+UTC and it will take 62500 seconds (about 17.36 hours) to finish. The frequency
+offset will be changing by 0.001024 ppm per second and will reach a maximum of
+32 ppm in 31250 seconds. The *leaponly* option makes the duration of the leap
+smear constant and allows the clients to safely synchronise with multiple
+identically configured leap smearing servers.
+
+The duration of the leap smear can be calculated from the specified wander as
+
+----
+duration = sqrt(4 / wander)
+----

 [[leapsectz]]*leapsectz* _timezone_::
 This directive specifies a timezone in the system tz database which *chronyd*
@@ -1050,7 +1258,7 @@ coefficients _T0_, _k0_, _k1_, _k2_.
 The frequency compensation is calculated (in ppm) as
 +
 ----
-k0 + (T - T0) * k1 + (T - T0)^2 * k2
+comp = k0 + (T - T0) * k1 + (T - T0)^2 * k2
 ----
 +
 The result has to be between -10 ppm and 10 ppm, otherwise the measurement is
@@ -1101,12 +1309,15 @@ _tempcomp.log_ file if enabled by the <<log,*log tempcomp*>> directive.

 [[allow]]*allow* [*all*] [_subnet_]::
 The *allow* directive is used to designate a particular subnet from which NTP
-clients are allowed to access the computer as an NTP server.
+clients are allowed to access the computer as an NTP server. It also controls
+access of NTS-KE clients when NTS is enabled on the server.
 +
 The default is that no clients are allowed access, i.e. *chronyd* operates
 purely as an NTP client. If the *allow* directive is used, *chronyd* will be
 both a client of its servers, and a server to other clients.
 +
+This directive can be used multiple times.
+
 Examples of the use of the directive are as follows:
 +
 ----
@@ -1173,18 +1384,19 @@ client access by this computer for it to work.

 [[deny]]*deny* [*all*] [_subnet_]::
 This is similar to the <<allow,*allow*>> directive, except that it denies NTP
-client access to a particular subnet or host, rather than allowing it.
+and NTS-KE client access to a particular subnet or host, rather than allowing
+it.
 +
-The syntax is identical.
+The syntax is identical and the directive can be used multiple times too.
 +
 There is also a *deny all* directive with similar behaviour to the *allow all*
 directive.

 [[bindaddress]]*bindaddress* _address_::
-The *bindaddress* directive binds the socket on which *chronyd* listens for NTP
-requests to a local address of the computer. On systems other than Linux, the
-address of the computer needs to be already configured when *chronyd* is
-started.
+The *bindaddress* directive binds the sockets on which *chronyd* listens for
+NTP and NTS-KE requests to a local address of the computer. On systems other
+than Linux, the address of the computer needs to be already configured when
+*chronyd* is started.
 +
 An example of the use of the directive is:
 +
@@ -1196,12 +1408,25 @@ Currently, for each of the IPv4 and IPv6 protocols, only one *bindaddress*
 directive can be specified. Therefore, it is not useful on computers which
 should serve NTP on multiple network interfaces.

+[[binddevice]]*binddevice* _interface_::
+The *binddevice* directive binds the NTP and NTS-KE server sockets to a network
+device specified by the interface name. This directive can specify only one
+interface and it is supported on Linux only.
+
+An example of the directive is:
+
+----
+binddevice eth0
+----
+
 [[broadcast]]*broadcast* _interval_ _address_ [_port_]::
 The *broadcast* directive is used to declare a broadcast address to which
 chronyd should send packets in the NTP broadcast mode (i.e. make *chronyd* act
 as a broadcast server). Broadcast clients on that subnet will be able to
 synchronise.
 +
+This directive can be used multiple times to specify multiple addresses.
+
 The syntax is as follows:
 +
 ----
@@ -1301,16 +1526,18 @@ configuration and to be synchronised to one another, without confusing clients
 that poll more than one server. Each server needs to be configured to poll all
 other servers with the *local* directive. This ensures only the server with the
 smallest reference ID has the local reference active and others are
-synchronised to it. When that server fails, another will take over.
+synchronised to it. If that server stops responding, the server with the second
+smallest reference ID will take over when its local reference mode activates
+(root distance reaches the threshold configured by the *distance* option).
 +
 The *orphan* mode is compatible with the *ntpd*'s orphan mode (enabled by the
 *tos orphan* command).
-::
+{blank}::
 +
 An example of the directive is:
 +
 ----
-local stratum 10 orphan
+local stratum 10 orphan distance 0.1
 ----

 [[ntpsigndsocket]]*ntpsigndsocket* _directory_::
@@ -1330,6 +1557,80 @@ An example of the directive is:
 ntpsigndsocket /var/lib/samba/ntp_signd
 ----

+[[ntsport]]*ntsport* _port_::
+This directive specifies the TCP port on which *chronyd* will provide the NTS
+Key Establishment (NTS-KE) service. The default port is 4460.
+
+The port will be open only when a certificate and key is specified by the
+*ntsservercert* and *ntsserverkey* directives.
+
+[[ntsservercert]]*ntsservercert* _file_::
+This directive specifies a file containing a certificate in the PEM format
+for *chronyd* to operate as an NTS server.
+
+[[ntsserverkey]]*ntsserverkey* _file_::
+This directive specifies a file containing a private key in the PEM format
+for *chronyd* to operate as an NTS server.
+
+[[ntsprocesses]]*ntsprocesses* _processes_::
+This directive specifies how many helper processes will *chronyd* operating
+as an NTS server start for handling client NTS-KE requests in order to improve
+performance with multi-core CPUs and multithreading. If set to 0, no helper
+process will be started and all NTS-KE requests will be handled by the main
+*chronyd* process. The default value is 1.
+
+[[maxntsconnections]]*maxntsconnections* _connections_::
+This directive specifies the maximum number of concurrent NTS-KE connections
+per process that the NTS server will accept. The default value is 100.
+
+[[ntsdumpdir2]]*ntsdumpdir* _directory_::
+This directive specifies a directory where *chronyd* operating as an NTS server
+can save the keys which encrypt NTS cookies provided to clients. The keys are
+saved to a single file named _ntskeys_. When *chronyd* is restarted, reloading
+the keys allows the clients to continue using old cookies and avoids a storm of
+NTS-KE requests. By default, the server does not save the keys.
+
+An example of the directive is:
+
+----
+ntsdumpdir @CHRONYVARDIR@
+----
+
+This directory is used also by the <<ntsdumpdir1,NTS client>> to save NTS cookies.
+
+[[ntsntpserver]]*ntsntpserver* _hostname_::
+This directive specifies the hostname or address of the NTP server(s) which is
+provided in the NTS-KE response to the clients. It allows the NTS-KE server to
+be separated from the NTP server. However, the servers need to share the keys,
+i.e. external key management needs to be enabled by setting
+<<ntsrotate,*ntsrotate*>> to 0. By default, no hostname or address is provided
+to the clients, which means they should use the same server for NTS-KE and NTP.
+
+[[ntsrotate]]*ntsrotate* _interval_::
+This directive specifies the rotation interval (in seconds) of the server key
+which encrypts the NTS cookies. New keys are generated automatically from the
+_/dev/urandom_ device. The server keeps two previous keys to give the clients
+time to get new cookies encrypted by the latest key. The interval is measured
+as the server's operating time, i.e. the actual interval can be longer if
+*chronyd* is not running continuously. The default interval is 604800 seconds
+(1 week).
+
+The automatic rotation of the keys can be disabled by setting *ntsrotate* to 0.
+In this case the keys are assumed to be managed externally. *chronyd* will not
+save the keys to the _ntskeys_ file and will reload the keys from the file when
+the <<chronyc.adoc#rekey,*rekey*>> command is issued in *chronyc*. The file can
+be periodically copied from another server running *chronyd* (which does
+not have *ntsrotate* set to 0) in order to have one or more servers dedicated
+to NTS-KE. The NTS-KE servers need to be configured with the
+<<ntsntpname,*ntsntpname*>> directive to point the clients to the right NTP
+server.
+
+An example of the directive is:
+
+----
+ntsrotate 2592000
+----
+
 [[port]]*port* _port_::
 This option allows you to configure the port on which *chronyd* will listen for
 NTP requests. The port will be open only when an address is allowed by the
@@ -1377,7 +1678,7 @@ source address from completely blocking responses to that address. The leak
 rate is defined as a power of 1/2 and it is 2 by default, i.e. on average at
 least every fourth request has a response. The minimum value is 1 and the
 maximum value is 4.
-::
+{blank}::
 +
 An example use of the directive is:
 +
@@ -1389,6 +1690,17 @@ This would reduce the response rate for IP addresses sending packets on average
 more than once per 2 seconds, or sending packets in bursts of more than 16
 packets, by up to 75% (with default *leak* of 2).

+[[ntsratelimit]]*ntsratelimit* [_option_]...::
+This directive enables rate limiting of NTS-KE requests. It is similar to the
+<<ratelimit,*ratelimit*>> directive, except the default interval is 6
+(1 connection per 64 seconds).
+
+An example of the use of the directive is:
+
+----
+ntsratelimit interval 3 burst 1
+----
+
 [[smoothtime]]*smoothtime* _max-freq_ _max-wander_ [*leaponly*]::
 The *smoothtime* directive can be used to enable smoothing of the time that
 *chronyd* serves to its clients to make it easier for them to track it and keep
@@ -1442,8 +1754,8 @@ smoothtime 50000 0.01
 === Command and monitoring access

 [[bindcmdaddress]]*bindcmdaddress* _address_::
-The *bindcmdaddress* directive allows you to specify an IP address of an
-interface on which *chronyd* will listen for monitoring command packets (issued
+The *bindcmdaddress* directive specifies a local IP address to which *chronyd*
+will bind the UDP socket listening for monitoring command packets (issued
 by *chronyc*). On systems other than Linux, the address of the interface needs
 to be already configured when *chronyd* is started.
 +
@@ -1454,9 +1766,10 @@ directory will be created on start if it does not exist. The compiled-in default
 path of the socket is _@CHRONYRUNDIR@/chronyd.sock_. The socket can be
 disabled by setting the path to _/_.
 +
-By default, *chronyd* binds to the loopback interface (with addresses
-_127.0.0.1_ and _::1_). This blocks all access except from localhost. To listen
-for command packets on all interfaces, you can add the lines:
+By default, *chronyd* binds the UDP sockets to the addresses _127.0.0.1_ and
+_::1_ (i.e. the loopback interface). This blocks all access except from
+localhost. To listen for command packets on all interfaces, you can add the
+lines:
 +
 ----
 bindcmdaddress 0.0.0.0
@@ -1474,6 +1787,17 @@ An example that sets the path of the Unix domain command socket is:
 bindcmdaddress /var/run/chrony/chronyd.sock
 ----

+[[bindcmddevice]]*bindcmddevice* _interface_::
+The *bindcmddevice* directive binds the UDP command sockets to a network device
+specified by the interface name. This directive can specify only one interface
+and it is supported on Linux only.
+
+An example of the directive is:
+
+----
+bindcmddevice eth0
+----
+
 [[cmdallow]]*cmdallow* [*all*] [_subnet_]::
 This is similar to the <<allow,*allow*>> directive, except that it allows
 monitoring access (rather than NTP client access) to a particular subnet or
@@ -1546,7 +1870,8 @@ The *rtcautotrim* directive is used to keep the RTC close to the system clock
 automatically. When the system clock is synchronised and the estimated error
 between the two clocks is larger than the specified threshold, *chronyd* will
 trim the RTC as if the <<chronyc.adoc#trimrtc,*trimrtc*>> command in *chronyc*
-was issued.
+was issued. The trimming operation is accurate to only about 1 second, which is
+the minimum effective threshold.
 +
 This directive is effective only with the <<rtcfile,*rtcfile*>> directive.
 +
@@ -1852,7 +2177,7 @@ from the example line above):
 . Applied compensation in ppm, positive means the system clock is running
  faster than it would be without the compensation. [3.6600e-01]
 +
-::
+{blank}::
 An example of the directive is:
 +
 ----
@@ -1885,8 +2210,9 @@ which would cause a syslog message to be generated if a system clock error of ov
 0.1 seconds starts to be compensated.

 [[logdir]]*logdir* _directory_::
-This directive allows the directory where log files are written to be
-specified.
+This directive specifies the directory for writing log files enabled by the
+*log* directive. If the directory does not exist, it will be created
+automatically.
 +
 An example of the use of this directive is:
 +
@@ -1914,6 +2240,56 @@ sendmail binary.

 === Miscellaneous

+[[confdir]]*confdir* _directory_...::
+The *confdir* directive includes configuration files with the _.conf_ suffix
+from a directory. The files are included in the lexicographical order of the
+file names.
+
+Multiple directories (up to 10) can be specified with a single *confdir*
+directive. In this case, if multiple directories contain a file with the same
+name, only the first file in the order of the specified directories will be
+included. This enables a fragmented configuration where existing fragments can
+be replaced by adding files to a different directory.
+
+This directive can be used multiple times.
+
+An example of the directive is:
+
+----
+confdir @SYSCONFDIR@/chrony.d
+----
+
+[[sourcedir]]*sourcedir* _directory_...::
+The *sourcedir* directive is identical to the *confdir* directive, except the
+configuration files have the _.sources_ suffix, they can only specify NTP
+sources (i.e. use the *server*, *pool*, and *peer* directive), and can be
+reloaded by the <<chronyc.adoc#reload,*reload sources*>> command in
+*chronyc*. It is particularly useful with dynamic sources like NTP servers
+received from a DHCP server, which can be written to a file specific to the
+network interface by a networking script.
+
+This directive can be used multiple times.
+
+An example of the directive is:
+
+----
+sourcedir /var/run/chrony-dhcp
+----
+
+[[include]]*include* _pattern_::
+The *include* directive includes a configuration file, or multiple configuration
+files if a wildcard pattern is specified. Unlike with the *confdir* directive,
+the full name of the files needs to be specified and at least one file is
+required to exist.
+
+This directive can be used multiple times.
+
+An example of the directive is:
+
+----
+include @SYSCONFDIR@/chrony.d/*.conf
+----
+
 [[hwtimestamp]]*hwtimestamp* _interface_ [_option_]...::
 This directive enables hardware timestamping of NTP packets sent to and
 received from the specified network interface. The network interface controller
@@ -1943,8 +2319,9 @@ indicated in the _measurements.log_ file if enabled by the <<log,*log
 measurements*>> directive, and the <<chronyc.adoc#ntpdata,*ntpdata*>> report in
 *chronyc*.
 +
-If the specified interface is _*_, *chronyd* will try to enable HW timestamping
-on all available interfaces.
+This directive can be used multiple times to enable HW timestamping on multiple
+interfaces. If the specified interface is _*_, *chronyd* will try to enable HW
+timestamping on all available interfaces.
 +
 The *hwtimestamp* directive has the following options:
 +
@@ -1984,14 +2361,14 @@ _ntp_::::
 Enables timestamping of received NTP packets.
 _none_::::
 Disables timestamping of received packets.
-:::
+{blank}:::
 The most specific filter for timestamping NTP packets which is supported by the
 NIC is selected by default. Some NICs can timestamp only PTP packets, which
 limits the selection to the _none_ filter. Forcing timestamping of all packets
 with the _all_ filter when the NIC supports both _all_ and _ntp_ filters can be
 useful when packets are received from or on a non-standard UDP port (e.g.
 specified by the *port* directive).
-::
+{blank}::
 +
 Examples of the directive are:
 +
@@ -2001,20 +2378,11 @@ hwtimestamp eth1 txcomp 300e-9 rxcomp 645e-9
 hwtimestamp *
 ----

-[[include]]*include* _pattern_::
-The *include* directive includes a configuration file or multiple configuration
-files if a wildcard pattern is specified. This can be useful when maintaining
-configuration on multiple hosts to keep the differences in separate files.
-+
-An example of the directive is:
-+
----
-include @SYSCONFDIR@/chrony.d/*.conf
----
-
 [[keyfile]]*keyfile* _file_::
-This directive is used to specify the location of the file containing ID-key
-pairs for authentication of NTP packets.
+This directive is used to specify the location of the file containing symmetric
+keys which are shared between NTP servers and clients, or peers, in order to
+authenticate NTP packets with a message authentication code (MAC) using a
+cryptographic hash function or cipher.
 +
 The format of the directive is shown in the example below:
 +
@@ -2029,31 +2397,41 @@ format of the file is shown below:
 10 tulip
 11 hyacinth
 20 MD5 ASCII:crocus
-25 SHA1 HEX:1dc764e0791b11fa67efc7ecbc4b0d73f68a070c
+25 SHA1 HEX:933F62BE1D604E68A81B557F18CFA200483F5B70
+30 AES128 HEX:7EA62AE64D190114D46D5A082F948EC1
+31 AES256 HEX:37DDCBC67BB902BCB8E995977FAB4D2B5642F5B32EBCEEE421921D97E5CBFE39
 ...
 ----
 +
-Each line consists of an ID, name of an authentication hash function (optional),
-and a password. The ID can be any unsigned integer in the range 1 through
-2^32-1. The default hash function is *MD5*, which is always supported.
+Each line consists of an ID, optional type, and key.
 +
+The ID can be any positive integer in the range 1 through 2^32-1.
+
+The type is a name of a cryptographic hash function or cipher which is used to
+generate and verify the MAC. The default type is *MD5*, which is always
+supported.
 If *chronyd* was built with enabled support for hashing using a crypto library
 (nettle, nss, or libtomcrypt), the following functions are available: *MD5*,
 *SHA1*, *SHA256*, *SHA384*, *SHA512*. Depending on which library and version is
-*chronyd* using, some or all of the following functions may also be available:
-*SHA3-224*, *SHA3-256*, *SHA3-384*, *SHA3-512*, *RMD128*, *RMD160*, *RMD256*,
-*RMD320*, *TIGER*, *WHIRLPOOL*.
+*chronyd* using, some of the following hash functions and ciphers may
+also be available:
+*SHA3-224*, *SHA3-256*, *SHA3-384*, *SHA3-512*, *TIGER*, *WHIRLPOOL*, *AES128*,
+*AES256*.
 +
-The password can be specified as a string of characters not containing white
+The key can be specified as a string of ASCII characters not containing white
 space with an optional *ASCII:* prefix, or as a hexadecimal number with the
 *HEX:* prefix. The maximum length of the line is 2047 characters.
+If the type is a cipher, the length of the key must match the cipher (i.e. 128
+bits for AES128 and 256 bits for AES256).
 +
-The password is used with the hash function to generate and verify a message
-authentication code (MAC) in NTP packets. It is recommended to use SHA1, or
-stronger, hash function with random passwords specified in the hexadecimal
-format that have at least 128 bits. *chronyd* will log a warning to
-syslog on start if a source is specified in the configuration file with a key
-that has password shorter than 80 bits.
+It is recommended to use randomly generated keys, specified in the hexadecimal
+format, which are at least 128 bits long (i.e. they have at least 32 characters
+after the *HEX:* prefix). *chronyd* will log a warning to syslog on start if a
+source is specified in the configuration file with a key shorter than 80 bits.
+
+The recommended key types are AES ciphers and SHA3 hash functions. MD5 should
+be avoided unless no other type is supported on the server and client, or
+peers.
 +
 The <<chronyc.adoc#keygen,*keygen*>> command of *chronyc* can be used to
 generate random keys for the key file. By default, it generates 160-bit MD5 or
@@ -2136,7 +2514,7 @@ the following methods:
  stratum 1 and stratum 2 servers. You should find one or more servers that are
  near to you. Check that their access policy allows you to use their
  facilities.
-* Use public servers from the http://www.pool.ntp.org/[pool.ntp.org] project.
+* Use public servers from the https://www.pool.ntp.org/[pool.ntp.org] project.

 Assuming that your NTP servers are called _foo.example.net_, _bar.example.net_
 and _baz.example.net_, your _chrony.conf_ file could contain as a minimum:
@@ -2175,6 +2553,20 @@ makestep 1.0 3
 rtcsync
 ----

+If the servers (or pool) support the Network Time Security (NTS)
+authentication mechanism and *chronyd* is compiled with NTS support, the *nts*
+option will enable a secure synchronisation to the servers. The configuration
+file could look like:
+
+----
+server foo.example.net iburst nts
+server bar.example.net iburst nts
+server baz.example.net iburst nts
+driftfile @CHRONYVARDIR@/drift
+makestep 1.0 3
+rtcsync
+----
+
 === NTP client with infrequent connection to NTP servers

 This section shows how to configure *chronyd* for computers that have
@@ -2222,7 +2614,7 @@ actually connected to the Internet.
 === Isolated networks

 This section shows how to configure *chronyd* for computers that never have
-network conectivity to any computer which ultimately derives its time from a
+network connectivity to any computer which ultimately derives its time from a
 reference clock.

 In this situation, one computer is selected to be the master timeserver. The
@@ -2414,7 +2806,7 @@ information to be saved.
 === Public NTP server

 *chronyd* can be configured to operate as a public NTP server, e.g. to join the
-http://www.pool.ntp.org/en/join.html[pool.ntp.org] project. The configuration
+https://www.pool.ntp.org/en/join.html[pool.ntp.org] project. The configuration
 is similar to the NTP client with permanent connection, except it needs to
 allow client access from all addresses. It is recommended to find at least four
 good servers (e.g. from the pool, or on the NTP homepage). If the server has a
--- a/doc/chronyc.adoc
+++ b/doc/chronyc.adoc
@@ -2,7 +2,7 @@
 //
 // Copyright (C) Richard P. Curnow  1997-2003
 // Copyright (C) Stephen Wadeley  2016
-// Copyright (C) Miroslav Lichvar  2009-2017
+// Copyright (C) Miroslav Lichvar  2009-2017, 2019-2020
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of version 2 of the GNU General Public License as
@@ -39,7 +39,7 @@ running.
 If no commands are specified on the command line, *chronyc* will expect input
 from the user. The prompt _chronyc>_ will be displayed when it is being run
 from a terminal. If *chronyc*'s input or output are redirected from or to a file,
-the prompt is not shown.
+the prompt will not be shown.

 There are two ways *chronyc* can access *chronyd*. One is the Internet
 Protocol (IPv4 or IPv6) and the other is a Unix domain socket, which is
@@ -51,7 +51,8 @@ running under a non-root user), it will try to connect to 127.0.0.1 and then

 Only the following monitoring commands, which do not affect the behaviour of
 *chronyd*, are allowed from the network: *activity*, *manual list*,
-*rtcdata*, *smoothing*, *sources*, *sourcestats*, *tracking*, *waitsync*. The
+*rtcdata*, *smoothing*, *sourcename*, *sources*, *sourcestats*, *tracking*,
+*waitsync*. The
 set of hosts from which *chronyd* will accept these commands can be configured
 with the <<chrony.conf.adoc#cmdallow,*cmdallow*>> directive in the *chronyd*'s
 configuration file or the <<cmdallow,*cmdallow*>> command in *chronyc*. By
@@ -59,9 +60,7 @@ default, the commands are accepted only from localhost (127.0.0.1 or ::1).

 All other commands are allowed only through the Unix domain socket. When sent
 over the network, *chronyd* will respond with a '`Not authorised`' error, even
-if it is from localhost. In chrony versions before 2.2 they were allowed
-from the network if they were authenticated with a password, but that is no
-longer supported.
+if it is from localhost.

 Having full access to *chronyd* via *chronyc* is more or less equivalent to
 being able to modify the *chronyd*'s configuration file and restart it.
@@ -78,11 +77,18 @@ With this option hostnames will be resolved only to IPv6 addresses.
 This option disables resolving of IP addresses to hostnames, e.g. to avoid slow
 DNS lookups. Long addresses will not be truncated to fit into the column.

+*-N*::
+This option enables printing of the original names of NTP sources that were
+specified in the configuration file, or *chronyc* commands, and are internally
+used by *chronyd*. Without the *-n* and *-N* option, the names of NTP sources
+are obtained from reverse DNS lookups and can be different from the original
+names.
+
 *-c*::
 This option enables printing of reports in a comma-separated values (CSV)
-format. IP addresses will not be resolved to hostnames, time will be printed as
-number of seconds since the epoch and values in seconds will not be converted
-to other units.
+format. Reverse DNS lookups will be disabled, time will be printed as number of
+seconds since the epoch, and values in seconds will not be converted to other
+units.

 *-d*::
 This option enables printing of debugging messages if *chronyc* was compiled
@@ -112,10 +118,14 @@ This option is ignored and is provided only for compatibility.
 *-a*::
 This option is ignored and is provided only for compatibility.

-*-v*::
+*-v*, *--version*::
 With this option *chronyc* displays its version number on the terminal and
 exits.

+*--help*::
+With this option *chronyc* displays a help message on the terminal and
+exits.
+
 == COMMANDS

 This section describes each of the commands available within the *chronyc*
@@ -175,10 +185,12 @@ speeding up or slowing down the system clock until the error has been removed,
 and then returning to the system clock's normal speed. A consequence of this is
 that there will be a period when the system clock (as read by other programs)
 will be different from *chronyd*'s estimate of the current true time (which it
-reports to NTP clients when it is operating in server mode). The value reported
+reports to NTP clients when it is operating as a server). The value reported
 on this line is the difference due to this effect.
 *Last offset*:::
-This is the estimated local offset on the last clock update.
+This is the estimated local offset on the last clock update. A positive value
+indicates the local time (as previously estimated true time) was ahead of the
+time sources.
 *RMS offset*:::
 This is a long-term average of the offset value.
 *Frequency*:::
@@ -284,15 +296,18 @@ milliseconds.

 === Time sources

-[[sources]]*sources* [*-v*]::
+[[sources]]*sources* [*-a*] [*-v*]::
 This command displays information about the current time sources that *chronyd*
 is accessing.
 +
-The optional argument *-v* can be specified, meaning _verbose_. In this case,
+If the *-a* option is specified, all sources are displayed, including those that
+do not have a known address yet. Such sources have an identifier in the format
+_ID#XXXXXXXXXX_, which can be used in other commands expecting a source address.
+
+The *-v* option enables a verbose output. In this case,
 extra caption lines are shown as a reminder of the meanings of the columns.
 +
 ----
-210 Number of sources = 3
 MS Name/IP address         Stratum Poll Reach LastRx Last sample
 ===============================================================================
 #* GPS0                          0   4   377    11   -479ns[ -621ns] +/-  134ns
@@ -306,18 +321,23 @@ The columns are as follows:
 This indicates the mode of the source. _^_ means a server, _=_ means a peer
 and _#_ indicates a locally connected reference clock.
 *S*:::
-This column indicates the state of the source.
-* _*_ indicates the source to which *chronyd* is currently synchronised.
-* _+_ indicates acceptable sources which are combined with the selected
-  source.
-* _-_ indicates acceptable sources which are excluded by the combining
-  algorithm.
-* _?_ indicates sources to which connectivity has been lost or whose packets
-  do not pass all tests. It is also shown at start-up, until at least 3 samples
-  have been gathered from it.
-* _x_ indicates a clock which *chronyd* thinks is a falseticker (i.e. its
-  time is inconsistent with a majority of other sources).
+This column indicates the selection state of the source.
+* _*_ indicates the best source which is currently selected for
+  synchronisation.
+* _+_ indicates other sources selected for synchronisation, which are combined
+  with the best source.
+* _-_ indicates a source which is considered to be selectable for
+  synchronisation, but not currently selected.
+* _x_ indicates a source which *chronyd* thinks is a falseticker (i.e. its
+  time is inconsistent with a majority of other sources, or sources specified
+  with the *trust* option).
 * _~_ indicates a source whose time appears to have too much variability.
+* _?_ indicates a source which is not considered to be selectable for
+  synchronisation for other reasons (e.g. unreachable, not synchronised, or
+  does not have enough measurements).
+{blank}:::
+The <<selectdata,*selectdata*>> command can be used to get more details about
+the selection state.
 *Name/IP address*:::
 This shows the name or the IP address of the source, or reference ID for reference
 clocks.
@@ -353,18 +373,21 @@ since. The number following the _+/-_ indicator shows the margin of error in
 the measurement. Positive offsets indicate that the local clock is ahead of
 the source.

-[[sourcestats]]*sourcestats* [*-v*]::
+[[sourcestats]]*sourcestats* [*-a*] [*-v*]::
 The *sourcestats* command displays information about the drift rate and offset
 estimation process for each of the sources currently being examined by
 *chronyd*.
 +
-The optional argument *-v* can be specified, meaning _verbose_. In this case,
+If the *-a* option is specified, all sources are displayed, including those that
+do not have a known address yet. Such sources have an identifier in the format
+_ID#XXXXXXXXXX_, which can be used in other commands expecting a source address.
+
+The *-v* option enables a verbose output. In this case,
 extra caption lines are shown as a reminder of the meanings of the columns.
 +
 An example report is:
 +
 ----
-210 Number of sources = 1
 Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
 ===============================================================================
 foo.example.net            11   5   46m     -0.001      0.045      1us    25us
@@ -400,6 +423,98 @@ This is the estimated offset of the source.
 *Std Dev*:::
 This is the estimated sample standard deviation.

+[[selectdata]]*selectdata* [*-a*] [*-v*]::
+The *selectdata* command displays information specific to the selection of time
+sources. If the *-a* option is specified, all sources are displayed, including
+those that do not have a known address yet. With the *-v* option, extra caption
+lines are shown as a reminder of the meanings of the columns.
+
+An example of the output is shown below.
+
+----
+S Name/IP Address        Auth COpts EOpts Last Score     Interval  Leap
+=======================================================================
+D foo.example.net           Y ----- --TR-    4   1.0   -61ms   +62ms  N
+* bar.example.net           N ----- -----    0   1.0 -6846us +7305us  N
+ baz.example.net           N ----- -----   10   1.0 -7381us +7355us  N
+----
+
+The columns are as follows:
+
+*S*:::
+This column indicates the state of the source after the last source selection.
+It is similar to the state reported by the *sources* command, but more
+states are reported.
+{blank}:::
+The following states indicate the source is not considered selectable for
+synchronisation:
+* _N_ - has the *noselect* option.
+* _M_ - does not have enough measurements.
+* _d_ - has a root distance larger than the maximum distance (configured by the
+        <<chrony.conf.adoc#maxdistance,*maxdistance*>> directive).
+* _~_ - has a jitter larger than the maximum jitter (configured by the
+        <<chrony.conf.adoc#maxjitter,*maxjitter*>> directive).
+* _w_ - waits for other sources to get out of the _M_ state.
+* _S_ - has older measurements than other sources.
+* _O_ - has a stratum equal or larger than the orphan stratum (configured by
+        the <<chrony.conf.adoc#local,*local*>> directive).
+* _T_ - does not fully agree with sources that have the *trust* option.
+* _x_ - does not agree with other sources (falseticker).
+{blank}:::
+The following states indicate the source is considered selectable, but it is
+not currently used for synchronisation:
+* _W_ - waits for other sources to be selectable (required by the
+        <<chrony.conf.adoc#minsources,*minsources*>> directive, or
+        the *require* option of another source).
+* _P_ - another selectable source is preferred due to the *prefer* option.
+* _U_ - waits for a new measurement (after selecting a different best source).
+* _D_ - has, or recently had, a root distance which is too large to be combined
+        with other sources (configured by the
+        <<chrony.conf.adoc#combinelimit,*combinelimit*>> directive).
+{blank}:::
+The following states indicate the source is used for synchronisation of the
+local clock:
+* _+_ - combined with the best source.
+* _*_ - selected as the best source to update the reference data (e.g. root
+        delay, root dispersion).
+*Name/IP address*:::
+This column shows the name or IP address of the source if it is an NTP server,
+or the reference ID if it is a reference clock.
+*Auth*:::
+This column indicites whether an authentication mechanism is enabled for the
+source. _Y_ means yes and _N_ means no.
+*COpts*:::
+This column displays the configured selection options of the source.
+* _N_ indicates the *noselect* option.
+* _P_ indicates the *prefer* option.
+* _T_ indicates the *trust* option.
+* _R_ indicates the *require* option.
+*EOpts*:::
+This column displays the current effective selection options of the source,
+which can be different from the configured options due to the authentication
+selection mode (configured by the
+<<chrony.conf.adoc#authselmode,*authselmode*>> directive). The symbols are the
+same as in the *COpts* column.
+*Last*:::
+This column displays how long ago was the last measurement of the source made
+when the selection was performed.
+*Score*:::
+This column displays the current score against the source in the _*_ state. The
+scoring system avoids frequent reselection when multiple sources have a similar
+root distance. A value larger than 1 indicates this source was better than the
+_*_ source in recent selections. If the score reaches 10, the best source will
+be reselected and the scores will be reset to 1.
+*Interval*:::
+This column displays the lower and upper endpoint of the interval which was
+expected to contain the true offset of the local clock considering the root
+distance at the time of the selection.
+*Leap*:::
+This column displays the current leap status of the source.
+* _N_ indicates the normal status (no leap second).
+* _+_ indicates that a leap second will be inserted at the end of the month.
+* _-_ indicates that a leap second will be deleted at the end of the month.
+* _?_ indicates the unknown status (i.e. no valid measurement was made).
+
 [[reselect]]*reselect*::
 To avoid excessive switching between sources, *chronyd* can stay synchronised
 to a source even when it is not currently the best one among the available
@@ -440,10 +555,82 @@ the offline state.
 the name of the server or peer was not resolved to an address yet; this source is
 not visible in the *sources* and *sourcestats* reports.

+[[authdata]]*authdata* [*-a*]::
+The *authdata* command displays information specific to authentication of NTP
+sources. If the *-a* option is specified, all sources are displayed, including
+those that do not have a known address yet. An example of the output is
+shown below.
+
+----
+Name/IP address             Mode KeyID Type KLen Last Atmp  NAK Cook CLen
+=========================================================================
+foo.example.net              NTS     1   15  256 135m    0    0    8  100
+bar.example.net               SK    30   13  128    -    0    0    0    0
+baz.example.net                -     0    0    0    -    0    0    0    0
+----
+
+The columns are as follows:
+
+*Name/IP address*:::
+This column shows the name or the IP address of the source.
+*Mode*:::
+This column shows which mechanism authenticates NTP packets received from the
+source. _NTS_ means Network Time Security, _SK_ means a symmetric key, and _-_
+means authentication is disabled.
+*KeyID*:::
+This column shows an identifier of the key used for authentication. With a
+symmetric key, it is the ID from the <<chrony.conf.adoc#keyfile,key file>>.
+With NTS, it is a number starting at zero and incremented by one with each
+successful key establishment using the NTS-KE protocol, i.e. it shows how many
+times the key establishment was performed with this source.
+*Type*:::
+This columns shows an identifier of the algorithm used for authentication.
+With a symmetric key, it is the hash function or cipher specified in the key
+file. With NTS, it is an authenticated encryption with associated data (AEAD)
+algorithm, which is negotiated in the NTS-KE protocol. The following values can
+be reported:
+* 1: MD5
+* 2: SHA1
+* 3: SHA256
+* 4: SHA384
+* 5: SHA512
+* 6: SHA3-224
+* 7: SHA3-256
+* 8: SHA3-384
+* 9: SHA3-512
+* 10: TIGER
+* 11: WHIRLPOOL
+* 13: AES128
+* 14: AES256
+* 15: AEAD-AES-SIV-CMAC-256
+*KLen*:::
+This column shows the length of the key in bits.
+*Last*:::
+This column shows how long ago the last successful key establishment was
+performed. It is in seconds, or letters _m_, _h_, _d_ or _y_ indicate minutes,
+hours, days, or years.
+*Atmp*:::
+This column shows the number of attempts to perform the key establishment since
+the last successful key establishment. A number larger than 1 indicates a
+problem with the network or server.
+*NAK*:::
+This column shows whether an NTS NAK was received since the last request.
+A NAK indicates that authentication failed on the server side due to
+*chronyd* using a cookie which is no longer valid and that it needs to perform
+the key establishment again in order to get new cookies.
+*Cook*:::
+This column shows the number of NTS cookies that *chronyd* currently has. If
+the key establishment was successful, a number smaller than 8 indicates a
+problem with the network or server.
+*CLen*:::
+This column shows the length in bytes of the NTS cookie which will be used in
+the next request.
+
 [[ntpdata]]*ntpdata* [_address_]::
 The *ntpdata* command displays the last valid measurement and other
-NTP-specific information about the specified NTP source, or all NTP sources if
-no address was specified. An example of the output is shown below.
+NTP-specific information about the specified NTP source, or all NTP sources
+(with a known address) if no address was specified. An example of the output is
+shown below.
 +
 ----
 Remote address  : 203.0.113.15 (CB00710F)
@@ -526,15 +713,13 @@ The number of all packets received from the source.
 *Total valid RX*:::
 The number of valid packets received from the source.

-[[add_peer]]*add peer* _address_ [_option_]...::
+[[add_peer]]*add peer* _name_ [_option_]...::
 The *add peer* command allows a new NTP peer to be added whilst
 *chronyd* is running.
 +
 Following the words *add peer*, the syntax of the following
-parameters and options is similar to that for the
+parameters and options is identical to that for the
 <<chrony.conf.adoc#peer,*peer*>> directive in the configuration file.
-The following peer options can be set in the command: *port*, *minpoll*,
-*maxpoll*, *presend*, *maxdelayratio*, *maxdelay*, *key*.
 +
 An example of using this command is shown below.
 +
@@ -542,15 +727,27 @@ An example of using this command is shown below.
 add peer foo.example.net minpoll 6 maxpoll 10 key 25
 ----

-[[add_server]]*add server* _address_ [_option_]...::
+[[add_pool]]*add pool* _name_ [_option_]...::
+The *add pool* command allows a pool of NTP servers to be added whilst
+*chronyd* is running.
+
+Following the words *add pool*, the syntax of the following parameters and
+options is identical to that for the <<chrony.conf.adoc#pool,*pool*>>
+directive in the configuration file.
+
+An example of using this command is shown below:
+
+----
+add pool foo.example.net maxsources 3 iburst
+----
+
+[[add_server]]*add server* _name_ [_option_]...::
 The *add server* command allows a new NTP server to be added whilst
 *chronyd* is running.
 +
 Following the words *add server*, the syntax of the following parameters and
-options is similar to that for the <<chrony.conf.adoc#server,*server*>>
+options is identical to that for the <<chrony.conf.adoc#server,*server*>>
 directive in the configuration file.
-The following server options can be set in the command: *port*, *minpoll*,
-*maxpoll*, *presend*, *maxdelayratio*, *maxdelay*, *key*.
 +
 An example of using this command is shown below:
 +
@@ -601,7 +798,7 @@ alternative to the form with mask.
 _address_:::
 This is an IP address or a hostname. The burst command is applied only to
 that source.
-::
+{blank}::
 +
 If no _mask_ or _masked-address_ arguments are provided, every source will be
 matched.
@@ -688,7 +885,8 @@ the loaded periods. The *offline* and *online* commands can be used to achieve
 this.
 +
 There are four forms of the *offline* command. The first form is a wildcard,
-meaning all sources. The second form allows an IP address mask and a masked
+meaning all sources (including sources that do not have a known address yet).
+The second form allows an IP address mask and a masked
 address to be specified. The third form uses CIDR notation. The fourth form
 uses an IP address or a hostname. These forms are illustrated below.
 +
@@ -725,10 +923,11 @@ The syntax is identical to that of the <<offline,*offline*>> command.

 [[onoffline]]
 *onoffline*::
-The *onoffline* command tells *chronyd* to switch all sources to the online or
+The *onoffline* command tells *chronyd* to switch all sources that have a known
+address to the online or
 offline status according to the current network configuration. A source is
-considered online if it is possible to send requests to it, i.e. a route to the
-network is present.
+considered online if it is possible to send requests to it, i.e. a network
+route to the source is present.

 [[polltarget]]*polltarget* _address_ _polltarget_::
 The *polltarget* command is used to modify the poll target for one of the
@@ -744,6 +943,20 @@ Sources that stop responding will be replaced with newly resolved addresses
 automatically after 8 polling intervals, but this command can still be useful
 to replace them immediately and not wait until they are marked as unreachable.

+[[reload]]*reload* *sources*::
+The *reload sources* command causes *chronyd* to re-read all _*.sources_ files
+from the directories specified by the
+<<chrony.conf.adoc#sourcedir,*sourcedir*>> directive.
+
+[[sourcename]]*sourcename* _address_::
+The *sourcename* command prints the original hostname or address that was
+specified for an NTP source in the configuration file, or the *add* command.
+This command is an alternative to the *-N* option, which can be useful in
+scripts.
+
+Note that different NTP sources can share the same name, e.g. servers from a
+pool.
+
 === Manual time input

 [[manual]]
@@ -780,7 +993,7 @@ The columns are as as follows:
 . The regression residual at this point, in seconds. This allows '`outliers`'
  to be easily spotted, so that they can be deleted using the *manual delete*
  command.
-::
+{blank}::
 +
 The *delete* form of the command deletes a single sample. The parameter is the
 index of the sample, as shown in the first column of the output from *manual
@@ -851,10 +1064,17 @@ This command can be used to examine the effect of a series of *allow*, *allow
 all*, *deny*, and *deny all* commands specified either via *chronyc*, or in
 *chronyd*'s configuration file.

-[[clients]]*clients*::
+[[clients]]*clients* [*-p* _packets_] [*-k*] [*-r*]::
 This command shows a list of clients that have accessed the server, through
-either the NTP or command ports. It does not include accesses over
-the Unix domain command socket. There are no arguments.
+the NTP, command, or NTS-KE port. It does not include accesses over the Unix
+domain command socket.
+
+The *-p* option specifies the minimum number of received NTP or command
+packets, or accepted NTS-KE connections, needed to include a client in the
+list. The default value is 0, i.e. all clients are reported. With the *-k*
+option the last four columns will show the NTS-KE accesses instead of command
+accesses. If the *-r* option is specified, *chronyd* will reset the counters of
+received and dropped packets or connections after reporting the current values.
 +
 An example of the output is:
 +
@@ -879,20 +1099,22 @@ The columns are as follows:
 . The average interval between NTP packets.
 . The average interval between NTP packets after limiting the response rate.
 . Time since the last NTP packet was received
-. The number of command packets received from the client.
-. The number of command packets dropped to limit the response rate.
-. The average interval between command packets.
-. Time since the last command packet was received.
+. The number of command packets or NTS-KE connections received/accepted from
+  the client.
+. The number of command packets or NTS-KE connections dropped to limit the
+  response rate.
+. The average interval between command packets or NTS-KE connections.
+. Time since the last command packet or NTS-KE connection was
+  received/accepted.

 [[serverstats]]*serverstats*::
-The *serverstats* command displays how many valid NTP and command requests
-*chronyd* as a server received from clients, how many of them were dropped to
-limit the response rate as configured by the
-<<chrony.conf.adoc#ratelimit,*ratelimit*>> and
-<<chrony.conf.adoc#cmdratelimit,*cmdratelimit*>> directives, and how many
+The *serverstats* command displays how many valid NTP and command requests, and
+NTS-KE connections, *chronyd* operating as a server received from clients, and
+how many of them were dropped due to rate limiting. It also displays how many
 client log records were dropped due to the memory limit configured by the
-<<chrony.conf.adoc#clientloglimit,*clientloglimit*>> directive. An example of
-the output is shown below.
+<<chrony.conf.adoc#clientloglimit,*clientloglimit*>> directive and how many of
+the NTP requests (from those which were not dropped) were authenticated. An
+example of the output is shown below.
 +
 ----
 NTP packets received       : 1598
@@ -900,6 +1122,9 @@ NTP packets dropped        : 8
 Command packets received   : 19
 Command packets dropped    : 0
 Client log records dropped : 0
+NTS-KE connections accepted: 3
+NTS-KE connections dropped : 0
+Authenticated NTP packets  : 189
 ----

 [[allow]]*allow* [*all*] [_subnet_]::
@@ -1085,7 +1310,7 @@ more than 1 second away from the system clock):
  error).
 . Save the RTC parameters to the RTC file (specified with the
  <<chrony.conf.adoc#rtcfile,*rtcfile*>> directive in the configuration file).
-::
+{blank}::
 +
 The last step is done as a precaution against the computer suffering a power
 failure before either the daemon exits or the <<writertc,*writertc*>> command
@@ -1118,25 +1343,36 @@ purged. An example of how to do this is shown below.
 ----
 # mv /var/log/chrony/measurements.log /var/log/chrony/measurements1.log
 # chronyc cyclelogs
-# ls -l /var/log/chrony
-rw-r--r--   1 root     root            0 Jun  8 18:17 measurements.log
-rw-r--r--   1 root     root        12345 Jun  8 18:17 measurements1.log
-# rm -f measurements1.log
+# rm /var/log/chrony/measurements1.log
 ----

 [[dump]]*dump*::
 The *dump* command causes *chronyd* to write its current history of
 measurements for each of its sources to dump files in the directory specified
 in the configuration file by the <<chrony.conf.adoc#dumpdir,*dumpdir*>>
+directive and also write server NTS keys and client NTS cookies to the
+directory specified by the <<chrony.conf.adoc#ntsdumpdir1,*ntsdumpdir*>>
 directive. Note that *chronyd* does this automatically when it exits. This
-command is mainly useful for inspection of the history whilst *chronyd* is
-running.
+command is mainly useful for inspection whilst *chronyd* is running.

 [[rekey]]*rekey*::
 The *rekey* command causes *chronyd* to re-read the key file specified in the
-configuration file by the <<chrony.conf.adoc#keyfile,*keyfile*>> directive.
+configuration file by the <<chrony.conf.adoc#keyfile,*keyfile*>> directive. It
+also re-reads the server NTS keys if
+<<chrony.conf.adoc#ntsdumpdir2,*ntsdumpdir*>> is specified and
+<<chrony.conf.adoc#ntsrotate,automatic rotation>> is disabled in the
+configuration file.

-[[rekey]]*shutdown*::
+[[reset]]*reset* *sources*::
+The *reset sources* command causes *chronyd* to drop all measurements and
+switch to the unsynchronised state. This command can help *chronyd* with
+recovery when the measurements are known to be no longer valid or accurate,
+e.g. due to moving the computer to a different network, or resuming the
+computer from a low-power state (which resets the system clock). *chronyd* will
+drop the measurements automatically when it detects the clock has made an
+unexpected jump, but the detection is not completely reliable.
+
+[[shutdown]]*shutdown*::
 The *shutdown* command causes *chronyd* to exit. This is equivalent to sending
 the process the SIGTERM signal.

@@ -1188,10 +1424,10 @@ generated from the _/dev/urandom_ device and it is printed to standard output.
 +
 The command has three optional arguments. The first argument is the key number
 (by default 1), which will be specified with the *key* option of the *server*
-or *peer* directives in the configuration file. The second argument is the hash
-function (by default SHA1 or MD5 if SHA1 is not available) and the third
-argument is the number of bits the key should have, between 80 and 4096 bits
-(by default 160 bits).
+or *peer* directives in the configuration file. The second argument is the name
+of the hash function or cipher (by default SHA1, or MD5 if SHA1 is not
+available). The third argument is the length of the key in bits if a hash
+function was selected, between 80 and 4096 bits (by default 160 bits).
 +
 An example is:
 +
@@ -1201,7 +1437,13 @@ keygen 73 SHA1 256
 +
 which generates a 256-bit SHA1 key with number 73. The printed line should
 then be securely transferred and added to the key files on both server and
-client, or peers.
+client, or peers. A different key should be generated for each client or peer.
+
+An example using the AES128 cipher is:
+
+----
+keygen 151 AES128
+----

 [[exit]]*exit*::
 [[quit]]*quit*::
--- a/doc/chronyd.adoc
+++ b/doc/chronyd.adoc
@@ -41,7 +41,7 @@ If no configuration directives are specified on the command line, *chronyd*
 will read them from a configuration file. The compiled-in default location of
 the file is _@SYSCONFDIR@/chrony.conf_.

-Information messages and warnings will be logged to syslog.
+Informational messages, warnings, and errors will be logged to syslog.

 == OPTIONS

@@ -55,20 +55,32 @@ IPv6 sockets will be created.

 *-f* _file_::
 This option can be used to specify an alternate location for the configuration
-file (default _@SYSCONFDIR@/chrony.conf_).
+file. The compiled-in default value is _@SYSCONFDIR@/chrony.conf_.

 *-n*::
 When run in this mode, the program will not detach itself from the terminal.

 *-d*::
 When run in this mode, the program will not detach itself from the terminal,
-and all messages will be written to the terminal instead of syslog. When
-*chronyd* was compiled with debugging support, this option can be used twice to
-print also debugging messages.
+and all messages will be written to the terminal instead of syslog. If
+*chronyd* was compiled with enabled support for debugging, this option can be
+used twice to enable debug messages.

 *-l* _file_::
-This option specifies a file which should be used for logging instead of syslog
-or terminal.
+This option enables writing of log messages to a file instead of syslog or the
+terminal.
+
+*-L* _level_::
+This option specifies the minimum severity level of messages to be written to
+the log file, syslog, or terminal. The following levels can be specified:
+0 (informational), 1 (warning), 2 (non-fatal error), and 3 (fatal error). The
+default value is 0.
+
+*-p*::
+When run in this mode, *chronyd* will print the configuration and exit. It will
+not detach from the terminal. This option can be used to verify the syntax of
+the configuration and get the whole configuration, even if it is split into
+multiple files and read by the *include* or *confdir* directive.

 *-q*::
 When run in this mode, *chronyd* will set the system clock once and exit. It
@@ -125,32 +137,44 @@ running, but still allow it to adjust the frequency of the system clock.
 *-u* _user_::
 This option sets the name of the system user to which *chronyd* will switch
 after start in order to drop root privileges. It overrides the
-<<chrony.conf.adoc#user,*user*>> directive (default _@DEFAULT_USER@_).
+<<chrony.conf.adoc#user,*user*>> directive. The compiled-in default value is
+_@DEFAULT_USER@_.
 +
 On Linux, *chronyd* needs to be compiled with support for the *libcap* library.
 On macOS, FreeBSD, NetBSD and Solaris *chronyd* forks into two processes.
 The child process retains root privileges, but can only perform a very limited
 range of privileged system calls on behalf of the parent.

+*-U*::
+This option disables a check for root privileges to allow *chronyd* to be
+started under a non-root user, assuming the process will have all capabilities
+(e.g. provided by the service manager) and access to all files, directories,
+and devices, needed to operate correctly in the specified configuration. Note
+that different capabilities might be needed with different configurations and
+different Linux kernel versions. Starting *chronyd* under a non-root user is
+not recommended when the configuration is not known, or at least limited to
+specific directives.
+
 *-F* _level_::
 This option configures a system call filter when *chronyd* is compiled with
 support for the Linux secure computing (seccomp) facility. In level 1 the
 process is killed when a forbidden system call is made, in level -1 the SIGSYS
-signal is thrown instead and in level 0 the filter is disabled (default 0).
+signal is thrown instead and in level 0 the filter is disabled. The default
+value is 0.
 +
-It's recommended to enable the filter only when it's known to work on the
+It is recommended to enable the filter only when it is known to work on the
 version of the system where *chrony* is installed as the filter needs to allow
 also system calls made from libraries that *chronyd* is using (e.g. libc) and
-different versions or implementations of the libraries may make different
+different versions or implementations of the libraries might make different
 system calls. If the filter is missing some system call, *chronyd* could be
 killed even in normal operation.

 *-P* _priority_::
 On Linux, this option will select the SCHED_FIFO real-time scheduler at the
 specified priority (which must be between 0 and 100). On macOS, this option
-must have either a value of 0 (the default) to disable the thread time
+must have either a value of 0 to disable the thread time
 constraint policy or 1 for the policy to be enabled. Other systems do not
-support this option.
+support this option. The default value is 0.

 *-m*::
 This option will lock *chronyd* into RAM so that it will never be paged out.
@@ -160,14 +184,15 @@ This mode is only supported on Linux.
 This option disables the control of the system clock. *chronyd* will not try to
 make any adjustments of the clock. It will assume the clock is free running and
 still track its offset and frequency relative to the estimated true time. This
-option allows *chronyd* to run without the capability to adjust or set the
-system clock (e.g. in some containers) in order to operate as an NTP server. It
-is not recommended to run *chronyd* (with or without *-x*) when another process
-is controlling the system clock.
+option allows *chronyd* to be started without the capability to adjust or set
+the system clock (e.g. in some containers) to operate as an NTP server.

-*-v*::
+*-v*, *--version*::
 With this option *chronyd* will print version number to the terminal and exit.

+*-h*, *--help*::
+With this option *chronyd* will print a help message to the terminal and exit.
+
 == FILES

 _@SYSCONFDIR@/chrony.conf_
--- a/doc/faq.adoc
+++ b/doc/faq.adoc
@@ -1,7 +1,7 @@
 // This file is part of chrony
 //
 // Copyright (C) Richard P. Curnow  1997-2003
-// Copyright (C) Miroslav Lichvar  2014-2016
+// Copyright (C) Miroslav Lichvar  2014-2016, 2020
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of version 2 of the GNU General Public License as
@@ -24,17 +24,20 @@

 === How does `chrony` compare to `ntpd`?

-`chronyd` was designed to work well in a wide range of conditions and it can
-usually synchronise the system clock faster and with better time accuracy. It
-doesn't implement some of the less useful NTP modes like broadcast client or
-multicast server/client.
+`chrony` and `ntpd` are two different implementations of the Network Time
+Protocol (NTP).
+
+`chrony` is a newer implementation, which was designed to work well in a wider
+range of conditions. It can usually synchronise the system clock faster and
+with better time accuracy. It has many features, but it does not implement some
+of the less useful NTP modes like broadcast client or multicast server/client.

 If your computer is connected to the Internet only for few minutes at a time,
 the network connection is often congested, you turn your computer off or
 suspend it frequently, the clock is not very stable (e.g. there are rapid
-changes in the temperature or it's a virtual machine), or you want to use NTP
+changes in the temperature or it is a virtual machine), or you want to use NTP
 on an isolated network with no hardware reference clocks in sight, `chrony`
-will probably work much better for you.
+will probably work better for you.

 For a more detailed comparison of features and performance, see the
 https://chrony.tuxfamily.org/comparison.html[comparison page] on the `chrony`
@@ -59,13 +62,13 @@ slewing, which would take a very long time. The `makestep` directive does
 that.

 In order to keep the real-time clock (RTC) close to the true time, so the
-system time is reasonably close to the true time when it's initialised on the
+system time is reasonably close to the true time when it is initialised on the
 next boot from the RTC, the `rtcsync` directive enables a mode in which the
 system time is periodically copied to the RTC. It is supported on Linux and
 macOS.

 If you want to use public NTP servers from the
-http://www.pool.ntp.org/[pool.ntp.org] project, the minimal _chrony.conf_ file
+https://www.pool.ntp.org/[pool.ntp.org] project, the minimal _chrony.conf_ file
 could be:

 ----
@@ -75,52 +78,36 @@ makestep 1 3
 rtcsync
 ----

-=== How do I make an NTP server from an NTP client?
+=== How do I make an NTP server?

 You need to add an `allow` directive to the _chrony.conf_ file in order to open
 the NTP port and allow `chronyd` to reply to client requests. `allow` with no
 specified subnet allows access from all IPv4 and IPv6 addresses.

-=== I have several computers on a LAN. Should be all clients of an external server?
+=== Should all computers on a LAN be clients of an external server?

-The best configuration is usually to make one computer the server, with
-the others as clients of it. Add a `local` directive to the server's
-_chrony.conf_ file. This configuration will be better because
+It depends on the requirements. Usually, the best configuration is to make one
+computer the server, with the others as clients of it. Add a `local` directive
+to the server's _chrony.conf_ file. This configuration will be better because

 * the load on the external connection is less
 * the load on the external NTP server(s) is less
 * if your external connection goes down, the computers on the LAN
  will maintain a common time with each other.

-=== Must I specify servers by IP address if DNS is not available on chronyd start?
+=== Must I specify servers by IP address if DNS is not available on `chronyd` start?

-No. Starting from version 1.25, `chronyd` will keep trying to resolve
+No, `chronyd` will keep trying to resolve
 the names specified by the `server`, `pool`, and `peer` directives in an
 increasing interval until it succeeds. The `online` command can be issued from
 `chronyc` to force `chronyd` to try to resolve the names immediately.

 === How can I make `chronyd` more secure?

-If you don't need to serve time to NTP clients or peers, you can add `port 0`
-to the _chrony.conf_ file to completely disable the NTP server functionality
-and prevent NTP requests from reaching `chronyd`. Starting from version 2.0,
-the NTP server port is open only when client access is allowed by the `allow`
-directive or command, an NTP peer is configured, or the `broadcast` directive
-is used.
-
-If you don't need to use `chronyc` remotely, you can add the following
-directives to the configuration file to bind the command sockets to the
-loopback interface. This is done by default since version 2.0.
-
----
-bindcmdaddress 127.0.0.1
-bindcmdaddress ::1
----
-
-If you don't need to use `chronyc` at all or you need to run `chronyc` only
+If you do not need to use `chronyc`, or you want to run `chronyc` only
 under the root or _chrony_ user (which can access `chronyd` through a Unix
-domain socket since version 2.2), you can disable the internet command sockets
-completely by adding `cmdport 0` to the configuration file.
+domain socket), you can disable the IPv4 and IPv6 command sockets (by default
+listening on localhost) by adding `cmdport 0` to the configuration file.

 You can specify an unprivileged user with the `-u` option, or the `user`
 directive in the _chrony.conf_ file, to which `chronyd` will switch after start
@@ -133,23 +120,23 @@ a very limited range of privileged system calls on behalf of the parent.
 Also, if `chronyd` is compiled with support for the Linux secure computing
 (seccomp) facility, you can enable a system call filter with the `-F` option.
 It will significantly reduce the kernel attack surface and possibly prevent
-kernel exploits from the `chronyd` process if it's compromised. It's
-recommended to enable the filter only when it's known to work on the version of
+kernel exploits from the `chronyd` process if it is compromised. It is
+recommended to enable the filter only when it is known to work on the version of
 the system where `chrony` is installed as the filter needs to allow also system
 calls made from libraries that `chronyd` is using (e.g. libc) and different
-versions or implementations of the libraries may make different system calls.
+versions or implementations of the libraries might make different system calls.
 If the filter is missing some system call, `chronyd` could be killed even in
 normal operation.

 === How can I improve the accuracy of the system clock with NTP sources?

 Select NTP servers that are well synchronised, stable and close to your
-network. It's better to use more than one server, three or four is usually
+network. It is better to use more than one server, three or four is usually
 recommended as the minimum, so `chronyd` can detect servers that serve false
 time and combine measurements from multiple sources.

 If you have a network card with hardware timestamping supported on Linux, it
-can be enabled by the *hwtimestamp* directive in the _chrony.conf_ file. It
+can be enabled by the `hwtimestamp` directive in the _chrony.conf_ file. It
 should make local receive and transmit timestamps of NTP packets much more
 accurate.

@@ -163,8 +150,8 @@ default values are 6 (64 seconds) for `minpoll`, 10 (1024 seconds) for
 `maxpoll` and 8 (samples) for `polltarget`. The default values should be used
 for general servers on the Internet. With your own NTP servers, or if you have
 permission to poll some servers more frequently, setting these options for
-shorter polling intervals may significantly improve the accuracy of the system
-clock.
+shorter polling intervals might significantly improve the accuracy of the
+system clock.

 The optimal polling interval depends mainly on two factors, stability of the
 network latency and stability of the system clock (which mainly depends on the
@@ -174,7 +161,7 @@ temperature change).
 Generally, if the `sourcestats` command usually reports a small number of
 samples retained for a source (e.g. fewer than 16), a shorter polling interval
 should be considered. If the number of samples is usually at the maximum of 64,
-a longer polling interval may work better.
+a longer polling interval might work better.

 An example of the directive for an NTP server on the Internet that you are
 allowed to poll frequently could be
@@ -210,7 +197,7 @@ server ntp.local minpoll 2 maxpoll 4 xleave

 When combined with local hardware timestamping, good network switches, and even
 shorter polling intervals, a sub-microsecond accuracy and stability of a few
-tens of nanoseconds may be possible. For example:
+tens of nanoseconds might be possible. For example:

 ----
 server ntp.local minpoll 0 maxpoll 0 xleave
@@ -221,10 +208,11 @@ For best stability, the CPU should be running at a constant frequency (i.e.
 disabled power saving and performance boosting). Energy-Efficient Ethernet
 (EEE) should be disabled in the network. The switches should be configured to
 prioritize NTP packets, especially if the network is expected to be heavily
-loaded.
+loaded. The `dscp` directive can be used to set the Differentiated Services
+Code Point in transmitted NTP packets if needed.

-If it is acceptable for NTP clients in the network to send requests at an
-excessive rate, a sub-second polling interval may be specified. A median filter
+If it is acceptable for NTP clients in the network to send requests at a high
+rate, a sub-second polling interval can be specified. A median filter
 can be enabled in order to update the clock at a reduced rate with more stable
 measurements. For example:

@@ -237,17 +225,40 @@ hwtimestamp eth0 minpoll -6

 Yes. With the `-q` option `chronyd` will set the system clock once and exit.
 With the `-Q` option it will print the measured offset without setting the
-clock. If you don't want to use a configuration file, NTP servers can be
+clock. If you do not want to use a configuration file, NTP servers can be
 specified on the command line. For example:

 ----
 # chronyd -q 'pool pool.ntp.org iburst'
 ----

+The command above would normally take about 5 seconds if the servers were
+well synchronised and responding to all requests. If not synchronised or
+responding, it would take about 10 seconds for `chronyd` to give up and exit
+with a non-zero status. A faster configuration is possible. A single server can
+be used instead of four servers, the number of measurements can be reduced with
+the `maxsamples` option to one (supported in `chrony` version 4.0), and a
+timeout can be specified with the `-t` option. The following command would take
+only up to about one second.
+
+----
+# chronyd -q -t 1 'server pool.ntp.org iburst maxsamples 1'
+----
+
+It is not recommended to run `chronyd` with the `-q` option periodically (e.g.
+from a cron job) as a replacement for the daemon mode, because it performs
+significantly worse (e.g. the clock is stepped and its frequency is not
+corrected). If you must run it this way and you are using a public NTP server,
+make sure `chronyd` does not always start around the first second of a minute,
+e.g. by adding a random sleep before the `chronyd` command. Public servers
+typically receive large bursts of requests around the first second as there is
+a large number of NTP clients started from cron with no delay.
+
 === Can `chronyd` be configured to control the clock like `ntpd`?

 It is not possible to perfectly emulate `ntpd`, but there are some options that
-can configure `chronyd` to behave more like `ntpd`.
+can configure `chronyd` to behave more like `ntpd` if there is a reason to
+prefer that.

 In the following example the `minsamples` directive slows down the response to
 changes in the frequency and offset of the clock. The `maxslewrate` and
@@ -267,10 +278,56 @@ maxchange 1000 1 1
 maxclockerror 15
 ----

-Note that increasing `minsamples` may cause the offsets in the `tracking` and
+Note that increasing `minsamples` might cause the offsets in the `tracking` and
 `sourcestats` reports/logs to be significantly smaller than the actual offsets
 and be unsuitable for monitoring.

+=== Can NTP server be separated from NTP client?
+
+Yes, it is possible to run multiple instances of `chronyd` on the same
+computer. One can be configured as an NTP client, and another as a server. They
+need to use different pidfiles, NTP ports, command ports, and Unix domain
+command sockets. The server instance should be started with the `-x` option to
+avoid touching the clock. It can be configured to serve the system time with
+the `local` directive, or synchronise its NTP clock to the client instance
+running on localhost using a non-standard NTP port.
+
+On Linux, starting with `chrony` version 4.0, it is also possible to run
+multiple server instances sharing a port to utilise multiple cores of the CPU.
+Note that the client/server interleaved mode requires that all packets from an
+address are handled by the same server instance.
+
+=== Should be a leap smear enabled on NTP server?
+
+With the `smoothtime` and `leapsecmode` directives it is possible to enable a
+server leap smear in order to hide leap seconds from clients and force them to
+follow a slow server's adjustment instead.
+
+This feature should be used only in local networks and only when necessary,
+e.g. when the clients cannot be configured to handle the leap seconds as
+needed, or their number is so large that configuring them all would be
+impractical. The clients should use only one leap-smearing server, or multiple
+identically configured leap-smearing servers. Note that some clients can get
+leap seconds from external sources (e.g. with the `leapsectz` directive in
+`chrony`) and they will not work correctly with a leap smearing server.
+
+=== Does `chrony` support PTP?
+
+No, the Precision Time Protocol (PTP) is not supported and there are no plans
+to support it. It is a complex protocol, which shares some issues with the
+NTP broadcast mode. One of the main differences between NTP and PTP is that PTP
+was designed to be easily supported in hardware (e.g. network switches and
+routers) in order to make more stable and accurate measurements. PTP relies on
+the hardware support. NTP does not rely on any support in the hardware, but if
+it had the same support as PTP, it could perform equally well.
+
+On Linux, `chrony` supports hardware clocks that some NICs have for PTP. They
+are called PTP hardware clocks (PHC). They can be used as reference clocks
+(specified by the `refclock` directive) and for hardware timestamping of NTP
+packets (enabled by the `hwtimestamp` directive) if the NIC can timestamp other
+packets than PTP, which is usually the case at least for transmitted packets.
+The `ethtool -T` command can be used to verify the timestamping support.
+
 === What happened to the `commandkey` and `generatecommandkey` directives?

 They were removed in version 2.2. Authentication is no longer supported in the
@@ -287,11 +344,11 @@ following questions.

 === Behind a firewall?

-Check the `Reach` value printed by the ``chronyc``'s `sources` command. If it's
-zero, it means `chronyd` did not get any valid responses from the NTP server
+Check the `Reach` value printed by the ``chronyc``'s `sources` command. If it
+is zero, it means `chronyd` did not get any valid responses from the NTP server
 you are trying to use. If there is a firewall between you and the server, the
-packets may be blocked. Try using a tool like `wireshark` or `tcpdump` to see
-if you're getting any responses from the server.
+packets might be blocked. Try using a tool like `wireshark` or `tcpdump` to see
+if you are getting any responses from the server.

 When `chronyd` is receiving responses from the servers, the output of the
 `sources` command issued few minutes after `chronyd` start might look like
@@ -308,9 +365,10 @@ MS Name/IP address         Stratum Poll Reach LastRx Last sample

 === Are NTP servers specified with the `offline` option?

-Check that you're using ``chronyc``'s `online` and `offline` commands
-appropriately. The `activity` command prints the number of sources that are
-currently online and offline. For example:
+Check that the ``chronyc``'s `online` and `offline` commands are used
+appropriately (e.g. in the system networking scripts). The `activity` command
+prints the number of sources that are currently online and offline. For
+example:

 ----
 200 OK
@@ -337,9 +395,9 @@ makestep 1 3
 ----

 the clock would be stepped in the first three updates if its offset was larger
-than one second. Normally, it's recommended to allow the step only in the first
+than one second. Normally, it is recommended to allow the step only in the first
 few updates, but in some cases (e.g. a computer without an RTC or virtual
-machine which can be suspended and resumed with an incorrect time) it may be
+machine which can be suspended and resumed with an incorrect time) it might be
 necessary to allow the step on any clock update. The example above would change
 to

@@ -351,7 +409,7 @@ makestep 1 -1

 A common issue with Windows NTP servers is that they report a very large root
 dispersion (e.g. three seconds or more), which causes `chronyd` to ignore the
-server for being too inaccurate. The `sources` command may show a valid
+server for being too inaccurate. The `sources` command might show a valid
 measurement, but the server is not selected for synchronisation. You can check
 the root dispersion of the server with the ``chronyc``'s `ntpdata` command.

@@ -362,6 +420,52 @@ synchronisation to such a server. For example:
 maxdistance 16.0
 ----

+=== An unreachable source is selected?
+
+When `chronyd` is configured with multiple time sources, it tries to select the
+most accurate and stable sources for synchronisation of the system clock. They
+are marked with the _*_ or _+_ symbol in the report printed by the `sources`
+command.
+
+When the best source (marked with the _*_ symbol) becomes unreachable (e.g. NTP
+server stops responding), `chronyd` will not immediately switch
+to the second best source in an attempt to minimise the error of the clock. It
+will let the clock run free for as long as its estimated error (in terms of
+root distance) based on previous measurements is smaller than the estimated
+error of the second source, and there is still an interval which contains some
+measurements from both sources.
+
+If the first source was significantly better than the second source, it can
+take many hours before the second source is selected, depending on its polling
+interval. You can force a faster reselection by increasing the clock error rate
+(`maxclockerror` directive), shortening the polling interval (`maxpoll`
+option), or reducing the number of samples (`maxsamples` option).
+
+=== Does selected source drop new measurements?
+
+`chronyd` can drop a large number of successive NTP measurements if they are
+not passing some of the NTP tests. The `sources` command can report for a
+selected source the fully-reachable value of 377 in the Reach column and at the
+same time a LastRx value that is much larger than the current polling interval.
+If the source is online, this indicates that a number of measurements was
+dropped. You can use the `ntpdata` command to check the NTP tests for the last
+measurement. Usually, it is the test C which fails.
+
+This can be an issue when there is a long-lasting increase in the measured
+delay, e.g. due to a routing change in the network. Unfortunately, `chronyd`
+does not know for how long it should wait for the delay to come back to the
+original values, or whether it is a permanent increase and it should start from
+scratch.
+
+The test C is an adaptive filter. It can take many hours before it accepts
+a measurement with the larger delay, and even much longer before it drops all
+measurements with smaller delay, which determine an expected delay used by the
+test. You can use the `reset sources` command to drop all measurements
+immediately (available in chrony 4.0 and later). If this issue happens
+frequently, you can effectively disable the test by setting the
+`maxdelaydevratio` option to a very large value (e.g. 1000000), or speed up the
+recovery by increasing the clock error rate with the `maxclockerror` directive.
+
 === Using a PPS reference clock?

 A pulse-per-second (PPS) reference clock requires a non-PPS time source to
@@ -397,31 +501,33 @@ to be used for synchronisation.
 When accessing `chronyd` remotely, make sure that the _chrony.conf_ file (on
 the computer where `chronyd` is running) has a `cmdallow` entry for the
 computer you are running `chronyc` on and an appropriate `bindcmdaddress`
-directive. This isn't necessary for localhost.
+directive. This is not necessary for localhost.

 Perhaps `chronyd` is not running. Try using the `ps` command (e.g. on Linux,
-`ps -auxw`) to see if it's running. Or try `netstat -a` and see if the ports
-123/udp and 323/udp are listening. If `chronyd` is not running, you may have a
-problem with the way you are trying to start it (e.g. at boot time).
+`ps -auxw`) to see if it is running. Or try `netstat -a` and see if the UDP
+port 323 is listening. If `chronyd` is not running, you might have a problem
+with the way you are trying to start it (e.g. at boot time).

-Perhaps you have a firewall set up in a way that blocks packets on port
-323/udp. You need to amend the firewall configuration in this case.
+Perhaps you have a firewall set up in a way that blocks packets on the UDP
+port 323. You need to amend the firewall configuration in this case.

 === I keep getting the error `501 Not authorised`

-Since version 2.2, the `password` command doesn't do anything and `chronyc`
-needs to run locally under the root or _chrony_ user, which are allowed to
-access the ``chronyd``'s Unix domain command socket.
+This error indicates that `chronyc` sent the command to `chronyd` using a UDP
+socket instead of the Unix domain socket (e.g. _/var/run/chrony/chronyd.sock_),
+which is required for some commands. For security reasons, only the root and
+_chrony_ users are allowed to access the socket.

-With older versions, you need to authenticate with the `password` command first
-or use the `-a` option to authenticate automatically on start. The
-configuration file needs to specify a file which contains keys (`keyfile`
-directive) and which key in the key file should be used for `chronyc`
-authentication (`commandkey` directive).
+It is also possible that the socket does not exist. `chronyd` will not create
+the socket if the directory has a wrong owner or permissions. In this case
+there should be an error message from `chronyd` in the system log.

-=== Why does `chronyc tracking` always print an IPv4 address as reference ID?
+=== What is the reference ID reported by the `tracking` command?

-The reference ID is a 32-bit value and in versions before 3.0 it was printed in
+The reference ID is a 32-bit value used in NTP to prevent synchronisation
+loops.
+
+In `chrony` versions before 3.0 it was printed in the
 quad-dotted notation, even if the reference source did not actually have an
 IPv4 address. For IPv4 addresses, the reference ID is equal to the address, but
 for IPv6 addresses it is the first 32 bits of the MD5 sum of the address. For
@@ -445,7 +551,7 @@ Only by the source code. See _cmdmon.c_ (`chronyd` side) and _client.c_
 === What is the real-time clock (RTC)?

 This is the clock which keeps the time even when your computer is turned off.
-It is used to initialise the system clock on boot. It normally doesn't drift
+It is used to initialise the system clock on boot. It normally does not drift
 more than few seconds per day.

 There are two approaches how `chronyd` can work with it. One is to use the
@@ -460,17 +566,17 @@ monitor the rate at which the RTC gains or loses time. When `chronyd` is
 started with the `-s` option on the next boot, it will set the system time from
 the RTC and also compensate for the drift it has measured previously. The
 `rtcautotrim` directive can be used to keep the RTC close to the true time, but
-it's not strictly necessary if its only purpose is to set the system clock when
+it is not strictly necessary if its only purpose is to set the system clock when
 `chronyd` is started on boot. See the documentation for details.

-=== I want to use ``chronyd``'s RTC support. Must I disable `hwclock`?
+=== Does `hwclock` have to be disabled?

 The `hwclock` program is often set-up by default in the boot and shutdown
 scripts with many Linux installations. With the kernel RTC synchronisation
 (`rtcsync` directive), the RTC will be set also every 11 minutes as long as the
 system clock is synchronised. If you want to use ``chronyd``'s RTC monitoring
-(`rtcfile` directive), it's important to disable `hwclock` in the shutdown
-procedure. If you don't, it will over-write the RTC with a new value, unknown
+(`rtcfile` directive), it is important to disable `hwclock` in the shutdown
+procedure. If you do not that, it will over-write the RTC with a new value, unknown
 to `chronyd`. At the next reboot, `chronyd` started with the `-s` option will
 compensate this (wrong) time with its estimate of how far the RTC has drifted
 whilst the power was off, giving a meaningless initial system time.
@@ -489,7 +595,7 @@ things

 === I get `Could not open /dev/rtc, Device or resource busy` in my syslog file

-Some other program running on the system may be using the device.
+Some other program running on the system might be using the device.

 === What if my computer does not have an RTC or backup battery?

@@ -504,7 +610,7 @@ observe backward steps.
 === Can `chronyd` be driven from broadcast/multicast NTP servers?

 No, the broadcast/multicast client mode is not supported and there is currently
-no plan to implement it. While the mode may be useful to simplify configuration
+no plan to implement it. While this mode can simplify configuration
 of clients in large networks, it is inherently less accurate and less secure
 (even with authentication) than the ordinary client/server mode.

@@ -521,7 +627,8 @@ thousands of clients using the ordinary client/server mode.

 Yes, the `broadcast` directive can be used to enable the broadcast server mode
 to serve time to clients in the network which support the broadcast client mode
-(it's not supported in `chronyd`, see the previous question).
+(it is not supported in `chronyd`). Note that this mode should generally be
+avoided. See the previous question.

 === Can `chronyd` keep the system clock a fixed offset away from real time?

@@ -537,9 +644,21 @@ offline, `chronyd` would make new measurements immediately after issuing the
 `online` command.

 Unless the network connection lasts only few minutes (less than the maximum
-polling interval), the delay is usually not a problem, and it may be acceptable
+polling interval), the delay is usually not a problem, and it might be acceptable
 to keep all sources online all the time.

+=== Why is an offset measured between two computers synchronised to each another?
+
+When two computers are synchronised to each other using the client/server or
+symmetric NTP mode, there is an expectation that NTP measurements between the
+two computers made on both ends show an average offset close to zero.
+
+With `chronyd` that can be expected only when the interleaved mode (`xleave`
+option) is enabled. Otherwise, `chronyd` will use different transmit timestamps
+(e.g. daemon timestamp vs kernel timestamp) for serving time and
+synchronisation of its own clock, which creates an asymmetry in the
+timestamping and causes the other end to measure a significant offset.
+
 == Operating systems

 === Does `chrony` support Windows?
--- a/doc/installation.adoc
+++ b/doc/installation.adoc
@@ -22,18 +22,25 @@ The software is distributed as source code which has to be compiled. The source
 code is supplied in the form of a gzipped tar file, which unpacks to a
 subdirectory identifying the name and version of the program.

-The following programs and libraries with their development files are needed to
-build `chrony`:
+A C compiler (e.g. `gcc` or `clang`) and GNU Make are needed to build `chrony`.
+The following libraries with their development files, and programs, are needed
+to enable optional features:

-* C compiler (gcc or clang recommended)
-* GNU Make
-* Nettle, NSS, or LibTomCrypt (optional)
-* Editline (optional)
-* libcap (Linux only, optional)
-* libseccomp (Linux only, optional)
-* timepps.h header (optional)
-* Asciidoctor (for HTML documentation)
-* Bash (for testing)
+* pkg-config: detection of development libraries
+* Nettle, NSS, or LibTomCrypt: secure hash functions (`SECHASH`)
+* libcap: dropping root privileges on Linux (`DROPROOT`)
+* libseccomp: system call filter on Linux (`SCFILTER`)
+* GnuTLS and Nettle: Network Time Security (`NTS`)
+* Editline: line editing in `chronyc` (`READLINE`)
+* timepps.h header: PPS reference clock
+* Asciidoctor: documentation in HTML format
+* Bash: test suite
+
+The following programs are needed when building `chrony` from the git
+repository instead of a released tar file:
+
+* Asciidoctor: manual pages
+* Bison: parser for chronyc settime command

 After unpacking the source code, change directory into it, and type

@@ -87,13 +94,13 @@ want to enable the support, specify the `--disable-asyncdns` flag to

 If development files for the https://www.lysator.liu.se/~nisse/nettle/[Nettle],
 https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS[NSS], or
-http://www.libtom.net/LibTomCrypt/[libtomcrypt] library are available,
+https://www.libtom.net/LibTomCrypt/[libtomcrypt] library are available,
 `chronyd` will be built with support for other cryptographic hash functions
 than MD5, which can be used for NTP authentication with a symmetric key. If you
 don't want to enable the support, specify the `--disable-sechash` flag to
 `configure`.

-If development files for the editline or readline library are available,
+If development files for the editline library are available,
 `chronyc` will be built with line editing support. If you don't want this,
 specify the `--disable-readline` flag to `configure`.

@@ -163,43 +170,6 @@ https://github.com/seccomp/libseccomp[libseccomp] library and the
 the kernel attack surface and possibly prevent kernel exploits from `chronyd`
 if it is compromised.

-== Support for line editing libraries
-
-`chronyc` can be built with support for line editing, this allows you to use
-the cursor keys to replay and edit old commands. Two libraries are supported
-which provide such functionality, editline and GNU readline.
-
-Please note that readline since version 6.0 is licensed under GPLv3+ which is
-incompatible with chrony's license GPLv2. You should use editline instead if
-you don't want to use older readline versions.
-
-The `configure` script will automatically enable the line editing support if
-one of the supported libraries is available. If they are both available, the
-editline library will be used.
-
-If you don't want to use it (in which case `chronyc` will use a minimal command
-line interface), invoke `configure` like this:
-
----
-./configure --disable-readline other-options...
----
-
-If you have editline, readline or ncurses installed in locations that aren't
-normally searched by the compiler and linker, you need to use extra options:
-
-`--with-readline-includes=directory_name`::
-  This defines the name of the directory above the one where `readline.h` is.
-  `readline.h` is assumed to be in `editline` or `readline` subdirectory of the
-  named directory.
-
-`--with-readline-library=directory_name`::
-  This defines the directory containing the `libedit.a` or `libedit.so` file,
-  or `libreadline.a` or `libreadline.so` file.
-
-`--with-ncurses-library=directory_name`::
-  This defines the directory containing the `libncurses.a` or `libncurses.so`
-  file.
-
 == Extra options for package builders

 The `configure` and `make` procedures have some extra options that may be
--- a/examples/chrony-wait.service
+++ b/examples/chrony-wait.service
@@ -8,9 +8,11 @@ Wants=time-sync.target

 [Service]
 Type=oneshot
-# Wait up to ~10 minutes for chronyd to synchronize and the remaining
-# clock correction to be less than 0.1 seconds
-ExecStart=/usr/bin/chronyc -h 127.0.0.1,::1 waitsync 600 0.1 0.0 1
+# Wait for chronyd to update the clock and the remaining
+# correction to be less than 0.1 seconds
+ExecStart=/usr/bin/chronyc -h 127.0.0.1,::1 waitsync 0 0.1 0.0 1
+# Wait for at most 3 minutes
+TimeoutStartSec=180
 RemainAfterExit=yes
 StandardOutput=null

--- a/examples/chrony.conf.example2
+++ b/examples/chrony.conf.example2
@@ -1,5 +1,5 @@
 # Use public servers from the pool.ntp.org project.
-# Please consider joining the pool (http://www.pool.ntp.org/join.html).
+# Please consider joining the pool (https://www.pool.ntp.org/join.html).
 pool pool.ntp.org iburst

 # Record the rate at which the system clock gains/losses time.
@@ -25,9 +25,18 @@ rtcsync
 # Serve time even if not synchronized to a time source.
 #local stratum 10

+# Require authentication (nts or key option) for all NTP sources.
+#authselectmode require
+
 # Specify file containing keys for NTP authentication.
 #keyfile /etc/chrony.keys

+# Save NTS keys and cookies.
+ntsdumpdir /var/lib/chrony
+
+# Insert/delete leap seconds by slewing instead of stepping.
+#leapsecmode slew
+
 # Get TAI-UTC offset and leap seconds from the system tz database.
 #leapsectz right/UTC

--- a/examples/chrony.conf.example3
+++ b/examples/chrony.conf.example3
@@ -57,6 +57,20 @@

 ! maxdrift 100

+# By default, chronyd allows synchronisation to an unauthenticated NTP
+# source (i.e. specified without the nts and key options) if it agrees with
+# a majority of authenticated NTP sources, or if no authenticated source is
+# specified.  If you don't want chronyd to ever synchronise to an
+# unauthenticated NTP source, uncomment the first from the following lines.
+# If you don't want to synchronise to an unauthenticated NTP source only
+# when an authenticated source is specified, uncomment the second line.
+# If you want chronyd to ignore authentication in the source selection,
+# uncomment the third line.
+
+! authselectmode require
+! authselectmode prefer
+! authselectmode ignore
+
 #######################################################################
 ### FILENAMES ETC
 # Chrony likes to keep information about your computer's clock in files.
@@ -72,22 +86,37 @@ driftfile /var/lib/chrony/drift

 ! keyfile /etc/chrony.keys

+# If you specify an NTP server with the nts option to enable authentication
+# with the Network Time Security (NTS) mechanism, or enable server NTS with
+# the ntsservercert and ntsserverkey directives below, the following line will
+# allow the client/server to save the NTS keys and cookies in order to reduce
+# the number of key establishments (NTS-KE sessions).
+
+ntsdumpdir /var/lib/chrony
+
+# If chronyd is configured to act as an NTP server and you want to enable NTS
+# for its clients, you will need a TLS certificate and private key.  Uncomment
+# and edit the following lines to specify the locations of the certificate and
+# key.
+
+! ntsservercert /etc/.../foo.example.net.crt
+! ntsserverkey /etc/.../foo.example.net.key
+
 # chronyd can save the measurement history for the servers to files when
-# it it exits.  This is useful in 2 situations:
+# it exits.  This is useful in 2 situations:
 #
-# 1. On Linux, if you stop chronyd and restart it with '-r' (e.g. after
+# 1. If you stop chronyd and restart it with the '-r' option (e.g. after
 # an upgrade), the old measurements will still be relevant when chronyd
 # is restarted.  This will reduce the time needed to get accurate
-# gain/loss measurements, especially with a dial-up link.
+# gain/loss measurements.
 #
-# 2. Again on Linux, if you use the RTC support and start chronyd with
+# 2. On Linux, if you use the RTC support and start chronyd with
 # '-r -s' on bootup, measurements from the last boot will still be
 # useful (the real time clock is used to 'flywheel' chronyd between
 # boots).
 #
-# Enable these two options to use this.
+# Uncomment the following line to use this.

-! dumponexit
 ! dumpdir /var/lib/chrony

 # chronyd writes its process ID to a file.  If you try to start a second
@@ -116,6 +145,18 @@ driftfile /var/lib/chrony/drift

 ! makestep 1.0 3

+#######################################################################
+### LEAP SECONDS
+# A leap second is an occasional one-second correction of the UTC
+# time scale.  By default, chronyd tells the kernel to insert/delete
+# the leap second, which makes a backward/forward step to correct the
+# clock for it.  As with the makestep directive, this jump can upset
+# some applications.  If you prefer chronyd to make a gradual
+# correction, causing the clock to be off for a longer time, uncomment
+# the following line.
+
+! leapsecmode slew
+
 #######################################################################
 ### LOGGING
 # If you want to log information about the time measurements chronyd has
@@ -135,8 +176,6 @@ driftfile /var/lib/chrony/drift
 #######################################################################
 ### ACTING AS AN NTP SERVER
 # You might want the computer to be an NTP server for other computers.
-# e.g.  you might be running chronyd on a dial-up machine that has a LAN
-# sitting behind it with several 'satellite' computers on it.
 #
 # By default, chronyd does not allow any clients to access it.  You need
 # to explicitly enable access using 'allow' and 'deny' directives.
@@ -152,15 +191,6 @@ driftfile /var/lib/chrony/drift
 # You can have as many allow and deny directives as you need.  The order
 # is unimportant.

-# If you want chronyd to act as an NTP broadcast server, enable and edit
-# (and maybe copy) the following line.  This means that a broadcast
-# packet is sent to the address 192.168.1.255 every 60 seconds.  The
-# address MUST correspond to the broadcast address of one of the network
-# interfaces on your machine.  If you have multiple network interfaces,
-# add a broadcast line for each.
-
-! broadcast 60 192.168.1.255
-
 # If you want to present your computer's time for others to synchronise
 # with, even if you don't seem to be synchronised to any NTP servers
 # yourself, enable the following line.  The value 10 may be varied
--- a/examples/chrony.nm-dispatcher.dhcp
+++ b/examples/chrony.nm-dispatcher.dhcp
@@ -0,0 +1,43 @@
+#!/bin/sh
+# This is a NetworkManager dispatcher script for chronyd to update
+# its NTP sources passed from DHCP options. Note that this script is
+# specific to NetworkManager-dispatcher due to use of the
+# DHCP4_NTP_SERVERS environment variable.
+
+export LC_ALL=C
+
+interface=$1
+action=$2
+
+chronyc=/usr/bin/chronyc
+default_server_options=iburst
+server_dir=/var/run/chrony-dhcp
+
+dhcp_server_file=$server_dir/$interface.sources
+# DHCP4_NTP_SERVERS is passed from DHCP options by NetworkManager.
+nm_dhcp_servers=$DHCP4_NTP_SERVERS
+
+add_servers_from_dhcp() {
+    rm -f "$dhcp_server_file"
+    for server in $nm_dhcp_servers; do
+        echo "server $server $default_server_options" >> "$dhcp_server_file"
+    done
+    $chronyc reload sources > /dev/null 2>&1 || :
+}
+
+clear_servers_from_dhcp() {
+    if [ -f "$dhcp_server_file" ]; then
+        rm -f "$dhcp_server_file"
+        $chronyc reload sources > /dev/null 2>&1 || :
+    fi
+}
+
+mkdir -p $server_dir
+
+if [ "$action" = "up" ] || [ "$action" = "dhcp4-change" ]; then
+    add_servers_from_dhcp
+elif [ "$action" = "down" ]; then
+    clear_servers_from_dhcp
+fi
+
+exit 0
--- a/examples/chrony.nm-dispatcher.onoffline
+++ b/examples/chrony.nm-dispatcher.onoffline
@@ -5,11 +5,13 @@

 export LC_ALL=C

+chronyc=/usr/bin/chronyc
+
 # For NetworkManager consider only up/down events
 [ $# -ge 2 ] && [ "$2" != "up" ] && [ "$2" != "down" ] && exit 0

 # Note: for networkd-dispatcher routable.d ~= on and off.d ~= off

-chronyc onoffline > /dev/null 2>&1
+$chronyc onoffline > /dev/null 2>&1

 exit 0
--- a/hash.h
+++ b/hash.h
@@ -31,12 +31,25 @@
 /* length of hash values produced by SHA512 */
 #define MAX_HASH_LENGTH 64

-extern int HSH_GetHashId(const char *name);
+typedef enum {
+  HSH_INVALID = 0,
+  HSH_MD5 = 1,
+  HSH_SHA1 = 2,
+  HSH_SHA256 = 3,
+  HSH_SHA384 = 4,
+  HSH_SHA512 = 5,
+  HSH_SHA3_224 = 6,
+  HSH_SHA3_256 = 7,
+  HSH_SHA3_384 = 8,
+  HSH_SHA3_512 = 9,
+  HSH_TIGER = 10,
+  HSH_WHIRLPOOL = 11,
+} HSH_Algorithm;

-extern unsigned int HSH_Hash(int id,
-    const unsigned char *in1, unsigned int in1_len,
-    const unsigned char *in2, unsigned int in2_len,
-    unsigned char *out, unsigned int out_len);
+extern int HSH_GetHashId(HSH_Algorithm algorithm);
+
+extern int HSH_Hash(int id, const void *in1, int in1_len, const void *in2, int in2_len,
+                    unsigned char *out, int out_len);

 extern void HSH_Finalise(void);

--- a/hash_intmd5.c
+++ b/hash_intmd5.c
@@ -36,20 +36,22 @@
 static MD5_CTX ctx;

 int
-HSH_GetHashId(const char *name)
+HSH_GetHashId(HSH_Algorithm algorithm)
 {
  /* only MD5 is supported */
-  if (strcmp(name, "MD5"))
+  if (algorithm != HSH_MD5)
    return -1;

  return 0;
 }

-unsigned int
-HSH_Hash(int id, const unsigned char *in1, unsigned int in1_len,
-    const unsigned char *in2, unsigned int in2_len,
-    unsigned char *out, unsigned int out_len)
+int
+HSH_Hash(int id, const void *in1, int in1_len, const void *in2, int in2_len,
+         unsigned char *out, int out_len)
 {
+  if (in1_len < 0 || in2_len < 0 || out_len < 0)
+    return 0;
+
  MD5Init(&ctx);
  MD5Update(&ctx, in1, in1_len);
  if (in2)
--- a/hash_nettle.c
+++ b/hash_nettle.c
@@ -35,37 +35,36 @@
 #include "memory.h"

 struct hash {
-  const char *name;
+  const HSH_Algorithm algorithm;
  const char *int_name;
  const struct nettle_hash *nettle_hash;
  void *context;
 };

 static struct hash hashes[] = {
-  { "MD5", "md5", NULL, NULL },
-  { "RMD160", "ripemd160", NULL, NULL },
-  { "SHA1", "sha1", NULL, NULL },
-  { "SHA256", "sha256", NULL, NULL },
-  { "SHA384", "sha384", NULL, NULL },
-  { "SHA512", "sha512", NULL, NULL },
-  { "SHA3-224", "sha3_224", NULL, NULL },
-  { "SHA3-256", "sha3_256", NULL, NULL },
-  { "SHA3-384", "sha3_384", NULL, NULL },
-  { "SHA3-512", "sha3_512", NULL, NULL },
-  { NULL, NULL, NULL, NULL }
+  { HSH_MD5, "md5", NULL, NULL },
+  { HSH_SHA1, "sha1", NULL, NULL },
+  { HSH_SHA256, "sha256", NULL, NULL },
+  { HSH_SHA384, "sha384", NULL, NULL },
+  { HSH_SHA512, "sha512", NULL, NULL },
+  { HSH_SHA3_224, "sha3_224", NULL, NULL },
+  { HSH_SHA3_256, "sha3_256", NULL, NULL },
+  { HSH_SHA3_384, "sha3_384", NULL, NULL },
+  { HSH_SHA3_512, "sha3_512", NULL, NULL },
+  { 0, NULL, NULL, NULL }
 };

 int
-HSH_GetHashId(const char *name)
+HSH_GetHashId(HSH_Algorithm algorithm)
 {
  int id, nid;

-  for (id = 0; hashes[id].name; id++) {
-    if (!strcmp(name, hashes[id].name))
+  for (id = 0; hashes[id].algorithm != 0; id++) {
+    if (hashes[id].algorithm == algorithm)
      break;
  }

-  if (!hashes[id].name)
+  if (hashes[id].algorithm == 0)
    return -1;

  if (hashes[id].context)
@@ -85,14 +84,16 @@ HSH_GetHashId(const char *name)
  return id;
 }

-unsigned int
-HSH_Hash(int id, const unsigned char *in1, unsigned int in1_len,
-         const unsigned char *in2, unsigned int in2_len,
-         unsigned char *out, unsigned int out_len)
+int
+HSH_Hash(int id, const void *in1, int in1_len, const void *in2, int in2_len,
+         unsigned char *out, int out_len)
 {
  const struct nettle_hash *hash;
  void *context;

+  if (in1_len < 0 || in2_len < 0 || out_len < 0)
+    return 0;
+
  hash = hashes[id].nettle_hash;
  context = hashes[id].context;

@@ -113,7 +114,7 @@ HSH_Finalise(void)
 {
  int i;

-  for (i = 0; hashes[i].name; i++) {
+  for (i = 0; hashes[i].algorithm != 0; i++) {
    if (hashes[i].context)
      Free(hashes[i].context);
  }
--- a/hash_nss.c
+++ b/hash_nss.c
@@ -38,30 +38,30 @@ static NSSLOWInitContext *ictx;

 struct hash {
  HASH_HashType type;
-  const char *name;
+  HSH_Algorithm algorithm;
  NSSLOWHASHContext *context;
 };

 static struct hash hashes[] = {
-  { HASH_AlgMD5, "MD5", NULL },
-  { HASH_AlgSHA1, "SHA1", NULL },
-  { HASH_AlgSHA256, "SHA256", NULL },
-  { HASH_AlgSHA384, "SHA384", NULL },
-  { HASH_AlgSHA512, "SHA512", NULL },
-  { 0, NULL, NULL }
+  { HASH_AlgMD5, HSH_MD5, NULL },
+  { HASH_AlgSHA1, HSH_SHA1, NULL },
+  { HASH_AlgSHA256, HSH_SHA256, NULL },
+  { HASH_AlgSHA384, HSH_SHA384, NULL },
+  { HASH_AlgSHA512, HSH_SHA512, NULL },
+  { 0, 0, NULL }
 };

 int
-HSH_GetHashId(const char *name)
+HSH_GetHashId(HSH_Algorithm algorithm)
 {
  int i;

-  for (i = 0; hashes[i].name; i++) {
-    if (!strcmp(name, hashes[i].name))
+  for (i = 0; hashes[i].algorithm != 0; i++) {
+    if (hashes[i].algorithm == algorithm)
      break;
  }

-  if (!hashes[i].name)
+  if (hashes[i].algorithm == 0)
    return -1; /* not found */

  if (!ictx && !(ictx = NSSLOW_Init()))
@@ -74,14 +74,16 @@ HSH_GetHashId(const char *name)
  return i;
 }

-unsigned int
-HSH_Hash(int id, const unsigned char *in1, unsigned int in1_len,
-    const unsigned char *in2, unsigned int in2_len,
-    unsigned char *out, unsigned int out_len)
+int
+HSH_Hash(int id, const void *in1, int in1_len, const void *in2, int in2_len,
+         unsigned char *out, int out_len)
 {
  unsigned char buf[MAX_HASH_LENGTH];
  unsigned int ret = 0;

+  if (in1_len < 0 || in2_len < 0 || out_len < 0)
+    return 0;
+
  NSSLOWHASH_Begin(hashes[id].context);
  NSSLOWHASH_Update(hashes[id].context, in1, in1_len);
  if (in2)
@@ -99,7 +101,7 @@ HSH_Finalise(void)
 {
  int i;

-  for (i = 0; hashes[i].name; i++) {
+  for (i = 0; hashes[i].algorithm != 0; i++) {
    if (hashes[i].context)
      NSSLOWHASH_Destroy(hashes[i].context);
  }
--- a/hash_tomcrypt.c
+++ b/hash_tomcrypt.c
@@ -32,63 +32,51 @@
 #include "util.h"

 struct hash {
-  const char *name;
+  HSH_Algorithm algorithm;
  const char *int_name;
  const struct ltc_hash_descriptor *desc;
 };

 static const struct hash hashes[] = {
-  { "MD5", "md5", &md5_desc },
-#ifdef LTC_RIPEMD128
-  { "RMD128", "rmd128", &rmd128_desc },
-#endif
-#ifdef LTC_RIPEMD160
-  { "RMD160", "rmd160", &rmd160_desc },
-#endif
-#ifdef LTC_RIPEMD256
-  { "RMD256", "rmd256", &rmd256_desc },
-#endif
-#ifdef LTC_RIPEMD320
-  { "RMD320", "rmd320", &rmd320_desc },
-#endif
+  { HSH_MD5, "md5", &md5_desc },
 #ifdef LTC_SHA1
-  { "SHA1", "sha1", &sha1_desc },
+  { HSH_SHA1, "sha1", &sha1_desc },
 #endif
 #ifdef LTC_SHA256
-  { "SHA256", "sha256", &sha256_desc },
+  { HSH_SHA256, "sha256", &sha256_desc },
 #endif
 #ifdef LTC_SHA384
-  { "SHA384", "sha384", &sha384_desc },
+  { HSH_SHA384, "sha384", &sha384_desc },
 #endif
 #ifdef LTC_SHA512
-  { "SHA512", "sha512", &sha512_desc },
+  { HSH_SHA512, "sha512", &sha512_desc },
 #endif
 #ifdef LTC_SHA3
-  { "SHA3-224", "sha3-224", &sha3_224_desc },
-  { "SHA3-256", "sha3-256", &sha3_256_desc },
-  { "SHA3-384", "sha3-384", &sha3_384_desc },
-  { "SHA3-512", "sha3-512", &sha3_512_desc },
+  { HSH_SHA3_224, "sha3-224", &sha3_224_desc },
+  { HSH_SHA3_256, "sha3-256", &sha3_256_desc },
+  { HSH_SHA3_384, "sha3-384", &sha3_384_desc },
+  { HSH_SHA3_512, "sha3-512", &sha3_512_desc },
 #endif
 #ifdef LTC_TIGER
-  { "TIGER", "tiger", &tiger_desc },
+  { HSH_TIGER, "tiger", &tiger_desc },
 #endif
 #ifdef LTC_WHIRLPOOL
-  { "WHIRLPOOL", "whirlpool", &whirlpool_desc },
+  { HSH_WHIRLPOOL, "whirlpool", &whirlpool_desc },
 #endif
-  { NULL, NULL, NULL }
+  { 0, NULL, NULL }
 };

 int
-HSH_GetHashId(const char *name)
+HSH_GetHashId(HSH_Algorithm algorithm)
 {
  int i, h;

-  for (i = 0; hashes[i].name; i++) {
-    if (!strcmp(name, hashes[i].name))
+  for (i = 0; hashes[i].algorithm != 0; i++) {
+    if (hashes[i].algorithm == algorithm)
      break;
  }

-  if (!hashes[i].name)
+  if (hashes[i].algorithm == 0)
    return -1; /* not found */

  h = find_hash(hashes[i].int_name);
@@ -101,15 +89,17 @@ HSH_GetHashId(const char *name)
  return find_hash(hashes[i].int_name);
 }

-unsigned int
-HSH_Hash(int id, const unsigned char *in1, unsigned int in1_len,
-    const unsigned char *in2, unsigned int in2_len,
-    unsigned char *out, unsigned int out_len)
+int
+HSH_Hash(int id, const void *in1, int in1_len, const void *in2, int in2_len,
+         unsigned char *out, int out_len)
 {
  unsigned char buf[MAX_HASH_LENGTH];
  unsigned long len;
  int r;

+  if (in1_len < 0 || in2_len < 0 || out_len < 0)
+    return 0;
+
  len = sizeof (buf);
  if (in2)
    r = hash_memory_multi(id, buf, &len,
--- a/keys.c
+++ b/keys.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2012-2016
+ * Copyright (C) Miroslav Lichvar  2012-2016, 2019-2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -32,6 +32,7 @@

 #include "array.h"
 #include "keys.h"
+#include "cmac.h"
 #include "cmdparse.h"
 #include "conf.h"
 #include "memory.h"
@@ -42,12 +43,23 @@
 /* Consider 80 bits as the absolute minimum for a secure key */
 #define MIN_SECURE_KEY_LENGTH 10

+typedef enum {
+  NTP_MAC,
+  CMAC,
+} KeyClass;
+
 typedef struct {
  uint32_t id;
-  char *val;
-  int len;
-  int hash_id;
-  int auth_delay;
+  int type;
+  int length;
+  KeyClass class;
+  union {
+    struct {
+      unsigned char *value;
+      int hash_id;
+    } ntp_mac;
+    CMC_Instance cmac;
+  } data;
 } Key;

 static ARR_Instance keys;
@@ -62,9 +74,21 @@ static void
 free_keys(void)
 {
  unsigned int i;
+  Key *key;

-  for (i = 0; i < ARR_GetSize(keys); i++)
-    Free(((Key *)ARR_GetElement(keys, i))->val);
+  for (i = 0; i < ARR_GetSize(keys); i++) {
+    key = ARR_GetElement(keys, i);
+    switch (key->class) {
+      case NTP_MAC:
+        Free(key->data.ntp_mac.value);
+        break;
+      case CMAC:
+        CMC_DestroyInstance(key->data.cmac);
+        break;
+      default:
+        assert(0);
+    }
+  }

  ARR_SetSize(keys, 0);
  cache_valid = 0;
@@ -98,62 +122,18 @@ get_key(unsigned int index)
 }

 /* ================================================== */
+/* Decode key encoded in ASCII or HEX */

 static int
-determine_hash_delay(uint32_t key_id)
+decode_key(char *key)
 {
-  NTP_Packet pkt;
-  struct timespec before, after;
-  double diff, min_diff;
-  int i, nsecs;
-
-  memset(&pkt, 0, sizeof (pkt));
-
-  for (i = 0; i < 10; i++) {
-    LCL_ReadRawTime(&before);
-    KEY_GenerateAuth(key_id, (unsigned char *)&pkt, NTP_NORMAL_PACKET_LENGTH,
-        (unsigned char *)&pkt.auth_data, sizeof (pkt.auth_data));
-    LCL_ReadRawTime(&after);
-
-    diff = UTI_DiffTimespecsToDouble(&after, &before);
-
-    if (i == 0 || min_diff > diff)
-      min_diff = diff;
-  }
-
-  /* Add on a bit extra to allow for copying, conversions etc */
-  nsecs = 1.0625e9 * min_diff;
-
-  DEBUG_LOG("authentication delay for key %"PRIu32": %d nsecs", key_id, nsecs);
-
-  return nsecs;
-}
-
-/* ================================================== */
-/* Decode password encoded in ASCII or HEX */
-
-static int
-decode_password(char *key)
-{
-  int i, j, len = strlen(key);
-  char buf[3], *p;
+  int len = strlen(key);

  if (!strncmp(key, "ASCII:", 6)) {
    memmove(key, key + 6, len - 6);
    return len - 6;
  } else if (!strncmp(key, "HEX:", 4)) {
-    if ((len - 4) % 2)
-      return 0;
-
-    for (i = 0, j = 4; j + 1 < len; i++, j += 2) {
-      buf[0] = key[j], buf[1] = key[j + 1], buf[2] = '\0';
-      key[i] = strtol(buf, &p, 16);
-
-      if (p != buf + 2)
-        return 0;
-    }
-
-    return i;
+    return UTI_HexToBytes(key + 4, key, len);
  } else {
    /* assume ASCII */
    return len;
@@ -185,11 +165,13 @@ compare_keys_by_id(const void *a, const void *b)
 void
 KEY_Reload(void)
 {
-  unsigned int i, line_number;
+  unsigned int i, line_number, key_length, cmac_key_length;
  FILE *in;
-  uint32_t key_id;
-  char line[2048], *keyval, *key_file;
-  const char *hashname;
+  char line[2048], *key_file, *key_value;
+  const char *key_type;
+  HSH_Algorithm hash_algorithm;
+  CMC_Algorithm cmac_algorithm;
+  int hash_id;
  Key key;

  free_keys();
@@ -200,7 +182,7 @@ KEY_Reload(void)
  if (!key_file)
    return;

-  in = fopen(key_file, "r");
+  in = UTI_OpenFile(NULL, key_file, NULL, 'r', 0);
  if (!in) {
    LOG(LOGS_WARN, "Could not open keyfile %s", key_file);
    return;
@@ -213,26 +195,56 @@ KEY_Reload(void)
    if (!*line)
      continue;

-    if (!CPS_ParseKey(line, &key_id, &hashname, &keyval)) {
+    memset(&key, 0, sizeof (key));
+
+    if (!CPS_ParseKey(line, &key.id, &key_type, &key_value)) {
      LOG(LOGS_WARN, "Could not parse key at line %u in file %s", line_number, key_file);
      continue;
    }

-    key.hash_id = HSH_GetHashId(hashname);
-    if (key.hash_id < 0) {
-      LOG(LOGS_WARN, "Unknown hash function in key %"PRIu32, key_id);
+    key_length = decode_key(key_value);
+    if (key_length == 0) {
+      LOG(LOGS_WARN, "Could not decode key %"PRIu32, key.id);
      continue;
    }

-    key.len = decode_password(keyval);
-    if (!key.len) {
-      LOG(LOGS_WARN, "Could not decode password in key %"PRIu32, key_id);
+    hash_algorithm = UTI_HashNameToAlgorithm(key_type);
+    cmac_algorithm = UTI_CmacNameToAlgorithm(key_type);
+
+    if (hash_algorithm != 0) {
+      hash_id = HSH_GetHashId(hash_algorithm);
+      if (hash_id < 0) {
+        LOG(LOGS_WARN, "Unsupported %s in key %"PRIu32, "hash function", key.id);
+        continue;
+      }
+      key.class = NTP_MAC;
+      key.type = hash_algorithm;
+      key.length = key_length;
+      key.data.ntp_mac.value = MallocArray(unsigned char, key_length);
+      memcpy(key.data.ntp_mac.value, key_value, key_length);
+      key.data.ntp_mac.hash_id = hash_id;
+    } else if (cmac_algorithm != 0) {
+      cmac_key_length = CMC_GetKeyLength(cmac_algorithm);
+      if (cmac_key_length == 0) {
+        LOG(LOGS_WARN, "Unsupported %s in key %"PRIu32, "cipher", key.id);
+        continue;
+      } else if (cmac_key_length != key_length) {
+        LOG(LOGS_WARN, "Invalid length of %s key %"PRIu32" (expected %u bits)",
+            key_type, key.id, 8 * cmac_key_length);
+        continue;
+      }
+
+      key.class = CMAC;
+      key.type = cmac_algorithm;
+      key.length = key_length;
+      key.data.cmac = CMC_CreateInstance(cmac_algorithm, (unsigned char *)key_value,
+                                         key_length);
+      assert(key.data.cmac);
+    } else {
+      LOG(LOGS_WARN, "Invalid type in key %"PRIu32, key.id);
      continue;
    }

-    key.id = key_id;
-    key.val = MallocArray(char, key.len);
-    memcpy(key.val, keyval, key.len);
    ARR_AppendElement(keys, &key);
  }

@@ -251,9 +263,6 @@ KEY_Reload(void)

  /* Erase any passwords from stack */
  memset(line, 0, sizeof (line));
-
-  for (i = 0; i < ARR_GetSize(keys); i++)
-    get_key(i)->auth_delay = determine_hash_delay(get_key(i)->id);
 }

 /* ================================================== */
@@ -309,21 +318,6 @@ KEY_KeyKnown(uint32_t key_id)

 /* ================================================== */

-int
-KEY_GetAuthDelay(uint32_t key_id)
-{
-  Key *key;
-
-  key = get_key_by_id(key_id);
-
-  if (!key)
-    return 0;
-
-  return key->auth_delay;
-}
-
-/* ================================================== */
-
 int
 KEY_GetAuthLength(uint32_t key_id)
 {
@@ -335,7 +329,15 @@ KEY_GetAuthLength(uint32_t key_id)
  if (!key)
    return 0;

-  return HSH_Hash(key->hash_id, buf, 0, buf, 0, buf, sizeof (buf));
+  switch (key->class) {
+    case NTP_MAC:
+      return HSH_Hash(key->data.ntp_mac.hash_id, buf, 0, buf, 0, buf, sizeof (buf));
+    case CMAC:
+      return CMC_Hash(key->data.cmac, buf, 0, buf, sizeof (buf));
+    default:
+      assert(0);
+      return 0;
+  }
 }

 /* ================================================== */
@@ -350,39 +352,13 @@ KEY_CheckKeyLength(uint32_t key_id)
  if (!key)
    return 0;

-  return key->len >= MIN_SECURE_KEY_LENGTH;
-}
-
-/* ================================================== */
-
-static int
-generate_ntp_auth(int hash_id, const unsigned char *key, int key_len,
-                  const unsigned char *data, int data_len,
-                  unsigned char *auth, int auth_len)
-{
-  return HSH_Hash(hash_id, key, key_len, data, data_len, auth, auth_len);
-}
-
-/* ================================================== */
-
-static int
-check_ntp_auth(int hash_id, const unsigned char *key, int key_len,
-               const unsigned char *data, int data_len,
-               const unsigned char *auth, int auth_len, int trunc_len)
-{
-  unsigned char buf[MAX_HASH_LENGTH];
-  int hash_len;
-
-  hash_len = generate_ntp_auth(hash_id, key, key_len, data, data_len, buf, sizeof (buf));
-
-  return MIN(hash_len, trunc_len) == auth_len && !memcmp(buf, auth, auth_len);
+  return key->length >= MIN_SECURE_KEY_LENGTH;
 }

 /* ================================================== */

 int
-KEY_GenerateAuth(uint32_t key_id, const unsigned char *data, int data_len,
-    unsigned char *auth, int auth_len)
+KEY_GetKeyInfo(uint32_t key_id, int *type, int *bits)
 {
  Key *key;

@@ -391,14 +367,62 @@ KEY_GenerateAuth(uint32_t key_id, const unsigned char *data, int data_len,
  if (!key)
    return 0;

-  return generate_ntp_auth(key->hash_id, (unsigned char *)key->val, key->len,
-                           data, data_len, auth, auth_len);
+  *type = key->type;
+  *bits = 8 * key->length;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static int
+generate_auth(Key *key, const void *data, int data_len, unsigned char *auth, int auth_len)
+{
+  switch (key->class) {
+    case NTP_MAC:
+      return HSH_Hash(key->data.ntp_mac.hash_id, key->data.ntp_mac.value,
+                      key->length, data, data_len, auth, auth_len);
+    case CMAC:
+      return CMC_Hash(key->data.cmac, data, data_len, auth, auth_len);
+    default:
+      return 0;
+  }
+}
+
+/* ================================================== */
+
+static int
+check_auth(Key *key, const void *data, int data_len,
+           const unsigned char *auth, int auth_len, int trunc_len)
+{
+  unsigned char buf[MAX_HASH_LENGTH];
+  int hash_len;
+
+  hash_len = generate_auth(key, data, data_len, buf, sizeof (buf));
+
+  return MIN(hash_len, trunc_len) == auth_len && !memcmp(buf, auth, auth_len);
 }

 /* ================================================== */

 int
-KEY_CheckAuth(uint32_t key_id, const unsigned char *data, int data_len,
+KEY_GenerateAuth(uint32_t key_id, const void *data, int data_len,
+                 unsigned char *auth, int auth_len)
+{
+  Key *key;
+
+  key = get_key_by_id(key_id);
+
+  if (!key)
+    return 0;
+
+  return generate_auth(key, data, data_len, auth, auth_len);
+}
+
+/* ================================================== */
+
+int
+KEY_CheckAuth(uint32_t key_id, const void *data, int data_len,
              const unsigned char *auth, int auth_len, int trunc_len)
 {
  Key *key;
@@ -408,6 +432,5 @@ KEY_CheckAuth(uint32_t key_id, const unsigned char *data, int data_len,
  if (!key)
    return 0;

-  return check_ntp_auth(key->hash_id, (unsigned char *)key->val, key->len,
-                        data, data_len, auth, auth_len, trunc_len);
+  return check_auth(key, data, data_len, auth, auth_len, trunc_len);
 }
--- a/keys.h
+++ b/keys.h
@@ -34,15 +34,14 @@ extern void KEY_Finalise(void);

 extern void KEY_Reload(void);

-extern int KEY_GetKey(uint32_t key_id, char **key, int *len);
 extern int KEY_KeyKnown(uint32_t key_id);
-extern int KEY_GetAuthDelay(uint32_t key_id);
 extern int KEY_GetAuthLength(uint32_t key_id);
 extern int KEY_CheckKeyLength(uint32_t key_id);
+extern int KEY_GetKeyInfo(uint32_t key_id, int *type, int *bits);

-extern int KEY_GenerateAuth(uint32_t key_id, const unsigned char *data,
-    int data_len, unsigned char *auth, int auth_len);
-extern int KEY_CheckAuth(uint32_t key_id, const unsigned char *data, int data_len,
+extern int KEY_GenerateAuth(uint32_t key_id, const void *data, int data_len,
+                            unsigned char *auth, int auth_len);
+extern int KEY_CheckAuth(uint32_t key_id, const void *data, int data_len,
                         const unsigned char *auth, int auth_len, int trunc_len);

 #endif /* GOT_KEYS_H */
--- a/local.c
+++ b/local.c
@@ -108,8 +108,8 @@ static double max_clock_error;

 #define NSEC_PER_SEC 1000000000

-static void
-calculate_sys_precision(void)
+static double
+measure_clock_precision(void)
 {
  struct timespec ts, old_ts;
  int iters, diff, best;
@@ -135,18 +135,7 @@ calculate_sys_precision(void)

  assert(best > 0);

-  precision_quantum = 1.0e-9 * best;
-
-  /* Get rounded log2 value of the measured precision */
-  precision_log = 0;
-  while (best < 707106781) {
-    precision_log--;
-    best *= 2;
-  }
-
-  assert(precision_log >= -30);
-
-  DEBUG_LOG("Clock precision %.9f (%d)", precision_quantum, precision_log);
+  return 1.0e-9 * best;
 }

 /* ================================================== */
@@ -170,7 +159,16 @@ LCL_Initialise(void)
  current_freq_ppm = 0.0;
  temp_comp_ppm = 0.0;

-  calculate_sys_precision();
+  precision_quantum = CNF_GetClockPrecision();
+  if (precision_quantum <= 0.0)
+    precision_quantum = measure_clock_precision();
+
+  precision_quantum = CLAMP(1.0e-9, precision_quantum, 1.0);
+  precision_log = round(log(precision_quantum) / log(2.0));
+  /* NTP code doesn't support smaller log than -30 */
+  assert(precision_log >= -30);
+
+  DEBUG_LOG("Clock precision %.9f (%d)", precision_quantum, precision_log);

  /* This is the maximum allowed frequency offset in ppm, the time must
     never stop or run backwards */
@@ -185,13 +183,11 @@ LCL_Initialise(void)
 void
 LCL_Finalise(void)
 {
-  while (change_list.next != &change_list)
-    LCL_RemoveParameterChangeHandler(change_list.next->handler,
-                                     change_list.next->anything);
-
-  while (dispersion_notify_list.next != &dispersion_notify_list)
-    LCL_RemoveDispersionNotifyHandler(dispersion_notify_list.next->handler,
-                                      dispersion_notify_list.next->anything);
+  /* Make sure all handlers have been removed */
+  if (change_list.next != &change_list)
+    assert(0);
+  if (dispersion_notify_list.next != &dispersion_notify_list)
+    assert(0);
 }

 /* ================================================== */
--- a/logging.c
+++ b/logging.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2011-2014, 2018
+ * Copyright (C) Miroslav Lichvar  2011-2014, 2018-2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -29,26 +29,25 @@

 #include "sysincl.h"

+#include <syslog.h>
+
 #include "conf.h"
 #include "logging.h"
+#include "memory.h"
 #include "util.h"

 /* This is used by DEBUG_LOG macro */
-int log_debug_enabled = 0;
+LOG_Severity log_min_severity = LOGS_INFO;

 /* ================================================== */
 /* Flag indicating we have initialised */
 static int initialised = 0;

-static FILE *file_log;
+static FILE *file_log = NULL;
 static int system_log = 0;

 static int parent_fd = 0;

-#define DEBUG_LEVEL_PRINT_FUNCTION 2
-#define DEBUG_LEVEL_PRINT_DEBUG 2
-static int debug_level = 0;
-
 struct LogFile {
  const char *name;
  const char *banner;
@@ -63,14 +62,18 @@ static int n_filelogs = 0;

 static struct LogFile logfiles[MAX_FILELOGS];

+/* Global prefix for debug messages */
+static char *debug_prefix;
+
 /* ================================================== */
 /* Init function */

 void
 LOG_Initialise(void)
 {
+  debug_prefix = Strdup("");
  initialised = 1;
-  file_log = stderr;
+  LOG_OpenFileLog(NULL);
 }

 /* ================================================== */
@@ -87,6 +90,8 @@ LOG_Finalise(void)

  LOG_CycleLogFiles();

+  Free(debug_prefix);
+
  initialised = 0;
 }

@@ -134,7 +139,9 @@ void LOG_Message(LOG_Severity severity,
  time_t t;
  struct tm *tm;

-  if (!system_log && file_log) {
+  assert(initialised);
+
+  if (!system_log && file_log && severity >= log_min_severity) {
    /* Don't clutter up syslog with timestamps and internal debugging info */
    time(&t);
    tm = gmtime(&t);
@@ -143,8 +150,8 @@ void LOG_Message(LOG_Severity severity,
      fprintf(file_log, "%s ", buf);
    }
 #if DEBUG > 0
-    if (debug_level >= DEBUG_LEVEL_PRINT_FUNCTION)
-      fprintf(file_log, "%s:%d:(%s) ", filename, line_number, function_name);
+    if (log_min_severity <= LOGS_DEBUG)
+      fprintf(file_log, "%s%s:%d:(%s) ", debug_prefix, filename, line_number, function_name);
 #endif
  }

@@ -157,10 +164,12 @@ void LOG_Message(LOG_Severity severity,
    case LOGS_INFO:
    case LOGS_WARN:
    case LOGS_ERR:
-      log_message(0, severity, buf);
+      if (severity >= log_min_severity)
+        log_message(0, severity, buf);
      break;
    case LOGS_FATAL:
-      log_message(1, severity, buf);
+      if (severity >= log_min_severity)
+        log_message(1, severity, buf);

      /* Send the message also to the foreground process if it is
         still running, or stderr if it is still open */
@@ -171,6 +180,7 @@ void LOG_Message(LOG_Severity severity,
        system_log = 0;
        log_message(1, severity, buf);
      }
+      exit(1);
      break;
    default:
      assert(0);
@@ -185,9 +195,7 @@ LOG_OpenFileLog(const char *log_file)
  FILE *f;

  if (log_file) {
-    f = fopen(log_file, "a");
-    if (!f)
-      LOG_FATAL("Could not open log file %s", log_file);
+    f = UTI_OpenFile(NULL, log_file, NULL, 'A', 0640);
  } else {
    f = stderr;
  }
@@ -213,12 +221,27 @@ LOG_OpenSystemLog(void)

 /* ================================================== */

-void LOG_SetDebugLevel(int level)
+void LOG_SetMinSeverity(LOG_Severity severity)
 {
-  debug_level = level;
-  if (level >= DEBUG_LEVEL_PRINT_DEBUG) {
-    log_debug_enabled = 1;
-  }
+  /* Don't print any debug messages in a non-debug build */
+  log_min_severity = CLAMP(DEBUG > 0 ? LOGS_DEBUG : LOGS_INFO, severity, LOGS_FATAL);
+}
+
+/* ================================================== */
+
+LOG_Severity
+LOG_GetMinSeverity(void)
+{
+  return log_min_severity;
+}
+
+/* ================================================== */
+
+void
+LOG_SetDebugPrefix(const char *prefix)
+{
+  Free(debug_prefix);
+  debug_prefix = Strdup(prefix);
 }

 /* ================================================== */
@@ -246,7 +269,10 @@ LOG_CloseParentFd()
 LOG_FileID
 LOG_FileOpen(const char *name, const char *banner)
 {
-  assert(n_filelogs < MAX_FILELOGS);
+  if (n_filelogs >= MAX_FILELOGS) {
+    assert(0);
+    return -1;
+  }

  logfiles[n_filelogs].name = name;
  logfiles[n_filelogs].banner = banner;
@@ -268,24 +294,20 @@ LOG_FileWrite(LOG_FileID id, const char *format, ...)
    return;

  if (!logfiles[id].file) {
-    char filename[512], *logdir = CNF_GetLogDir();
+    char *logdir = CNF_GetLogDir();

-    if (logdir[0] == '\0') {
+    if (!logdir) {
      LOG(LOGS_WARN, "logdir not specified");
      logfiles[id].name = NULL;
      return;
    }

-    if (snprintf(filename, sizeof(filename), "%s/%s.log",
-                 logdir, logfiles[id].name) >= sizeof (filename) ||
-        !(logfiles[id].file = fopen(filename, "a"))) {
-      LOG(LOGS_WARN, "Could not open log file %s", filename);
+    logfiles[id].file = UTI_OpenFile(logdir, logfiles[id].name, ".log", 'a', 0644);
+    if (!logfiles[id].file) {
+      /* Disable the log */
      logfiles[id].name = NULL;
      return;
    }
-
-    /* Close on exec */
-    UTI_FdSetCloexec(fileno(logfiles[id].file));
  }

  banner = CNF_GetLogBanner();
@@ -293,7 +315,7 @@ LOG_FileWrite(LOG_FileID id, const char *format, ...)
    char bannerline[256];
    int i, bannerlen;

-    bannerlen = strlen(logfiles[id].banner);
+    bannerlen = MIN(strlen(logfiles[id].banner), sizeof (bannerline) - 1);

    for (i = 0; i < bannerlen; i++)
      bannerline[i] = '=';
--- a/logging.h
+++ b/logging.h
@@ -31,9 +31,6 @@

 #include "sysincl.h"

-/* Flag indicating whether debug messages are logged */
-extern int log_debug_enabled;
-
 /* Line logging macros.  If the compiler is GNU C, we take advantage of
   being able to get the function name also. */

@@ -55,7 +52,7 @@ extern int log_debug_enabled;

 #define DEBUG_LOG(...) \
  do { \
-    if (DEBUG && log_debug_enabled) \
+    if (DEBUG && log_min_severity == LOGS_DEBUG) \
      LOG_MESSAGE(LOGS_DEBUG, __VA_ARGS__); \
  } while (0)

@@ -69,13 +66,16 @@ extern int log_debug_enabled;

 /* Definition of severity */
 typedef enum {
-  LOGS_INFO,
+  LOGS_DEBUG = -1,
+  LOGS_INFO = 0,
  LOGS_WARN,
  LOGS_ERR,
  LOGS_FATAL,
-  LOGS_DEBUG
 } LOG_Severity;

+/* Minimum severity of messages to be logged */
+extern LOG_Severity log_min_severity;
+
 /* Init function */
 extern void LOG_Initialise(void);

@@ -92,12 +92,16 @@ FORMAT_ATTRIBUTE_PRINTF(2, 3)
 extern void LOG_Message(LOG_Severity severity, const char *format, ...);
 #endif

-/* Set debug level:
-   0, 1 - only non-debug messages are logged
-   2    - debug messages are logged too, all messages are prefixed with
-          filename, line, and function name
-   */
-extern void LOG_SetDebugLevel(int level);
+/* Set the minimum severity of a message to be logged or printed to terminal.
+   If the severity is LOGS_DEBUG and DEBUG is enabled, all messages will be
+   prefixed with the filename, line number, and function name. */
+extern void LOG_SetMinSeverity(LOG_Severity severity);
+
+/* Get the minimum severity */
+extern LOG_Severity LOG_GetMinSeverity(void);
+
+/* Set a prefix for debug messages */
+extern void LOG_SetDebugPrefix(const char *prefix);

 /* Log messages to a file instead of stderr, or stderr again if NULL */
 extern void LOG_OpenFileLog(const char *log_file);
--- a/main.c
+++ b/main.c
@@ -4,7 +4,7 @@
 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
 * Copyright (C) John G. Hasler  2009
- * Copyright (C) Miroslav Lichvar  2012-2018
+ * Copyright (C) Miroslav Lichvar  2012-2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -38,6 +38,9 @@
 #include "ntp_signd.h"
 #include "ntp_sources.h"
 #include "ntp_core.h"
+#include "nts_ke_server.h"
+#include "nts_ntp_server.h"
+#include "socket.h"
 #include "sources.h"
 #include "sourcestats.h"
 #include "reference.h"
@@ -87,11 +90,11 @@ delete_pidfile(void)
 {
  const char *pidfile = CNF_GetPidFile();

-  if (!pidfile[0])
+  if (!pidfile)
    return;

-  /* Don't care if this fails, there's not a lot we can do */
-  unlink(pidfile);
+  if (!UTI_RemoveFile(NULL, pidfile, NULL))
+    ;
 }

 /* ================================================== */
@@ -101,9 +104,7 @@ MAI_CleanupAndExit(void)
 {
  if (!initialised) exit(exit_status);
  
-  if (CNF_GetDumpDir()[0] != '\0') {
-    SRC_DumpSources();
-  }
+  SRC_DumpSources();

  /* Don't update clock when removing sources */
  REF_SetMode(REF_ModeIgnore);
@@ -112,18 +113,23 @@ MAI_CleanupAndExit(void)
  TMC_Finalise();
  MNL_Finalise();
  CLG_Finalise();
+  NKS_Finalise();
+  NNS_Finalise();
  NSD_Finalise();
  NSR_Finalise();
  SST_Finalise();
  NCR_Finalise();
  NIO_Finalise();
  CAM_Finalise();
+
  KEY_Finalise();
  RCL_Finalise();
  SRC_Finalise();
  REF_Finalise();
  RTC_Finalise();
  SYS_Finalise();
+
+  SCK_Finalise();
  SCH_Finalise();
  LCL_Finalise();
  PRV_Finalise();
@@ -142,7 +148,6 @@ MAI_CleanupAndExit(void)
 static void
 signal_cleanup(int x)
 {
-  if (!initialised) exit(0);
  SCH_QuitProgram();
 }

@@ -253,7 +258,10 @@ check_pidfile(void)
  FILE *in;
  int pid, count;
  
-  in = fopen(pidfile, "r");
+  if (!pidfile)
+    return;
+
+  in = UTI_OpenFile(NULL, pidfile, NULL, 'r', 0);
  if (!in)
    return;

@@ -278,16 +286,12 @@ write_pidfile(void)
  const char *pidfile = CNF_GetPidFile();
  FILE *out;

-  if (!pidfile[0])
+  if (!pidfile)
    return;

-  out = fopen(pidfile, "w");
-  if (!out) {
-    LOG_FATAL("Could not open %s : %s", pidfile, strerror(errno));
-  } else {
-    fprintf(out, "%d\n", (int)getpid());
-    fclose(out);
-  }
+  out = UTI_OpenFile(NULL, pidfile, NULL, 'W', 0644);
+  fprintf(out, "%d\n", (int)getpid());
+  fclose(out);
 }

 /* ================================================== */
@@ -370,8 +374,34 @@ go_daemon(void)
 static void
 print_help(const char *progname)
 {
-      printf("Usage: %s [-4|-6] [-n|-d] [-q|-Q] [-r] [-R] [-s] [-t TIMEOUT] [-f FILE|COMMAND...]\n",
-             progname);
+      printf("Usage: %s [OPTION]... [DIRECTIVE]...\n\n"
+             "Options:\n"
+             "  -4\t\tUse IPv4 addresses only\n"
+             "  -6\t\tUse IPv6 addresses only\n"
+             "  -f FILE\tSpecify configuration file (%s)\n"
+             "  -n\t\tDon't run as daemon\n"
+             "  -d\t\tDon't run as daemon and log to stderr\n"
+#if DEBUG > 0
+             "  -d -d\t\tEnable debug messages\n"
+#endif
+             "  -l FILE\tLog to file\n"
+             "  -L LEVEL\tSet logging threshold (0)\n"
+             "  -p\t\tPrint configuration and exit\n"
+             "  -q\t\tSet clock and exit\n"
+             "  -Q\t\tLog offset and exit\n"
+             "  -r\t\tReload dump files\n"
+             "  -R\t\tAdapt configuration for restart\n"
+             "  -s\t\tSet clock from RTC\n"
+             "  -t SECONDS\tExit after elapsed time\n"
+             "  -u USER\tSpecify user (%s)\n"
+             "  -U\t\tDon't check for root\n"
+             "  -F LEVEL\tSet system call filter level (0)\n"
+             "  -P PRIORITY\tSet process priority (0)\n"
+             "  -m\t\tLock memory\n"
+             "  -x\t\tDon't control clock\n"
+             "  -v, --version\tPrint version and exit\n"
+             "  -h, --help\tPrint usage and exit\n",
+             progname, DEFAULT_CONF_FILE, DEFAULT_USER);
 }

 /* ================================================== */
@@ -404,16 +434,16 @@ int main
  char *user = NULL, *log_file = NULL;
  struct passwd *pw;
  int opt, debug = 0, nofork = 0, address_family = IPADDR_UNSPEC;
-  int do_init_rtc = 0, restarted = 0, client_only = 0, timeout = 0;
+  int do_init_rtc = 0, restarted = 0, client_only = 0, timeout = -1;
  int scfilter_level = 0, lock_memory = 0, sched_priority = 0;
-  int clock_control = 1, system_log = 1;
-  int config_args = 0;
+  int clock_control = 1, system_log = 1, log_severity = LOGS_INFO;
+  int user_check = 1, config_args = 0, print_config = 0;

  do_platform_checks();

  LOG_Initialise();

-  /* Parse (undocumented) long command-line options */
+  /* Parse long command-line options */
  for (optind = 1; optind < argc; optind++) {
    if (!strcmp("--help", argv[optind])) {
      print_help(progname);
@@ -427,7 +457,7 @@ int main
  optind = 1;

  /* Parse short command-line options */
-  while ((opt = getopt(argc, argv, "46df:F:hl:mnP:qQrRst:u:vx")) != -1) {
+  while ((opt = getopt(argc, argv, "46df:F:hl:L:mnpP:qQrRst:u:Uvx")) != -1) {
    switch (opt) {
      case '4':
      case '6':
@@ -447,12 +477,21 @@ int main
      case 'l':
        log_file = optarg;
        break;
+      case 'L':
+        log_severity = parse_int_arg(optarg);
+        break;
      case 'm':
        lock_memory = 1;
        break;
      case 'n':
        nofork = 1;
        break;
+      case 'p':
+        print_config = 1;
+        user_check = 0;
+        nofork = 1;
+        system_log = 0;
+        break;
      case 'P':
        sched_priority = parse_int_arg(optarg);
        break;
@@ -466,6 +505,7 @@ int main
        ref_mode = REF_ModePrintOnce;
        nofork = 1;
        client_only = 1;
+        user_check = 0;
        clock_control = 0;
        system_log = 0;
        break;
@@ -484,6 +524,9 @@ int main
      case 'u':
        user = optarg;
        break;
+      case 'U':
+        user_check = 0;
+        break;
      case 'v':
        print_version();
        return 0;
@@ -496,7 +539,7 @@ int main
    }
  }

-  if (getuid() && !client_only)
+  if (user_check && getuid() != 0)
    LOG_FATAL("Not superuser");

  /* Turn into a daemon */
@@ -510,13 +553,15 @@ int main
    LOG_OpenSystemLog();
  }
  
-  LOG_SetDebugLevel(debug);
+  LOG_SetMinSeverity(debug >= 2 ? LOGS_DEBUG : log_severity);
  
  LOG(LOGS_INFO, "chronyd version %s starting (%s)", CHRONY_VERSION, CHRONYD_FEATURES);

  DNS_SetAddressFamily(address_family);

  CNF_Initialise(restarted, client_only);
+  if (print_config)
+    CNF_EnablePrint();

  /* Parse the config file or the remaining command line arguments */
  config_args = argc - optind;
@@ -527,6 +572,9 @@ int main
      CNF_ParseLine(NULL, config_args + optind - argc + 1, argv[optind]);
  }

+  if (print_config)
+    return 0;
+
  /* Check whether another chronyd may already be running */
  check_pidfile();

@@ -546,6 +594,11 @@ int main
  PRV_Initialise();
  LCL_Initialise();
  SCH_Initialise();
+  SCK_Initialise(address_family);
+
+  /* Start helper processes if needed */
+  NKS_PreInitialise(pw->pw_uid, pw->pw_gid, scfilter_level);
+
  SYS_Initialise(clock_control);
  RTC_Initialise(do_init_rtc);
  SRC_Initialise();
@@ -553,8 +606,8 @@ int main
  KEY_Initialise();

  /* Open privileged ports before dropping root */
-  CAM_Initialise(address_family);
-  NIO_Initialise(address_family);
+  CAM_Initialise();
+  NIO_Initialise();
  NCR_Initialise();
  CNF_SetupAccessRestrictions();

@@ -572,12 +625,14 @@ int main

  /* Drop root privileges if the specified user has a non-zero UID */
  if (!geteuid() && (pw->pw_uid || pw->pw_gid))
-    SYS_DropRoot(pw->pw_uid, pw->pw_gid);
+    SYS_DropRoot(pw->pw_uid, pw->pw_gid, SYS_MAIN_PROCESS);

  REF_Initialise();
  SST_Initialise();
  NSR_Initialise();
  NSD_Initialise();
+  NNS_Initialise();
+  NKS_Initialise();
  CLG_Initialise();
  MNL_Initialise();
  TMC_Initialise();
@@ -591,7 +646,7 @@ int main
  CAM_OpenUnixSocket();

  if (scfilter_level)
-    SYS_EnableSystemCallFilter(scfilter_level);
+    SYS_EnableSystemCallFilter(scfilter_level, SYS_MAIN_PROCESS);

  if (ref_mode == REF_ModeNormal && CNF_GetInitSources() > 0) {
    ref_mode = REF_ModeInitStepSlew;
@@ -600,7 +655,7 @@ int main
  REF_SetModeEndHandler(reference_mode_end);
  REF_SetMode(ref_mode);

-  if (timeout > 0)
+  if (timeout >= 0)
    SCH_AddTimeoutByDelay(timeout, quit_timeout, NULL);

  if (do_init_rtc) {
--- a/manual.c
+++ b/manual.c
@@ -92,6 +92,7 @@ MNL_Initialise(void)
 void
 MNL_Finalise(void)
 {
+  LCL_RemoveParameterChangeHandler(slew_samples, NULL);
 }

 /* ================================================== */
--- a/nameserv.c
+++ b/nameserv.c
@@ -34,6 +34,7 @@
 #include <resolv.h>

 #include "nameserv.h"
+#include "socket.h"
 #include "util.h"

 /* ================================================== */
@@ -69,7 +70,7 @@ DNS_Name2IPAddress(const char *name, IPAddr *ip_addrs, int max_addrs)
    default:
      hints.ai_family = AF_UNSPEC;
  }
-  hints.ai_socktype = SOCK_STREAM;
+  hints.ai_socktype = SOCK_DGRAM;

  result = getaddrinfo(name, NULL, &hints, &res);

@@ -94,6 +95,9 @@ DNS_Name2IPAddress(const char *name, IPAddr *ip_addrs, int max_addrs)
      case AF_INET6:
        if (address_family != IPADDR_UNSPEC && address_family != IPADDR_INET6)
          continue;
+        /* Don't return an address that would lose a scope ID */
+        if (((struct sockaddr_in6 *)ai->ai_addr)->sin6_scope_id != 0)
+          continue;
        ip_addrs[i].family = IPADDR_INET6;
        memcpy(&ip_addrs[i].addr.in6, &((struct sockaddr_in6 *)ai->ai_addr)->sin6_addr.s6_addr,
               sizeof (ip_addrs->addr.in6));
@@ -156,10 +160,14 @@ DNS_IPAddress2Name(IPAddr *ip_addr, char *name, int len)

 #ifdef FEAT_IPV6
  struct sockaddr_in6 in6;
+  IPSockAddr ip_saddr;
  socklen_t slen;
  char hbuf[NI_MAXHOST];

-  slen = UTI_IPAndPortToSockaddr(ip_addr, 0, (struct sockaddr *)&in6);
+  ip_saddr.ip_addr = *ip_addr;
+  ip_saddr.port = 0;
+
+  slen = SCK_IPSockAddrToSockaddr(&ip_saddr, (struct sockaddr *)&in6, sizeof (in6));
  if (!getnameinfo((struct sockaddr *)&in6, slen, hbuf, sizeof (hbuf), NULL, 0, 0))
    result = hbuf;
 #else
--- a/nameserv_async.c
+++ b/nameserv_async.c
@@ -51,7 +51,7 @@ struct DNS_Async_Instance {
  int pipe[2];
 };

-static int resolving_threads = 0;
+static pthread_mutex_t privops_lock = PTHREAD_MUTEX_INITIALIZER;

 /* ================================================== */

@@ -60,7 +60,9 @@ start_resolving(void *anything)
 {
  struct DNS_Async_Instance *inst = (struct DNS_Async_Instance *)anything;

+  pthread_mutex_lock(&privops_lock);
  inst->status = PRV_Name2IPAddress(inst->name, inst->addresses, DNS_MAX_ADDRESSES);
+  pthread_mutex_unlock(&privops_lock);

  /* Notify the main thread that the result is ready */
  if (write(inst->pipe[1], "", 1) < 0)
@@ -81,8 +83,6 @@ end_resolving(int fd, int event, void *anything)
    LOG_FATAL("pthread_join() failed");
  }

-  resolving_threads--;
-
  SCH_RemoveFileHandler(inst->pipe[0]);
  close(inst->pipe[0]);
  close(inst->pipe[1]);
@@ -116,9 +116,6 @@ DNS_Name2IPAddressAsync(const char *name, DNS_NameResolveHandler handler, void *
  UTI_FdSetCloexec(inst->pipe[0]);
  UTI_FdSetCloexec(inst->pipe[1]);

-  resolving_threads++;
-  assert(resolving_threads <= 1);
-
  if (pthread_create(&inst->thread, NULL, start_resolving, inst)) {
    LOG_FATAL("pthread_create() failed");
  }
--- a/ntp.h
+++ b/ntp.h
@@ -47,18 +47,21 @@ typedef uint32_t NTP_int32;
 /* Maximum stratum number (infinity) */
 #define NTP_MAX_STRATUM 16

-/* The minimum valid length of an extension field */
-#define NTP_MIN_EXTENSION_LENGTH 16
-
-/* The maximum assumed length of all extension fields in received
-   packets (RFC 5905 doesn't specify a limit on length or number of
-   extension fields in one packet) */
-#define NTP_MAX_EXTENSIONS_LENGTH 1024
+/* Invalid stratum number */
+#define NTP_INVALID_STRATUM 0

 /* The minimum and maximum supported length of MAC */
 #define NTP_MIN_MAC_LENGTH (4 + 16)
 #define NTP_MAX_MAC_LENGTH (4 + MAX_HASH_LENGTH)

+/* The minimum valid length of an extension field */
+#define NTP_MIN_EF_LENGTH 16
+
+/* The maximum assumed length of all extension fields in an NTP packet,
+   including a MAC (RFC 5905 doesn't specify a limit on length or number of
+   extension fields in one packet) */
+#define NTP_MAX_EXTENSIONS_LENGTH (1024 + NTP_MAX_MAC_LENGTH)
+
 /* The maximum length of MAC in NTPv4 packets which allows deterministic
   parsing of extension fields (RFC 7822) */
 #define NTP_MAX_V4_MAC_LENGTH (4 + 20)
@@ -93,21 +96,10 @@ typedef struct {
  NTP_int64 receive_ts;
  NTP_int64 transmit_ts;

-  /* Optional extension fields, we don't send packets with them yet */
-  /* uint8_t extensions[] */
-
-  /* Optional message authentication code (MAC) */
-  NTP_int32 auth_keyid;
-  uint8_t auth_data[NTP_MAX_MAC_LENGTH - 4];
+  uint8_t extensions[NTP_MAX_EXTENSIONS_LENGTH];
 } NTP_Packet;

-#define NTP_NORMAL_PACKET_LENGTH (int)offsetof(NTP_Packet, auth_keyid)
-
-/* The buffer used to hold a datagram read from the network */
-typedef struct {
-  NTP_Packet ntp_pkt;
-  uint8_t extensions[NTP_MAX_EXTENSIONS_LENGTH];
-} NTP_Receive_Buffer;
+#define NTP_HEADER_LENGTH (int)offsetof(NTP_Packet, extensions)

 /* Macros to work with the lvm field */
 #define NTP_LVM_TO_LEAP(lvm) (((lvm) >> 6) & 0x3)
@@ -121,6 +113,34 @@ typedef struct {
 #define NTP_REFID_LOCAL 0x7F7F0101UL /* 127.127.1.1 */
 #define NTP_REFID_SMOOTH 0x7F7F01FFUL /* 127.127.1.255 */

+/* Enumeration for authentication modes of NTP packets */
+typedef enum {
+  NTP_AUTH_NONE = 0,            /* No authentication */
+  NTP_AUTH_SYMMETRIC,           /* NTP MAC or CMAC using a symmetric key
+                                   (RFC 1305, RFC 5905, RFC 8573) */
+  NTP_AUTH_MSSNTP,              /* MS-SNTP authenticator field */
+  NTP_AUTH_MSSNTP_EXT,          /* MS-SNTP extended authenticator field */
+  NTP_AUTH_NTS,                 /* Network Time Security (RFC 8915) */
+} NTP_AuthMode;
+
+/* Structure describing an NTP packet */
+typedef struct {
+  int length;
+  int version;
+  NTP_Mode mode;
+
+  int ext_fields;
+
+  struct {
+    NTP_AuthMode mode;
+    struct {
+      int start;
+      int length;
+      uint32_t key_id;
+    } mac;
+  } auth;
+} NTP_PacketInfo;
+
 /* Structure used to save NTP measurements.  time is the local time at which
   the sample is to be considered to have been made and offset is the offset at
   the time (positive indicates that the local clock is slow relative to the
@@ -133,7 +153,6 @@ typedef struct {
  double root_delay;
  double root_dispersion;
  int stratum;
-  NTP_Leap leap;
 } NTP_Sample;

 #endif /* GOT_NTP_H */
--- a/ntp_auth.c
+++ b/ntp_auth.c
@@ -0,0 +1,494 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2019-2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  NTP authentication
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include "keys.h"
+#include "logging.h"
+#include "memory.h"
+#include "ntp_auth.h"
+#include "ntp_ext.h"
+#include "ntp_signd.h"
+#include "nts_ntp.h"
+#include "nts_ntp_client.h"
+#include "nts_ntp_server.h"
+#include "srcparams.h"
+#include "util.h"
+
+/* Structure to hold authentication configuration and state */
+
+struct NAU_Instance_Record {
+  NTP_AuthMode mode;            /* Authentication mode of NTP packets */
+  uint32_t key_id;              /* Identifier of a symmetric key */
+  NNC_Instance nts;             /* Client NTS state */
+};
+
+/* ================================================== */
+
+static int
+generate_symmetric_auth(uint32_t key_id, NTP_Packet *packet, NTP_PacketInfo *info)
+{
+  int auth_len, max_auth_len;
+
+  if (info->length + NTP_MIN_MAC_LENGTH > sizeof (*packet)) {
+    DEBUG_LOG("Packet too long");
+    return 0;
+  }
+
+  /* Truncate long MACs in NTPv4 packets to allow deterministic parsing
+     of extension fields (RFC 7822) */
+  max_auth_len = (info->version == 4 ? NTP_MAX_V4_MAC_LENGTH : NTP_MAX_MAC_LENGTH) - 4;
+  max_auth_len = MIN(max_auth_len, sizeof (*packet) - info->length - 4);
+
+  auth_len = KEY_GenerateAuth(key_id, packet, info->length,
+                              (unsigned char *)packet + info->length + 4, max_auth_len);
+  if (auth_len < NTP_MIN_MAC_LENGTH - 4) {
+    DEBUG_LOG("Could not generate auth data with key %"PRIu32, key_id);
+    return 0;
+  }
+
+  *(uint32_t *)((unsigned char *)packet + info->length) = htonl(key_id);
+
+  info->auth.mac.start = info->length;
+  info->auth.mac.length = 4 + auth_len;
+  info->auth.mac.key_id = key_id;
+  info->length += info->auth.mac.length;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static int
+check_symmetric_auth(NTP_Packet *packet, NTP_PacketInfo *info)
+{
+  int trunc_len;
+
+  if (info->auth.mac.length < NTP_MIN_MAC_LENGTH)
+    return 0;
+
+  trunc_len = info->version == 4 && info->auth.mac.length <= NTP_MAX_V4_MAC_LENGTH ?
+              NTP_MAX_V4_MAC_LENGTH : NTP_MAX_MAC_LENGTH;
+
+  if (!KEY_CheckAuth(info->auth.mac.key_id, packet, info->auth.mac.start,
+                     (unsigned char *)packet + info->auth.mac.start + 4,
+                     info->auth.mac.length - 4, trunc_len - 4))
+    return 0;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static int
+is_zero_data(unsigned char *data, int length)
+{
+  int i;
+
+  for (i = 0; i < length; i++)
+    if (data[i] != 0)
+      return 0;
+  return 1;
+}
+
+/* ================================================== */
+
+static NAU_Instance
+create_instance(NTP_AuthMode mode)
+{
+  NAU_Instance instance;
+
+  instance = MallocNew(struct NAU_Instance_Record);
+  instance->mode = mode;
+  instance->key_id = INACTIVE_AUTHKEY;
+  instance->nts = NULL;
+
+  assert(sizeof (instance->key_id) == 4);
+
+  return instance;
+}
+
+/* ================================================== */
+
+NAU_Instance
+NAU_CreateNoneInstance(void)
+{
+  return create_instance(NTP_AUTH_NONE);
+}
+
+/* ================================================== */
+
+NAU_Instance
+NAU_CreateSymmetricInstance(uint32_t key_id)
+{
+  NAU_Instance instance = create_instance(NTP_AUTH_SYMMETRIC);
+
+  instance->key_id = key_id;
+
+  if (!KEY_KeyKnown(key_id))
+    LOG(LOGS_WARN, "Key %"PRIu32" is %s", key_id, "missing");
+  else if (!KEY_CheckKeyLength(key_id))
+    LOG(LOGS_WARN, "Key %"PRIu32" is %s", key_id, "too short");
+
+  return instance;
+}
+
+/* ================================================== */
+
+NAU_Instance
+NAU_CreateNtsInstance(IPSockAddr *nts_address, const char *name, const IPSockAddr *ntp_address)
+{
+  NAU_Instance instance = create_instance(NTP_AUTH_NTS);
+
+  instance->nts = NNC_CreateInstance(nts_address, name, ntp_address);
+
+  return instance;
+}
+
+/* ================================================== */
+
+void
+NAU_DestroyInstance(NAU_Instance instance)
+{
+  if (instance->mode == NTP_AUTH_NTS)
+    NNC_DestroyInstance(instance->nts);
+  Free(instance);
+}
+
+/* ================================================== */
+
+int
+NAU_IsAuthEnabled(NAU_Instance instance)
+{
+  return instance->mode != NTP_AUTH_NONE;
+}
+
+/* ================================================== */
+
+int
+NAU_GetSuggestedNtpVersion(NAU_Instance instance)
+{
+  /* If the MAC in NTPv4 packets would be truncated, prefer NTPv3 for
+     compatibility with older chronyd servers */
+  if (instance->mode == NTP_AUTH_SYMMETRIC &&
+      KEY_GetAuthLength(instance->key_id) + sizeof (instance->key_id) > NTP_MAX_V4_MAC_LENGTH)
+    return 3;
+
+  return NTP_VERSION;
+}
+
+/* ================================================== */
+
+int
+NAU_PrepareRequestAuth(NAU_Instance instance)
+{
+  switch (instance->mode) {
+    case NTP_AUTH_NTS:
+      if (!NNC_PrepareForAuth(instance->nts))
+        return 0;
+      break;
+    default:
+      break;
+  }
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NAU_GenerateRequestAuth(NAU_Instance instance, NTP_Packet *request, NTP_PacketInfo *info)
+{
+  switch (instance->mode) {
+    case NTP_AUTH_NONE:
+      break;
+    case NTP_AUTH_SYMMETRIC:
+      if (!generate_symmetric_auth(instance->key_id, request, info))
+        return 0;
+      break;
+    case NTP_AUTH_NTS:
+      if (!NNC_GenerateRequestAuth(instance->nts, request, info))
+        return 0;
+      break;
+    default:
+      assert(0);
+  }
+
+  info->auth.mode = instance->mode;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NAU_ParsePacket(NTP_Packet *packet, NTP_PacketInfo *info)
+{
+  int parsed, remainder, ef_length, ef_type;
+  unsigned char *data;
+
+  data = (void *)packet;
+  parsed = NTP_HEADER_LENGTH;
+  remainder = info->length - parsed;
+
+  info->ext_fields = 0;
+
+  /* Check if this is a plain NTP packet with no extension fields or MAC */
+  if (remainder <= 0)
+    return 1;
+
+  assert(remainder % 4 == 0);
+
+  /* In NTPv3 and older packets don't have extension fields.  Anything after
+     the header is assumed to be a MAC. */
+  if (info->version <= 3) {
+    info->auth.mode = NTP_AUTH_SYMMETRIC;
+    info->auth.mac.start = parsed;
+    info->auth.mac.length = remainder;
+    info->auth.mac.key_id = ntohl(*(uint32_t *)(data + parsed));
+
+    /* Check if it is an MS-SNTP authenticator field or extended authenticator
+       field with zeroes as digest */
+    if (info->version == 3 && info->auth.mac.key_id != 0) {
+      if (remainder == 20 && is_zero_data(data + parsed + 4, remainder - 4))
+        info->auth.mode = NTP_AUTH_MSSNTP;
+      else if (remainder == 72 && is_zero_data(data + parsed + 8, remainder - 8))
+        info->auth.mode = NTP_AUTH_MSSNTP_EXT;
+    }
+
+    return 1;
+  }
+
+  /* Check for a crypto NAK */
+  if (remainder == 4 && ntohl(*(uint32_t *)(data + parsed)) == 0) {
+    info->auth.mode = NTP_AUTH_SYMMETRIC;
+    info->auth.mac.start = parsed;
+    info->auth.mac.length = remainder;
+    info->auth.mac.key_id = 0;
+    return 1;
+  }
+
+  /* Parse the rest of the NTPv4 packet */
+
+  while (remainder > 0) {
+    /* Check if the remaining data is a MAC */
+    if (remainder >= NTP_MIN_MAC_LENGTH && remainder <= NTP_MAX_V4_MAC_LENGTH)
+      break;
+
+    /* Check if this is a valid NTPv4 extension field and skip it */
+    if (!NEF_ParseField(packet, info->length, parsed, &ef_length, &ef_type, NULL, NULL)) {
+      DEBUG_LOG("Invalid format");
+      return 0;
+    }
+
+    assert(ef_length > 0 && ef_length % 4 == 0);
+
+    switch (ef_type) {
+      case NTP_EF_NTS_UNIQUE_IDENTIFIER:
+      case NTP_EF_NTS_COOKIE:
+      case NTP_EF_NTS_COOKIE_PLACEHOLDER:
+      case NTP_EF_NTS_AUTH_AND_EEF:
+        info->auth.mode = NTP_AUTH_NTS;
+        break;
+      default:
+        DEBUG_LOG("Unknown extension field type=%x", (unsigned int)ef_type);
+    }
+
+    info->ext_fields++;
+    parsed += ef_length;
+    remainder = info->length - parsed;
+  }
+
+  if (remainder == 0) {
+    /* No MAC */
+    return 1;
+  } else if (remainder >= NTP_MIN_MAC_LENGTH) {
+    info->auth.mode = NTP_AUTH_SYMMETRIC;
+    info->auth.mac.start = parsed;
+    info->auth.mac.length = remainder;
+    info->auth.mac.key_id = ntohl(*(uint32_t *)(data + parsed));
+    return 1;
+  }
+
+  DEBUG_LOG("Invalid format");
+  return 0;
+}
+
+/* ================================================== */
+
+int
+NAU_CheckRequestAuth(NTP_Packet *request, NTP_PacketInfo *info, uint32_t *kod)
+{
+  *kod = 0;
+
+  switch (info->auth.mode) {
+    case NTP_AUTH_NONE:
+      break;
+    case NTP_AUTH_SYMMETRIC:
+      if (!check_symmetric_auth(request, info))
+        return 0;
+      break;
+    case NTP_AUTH_MSSNTP:
+      /* MS-SNTP requests are not authenticated */
+      break;
+    case NTP_AUTH_MSSNTP_EXT:
+      /* Not supported yet */
+      return 0;
+    case NTP_AUTH_NTS:
+      if (!NNS_CheckRequestAuth(request, info, kod))
+        return 0;
+      break;
+    default:
+      return 0;
+  }
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NAU_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *request_info,
+                         NTP_Packet *response, NTP_PacketInfo *response_info,
+                         NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr,
+                         uint32_t kod)
+{
+  switch (request_info->auth.mode) {
+    case NTP_AUTH_NONE:
+      break;
+    case NTP_AUTH_SYMMETRIC:
+      if (!generate_symmetric_auth(request_info->auth.mac.key_id, response, response_info))
+        return 0;
+      break;
+    case NTP_AUTH_MSSNTP:
+      /* Sign the packet asynchronously by ntp_signd */
+      if (!NSD_SignAndSendPacket(request_info->auth.mac.key_id, response, response_info,
+                                 remote_addr, local_addr))
+        return 0;
+      /* Don't send the original packet */
+      return 0;
+    case NTP_AUTH_NTS:
+      if (!NNS_GenerateResponseAuth(request, request_info, response, response_info, kod))
+        return 0;
+      break;
+    default:
+      DEBUG_LOG("Could not authenticate response auth_mode=%d", (int)request_info->auth.mode);
+      return 0;
+  }
+
+  response_info->auth.mode = request_info->auth.mode;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NAU_CheckResponseAuth(NAU_Instance instance, NTP_Packet *response, NTP_PacketInfo *info)
+{
+  /* The authentication must match the expected mode */
+  if (info->auth.mode != instance->mode)
+    return 0;
+
+  switch (info->auth.mode) {
+    case NTP_AUTH_NONE:
+      break;
+    case NTP_AUTH_SYMMETRIC:
+      /* Check if it is authenticated with the specified key */
+      if (info->auth.mac.key_id != instance->key_id)
+        return 0;
+      /* and that the MAC is valid */
+      if (!check_symmetric_auth(response, info))
+        return 0;
+      break;
+    case NTP_AUTH_NTS:
+      if (!NNC_CheckResponseAuth(instance->nts, response, info))
+        return 0;
+      break;
+    default:
+      return 0;
+  }
+
+  return 1;
+}
+
+/* ================================================== */
+
+void
+NAU_ChangeAddress(NAU_Instance instance, IPAddr *address)
+{
+  switch (instance->mode) {
+    case NTP_AUTH_NONE:
+    case NTP_AUTH_SYMMETRIC:
+      break;
+    case NTP_AUTH_NTS:
+      NNC_ChangeAddress(instance->nts, address);
+      break;
+    default:
+      assert(0);
+  }
+}
+
+/* ================================================== */
+
+void
+NAU_DumpData(NAU_Instance instance)
+{
+  switch (instance->mode) {
+    case NTP_AUTH_NTS:
+      NNC_DumpData(instance->nts);
+      break;
+    default:
+      break;
+  }
+}
+
+/* ================================================== */
+
+void
+NAU_GetReport(NAU_Instance instance, RPT_AuthReport *report)
+{
+  memset(report, 0, sizeof (*report));
+
+  report->mode = instance->mode;
+  report->last_ke_ago = -1;
+
+  switch (instance->mode) {
+    case NTP_AUTH_NONE:
+      break;
+    case NTP_AUTH_SYMMETRIC:
+      report->key_id = instance->key_id;
+      KEY_GetKeyInfo(instance->key_id, &report->key_type, &report->key_length);
+      break;
+    case NTP_AUTH_NTS:
+      NNC_GetReport(instance->nts, report);
+      break;
+    default:
+      assert(0);
+  }
+}
--- a/ntp_auth.h
+++ b/ntp_auth.h
@@ -0,0 +1,87 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2019
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for NTP authentication
+  */
+
+#ifndef GOT_NTP_AUTH_H
+#define GOT_NTP_AUTH_H
+
+#include "addressing.h"
+#include "ntp.h"
+#include "reports.h"
+
+typedef struct NAU_Instance_Record *NAU_Instance;
+
+/* Create an authenticator instance in a specific mode */
+extern NAU_Instance NAU_CreateNoneInstance(void);
+extern NAU_Instance NAU_CreateSymmetricInstance(uint32_t key_id);
+extern NAU_Instance NAU_CreateNtsInstance(IPSockAddr *nts_address, const char *name,
+                                          const IPSockAddr *ntp_address);
+
+/* Destroy an instance */
+extern void NAU_DestroyInstance(NAU_Instance instance);
+
+/* Check if an instance is not in the None mode */
+extern int NAU_IsAuthEnabled(NAU_Instance instance);
+
+/* Get NTP version recommended for better compatibility */
+extern int NAU_GetSuggestedNtpVersion(NAU_Instance instance);
+
+/* Perform operations necessary for NAU_GenerateRequestAuth() */
+extern int NAU_PrepareRequestAuth(NAU_Instance instance);
+
+/* Extend a request with data required by the authentication mode */
+extern int NAU_GenerateRequestAuth(NAU_Instance instance, NTP_Packet *request,
+                                   NTP_PacketInfo *info);
+
+/* Parse a request or response to detect the authentication mode */
+extern int NAU_ParsePacket(NTP_Packet *packet, NTP_PacketInfo *info);
+
+/* Verify that a request is authentic.  If it is not authentic and a non-zero
+   kod code is returned, a KoD response should be sent back. */
+extern int NAU_CheckRequestAuth(NTP_Packet *request, NTP_PacketInfo *info, uint32_t *kod);
+
+/* Extend a response with data required by the authentication mode.  This
+   function can be called only if the previous call of NAU_CheckRequestAuth()
+   was on the same request. */
+extern int NAU_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *request_info,
+                                    NTP_Packet *response, NTP_PacketInfo *response_info,
+                                    NTP_Remote_Address *remote_addr,
+                                    NTP_Local_Address *local_addr,
+                                    uint32_t kod);
+
+/* Verify that a response is authentic */
+extern int NAU_CheckResponseAuth(NAU_Instance instance, NTP_Packet *response,
+                                 NTP_PacketInfo *info);
+
+/* Change an authentication-specific address (e.g. after replacing a source) */
+extern void NAU_ChangeAddress(NAU_Instance instance, IPAddr *address);
+
+/* Save authentication-specific data to speed up the next start */
+extern void NAU_DumpData(NAU_Instance instance);
+
+/* Provide a report about the current authentication state */
+extern void NAU_GetReport(NAU_Instance instance, RPT_AuthReport *report);
+
+#endif
--- a/ntp_core.c
+++ b/ntp_core.c
--- a/ntp_core.h
+++ b/ntp_core.h
@@ -59,7 +59,8 @@ extern void NCR_Initialise(void);
 extern void NCR_Finalise(void);

 /* Get a new instance for a server or peer */
-extern NCR_Instance NCR_GetInstance(NTP_Remote_Address *remote_addr, NTP_Source_Type type, SourceParameters *params);
+extern NCR_Instance NCR_CreateInstance(NTP_Remote_Address *remote_addr, NTP_Source_Type type,
+                                       SourceParameters *params, const char *name);

 /* Destroy an instance */
 extern void NCR_DestroyInstance(NCR_Instance instance);
@@ -74,7 +75,8 @@ extern void NCR_ResetInstance(NCR_Instance inst);
 extern void NCR_ResetPoll(NCR_Instance instance);

 /* Change the remote address of an instance */
-extern void NCR_ChangeRemoteAddress(NCR_Instance inst, NTP_Remote_Address *remote_addr);
+extern void NCR_ChangeRemoteAddress(NCR_Instance inst, NTP_Remote_Address *remote_addr,
+                                    int ntp_only);

 /* This routine is called when a new packet arrives off the network,
   and it relates to a source we have an ongoing protocol exchange with */
@@ -120,6 +122,7 @@ extern void NCR_ModifyPolltarget(NCR_Instance inst, int new_poll_target);
 extern void NCR_InitiateSampleBurst(NCR_Instance inst, int n_good_samples, int n_total_samples);

 extern void NCR_ReportSource(NCR_Instance inst, RPT_SourceReport *report, struct timespec *now);
+extern void NCR_GetAuthReport(NCR_Instance inst, RPT_AuthReport *report);
 extern void NCR_GetNTPReport(NCR_Instance inst, RPT_NTPReport *report);

 extern int NCR_AddAccessRestriction(IPAddr *ip_addr, int subnet_bits, int allow, int all);
@@ -134,6 +137,8 @@ extern uint32_t NCR_GetLocalRefid(NCR_Instance inst);

 extern int NCR_IsSyncPeer(NCR_Instance instance);

-extern void NCR_AddBroadcastDestination(IPAddr *addr, unsigned short port, int interval);
+extern void NCR_DumpAuthData(NCR_Instance inst);
+
+extern void NCR_AddBroadcastDestination(NTP_Remote_Address *addr, int interval);

 #endif /* GOT_NTP_CORE_H */
--- a/ntp_ext.c
+++ b/ntp_ext.c
@@ -0,0 +1,192 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2019-2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Functions for adding and parsing NTPv4 extension fields
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include "ntp_ext.h"
+
+struct ExtFieldHeader {
+  uint16_t type;
+  uint16_t length;
+};
+
+/* ================================================== */
+
+static int
+format_field(unsigned char *buffer, int buffer_length, int start,
+             int type, int body_length, int *length, void **body)
+{
+  struct ExtFieldHeader *header;
+
+  if (buffer_length < 0 || start < 0 || buffer_length <= start ||
+      buffer_length - start < sizeof (*header) || start % 4 != 0)
+    return 0;
+
+  header = (struct ExtFieldHeader *)(buffer + start);
+
+  if (body_length < 0 || sizeof (*header) + body_length > 0xffff ||
+      start + sizeof (*header) + body_length > buffer_length || body_length % 4 != 0)
+    return 0;
+
+  header->type = htons(type);
+  header->length = htons(sizeof (*header) + body_length);
+  *length = sizeof (*header) + body_length;
+  *body = header + 1;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NEF_SetField(unsigned char *buffer, int buffer_length, int start,
+             int type, void *body, int body_length, int *length)
+{
+  void *ef_body;
+
+  if (!format_field(buffer, buffer_length, start, type, body_length, length, &ef_body))
+    return 0;
+
+  memcpy(ef_body, body, body_length);
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NEF_AddBlankField(NTP_Packet *packet, NTP_PacketInfo *info, int type, int body_length, void **body)
+{
+  int ef_length, length = info->length;
+
+  if (length < NTP_HEADER_LENGTH || length >= sizeof (*packet) || length % 4 != 0)
+    return 0;
+
+  /* Only NTPv4 packets can have extension fields */
+  if (info->version != 4)
+    return 0;
+
+  if (!format_field((unsigned char *)packet, sizeof (*packet), length,
+                    type, body_length, &ef_length, body))
+    return 0;
+
+  if (ef_length < NTP_MIN_EF_LENGTH)
+    return 0;
+
+  info->length += ef_length;
+  info->ext_fields++;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NEF_AddField(NTP_Packet *packet, NTP_PacketInfo *info,
+             int type, void *body, int body_length)
+{
+  void *ef_body;
+
+  if (!NEF_AddBlankField(packet, info, type, body_length, &ef_body))
+    return 0;
+
+  memcpy(ef_body, body, body_length);
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NEF_ParseSingleField(unsigned char *buffer, int buffer_length, int start,
+                     int *length, int *type, void **body, int *body_length)
+{
+  struct ExtFieldHeader *header;
+  int ef_length;
+
+  if (buffer_length < 0 || start < 0 || buffer_length <= start ||
+      buffer_length - start < sizeof (*header))
+    return 0;
+
+  header = (struct ExtFieldHeader *)(buffer + start);
+
+  assert(sizeof (*header) == 4);
+
+  ef_length = ntohs(header->length);
+
+  if (ef_length < (int)(sizeof (*header)) || start + ef_length > buffer_length ||
+      ef_length % 4 != 0)
+    return 0;
+
+  if (length)
+    *length = ef_length;
+  if (type)
+    *type = ntohs(header->type);
+  if (body)
+    *body = header + 1;
+  if (body_length)
+    *body_length = ef_length - sizeof (*header);
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NEF_ParseField(NTP_Packet *packet, int packet_length, int start,
+               int *length, int *type, void **body, int *body_length)
+{
+  int ef_length;
+
+  if (packet_length <= NTP_HEADER_LENGTH || packet_length > sizeof (*packet) ||
+      packet_length <= start || packet_length % 4 != 0 ||
+      start < NTP_HEADER_LENGTH || start % 4 != 0)
+    return 0;
+
+  /* Only NTPv4 packets have extension fields */
+  if (NTP_LVM_TO_VERSION(packet->lvm) != 4)
+    return 0;
+
+  /* Check if the remaining data is a MAC.  RFC 7822 specifies the maximum
+     length of a MAC in NTPv4 packets in order to enable deterministic
+     parsing. */
+  if (packet_length - start <= NTP_MAX_V4_MAC_LENGTH)
+    return 0;
+
+  if (!NEF_ParseSingleField((unsigned char *)packet, packet_length, start,
+                            &ef_length, type, body, body_length))
+    return 0;
+
+  if (ef_length < NTP_MIN_EF_LENGTH)
+    return 0;
+
+  if (length)
+    *length = ef_length;
+
+  return 1;
+}
--- a/ntp_ext.h
+++ b/ntp_ext.h
@@ -0,0 +1,43 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2019
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for NTP extension fields
+  */
+
+#ifndef GOT_NTP_EXT_H
+#define GOT_NTP_EXT_H
+
+#include "ntp.h"
+
+extern int NEF_SetField(unsigned char *buffer, int buffer_length, int start,
+                        int type, void *body, int body_length, int *length);
+extern int NEF_AddBlankField(NTP_Packet *packet, NTP_PacketInfo *info, int type,
+                             int body_length, void **body);
+extern int NEF_AddField(NTP_Packet *packet, NTP_PacketInfo *info,
+                        int type, void *body, int body_length);
+extern int NEF_ParseSingleField(unsigned char *buffer, int buffer_length, int start,
+                                int *length, int *type, void **body, int *body_length);
+extern int NEF_ParseField(NTP_Packet *packet, int packet_length, int start,
+                          int *length, int *type, void **body, int *body_length);
+
+#endif
--- a/ntp_io.c
+++ b/ntp_io.c
@@ -4,7 +4,7 @@
 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
 * Copyright (C) Timo Teras  2009
- * Copyright (C) Miroslav Lichvar  2009, 2013-2016, 2018
+ * Copyright (C) Miroslav Lichvar  2009, 2013-2016, 2018-2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -30,11 +30,11 @@

 #include "sysincl.h"

-#include "array.h"
 #include "ntp_io.h"
 #include "ntp_core.h"
 #include "ntp_sources.h"
 #include "sched.h"
+#include "socket.h"
 #include "local.h"
 #include "logging.h"
 #include "conf.h"
@@ -46,54 +46,16 @@
 #endif

 #define INVALID_SOCK_FD -1
-#define CMSGBUF_SIZE 256
-
-union sockaddr_in46 {
-  struct sockaddr_in in4;
-#ifdef FEAT_IPV6
-  struct sockaddr_in6 in6;
-#endif
-  struct sockaddr u;
-};
-
-struct Message {
-  union sockaddr_in46 name;
-  struct iovec iov;
-  NTP_Receive_Buffer buf;
-  /* Aligned buffer for control messages */
-  struct cmsghdr cmsgbuf[CMSGBUF_SIZE / sizeof (struct cmsghdr)];
-};
-
-#ifdef HAVE_RECVMMSG
-#define MAX_RECV_MESSAGES 4
-#define MessageHeader mmsghdr
-#else
-/* Compatible with mmsghdr */
-struct MessageHeader {
-  struct msghdr msg_hdr;
-  unsigned int msg_len;
-};
-
-#define MAX_RECV_MESSAGES 1
-#endif
-
-/* Arrays of Message and MessageHeader */
-static ARR_Instance recv_messages;
-static ARR_Instance recv_headers;

 /* The server/peer and client sockets for IPv4 and IPv6 */
 static int server_sock_fd4;
-static int client_sock_fd4;
-#ifdef FEAT_IPV6
 static int server_sock_fd6;
+static int client_sock_fd4;
 static int client_sock_fd6;
-#endif

 /* Reference counters for server sockets to keep them open only when needed */
 static int server_sock_ref4;
-#ifdef FEAT_IPV6
 static int server_sock_ref6;
-#endif

 /* Flag indicating we create a new connected client socket for each
   server instead of sharing client_sock_fd4 and client_sock_fd6 */
@@ -119,162 +81,54 @@ static void read_from_socket(int sock_fd, int event, void *anything);
 /* ================================================== */

 static int
-prepare_socket(int family, int port_number, int client_only)
+open_socket(int family, int local_port, int client_only, IPSockAddr *remote_addr)
 {
-  union sockaddr_in46 my_addr;
-  socklen_t my_addr_len;
-  int sock_fd;
-  IPAddr bind_address;
-  int events = SCH_FILE_INPUT, on_off = 1;
+  int sock_fd, sock_flags, dscp, events = SCH_FILE_INPUT;
+  IPSockAddr local_addr;
+  char *iface;

-  /* Open Internet domain UDP socket for NTP message transmissions */
+  if (!SCK_IsIpFamilyEnabled(family))
+    return INVALID_SOCK_FD;

-  sock_fd = socket(family, SOCK_DGRAM, 0);
+  if (!client_only) {
+    CNF_GetBindAddress(family, &local_addr.ip_addr);
+    iface = CNF_GetBindNtpInterface();
+  } else {
+    CNF_GetBindAcquisitionAddress(family, &local_addr.ip_addr);
+    iface = CNF_GetBindAcquisitionInterface();
+  }

+  local_addr.port = local_port;
+
+  sock_flags = SCK_FLAG_RX_DEST_ADDR | SCK_FLAG_PRIV_BIND;
+  if (!client_only)
+    sock_flags |= SCK_FLAG_BROADCAST;
+
+  sock_fd = SCK_OpenUdpSocket(remote_addr, &local_addr, iface, sock_flags);
  if (sock_fd < 0) {
-    if (!client_only) {
-      LOG(LOGS_ERR, "Could not open %s NTP socket : %s",
-          UTI_SockaddrFamilyToString(family), strerror(errno));
-    } else {
-      DEBUG_LOG("Could not open %s NTP socket : %s",
-                UTI_SockaddrFamilyToString(family), strerror(errno));
-    }
+    if (!client_only)
+      LOG(LOGS_ERR, "Could not open NTP socket on %s", UTI_IPSockAddrToString(&local_addr));
    return INVALID_SOCK_FD;
  }

-  /* Close on exec */
-  UTI_FdSetCloexec(sock_fd);
-
-  /* Enable non-blocking mode on server sockets */
-  if (!client_only && fcntl(sock_fd, F_SETFL, O_NONBLOCK))
-    DEBUG_LOG("Could not set O_NONBLOCK : %s", strerror(errno));
-
-  /* Prepare local address */
-  memset(&my_addr, 0, sizeof (my_addr));
-  my_addr_len = 0;
-
-  switch (family) {
-    case AF_INET:
-      if (!client_only)
-        CNF_GetBindAddress(IPADDR_INET4, &bind_address);
-      else
-        CNF_GetBindAcquisitionAddress(IPADDR_INET4, &bind_address);
-
-      if (bind_address.family == IPADDR_INET4)
-        my_addr.in4.sin_addr.s_addr = htonl(bind_address.addr.in4);
-      else if (port_number)
-        my_addr.in4.sin_addr.s_addr = htonl(INADDR_ANY);
-      else
-        break;
-
-      my_addr.in4.sin_family = family;
-      my_addr.in4.sin_port = htons(port_number);
-      my_addr_len = sizeof (my_addr.in4);
-
-      if (!client_only)
-        bound_server_sock_fd4 = my_addr.in4.sin_addr.s_addr != htonl(INADDR_ANY);
-
-      break;
-#ifdef FEAT_IPV6
-    case AF_INET6:
-      if (!client_only)
-        CNF_GetBindAddress(IPADDR_INET6, &bind_address);
-      else
-        CNF_GetBindAcquisitionAddress(IPADDR_INET6, &bind_address);
-
-      if (bind_address.family == IPADDR_INET6)
-        memcpy(my_addr.in6.sin6_addr.s6_addr, bind_address.addr.in6,
-            sizeof (my_addr.in6.sin6_addr.s6_addr));
-      else if (port_number)
-        my_addr.in6.sin6_addr = in6addr_any;
-      else
-        break;
-
-      my_addr.in6.sin6_family = family;
-      my_addr.in6.sin6_port = htons(port_number);
-      my_addr_len = sizeof (my_addr.in6);
-
-      break;
+  dscp = CNF_GetNtpDscp();
+  if (dscp > 0 && dscp < 64) {
+#ifdef IP_TOS
+    if (!SCK_SetIntOption(sock_fd, IPPROTO_IP, IP_TOS, dscp << 2))
+      ;
 #endif
-    default:
-      assert(0);
  }

-  /* Make the socket capable of re-using an old address if binding to a specific port */
-  if (port_number &&
-      setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, (char *)&on_off, sizeof(on_off)) < 0) {
-    LOG(LOGS_ERR, "Could not set %s socket option", "SO_REUSEADDR");
-    /* Don't quit - we might survive anyway */
-  }
-  
-  /* Make the socket capable of sending broadcast pkts - needed for NTP broadcast mode */
-  if (!client_only &&
-      setsockopt(sock_fd, SOL_SOCKET, SO_BROADCAST, (char *)&on_off, sizeof(on_off)) < 0) {
-    LOG(LOGS_ERR, "Could not set %s socket option", "SO_BROADCAST");
-    /* Don't quit - we might survive anyway */
-  }
+  if (!client_only && family == IPADDR_INET4 && local_addr.port > 0)
+    bound_server_sock_fd4 = local_addr.ip_addr.addr.in4 != INADDR_ANY;

  /* Enable kernel/HW timestamping of packets */
 #ifdef HAVE_LINUX_TIMESTAMPING
  if (!NIO_Linux_SetTimestampSocketOptions(sock_fd, client_only, &events))
 #endif
-#ifdef SO_TIMESTAMPNS
-    if (setsockopt(sock_fd, SOL_SOCKET, SO_TIMESTAMPNS, (char *)&on_off, sizeof(on_off)) < 0)
-#endif
-#ifdef SO_TIMESTAMP
-      if (setsockopt(sock_fd, SOL_SOCKET, SO_TIMESTAMP, (char *)&on_off, sizeof(on_off)) < 0)
-        LOG(LOGS_ERR, "Could not set %s socket option", "SO_TIMESTAMP");
-#endif
+    if (!SCK_EnableKernelRxTimestamping(sock_fd))
      ;

-#ifdef IP_FREEBIND
-  /* Allow binding to address that doesn't exist yet */
-  if (my_addr_len > 0 &&
-      setsockopt(sock_fd, IPPROTO_IP, IP_FREEBIND, (char *)&on_off, sizeof(on_off)) < 0) {
-    LOG(LOGS_ERR, "Could not set %s socket option", "IP_FREEBIND");
-  }
-#endif
-
-  if (family == AF_INET) {
-#ifdef HAVE_IN_PKTINFO
-    if (setsockopt(sock_fd, IPPROTO_IP, IP_PKTINFO, (char *)&on_off, sizeof(on_off)) < 0)
-      LOG(LOGS_ERR, "Could not set %s socket option", "IP_PKTINFO");
-#elif defined(IP_RECVDSTADDR)
-    if (setsockopt(sock_fd, IPPROTO_IP, IP_RECVDSTADDR, (char *)&on_off, sizeof(on_off)) < 0)
-      LOG(LOGS_ERR, "Could not set %s socket option", "IP_RECVDSTADDR");
-#endif
-  }
-#ifdef FEAT_IPV6
-  else if (family == AF_INET6) {
-#ifdef IPV6_V6ONLY
-    /* Receive IPv6 packets only */
-    if (setsockopt(sock_fd, IPPROTO_IPV6, IPV6_V6ONLY, (char *)&on_off, sizeof(on_off)) < 0) {
-      LOG(LOGS_ERR, "Could not set %s socket option", "IPV6_V6ONLY");
-    }
-#endif
-
-#ifdef HAVE_IN6_PKTINFO
-#ifdef IPV6_RECVPKTINFO
-    if (setsockopt(sock_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, (char *)&on_off, sizeof(on_off)) < 0) {
-      LOG(LOGS_ERR, "Could not set %s socket option", "IPV6_RECVPKTINFO");
-    }
-#else
-    if (setsockopt(sock_fd, IPPROTO_IPV6, IPV6_PKTINFO, (char *)&on_off, sizeof(on_off)) < 0) {
-      LOG(LOGS_ERR, "Could not set %s socket option", "IPV6_PKTINFO");
-    }
-#endif
-#endif
-  }
-#endif
-
-  /* Bind the socket if a port or address was specified */
-  if (my_addr_len > 0 && PRV_BindSocket(sock_fd, &my_addr.u, my_addr_len) < 0) {
-    LOG(LOGS_ERR, "Could not bind %s NTP socket : %s",
-        UTI_SockaddrFamilyToString(family), strerror(errno));
-    close(sock_fd);
-    return INVALID_SOCK_FD;
-  }
-
  /* Register handler for read and possibly exception events on the socket */
  SCH_AddFileHandler(sock_fd, events, read_from_socket, NULL);

@@ -284,40 +138,9 @@ prepare_socket(int family, int port_number, int client_only)
 /* ================================================== */

 static int
-prepare_separate_client_socket(int family)
+open_separate_client_socket(IPSockAddr *remote_addr)
 {
-  switch (family) {
-    case IPADDR_INET4:
-      return prepare_socket(AF_INET, 0, 1);
-#ifdef FEAT_IPV6
-    case IPADDR_INET6:
-      return prepare_socket(AF_INET6, 0, 1);
-#endif
-    default:
-      return INVALID_SOCK_FD;
-  }
-}
-
-/* ================================================== */
-
-static int
-connect_socket(int sock_fd, NTP_Remote_Address *remote_addr)
-{
-  union sockaddr_in46 addr;
-  socklen_t addr_len;
-
-  addr_len = UTI_IPAndPortToSockaddr(&remote_addr->ip_addr, remote_addr->port, &addr.u);
-
-  assert(addr_len);
-
-  if (connect(sock_fd, &addr.u, addr_len) < 0) {
-    DEBUG_LOG("Could not connect NTP socket to %s:%d : %s",
-        UTI_IPToString(&remote_addr->ip_addr), remote_addr->port,
-        strerror(errno));
-    return 0;
-  }
-
-  return 1;
+  return open_socket(remote_addr->ip_addr.family, 0, 1, remote_addr);
 }

 /* ================================================== */
@@ -332,45 +155,23 @@ close_socket(int sock_fd)
  NIO_Linux_NotifySocketClosing(sock_fd);
 #endif
  SCH_RemoveFileHandler(sock_fd);
-  close(sock_fd);
-}
-
-/* ================================================== */
-
-static void
-prepare_buffers(unsigned int n)
-{
-  struct MessageHeader *hdr;
-  struct Message *msg;
-  unsigned int i;
-
-  for (i = 0; i < n; i++) {
-    msg = ARR_GetElement(recv_messages, i);
-    hdr = ARR_GetElement(recv_headers, i);
-
-    msg->iov.iov_base = &msg->buf;
-    msg->iov.iov_len = sizeof (msg->buf);
-    hdr->msg_hdr.msg_name = &msg->name;
-    hdr->msg_hdr.msg_namelen = sizeof (msg->name);
-    hdr->msg_hdr.msg_iov = &msg->iov;
-    hdr->msg_hdr.msg_iovlen = 1;
-    hdr->msg_hdr.msg_control = &msg->cmsgbuf;
-    hdr->msg_hdr.msg_controllen = sizeof (msg->cmsgbuf);
-    hdr->msg_hdr.msg_flags = 0;
-    hdr->msg_len = 0;
-  }
+  SCK_CloseSocket(sock_fd);
 }

 /* ================================================== */

 void
-NIO_Initialise(int family)
+NIO_Initialise(void)
 {
  int server_port, client_port;

  assert(!initialised);
  initialised = 1;

+#ifdef PRIVOPS_BINDSOCKET
+  SCK_SetPrivBind(PRV_BindSocket);
+#endif
+
 #ifdef HAVE_LINUX_TIMESTAMPING
  NIO_Linux_Initialise();
 #else
@@ -381,12 +182,6 @@ NIO_Initialise(int family)
  }
 #endif

-  recv_messages = ARR_CreateInstance(sizeof (struct Message));
-  ARR_SetSize(recv_messages, MAX_RECV_MESSAGES);
-  recv_headers = ARR_CreateInstance(sizeof (struct MessageHeader));
-  ARR_SetSize(recv_headers, MAX_RECV_MESSAGES);
-  prepare_buffers(MAX_RECV_MESSAGES);
-
  server_port = CNF_GetNTPPort();
  client_port = CNF_GetAcquisitionPort();

@@ -399,47 +194,31 @@ NIO_Initialise(int family)
                                              client_port == server_port);

  server_sock_fd4 = INVALID_SOCK_FD;
-  client_sock_fd4 = INVALID_SOCK_FD;
-  server_sock_ref4 = 0;
-#ifdef FEAT_IPV6
  server_sock_fd6 = INVALID_SOCK_FD;
+  client_sock_fd4 = INVALID_SOCK_FD;
  client_sock_fd6 = INVALID_SOCK_FD;
+  server_sock_ref4 = 0;
  server_sock_ref6 = 0;
-#endif

-  if (family == IPADDR_UNSPEC || family == IPADDR_INET4) {
-    if (permanent_server_sockets && server_port)
-      server_sock_fd4 = prepare_socket(AF_INET, server_port, 0);
-    if (!separate_client_sockets) {
-      if (client_port != server_port || !server_port)
-        client_sock_fd4 = prepare_socket(AF_INET, client_port, 1);
-      else
-        client_sock_fd4 = server_sock_fd4;
+  if (permanent_server_sockets && server_port) {
+    server_sock_fd4 = open_socket(IPADDR_INET4, server_port, 0, NULL);
+    server_sock_fd6 = open_socket(IPADDR_INET6, server_port, 0, NULL);
+  }
+
+  if (!separate_client_sockets) {
+    if (client_port != server_port || !server_port) {
+      client_sock_fd4 = open_socket(IPADDR_INET4, client_port, 1, NULL);
+      client_sock_fd6 = open_socket(IPADDR_INET6, client_port, 1, NULL);
+    } else {
+      client_sock_fd4 = server_sock_fd4;
+      client_sock_fd6 = server_sock_fd6;
    }
  }
-#ifdef FEAT_IPV6
-  if (family == IPADDR_UNSPEC || family == IPADDR_INET6) {
-    if (permanent_server_sockets && server_port)
-      server_sock_fd6 = prepare_socket(AF_INET6, server_port, 0);
-    if (!separate_client_sockets) {
-      if (client_port != server_port || !server_port)
-        client_sock_fd6 = prepare_socket(AF_INET6, client_port, 1);
-      else
-        client_sock_fd6 = server_sock_fd6;
-    }
-  }
-#endif

-  if ((server_port && server_sock_fd4 == INVALID_SOCK_FD &&
-       permanent_server_sockets 
-#ifdef FEAT_IPV6
-       && server_sock_fd6 == INVALID_SOCK_FD
-#endif
-      ) || (!separate_client_sockets && client_sock_fd4 == INVALID_SOCK_FD
-#ifdef FEAT_IPV6
-       && client_sock_fd6 == INVALID_SOCK_FD
-#endif
-      )) {
+  if ((server_port && permanent_server_sockets &&
+       server_sock_fd4 == INVALID_SOCK_FD && server_sock_fd6 == INVALID_SOCK_FD) ||
+      (!separate_client_sockets &&
+       client_sock_fd4 == INVALID_SOCK_FD && client_sock_fd6 == INVALID_SOCK_FD)) {
    LOG_FATAL("Could not open NTP sockets");
  }
 }
@@ -453,14 +232,11 @@ NIO_Finalise(void)
    close_socket(client_sock_fd4);
  close_socket(server_sock_fd4);
  server_sock_fd4 = client_sock_fd4 = INVALID_SOCK_FD;
-#ifdef FEAT_IPV6
+
  if (server_sock_fd6 != client_sock_fd6)
    close_socket(client_sock_fd6);
  close_socket(server_sock_fd6);
  server_sock_fd6 = client_sock_fd6 = INVALID_SOCK_FD;
-#endif
-  ARR_DestroyInstance(recv_headers);
-  ARR_DestroyInstance(recv_messages);

 #ifdef HAVE_LINUX_TIMESTAMPING
  NIO_Linux_Finalise();
@@ -475,25 +251,13 @@ int
 NIO_OpenClientSocket(NTP_Remote_Address *remote_addr)
 {
  if (separate_client_sockets) {
-    int sock_fd = prepare_separate_client_socket(remote_addr->ip_addr.family);
-
-    if (sock_fd == INVALID_SOCK_FD)
-      return INVALID_SOCK_FD;
-
-    if (!connect_socket(sock_fd, remote_addr)) {
-      close_socket(sock_fd);
-      return INVALID_SOCK_FD;
-    }
-
-    return sock_fd;
+    return open_separate_client_socket(remote_addr);
  } else {
    switch (remote_addr->ip_addr.family) {
      case IPADDR_INET4:
        return client_sock_fd4;
-#ifdef FEAT_IPV6
      case IPADDR_INET6:
        return client_sock_fd6;
-#endif
      default:
        return INVALID_SOCK_FD;
    }
@@ -510,20 +274,18 @@ NIO_OpenServerSocket(NTP_Remote_Address *remote_addr)
      if (permanent_server_sockets)
        return server_sock_fd4;
      if (server_sock_fd4 == INVALID_SOCK_FD)
-        server_sock_fd4 = prepare_socket(AF_INET, CNF_GetNTPPort(), 0);
+        server_sock_fd4 = open_socket(IPADDR_INET4, CNF_GetNTPPort(), 0, NULL);
      if (server_sock_fd4 != INVALID_SOCK_FD)
        server_sock_ref4++;
      return server_sock_fd4;
-#ifdef FEAT_IPV6
    case IPADDR_INET6:
      if (permanent_server_sockets)
        return server_sock_fd6;
      if (server_sock_fd6 == INVALID_SOCK_FD)
-        server_sock_fd6 = prepare_socket(AF_INET6, CNF_GetNTPPort(), 0);
+        server_sock_fd6 = open_socket(IPADDR_INET6, CNF_GetNTPPort(), 0, NULL);
      if (server_sock_fd6 != INVALID_SOCK_FD)
        server_sock_ref6++;
      return server_sock_fd6;
-#endif
    default:
      return INVALID_SOCK_FD;
  }
@@ -551,16 +313,12 @@ NIO_CloseServerSocket(int sock_fd)
      close_socket(server_sock_fd4);
      server_sock_fd4 = INVALID_SOCK_FD;
    }
-  }
-#ifdef FEAT_IPV6
-  else if (sock_fd == server_sock_fd6) {
+  } else if (sock_fd == server_sock_fd6) {
    if (--server_sock_ref6 <= 0) {
      close_socket(server_sock_fd6);
      server_sock_fd6 = INVALID_SOCK_FD;
    }
-  }
-#endif
-  else {
+  } else {
    assert(0);
  }
 }
@@ -571,11 +329,15 @@ int
 NIO_IsServerSocket(int sock_fd)
 {
  return sock_fd != INVALID_SOCK_FD &&
-    (sock_fd == server_sock_fd4
-#ifdef FEAT_IPV6
-     || sock_fd == server_sock_fd6
-#endif
-    );
+    (sock_fd == server_sock_fd4 || sock_fd == server_sock_fd6);
+}
+
+/* ================================================== */
+
+int
+NIO_IsServerSocketOpen(void)
+{
+  return server_sock_fd4 != INVALID_SOCK_FD || server_sock_fd6 != INVALID_SOCK_FD;
 }

 /* ================================================== */
@@ -583,132 +345,60 @@ NIO_IsServerSocket(int sock_fd)
 int
 NIO_IsServerConnectable(NTP_Remote_Address *remote_addr)
 {
-  int sock_fd, r;
+  int sock_fd;

-  sock_fd = prepare_separate_client_socket(remote_addr->ip_addr.family);
+  sock_fd = open_separate_client_socket(remote_addr);
  if (sock_fd == INVALID_SOCK_FD)
    return 0;

-  r = connect_socket(sock_fd, remote_addr);
  close_socket(sock_fd);

-  return r;
+  return 1;
 }

 /* ================================================== */

 static void
-process_message(struct msghdr *hdr, int length, int sock_fd)
+process_message(SCK_Message *message, int sock_fd, int event)
 {
-  NTP_Remote_Address remote_addr;
  NTP_Local_Address local_addr;
  NTP_Local_Timestamp local_ts;
  struct timespec sched_ts;
-  struct cmsghdr *cmsg;

  SCH_GetLastEventTime(&local_ts.ts, &local_ts.err, NULL);
  local_ts.source = NTP_TS_DAEMON;
  sched_ts = local_ts.ts;

-  if (hdr->msg_namelen > sizeof (union sockaddr_in46)) {
-    DEBUG_LOG("Truncated source address");
+  if (message->addr_type != SCK_ADDR_IP) {
+    DEBUG_LOG("Unexpected address type");
    return;
  }

-  if (hdr->msg_namelen >= sizeof (((struct sockaddr *)hdr->msg_name)->sa_family)) {
-    UTI_SockaddrToIPAndPort((struct sockaddr *)hdr->msg_name,
-                            &remote_addr.ip_addr, &remote_addr.port);
-  } else {
-    remote_addr.ip_addr.family = IPADDR_UNSPEC;
-    remote_addr.port = 0;
-  }
-
-  local_addr.ip_addr.family = IPADDR_UNSPEC;
-  local_addr.if_index = INVALID_IF_INDEX;
+  local_addr.ip_addr = message->local_addr.ip;
+  local_addr.if_index = message->if_index;;
  local_addr.sock_fd = sock_fd;

-  if (hdr->msg_flags & MSG_TRUNC) {
-    DEBUG_LOG("Received truncated message from %s:%d",
-              UTI_IPToString(&remote_addr.ip_addr), remote_addr.port);
-    return;
-  }
-
-  if (hdr->msg_flags & MSG_CTRUNC) {
-    DEBUG_LOG("Truncated control message");
-    /* Continue */
-  }
-
-  for (cmsg = CMSG_FIRSTHDR(hdr); cmsg; cmsg = CMSG_NXTHDR(hdr, cmsg)) {
-#ifdef HAVE_IN_PKTINFO
-    if (cmsg->cmsg_level == IPPROTO_IP && cmsg->cmsg_type == IP_PKTINFO) {
-      struct in_pktinfo ipi;
-
-      memcpy(&ipi, CMSG_DATA(cmsg), sizeof(ipi));
-      local_addr.ip_addr.addr.in4 = ntohl(ipi.ipi_addr.s_addr);
-      local_addr.ip_addr.family = IPADDR_INET4;
-      local_addr.if_index = ipi.ipi_ifindex;
-    }
-#elif defined(IP_RECVDSTADDR)
-    if (cmsg->cmsg_level == IPPROTO_IP && cmsg->cmsg_type == IP_RECVDSTADDR) {
-      struct in_addr addr;
-
-      memcpy(&addr, CMSG_DATA(cmsg), sizeof (addr));
-      local_addr.ip_addr.addr.in4 = ntohl(addr.s_addr);
-      local_addr.ip_addr.family = IPADDR_INET4;
-    }
-#endif
-
-#ifdef HAVE_IN6_PKTINFO
-    if (cmsg->cmsg_level == IPPROTO_IPV6 && cmsg->cmsg_type == IPV6_PKTINFO) {
-      struct in6_pktinfo ipi;
-
-      memcpy(&ipi, CMSG_DATA(cmsg), sizeof(ipi));
-      memcpy(&local_addr.ip_addr.addr.in6, &ipi.ipi6_addr.s6_addr,
-             sizeof (local_addr.ip_addr.addr.in6));
-      local_addr.ip_addr.family = IPADDR_INET6;
-      local_addr.if_index = ipi.ipi6_ifindex;
-    }
-#endif
-
-#ifdef SCM_TIMESTAMP
-    if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_TIMESTAMP) {
-      struct timeval tv;
-      struct timespec ts;
-
-      memcpy(&tv, CMSG_DATA(cmsg), sizeof(tv));
-      UTI_TimevalToTimespec(&tv, &ts);
-      LCL_CookTime(&ts, &local_ts.ts, &local_ts.err);
-      local_ts.source = NTP_TS_KERNEL;
-    }
-#endif
-
-#ifdef SCM_TIMESTAMPNS
-    if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_TIMESTAMPNS) {
-      struct timespec ts;
-
-      memcpy(&ts, CMSG_DATA(cmsg), sizeof (ts));
-      LCL_CookTime(&ts, &local_ts.ts, &local_ts.err);
-      local_ts.source = NTP_TS_KERNEL;
-    }
-#endif
-  }
-
 #ifdef HAVE_LINUX_TIMESTAMPING
-  if (NIO_Linux_ProcessMessage(&remote_addr, &local_addr, &local_ts, hdr, length))
+  if (NIO_Linux_ProcessMessage(message, &local_addr, &local_ts, event))
    return;
+#else
+  if (!UTI_IsZeroTimespec(&message->timestamp.kernel)) {
+    LCL_CookTime(&message->timestamp.kernel, &local_ts.ts, &local_ts.err);
+    local_ts.source = NTP_TS_KERNEL;
+  }
 #endif

-  DEBUG_LOG("Received %d bytes from %s:%d to %s fd=%d if=%d tss=%u delay=%.9f",
-            length, UTI_IPToString(&remote_addr.ip_addr), remote_addr.port,
-            UTI_IPToString(&local_addr.ip_addr), local_addr.sock_fd, local_addr.if_index,
-            local_ts.source, UTI_DiffTimespecsToDouble(&sched_ts, &local_ts.ts));
+  if (local_ts.source != NTP_TS_DAEMON)
+    DEBUG_LOG("Updated RX timestamp delay=%.9f tss=%u",
+              UTI_DiffTimespecsToDouble(&sched_ts, &local_ts.ts), local_ts.source);

  /* Just ignore the packet if it's not of a recognized length */
-  if (length < NTP_NORMAL_PACKET_LENGTH || length > sizeof (NTP_Receive_Buffer))
+  if (message->length < NTP_HEADER_LENGTH || message->length > sizeof (NTP_Packet)) {
+    DEBUG_LOG("Unexpected length");
    return;
+  }

-  NSR_ProcessRx(&remote_addr, &local_addr, &local_ts,
-                (NTP_Packet *)hdr->msg_iov[0].iov_base, length);
+  NSR_ProcessRx(&message->remote_addr.ip, &local_addr, &local_ts, message->data, message->length);
 }

 /* ================================================== */
@@ -716,68 +406,28 @@ process_message(struct msghdr *hdr, int length, int sock_fd)
 static void
 read_from_socket(int sock_fd, int event, void *anything)
 {
-  /* This should only be called when there is something
-     to read, otherwise it may block */
-
-  struct MessageHeader *hdr;
-  unsigned int i, n;
-  int status, flags = 0;
+  SCK_Message *messages;
+  int i, received, flags = 0;

 #ifdef HAVE_LINUX_TIMESTAMPING
  if (NIO_Linux_ProcessEvent(sock_fd, event))
    return;
 #endif

-  hdr = ARR_GetElements(recv_headers);
-  n = ARR_GetSize(recv_headers);
-  assert(n >= 1);
-
  if (event == SCH_FILE_EXCEPTION) {
 #ifdef HAVE_LINUX_TIMESTAMPING
-    flags |= MSG_ERRQUEUE;
+    flags |= SCK_FLAG_MSG_ERRQUEUE;
 #else
    assert(0);
 #endif
  }

-#ifdef HAVE_RECVMMSG
-  status = recvmmsg(sock_fd, hdr, n, flags | MSG_DONTWAIT, NULL);
-  if (status >= 0)
-    n = status;
-#else
-  n = 1;
-  status = recvmsg(sock_fd, &hdr[0].msg_hdr, flags);
-  if (status >= 0)
-    hdr[0].msg_len = status;
-#endif
-
-  if (status < 0) {
-#ifdef HAVE_LINUX_TIMESTAMPING
-    /* If reading from the error queue failed, the exception should be
-       for a socket error.  Clear the error to avoid a busy loop. */
-    if (flags & MSG_ERRQUEUE) {
-      int error = 0;
-      socklen_t len = sizeof (error);
-
-      if (getsockopt(sock_fd, SOL_SOCKET, SO_ERROR, &error, &len))
-        DEBUG_LOG("Could not get SO_ERROR");
-      if (error)
-        errno = error;
-    }
-#endif
-
-    DEBUG_LOG("Could not receive from fd %d : %s", sock_fd,
-              strerror(errno));
+  messages = SCK_ReceiveMessages(sock_fd, flags, &received);
+  if (!messages)
    return;
-  }

-  for (i = 0; i < n; i++) {
-    hdr = ARR_GetElement(recv_headers, i);
-    process_message(&hdr->msg_hdr, hdr->msg_len, sock_fd);
-  }
-
-  /* Restore the buffers to their original state */
-  prepare_buffers(n);
+  for (i = 0; i < received; i++)
+    process_message(&messages[i], sock_fd, event);
 }

 /* ================================================== */
@@ -787,123 +437,47 @@ int
 NIO_SendPacket(NTP_Packet *packet, NTP_Remote_Address *remote_addr,
               NTP_Local_Address *local_addr, int length, int process_tx)
 {
-  union sockaddr_in46 remote;
-  struct msghdr msg;
-  struct iovec iov;
-  struct cmsghdr *cmsg, cmsgbuf[CMSGBUF_SIZE / sizeof (struct cmsghdr)];
-  int cmsglen;
-  socklen_t addrlen = 0;
+  SCK_Message message;

  assert(initialised);

  if (local_addr->sock_fd == INVALID_SOCK_FD) {
-    DEBUG_LOG("No socket to send to %s:%d",
-              UTI_IPToString(&remote_addr->ip_addr), remote_addr->port);
+    DEBUG_LOG("No socket to send to %s", UTI_IPSockAddrToString(remote_addr));
    return 0;
  }

-  /* Don't set address with connected socket */
+  SCK_InitMessage(&message, SCK_ADDR_IP);
+
+  message.data = packet;
+  message.length = length;
+
+  /* Specify remote address if the socket is not connected */
  if (NIO_IsServerSocket(local_addr->sock_fd) || !separate_client_sockets) {
-    addrlen = UTI_IPAndPortToSockaddr(&remote_addr->ip_addr, remote_addr->port,
-                                      &remote.u);
-    if (!addrlen)
-      return 0;
+    message.remote_addr.ip.ip_addr = remote_addr->ip_addr;
+    message.remote_addr.ip.port = remote_addr->port;
  }

-  if (addrlen) {
-    msg.msg_name = &remote.u;
-    msg.msg_namelen = addrlen;
-  } else {
-    msg.msg_name = NULL;
-    msg.msg_namelen = 0;
-  }
+  message.local_addr.ip = local_addr->ip_addr;

-  iov.iov_base = packet;
-  iov.iov_len = length;
-  msg.msg_iov = &iov;
-  msg.msg_iovlen = 1;
-  msg.msg_control = cmsgbuf;
-  msg.msg_controllen = sizeof(cmsgbuf);
-  msg.msg_flags = 0;
-  cmsglen = 0;
+  /* Don't require responses to non-link-local addresses to use the same
+     interface */
+  message.if_index = SCK_IsLinkLocalIPAddress(&message.remote_addr.ip.ip_addr) ?
+                       local_addr->if_index : INVALID_IF_INDEX;

-#ifdef HAVE_IN_PKTINFO
-  if (local_addr->ip_addr.family == IPADDR_INET4) {
-    struct in_pktinfo *ipi;
-
-    cmsg = CMSG_FIRSTHDR(&msg);
-    memset(cmsg, 0, CMSG_SPACE(sizeof(struct in_pktinfo)));
-    cmsglen += CMSG_SPACE(sizeof(struct in_pktinfo));
-
-    cmsg->cmsg_level = IPPROTO_IP;
-    cmsg->cmsg_type = IP_PKTINFO;
-    cmsg->cmsg_len = CMSG_LEN(sizeof(struct in_pktinfo));
-
-    ipi = (struct in_pktinfo *) CMSG_DATA(cmsg);
-    ipi->ipi_spec_dst.s_addr = htonl(local_addr->ip_addr.addr.in4);
-    if (local_addr->if_index != INVALID_IF_INDEX)
-      ipi->ipi_ifindex = local_addr->if_index;
-  }
-#elif defined(IP_SENDSRCADDR)
-  /* Specify the IPv4 source address only if the socket is not bound */
-  if (local_addr->ip_addr.family == IPADDR_INET4 &&
-      local_addr->sock_fd == server_sock_fd4 && !bound_server_sock_fd4) {
-    struct in_addr *addr;
-
-    cmsg = CMSG_FIRSTHDR(&msg);
-    memset(cmsg, 0, CMSG_SPACE(sizeof (struct in_addr)));
-    cmsglen += CMSG_SPACE(sizeof (struct in_addr));
-
-    cmsg->cmsg_level = IPPROTO_IP;
-    cmsg->cmsg_type = IP_SENDSRCADDR;
-    cmsg->cmsg_len = CMSG_LEN(sizeof (struct in_addr));
-
-    addr = (struct in_addr *)CMSG_DATA(cmsg);
-    addr->s_addr = htonl(local_addr->ip_addr.addr.in4);
-  }
-#endif
-
-#ifdef HAVE_IN6_PKTINFO
-  if (local_addr->ip_addr.family == IPADDR_INET6) {
-    struct in6_pktinfo *ipi;
-
-    cmsg = CMSG_FIRSTHDR(&msg);
-    memset(cmsg, 0, CMSG_SPACE(sizeof(struct in6_pktinfo)));
-    cmsglen += CMSG_SPACE(sizeof(struct in6_pktinfo));
-
-    cmsg->cmsg_level = IPPROTO_IPV6;
-    cmsg->cmsg_type = IPV6_PKTINFO;
-    cmsg->cmsg_len = CMSG_LEN(sizeof(struct in6_pktinfo));
-
-    ipi = (struct in6_pktinfo *) CMSG_DATA(cmsg);
-    memcpy(&ipi->ipi6_addr.s6_addr, &local_addr->ip_addr.addr.in6,
-        sizeof(ipi->ipi6_addr.s6_addr));
-    if (local_addr->if_index != INVALID_IF_INDEX)
-      ipi->ipi6_ifindex = local_addr->if_index;
-  }
+#if !defined(HAVE_IN_PKTINFO) && defined(IP_SENDSRCADDR)
+  /* On FreeBSD a local IPv4 address cannot be specified on bound socket */
+  if (message.local_addr.ip.family == IPADDR_INET4 &&
+      (local_addr->sock_fd != server_sock_fd4 || bound_server_sock_fd4))
+    message.local_addr.ip.family = IPADDR_UNSPEC;
 #endif

 #ifdef HAVE_LINUX_TIMESTAMPING
  if (process_tx)
-   cmsglen = NIO_Linux_RequestTxTimestamp(&msg, cmsglen, local_addr->sock_fd);
+    NIO_Linux_RequestTxTimestamp(&message, local_addr->sock_fd);
 #endif

-  msg.msg_controllen = cmsglen;
-  /* This is apparently required on some systems */
-  if (!cmsglen)
-    msg.msg_control = NULL;
-
-  if (sendmsg(local_addr->sock_fd, &msg, 0) < 0) {
-    DEBUG_LOG("Could not send to %s:%d from %s fd %d : %s",
-        UTI_IPToString(&remote_addr->ip_addr), remote_addr->port,
-        UTI_IPToString(&local_addr->ip_addr), local_addr->sock_fd,
-        strerror(errno));
+  if (!SCK_SendMessage(local_addr->sock_fd, &message, 0))
    return 0;
-  }
-
-  DEBUG_LOG("Sent %d bytes to %s:%d from %s fd %d", length,
-      UTI_IPToString(&remote_addr->ip_addr), remote_addr->port,
-      UTI_IPToString(&local_addr->ip_addr), local_addr->sock_fd);

  return 1;
 }
--- a/ntp_io.h
+++ b/ntp_io.h
@@ -33,7 +33,7 @@
 #include "addressing.h"

 /* Function to initialise the module. */
-extern void NIO_Initialise(int family);
+extern void NIO_Initialise(void);

 /* Function to finalise the module */
 extern void NIO_Finalise(void);
@@ -53,6 +53,9 @@ extern void NIO_CloseServerSocket(int sock_fd);
 /* Function to check if socket is a server socket */
 extern int NIO_IsServerSocket(int sock_fd);

+/* Function to check if a server socket is currently open */
+extern int NIO_IsServerSocketOpen(void);
+
 /* Function to check if client packets can be sent to a server */
 extern int NIO_IsServerConnectable(NTP_Remote_Address *remote_addr);

--- a/ntp_io_linux.c
+++ b/ntp_io_linux.c
@@ -29,7 +29,6 @@
 #include "sysincl.h"

 #include <ifaddrs.h>
-#include <linux/errqueue.h>
 #include <linux/ethtool.h>
 #include <linux/net_tstamp.h>
 #include <linux/sockios.h>
@@ -45,17 +44,10 @@
 #include "ntp_io_linux.h"
 #include "ntp_sources.h"
 #include "sched.h"
+#include "socket.h"
 #include "sys_linux.h"
 #include "util.h"

-union sockaddr_in46 {
-  struct sockaddr_in in4;
-#ifdef FEAT_IPV6
-  struct sockaddr_in6 in6;
-#endif
-  struct sockaddr u;
-};
-
 struct Interface {
  char name[IF_NAMESIZE];
  int if_index;
@@ -133,7 +125,7 @@ add_interface(CNF_HwTsInterface *conf_iface)
      return 1;
  }

-  sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
+  sock_fd = SCK_OpenUdpSocket(NULL, NULL, NULL, 0);
  if (sock_fd < 0)
    return 0;

@@ -142,13 +134,13 @@ add_interface(CNF_HwTsInterface *conf_iface)

  if (snprintf(req.ifr_name, sizeof (req.ifr_name), "%s", conf_iface->name) >=
      sizeof (req.ifr_name)) {
-    close(sock_fd);
+    SCK_CloseSocket(sock_fd);
    return 0;
  }

  if (ioctl(sock_fd, SIOCGIFINDEX, &req)) {
    DEBUG_LOG("ioctl(%s) failed : %s", "SIOCGIFINDEX", strerror(errno));
-    close(sock_fd);
+    SCK_CloseSocket(sock_fd);
    return 0;
  }

@@ -159,7 +151,7 @@ add_interface(CNF_HwTsInterface *conf_iface)

  if (ioctl(sock_fd, SIOCETHTOOL, &req)) {
    DEBUG_LOG("ioctl(%s) failed : %s", "SIOCETHTOOL", strerror(errno));
-    close(sock_fd);
+    SCK_CloseSocket(sock_fd);
    return 0;
  }

@@ -167,13 +159,13 @@ add_interface(CNF_HwTsInterface *conf_iface)
                   SOF_TIMESTAMPING_RAW_HARDWARE;
  if ((ts_info.so_timestamping & req_hwts_flags) != req_hwts_flags) {
    DEBUG_LOG("HW timestamping not supported on %s", req.ifr_name);
-    close(sock_fd);
+    SCK_CloseSocket(sock_fd);
    return 0;
  }

  if (ts_info.phc_index < 0) {
    DEBUG_LOG("PHC missing on %s", req.ifr_name);
-    close(sock_fd);
+    SCK_CloseSocket(sock_fd);
    return 0;
  }

@@ -208,7 +200,8 @@ add_interface(CNF_HwTsInterface *conf_iface)
  req.ifr_data = (char *)&ts_config;

  if (ioctl(sock_fd, SIOCSHWTSTAMP, &req)) {
-    DEBUG_LOG("ioctl(%s) failed : %s", "SIOCSHWTSTAMP", strerror(errno));
+    LOG(errno == EPERM ? LOGS_ERR : LOGS_DEBUG,
+        "ioctl(%s) failed : %s", "SIOCSHWTSTAMP", strerror(errno));

    /* Check the current timestamping configuration in case this interface
       allows only reading of the configuration and it was already configured
@@ -219,12 +212,12 @@ add_interface(CNF_HwTsInterface *conf_iface)
        ts_config.tx_type != HWTSTAMP_TX_ON || ts_config.rx_filter != rx_filter)
 #endif
    {
-      close(sock_fd);
+      SCK_CloseSocket(sock_fd);
      return 0;
    }
  }

-  close(sock_fd);
+  SCK_CloseSocket(sock_fd);

  phc_fd = SYS_Linux_OpenPHC(NULL, ts_info.phc_index);
  if (phc_fd < 0)
@@ -293,7 +286,7 @@ update_interface_speed(struct Interface *iface)
  struct ifreq req;
  int sock_fd, link_speed;

-  sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
+  sock_fd = SCK_OpenUdpSocket(NULL, NULL, NULL, 0);
  if (sock_fd < 0)
    return;

@@ -306,11 +299,11 @@ update_interface_speed(struct Interface *iface)

  if (ioctl(sock_fd, SIOCETHTOOL, &req)) {
    DEBUG_LOG("ioctl(%s) failed : %s", "SIOCETHTOOL", strerror(errno));
-    close(sock_fd);
+    SCK_CloseSocket(sock_fd);
    return;
  }

-  close(sock_fd);
+  SCK_CloseSocket(sock_fd);

  link_speed = ethtool_cmd_speed(&cmd);

@@ -328,17 +321,16 @@ check_timestamping_option(int option)
 {
  int sock_fd;

-  sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
+  sock_fd = SCK_OpenUdpSocket(NULL, NULL, NULL, 0);
  if (sock_fd < 0)
    return 0;

-  if (setsockopt(sock_fd, SOL_SOCKET, SO_TIMESTAMPING, &option, sizeof (option)) < 0) {
-    DEBUG_LOG("Could not enable timestamping option %x", (unsigned int)option);
-    close(sock_fd);
+  if (!SCK_SetIntOption(sock_fd, SOL_SOCKET, SO_TIMESTAMPING, option)) {
+    SCK_CloseSocket(sock_fd);
    return 0;
  }

-  close(sock_fd);
+  SCK_CloseSocket(sock_fd);
  return 1;
 }
 #endif
@@ -350,19 +342,15 @@ open_dummy_socket(void)
 {
  int sock_fd, events = 0;

-  if ((sock_fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0
-#ifdef FEAT_IPV6
-      && (sock_fd = socket(AF_INET6, SOCK_DGRAM, 0)) < 0
-#endif
-     )
+  sock_fd = SCK_OpenUdpSocket(NULL, NULL, NULL, 0);
+  if (sock_fd < 0)
    return INVALID_SOCK_FD;

  if (!NIO_Linux_SetTimestampSocketOptions(sock_fd, 1, &events)) {
-    close(sock_fd);
+    SCK_CloseSocket(sock_fd);
    return INVALID_SOCK_FD;
  }

-  UTI_FdSetCloexec(sock_fd);
  return sock_fd;
 }

@@ -432,7 +420,7 @@ NIO_Linux_Finalise(void)
  unsigned int i;

  if (dummy_rxts_socket != INVALID_SOCK_FD)
-    close(dummy_rxts_socket);
+    SCK_CloseSocket(dummy_rxts_socket);

  for (i = 0; i < ARR_GetSize(interfaces); i++) {
    iface = ARR_GetElement(interfaces, i);
@@ -462,14 +450,12 @@ NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events)
  if (client_only || permanent_ts_options)
    flags |= ts_tx_flags;

-  if (setsockopt(sock_fd, SOL_SOCKET, SO_SELECT_ERR_QUEUE, &val, sizeof (val)) < 0) {
-    LOG(LOGS_ERR, "Could not set %s socket option", "SO_SELECT_ERR_QUEUE");
+  if (!SCK_SetIntOption(sock_fd, SOL_SOCKET, SO_SELECT_ERR_QUEUE, val)) {
    ts_flags = 0;
    return 0;
  }

-  if (setsockopt(sock_fd, SOL_SOCKET, SO_TIMESTAMPING, &flags, sizeof (flags)) < 0) {
-    LOG(LOGS_ERR, "Could not set %s socket option", "SO_TIMESTAMPING");
+  if (!SCK_SetIntOption(sock_fd, SOL_SOCKET, SO_TIMESTAMPING, flags)) {
    ts_flags = 0;
    return 0;
  }
@@ -633,7 +619,6 @@ static int
 extract_udp_data(unsigned char *msg, NTP_Remote_Address *remote_addr, int len)
 {
  unsigned char *msg_start = msg;
-  union sockaddr_in46 addr;

  remote_addr->ip_addr.family = IPADDR_UNSPEC;
  remote_addr->port = 0;
@@ -656,19 +641,21 @@ extract_udp_data(unsigned char *msg, NTP_Remote_Address *remote_addr, int len)
  /* Parse destination address and port from IPv4/IPv6 and UDP headers */
  if (len >= 20 && msg[0] >> 4 == 4) {
    int ihl = (msg[0] & 0xf) * 4;
+    uint32_t addr;

    if (len < ihl + 8 || msg[9] != 17)
      return 0;

-    memcpy(&addr.in4.sin_addr.s_addr, msg + 16, sizeof (uint32_t));
-    addr.in4.sin_port = *(uint16_t *)(msg + ihl + 2);
-    addr.in4.sin_family = AF_INET;
+    memcpy(&addr, msg + 16, sizeof (addr));
+    remote_addr->ip_addr.addr.in4 = ntohl(addr);
+    remote_addr->port = ntohs(*(uint16_t *)(msg + ihl + 2));
+    remote_addr->ip_addr.family = IPADDR_INET4;
    len -= ihl + 8, msg += ihl + 8;
 #ifdef FEAT_IPV6
  } else if (len >= 48 && msg[0] >> 4 == 6) {
    int eh_len, next_header = msg[6];

-    memcpy(&addr.in6.sin6_addr.s6_addr, msg + 24, 16);
+    memcpy(&remote_addr->ip_addr.addr.in6, msg + 24, sizeof (remote_addr->ip_addr.addr.in6));
    len -= 40, msg += 40;

    /* Skip IPv6 extension headers if present */
@@ -700,16 +687,14 @@ extract_udp_data(unsigned char *msg, NTP_Remote_Address *remote_addr, int len)
      len -= eh_len, msg += eh_len;
    }

-    addr.in6.sin6_port = *(uint16_t *)(msg + 2);
-    addr.in6.sin6_family = AF_INET6;
+    remote_addr->port = ntohs(*(uint16_t *)(msg + 2));
+    remote_addr->ip_addr.family = IPADDR_INET6;
    len -= 8, msg += 8;
 #endif
  } else {
    return 0;
  }

-  UTI_SockaddrToIPAndPort(&addr.u, &remote_addr->ip_addr, &remote_addr->port);
-
  /* Move the message to fix alignment of its fields */
  if (len > 0)
    memmove(msg_start, msg, len);
@@ -720,72 +705,39 @@ extract_udp_data(unsigned char *msg, NTP_Remote_Address *remote_addr, int len)
 /* ================================================== */

 int
-NIO_Linux_ProcessMessage(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr,
-                         NTP_Local_Timestamp *local_ts, struct msghdr *hdr, int length)
+NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
+                         NTP_Local_Timestamp *local_ts, int event)
 {
  struct Interface *iface;
-  struct cmsghdr *cmsg;
  int is_tx, ts_if_index, l2_length;

-  is_tx = hdr->msg_flags & MSG_ERRQUEUE;
+  is_tx = event == SCH_FILE_EXCEPTION;
  iface = NULL;
-  ts_if_index = local_addr->if_index;
-  l2_length = 0;

-  for (cmsg = CMSG_FIRSTHDR(hdr); cmsg; cmsg = CMSG_NXTHDR(hdr, cmsg)) {
-#ifdef HAVE_LINUX_TIMESTAMPING_OPT_PKTINFO
-    if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_TIMESTAMPING_PKTINFO) {
-      struct scm_ts_pktinfo ts_pktinfo;
+  ts_if_index = message->timestamp.if_index;
+  if (ts_if_index == INVALID_IF_INDEX)
+    ts_if_index = message->if_index;
+  l2_length = message->timestamp.l2_length;

-      memcpy(&ts_pktinfo, CMSG_DATA(cmsg), sizeof (ts_pktinfo));
-
-      ts_if_index = ts_pktinfo.if_index;
-      l2_length = ts_pktinfo.pkt_length;
-
-      DEBUG_LOG("Received HW timestamp info if=%d length=%d", ts_if_index, l2_length);
-    }
-#endif
-
-    if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_TIMESTAMPING) {
-      struct scm_timestamping ts3;
-
-      memcpy(&ts3, CMSG_DATA(cmsg), sizeof (ts3));
-
-      if (!UTI_IsZeroTimespec(&ts3.ts[2])) {
-        iface = get_interface(ts_if_index);
-        if (iface) {
-          process_hw_timestamp(iface, &ts3.ts[2], local_ts, !is_tx ? length : 0,
-                               remote_addr->ip_addr.family, l2_length);
-        } else {
-          DEBUG_LOG("HW clock not found for interface %d", ts_if_index);
-        }
-
-        /* If a HW transmit timestamp was received, resume processing
-           of non-error messages on this socket */
-        if (is_tx)
-          resume_socket(local_addr->sock_fd);
-      }
-
-      if (local_ts->source == NTP_TS_DAEMON && !UTI_IsZeroTimespec(&ts3.ts[0]) &&
-          (!is_tx || UTI_IsZeroTimespec(&ts3.ts[2]))) {
-        LCL_CookTime(&ts3.ts[0], &local_ts->ts, &local_ts->err);
-        local_ts->source = NTP_TS_KERNEL;
-      }
+  if (!UTI_IsZeroTimespec(&message->timestamp.hw)) {
+    iface = get_interface(ts_if_index);
+    if (iface) {
+      process_hw_timestamp(iface, &message->timestamp.hw, local_ts, !is_tx ? message->length : 0,
+                           message->remote_addr.ip.ip_addr.family, l2_length);
+    } else {
+      DEBUG_LOG("HW clock not found for interface %d", ts_if_index);
    }

-    if ((cmsg->cmsg_level == SOL_IP && cmsg->cmsg_type == IP_RECVERR) ||
-        (cmsg->cmsg_level == SOL_IPV6 && cmsg->cmsg_type == IPV6_RECVERR)) {
-      struct sock_extended_err err;
+    /* If a HW transmit timestamp was received, resume processing
+       of non-error messages on this socket */
+    if (is_tx)
+      resume_socket(local_addr->sock_fd);
+  }

-      memcpy(&err, CMSG_DATA(cmsg), sizeof (err));
-
-      if (err.ee_errno != ENOMSG || err.ee_info != SCM_TSTAMP_SND ||
-          err.ee_origin != SO_EE_ORIGIN_TIMESTAMPING) {
-        DEBUG_LOG("Unknown extended error");
-        /* Drop the message */
-        return 1;
-      }
-    }
+  if (local_ts->source == NTP_TS_DAEMON && !UTI_IsZeroTimespec(&message->timestamp.kernel) &&
+      (!is_tx || UTI_IsZeroTimespec(&message->timestamp.hw))) {
+    LCL_CookTime(&message->timestamp.kernel, &local_ts->ts, &local_ts->err);
+    local_ts->source = NTP_TS_KERNEL;
  }

  /* If the kernel is slow with enabling RX timestamping, open a dummy
@@ -803,19 +755,19 @@ NIO_Linux_ProcessMessage(NTP_Remote_Address *remote_addr, NTP_Local_Address *loc
  /* The data from the error queue includes all layers up to UDP.  We have to
     extract the UDP data and also the destination address with port as there
     currently doesn't seem to be a better way to get them both. */
-  l2_length = length;
-  length = extract_udp_data(hdr->msg_iov[0].iov_base, remote_addr, length);
+  l2_length = message->length;
+  message->length = extract_udp_data(message->data, &message->remote_addr.ip, message->length);

-  DEBUG_LOG("Received %d (%d) bytes from error queue for %s:%d fd=%d if=%d tss=%u",
-            l2_length, length, UTI_IPToString(&remote_addr->ip_addr), remote_addr->port,
-            local_addr->sock_fd, local_addr->if_index, local_ts->source);
+  DEBUG_LOG("Extracted message for %s fd=%d len=%d",
+            UTI_IPSockAddrToString(&message->remote_addr.ip),
+            local_addr->sock_fd, message->length);

  /* Update assumed position of UDP data at layer 2 for next received packet */
-  if (iface && length) {
-    if (remote_addr->ip_addr.family == IPADDR_INET4)
-      iface->l2_udp4_ntp_start = l2_length - length;
-    else if (remote_addr->ip_addr.family == IPADDR_INET6)
-      iface->l2_udp6_ntp_start = l2_length - length;
+  if (iface && message->length) {
+    if (message->remote_addr.ip.ip_addr.family == IPADDR_INET4)
+      iface->l2_udp4_ntp_start = l2_length - message->length;
+    else if (message->remote_addr.ip.ip_addr.family == IPADDR_INET6)
+      iface->l2_udp6_ntp_start = l2_length - message->length;
  }

  /* Drop the message if it has no timestamp or its processing failed */
@@ -824,24 +776,21 @@ NIO_Linux_ProcessMessage(NTP_Remote_Address *remote_addr, NTP_Local_Address *loc
    return 1;
  }

-  if (length < NTP_NORMAL_PACKET_LENGTH)
+  if (message->length < NTP_HEADER_LENGTH)
    return 1;

-  NSR_ProcessTx(remote_addr, local_addr, local_ts,
-                (NTP_Packet *)hdr->msg_iov[0].iov_base, length);
+  NSR_ProcessTx(&message->remote_addr.ip, local_addr, local_ts, message->data, message->length);

  return 1;
 }

 /* ================================================== */

-int
-NIO_Linux_RequestTxTimestamp(struct msghdr *msg, int cmsglen, int sock_fd)
+void
+NIO_Linux_RequestTxTimestamp(SCK_Message *message, int sock_fd)
 {
-  struct cmsghdr *cmsg;
-
  if (!ts_flags)
-    return cmsglen;
+    return;

  /* If a HW transmit timestamp is requested on a client socket, monitor
     events on the socket in order to avoid processing of a fast response
@@ -851,27 +800,9 @@ NIO_Linux_RequestTxTimestamp(struct msghdr *msg, int cmsglen, int sock_fd)

  /* Check if TX timestamping is disabled on this socket */
  if (permanent_ts_options || !NIO_IsServerSocket(sock_fd))
-    return cmsglen;
+    return;

-  /* Add control message that will enable TX timestamping for this message.
-     Don't use CMSG_NXTHDR as the one in glibc is buggy for creating new
-     control messages. */
-
-  cmsg = CMSG_FIRSTHDR(msg);
-  if (!cmsg || cmsglen + CMSG_SPACE(sizeof (ts_tx_flags)) > msg->msg_controllen)
-    return cmsglen;
-
-  cmsg = (struct cmsghdr *)((char *)cmsg + cmsglen);
-  memset(cmsg, 0, CMSG_SPACE(sizeof (ts_tx_flags)));
-  cmsglen += CMSG_SPACE(sizeof (ts_tx_flags));
-
-  cmsg->cmsg_level = SOL_SOCKET;
-  cmsg->cmsg_type = SO_TIMESTAMPING;
-  cmsg->cmsg_len = CMSG_LEN(sizeof (ts_tx_flags));
-
-  memcpy(CMSG_DATA(cmsg), &ts_tx_flags, sizeof (ts_tx_flags));
-
-  return cmsglen;
+  message->timestamp.tx_flags = ts_tx_flags;
 }

 /* ================================================== */
--- a/ntp_io_linux.h
+++ b/ntp_io_linux.h
@@ -27,6 +27,8 @@
 #ifndef GOT_NTP_IO_LINUX_H
 #define GOT_NTP_IO_LINUX_H

+#include "socket.h"
+
 extern void NIO_Linux_Initialise(void);

 extern void NIO_Linux_Finalise(void);
@@ -35,10 +37,10 @@ extern int NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int

 extern int NIO_Linux_ProcessEvent(int sock_fd, int event);

-extern int NIO_Linux_ProcessMessage(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr,
-                                    NTP_Local_Timestamp *local_ts, struct msghdr *hdr, int length);
+extern int NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
+                                    NTP_Local_Timestamp *local_ts, int event);

-extern int NIO_Linux_RequestTxTimestamp(struct msghdr *msg, int cmsglen, int sock_fd);
+extern void NIO_Linux_RequestTxTimestamp(SCK_Message *message, int sock_fd);

 extern void NIO_Linux_NotifySocketClosing(int sock_fd);

--- a/ntp_signd.c
+++ b/ntp_signd.c
@@ -34,6 +34,7 @@
 #include "ntp_io.h"
 #include "ntp_signd.h"
 #include "sched.h"
+#include "socket.h"
 #include "util.h"

 /* Declarations per samba/source4/librpc/idl/ntp_signd.idl */
@@ -90,19 +91,11 @@ static ARR_Instance queue;
 static unsigned int queue_head;
 static unsigned int queue_tail;

-#define INVALID_SOCK_FD -1
+#define INVALID_SOCK_FD (-6)

 /* Unix domain socket connected to ntp_signd */
 static int sock_fd;

-#define MIN_AUTH_DELAY 1.0e-5
-#define MAX_AUTH_DELAY 1.0e-2
-
-/* Average time needed for signing one packet.  This is used to adjust the
-   transmit timestamp in NTP packets.  The timestamp won't be very accurate as
-   the delay is variable, but it should be good enough for MS-SNTP clients. */
-static double auth_delay;
-
 /* Flag indicating if the MS-SNTP authentication is enabled */
 static int enabled;

@@ -116,7 +109,7 @@ static void
 close_socket(void)
 {
  SCH_RemoveFileHandler(sock_fd);
-  close(sock_fd);
+  SCK_CloseSocket(sock_fd);
  sock_fd = INVALID_SOCK_FD;

  /* Empty the queue */
@@ -128,35 +121,23 @@ close_socket(void)
 static int
 open_socket(void)
 {
-  struct sockaddr_un s;
+  char path[PATH_MAX];

-  if (sock_fd >= 0)
+  if (sock_fd != INVALID_SOCK_FD)
    return 1;

-  sock_fd = socket(AF_UNIX, SOCK_STREAM, 0);
-  if (sock_fd < 0) {
-    DEBUG_LOG("Could not open signd socket : %s", strerror(errno));
-    return 0;
-  }
-
-  UTI_FdSetCloexec(sock_fd);
-  SCH_AddFileHandler(sock_fd, SCH_FILE_INPUT, read_write_socket, NULL);
-
-  s.sun_family = AF_UNIX;
-  if (snprintf(s.sun_path, sizeof (s.sun_path), "%s/socket",
-               CNF_GetNtpSigndSocket()) >= sizeof (s.sun_path)) {
+  if (snprintf(path, sizeof (path), "%s/socket", CNF_GetNtpSigndSocket()) >= sizeof (path)) {
    DEBUG_LOG("signd socket path too long");
-    close_socket();
    return 0;
  }

-  if (connect(sock_fd, (struct sockaddr *)&s, sizeof (s)) < 0) {
-    DEBUG_LOG("Could not connect to signd : %s", strerror(errno));
-    close_socket();
+  sock_fd = SCK_OpenUnixStreamSocket(path, NULL, 0);
+  if (sock_fd < 0) {
+    sock_fd = INVALID_SOCK_FD;
    return 0;
  }

-  DEBUG_LOG("Connected to signd");
+  SCH_AddFileHandler(sock_fd, SCH_FILE_INPUT, read_write_socket, NULL);

  return 1;
 }
@@ -194,10 +175,6 @@ process_response(SignInstance *inst)
  NIO_SendPacket(&inst->response.signed_packet, &inst->remote_addr, &inst->local_addr,
                 ntohl(inst->response.length) + sizeof (inst->response.length) -
                 offsetof(SigndResponse, signed_packet), 0);
-
-  /* Update exponential moving average of the authentication delay */
-  delay = CLAMP(MIN_AUTH_DELAY, delay, MAX_AUTH_DELAY);
-  auth_delay += 0.1 * (delay - auth_delay);
 }

 /* ================================================== */
@@ -218,16 +195,14 @@ read_write_socket(int sock_fd, int event, void *anything)
    if (!inst->sent)
      SCH_GetLastEventTime(NULL, NULL, &inst->request_ts);

-    s = send(sock_fd, (char *)&inst->request + inst->sent,
-             inst->request_length - inst->sent, 0);
+    s = SCK_Send(sock_fd, (char *)&inst->request + inst->sent,
+                 inst->request_length - inst->sent, 0);

    if (s < 0) {
-      DEBUG_LOG("signd socket error: %s", strerror(errno));
      close_socket();
      return;
    }

-    DEBUG_LOG("Sent %d bytes to signd", s);
    inst->sent += s;

    /* Try again later if the request is not complete yet */
@@ -246,20 +221,14 @@ read_write_socket(int sock_fd, int event, void *anything)
    }

    assert(inst->received < sizeof (inst->response));
-    s = recv(sock_fd, (char *)&inst->response + inst->received,
-             sizeof (inst->response) - inst->received, 0);
+    s = SCK_Receive(sock_fd, (char *)&inst->response + inst->received,
+                    sizeof (inst->response) - inst->received, 0);

    if (s <= 0) {
-      if (s < 0)
-        DEBUG_LOG("signd socket error: %s", strerror(errno));
-      else
-        DEBUG_LOG("signd socket closed");
-
      close_socket();
      return;
    }

-    DEBUG_LOG("Received %d bytes from signd", s);
    inst->received += s;

    if (inst->received < sizeof (inst->response.length))
@@ -293,7 +262,6 @@ void
 NSD_Initialise()
 {
  sock_fd = INVALID_SOCK_FD;
-  auth_delay = MIN_AUTH_DELAY;
  enabled = CNF_GetNtpSigndSocket() && CNF_GetNtpSigndSocket()[0];

  if (!enabled)
@@ -320,15 +288,9 @@ NSD_Finalise()

 /* ================================================== */

-extern int NSD_GetAuthDelay(uint32_t key_id)
-{
-  return 1.0e9 * auth_delay;
-}
-
-/* ================================================== */
-
 int
-NSD_SignAndSendPacket(uint32_t key_id, NTP_Packet *packet, NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr, int length)
+NSD_SignAndSendPacket(uint32_t key_id, NTP_Packet *packet, NTP_PacketInfo *info,
+                      NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr)
 {
  SignInstance *inst;

@@ -342,7 +304,7 @@ NSD_SignAndSendPacket(uint32_t key_id, NTP_Packet *packet, NTP_Remote_Address *r
    return 0;
  }

-  if (length != NTP_NORMAL_PACKET_LENGTH) {
+  if (info->length != NTP_HEADER_LENGTH) {
    DEBUG_LOG("Invalid packet length");
    return 0;
  }
@@ -355,7 +317,7 @@ NSD_SignAndSendPacket(uint32_t key_id, NTP_Packet *packet, NTP_Remote_Address *r
  inst->local_addr = *local_addr;
  inst->sent = 0;
  inst->received = 0;
-  inst->request_length = offsetof(SigndRequest, packet_to_sign) + length;
+  inst->request_length = offsetof(SigndRequest, packet_to_sign) + info->length;

  /* The length field doesn't include itself */
  inst->request.length = htonl(inst->request_length - sizeof (inst->request.length));
@@ -365,7 +327,7 @@ NSD_SignAndSendPacket(uint32_t key_id, NTP_Packet *packet, NTP_Remote_Address *r
  inst->request._pad = 0;
  inst->request.key_id = htonl(key_id);

-  memcpy(&inst->request.packet_to_sign, packet, length);
+  memcpy(&inst->request.packet_to_sign, packet, info->length);

  /* Enable output if there was no pending request */
  if (IS_QUEUE_EMPTY())
--- a/ntp_signd.h
+++ b/ntp_signd.h
@@ -35,10 +35,8 @@ extern void NSD_Initialise(void);
 /* Finalisation function */
 extern void NSD_Finalise(void);

-/* Function to get an estimate of delay due to signing */
-extern int NSD_GetAuthDelay(uint32_t key_id);
-
 /* Function to sign an NTP packet and send it */
-extern int NSD_SignAndSendPacket(uint32_t key_id, NTP_Packet *packet, NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr, int length);
+extern int NSD_SignAndSendPacket(uint32_t key_id, NTP_Packet *packet, NTP_PacketInfo *info,
+                                 NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr);

 #endif
--- a/ntp_sources.c
+++ b/ntp_sources.c
--- a/ntp_sources.h
+++ b/ntp_sources.h
@@ -44,16 +44,21 @@ typedef enum {
  NSR_NoSuchSource, /* Remove - attempt to remove a source that is not known */
  NSR_AlreadyInUse, /* AddSource - attempt to add a source that is already known */ 
  NSR_TooManySources, /* AddSource - too many sources already present */
-  NSR_InvalidAF /* AddSource - attempt to add a source with invalid address family */
+  NSR_InvalidAF, /* AddSource - attempt to add a source with invalid address family */
+  NSR_InvalidName, /* AddSourceByName - attempt to add a source with invalid name */
+  NSR_UnresolvedName, /* AddSourceByName - name will be resolved later */
 } NSR_Status;

 /* Procedure to add a new server or peer source. */
-extern NSR_Status NSR_AddSource(NTP_Remote_Address *remote_addr, NTP_Source_Type type, SourceParameters *params);
+extern NSR_Status NSR_AddSource(NTP_Remote_Address *remote_addr, NTP_Source_Type type,
+                                SourceParameters *params, uint32_t *conf_id);

 /* Procedure to add a new server, peer source, or pool of servers specified by
   name instead of address.  The name is resolved in exponentially increasing
-   intervals until it succeeds or fails with a non-temporary error. */
-extern void NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type, SourceParameters *params);
+   intervals until it succeeds or fails with a non-temporary error.  If the
+   name is an address, it is equivalent to NSR_AddSource(). */
+extern NSR_Status NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,
+                                      SourceParameters *params, uint32_t *conf_id);

 /* Function type for handlers to be called back when an attempt
 * (possibly unsuccessful) to resolve unresolved sources ends */
@@ -72,7 +77,10 @@ extern void NSR_StartSources(void);
 extern void NSR_AutoStartSources(void);

 /* Procedure to remove a source */
-extern NSR_Status NSR_RemoveSource(NTP_Remote_Address *remote_addr);
+extern NSR_Status NSR_RemoveSource(IPAddr *address);
+
+/* Procedure to remove all sources matching a configuration ID */
+extern void NSR_RemoveSourcesById(uint32_t conf_id);

 /* Procedure to remove all sources */
 extern void NSR_RemoveAllSources(void);
@@ -83,9 +91,17 @@ extern void NSR_HandleBadSource(IPAddr *address);
 /* Procedure to resolve all names again */
 extern void NSR_RefreshAddresses(void);

+/* Procedure to update the address of a source */
+extern NSR_Status NSR_UpdateSourceNtpAddress(NTP_Remote_Address *old_addr,
+                                             NTP_Remote_Address *new_addr);
+
 /* Procedure to get local reference ID corresponding to a source */
 extern uint32_t NSR_GetLocalRefid(IPAddr *address);

+/* Procedure to get the name of a source.  If the source doesn't have a name,
+   it returns a temporary string containing formatted address. */
+extern char *NSR_GetName(IPAddr *address);
+
 /* This routine is called by ntp_io when a new packet arrives off the network */
 extern void NSR_ProcessRx(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr,
                          NTP_Local_Timestamp *rx_ts, NTP_Packet *message, int length);
@@ -124,8 +140,12 @@ extern int NSR_InitiateSampleBurst(int n_good_samples, int n_total_samples, IPAd

 extern void NSR_ReportSource(RPT_SourceReport *report, struct timespec *now);

+extern int NSR_GetAuthReport(IPAddr *address, RPT_AuthReport *report);
+
 extern int NSR_GetNTPReport(RPT_NTPReport *report);

 extern void NSR_GetActivityReport(RPT_ActivityReport *report);

+extern void NSR_DumpAuthData(void);
+
 #endif /* GOT_NTP_SOURCES_H */
--- a/nts_ke.h
+++ b/nts_ke.h
@@ -0,0 +1,81 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for the NTS Key Establishment protocol
+  */
+
+#ifndef GOT_NTS_KE_H
+#define GOT_NTS_KE_H
+
+#include "siv.h"
+
+#define NKE_PORT                        4460
+
+#define NKE_RECORD_CRITICAL_BIT         (1U << 15)
+#define NKE_RECORD_END_OF_MESSAGE       0
+#define NKE_RECORD_NEXT_PROTOCOL        1
+#define NKE_RECORD_ERROR                2
+#define NKE_RECORD_WARNING              3
+#define NKE_RECORD_AEAD_ALGORITHM       4
+#define NKE_RECORD_COOKIE               5
+#define NKE_RECORD_NTPV4_SERVER_NEGOTIATION 6
+#define NKE_RECORD_NTPV4_PORT_NEGOTIATION 7
+
+#define NKE_NEXT_PROTOCOL_NTPV4         0
+
+#define NKE_ERROR_UNRECOGNIZED_CRITICAL_RECORD 0
+#define NKE_ERROR_BAD_REQUEST           1
+#define NKE_ERROR_INTERNAL_SERVER_ERROR 2
+
+#define NKE_ALPN_NAME                   "ntske/1"
+#define NKE_EXPORTER_LABEL              "EXPORTER-network-time-security"
+#define NKE_EXPORTER_CONTEXT_C2S        "\x0\x0\x0\xf\x0"
+#define NKE_EXPORTER_CONTEXT_S2C        "\x0\x0\x0\xf\x1"
+
+#define NKE_MAX_MESSAGE_LENGTH          16384
+#define NKE_MAX_RECORD_BODY_LENGTH      256
+#define NKE_MAX_COOKIE_LENGTH           256
+#define NKE_MAX_COOKIES                 8
+#define NKE_MAX_KEY_LENGTH SIV_MAX_KEY_LENGTH
+
+#define NKE_RETRY_FACTOR2_CONNECT       4
+#define NKE_RETRY_FACTOR2_TLS           10
+#define NKE_MAX_RETRY_INTERVAL2         19
+
+typedef struct {
+  int length;
+  unsigned char key[NKE_MAX_KEY_LENGTH];
+} NKE_Key;
+
+typedef struct {
+  SIV_Algorithm algorithm;
+  NKE_Key c2s;
+  NKE_Key s2c;
+} NKE_Context;
+
+typedef struct {
+  int length;
+  unsigned char cookie[NKE_MAX_COOKIE_LENGTH];
+} NKE_Cookie;
+
+#endif
--- a/nts_ke_client.c
+++ b/nts_ke_client.c
@@ -0,0 +1,402 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  NTS-KE client
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include "nts_ke_client.h"
+
+#include "conf.h"
+#include "logging.h"
+#include "memory.h"
+#include "nameserv_async.h"
+#include "nts_ke_session.h"
+#include "siv.h"
+#include "socket.h"
+#include "util.h"
+
+#define CLIENT_TIMEOUT 16.0
+
+struct NKC_Instance_Record {
+  char *name;
+  IPSockAddr address;
+  NKSN_Instance session;
+  int destroying;
+  int got_response;
+  int resolving_name;
+
+  NKE_Context context;
+  NKE_Cookie cookies[NKE_MAX_COOKIES];
+  int num_cookies;
+  char server_name[NKE_MAX_RECORD_BODY_LENGTH + 1];
+  IPSockAddr ntp_address;
+};
+
+/* ================================================== */
+
+static void *client_credentials = NULL;
+static int client_credentials_refs = 0;
+
+/* ================================================== */
+
+static void
+name_resolve_handler(DNS_Status status, int n_addrs, IPAddr *ip_addrs, void *arg)
+{
+  NKC_Instance inst = arg;
+  int i;
+
+  inst->resolving_name = 0;
+
+  if (inst->destroying) {
+    Free(inst);
+    return;
+  }
+
+  if (status != DNS_Success || n_addrs < 1) {
+    LOG(LOGS_ERR, "Could not resolve NTP server %s from %s", inst->server_name, inst->name);
+    /* Force restart */
+    inst->got_response = 0;
+    return;
+  }
+
+  inst->ntp_address.ip_addr = ip_addrs[0];
+
+  /* Prefer an address in the same family as the NTS-KE server */
+  for (i = 0; i < n_addrs; i++) {
+    DEBUG_LOG("%s resolved to %s", inst->server_name, UTI_IPToString(&ip_addrs[i]));
+    if (ip_addrs[i].family == inst->address.ip_addr.family) {
+      inst->ntp_address.ip_addr = ip_addrs[i];
+      break;
+    }
+  }
+}
+
+/* ================================================== */
+
+static int
+prepare_request(NKC_Instance inst)
+{
+  NKSN_Instance session = inst->session;
+  uint16_t datum;
+
+  NKSN_BeginMessage(session);
+
+  datum = htons(NKE_NEXT_PROTOCOL_NTPV4);
+  if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, &datum, sizeof (datum)))
+    return 0;
+
+  datum = htons(AEAD_AES_SIV_CMAC_256);
+  if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, &datum, sizeof (datum)))
+    return 0;
+
+  if (!NKSN_EndMessage(session))
+    return 0;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static int
+process_response(NKC_Instance inst)
+{
+  int next_protocol = -1, aead_algorithm = -1, error = 0;
+  int i, critical, type, length;
+  uint16_t data[NKE_MAX_COOKIE_LENGTH / sizeof (uint16_t)];
+
+  assert(NKE_MAX_COOKIE_LENGTH % sizeof (uint16_t) == 0);
+  assert(sizeof (uint16_t) == 2);
+
+  inst->num_cookies = 0;
+  inst->ntp_address.ip_addr.family = IPADDR_UNSPEC;
+  inst->ntp_address.port = 0;
+  inst->server_name[0] = '\0';
+
+  while (!error) {
+    if (!NKSN_GetRecord(inst->session, &critical, &type, &length, &data, sizeof (data)))
+      break;
+
+    switch (type) {
+      case NKE_RECORD_NEXT_PROTOCOL:
+        if (!critical || length != 2 || ntohs(data[0]) != NKE_NEXT_PROTOCOL_NTPV4) {
+          DEBUG_LOG("Unexpected NTS-KE next protocol");
+          error = 1;
+          break;
+        }
+        next_protocol = NKE_NEXT_PROTOCOL_NTPV4;
+        break;
+      case NKE_RECORD_AEAD_ALGORITHM:
+        if (length != 2 || ntohs(data[0]) != AEAD_AES_SIV_CMAC_256) {
+          DEBUG_LOG("Unexpected NTS-KE AEAD algorithm");
+          error = 1;
+          break;
+        }
+        aead_algorithm = AEAD_AES_SIV_CMAC_256;
+        inst->context.algorithm = aead_algorithm;
+        break;
+      case NKE_RECORD_ERROR:
+        if (length == 2)
+          DEBUG_LOG("NTS-KE error %d", ntohs(data[0]));
+        error = 1;
+        break;
+      case NKE_RECORD_WARNING:
+        if (length == 2)
+          DEBUG_LOG("NTS-KE warning %d", ntohs(data[0]));
+        error = 1;
+        break;
+      case NKE_RECORD_COOKIE:
+        DEBUG_LOG("Got cookie length=%d", length);
+
+        if (length < 1 || length > NKE_MAX_COOKIE_LENGTH || length % 4 != 0 ||
+            inst->num_cookies >= NKE_MAX_COOKIES) {
+          DEBUG_LOG("Unexpected length/cookie");
+          break;
+        }
+
+        assert(NKE_MAX_COOKIE_LENGTH == sizeof (inst->cookies[inst->num_cookies].cookie));
+        assert(NKE_MAX_COOKIES == sizeof (inst->cookies) /
+                                  sizeof (inst->cookies[inst->num_cookies]));
+        inst->cookies[inst->num_cookies].length = length;
+        memcpy(inst->cookies[inst->num_cookies].cookie, data, length);
+
+        inst->num_cookies++;
+        break;
+      case NKE_RECORD_NTPV4_SERVER_NEGOTIATION:
+        if (length < 1 || length >= sizeof (inst->server_name)) {
+          DEBUG_LOG("Invalid server name");
+          error = 1;
+          break;
+        }
+
+        memcpy(inst->server_name, data, length);
+        inst->server_name[length] = '\0';
+
+        /* Make sure the name is printable and has no spaces */
+        for (i = 0; i < length && isgraph((unsigned char)inst->server_name[i]); i++)
+          ;
+        if (i != length) {
+          DEBUG_LOG("Invalid server name");
+          error = 1;
+          break;
+        }
+
+        DEBUG_LOG("Negotiated server %s", inst->server_name);
+        break;
+      case NKE_RECORD_NTPV4_PORT_NEGOTIATION:
+        if (length != 2) {
+          DEBUG_LOG("Invalid port");
+          error = 1;
+          break;
+        }
+        inst->ntp_address.port = ntohs(data[0]);
+        DEBUG_LOG("Negotiated port %d", inst->ntp_address.port);
+        break;
+      default:
+        DEBUG_LOG("Unknown record type=%d length=%d critical=%d", type, length, critical);
+        if (critical)
+          error = 1;
+    }
+  }
+
+  DEBUG_LOG("NTS-KE response: error=%d next=%d aead=%d",
+            error, next_protocol, aead_algorithm);
+
+  if (error || inst->num_cookies == 0 ||
+      next_protocol != NKE_NEXT_PROTOCOL_NTPV4 ||
+      aead_algorithm != AEAD_AES_SIV_CMAC_256)
+    return 0;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static int
+handle_message(void *arg)
+{
+  NKC_Instance inst = arg;
+
+  if (!process_response(inst)) {
+    LOG(LOGS_ERR, "Received invalid NTS-KE response from %s", inst->name);
+    return 0;
+  }
+
+  if (!NKSN_GetKeys(inst->session, inst->context.algorithm,
+                    &inst->context.c2s, &inst->context.s2c))
+    return 0;
+
+  if (inst->server_name[0] != '\0') {
+    if (inst->resolving_name)
+      return 0;
+    if (!UTI_StringToIP(inst->server_name, &inst->ntp_address.ip_addr)) {
+      DNS_Name2IPAddressAsync(inst->server_name, name_resolve_handler, inst);
+      inst->resolving_name = 1;
+    }
+  }
+
+  inst->got_response = 1;
+
+  return 1;
+}
+
+/* ================================================== */
+
+NKC_Instance
+NKC_CreateInstance(IPSockAddr *address, const char *name)
+{
+  NKC_Instance inst;
+
+  inst = MallocNew(struct NKC_Instance_Record);
+
+  inst->address = *address;
+  inst->name = Strdup(name);
+  inst->session = NKSN_CreateInstance(0, inst->name, handle_message, inst);
+  inst->resolving_name = 0;
+  inst->destroying = 0;
+  inst->got_response = 0;
+
+  /* Share the credentials with other client instances */
+  if (!client_credentials)
+    client_credentials = NKSN_CreateCertCredentials(NULL, NULL, CNF_GetNtsTrustedCertFile());
+  client_credentials_refs++;
+
+  return inst;
+}
+
+/* ================================================== */
+
+void
+NKC_DestroyInstance(NKC_Instance inst)
+{
+  NKSN_DestroyInstance(inst->session);
+
+  Free(inst->name);
+
+  client_credentials_refs--;
+  if (client_credentials_refs <= 0 && client_credentials) {
+    NKSN_DestroyCertCredentials(client_credentials);
+    client_credentials = NULL;
+  }
+
+  /* If the asynchronous resolver is running, let the handler free
+     the instance later */
+  if (inst->resolving_name) {
+    inst->destroying = 1;
+    return;
+  }
+
+  Free(inst);
+}
+
+/* ================================================== */
+
+int
+NKC_Start(NKC_Instance inst)
+{
+  IPSockAddr local_addr;
+  char label[512], *iface;
+  int sock_fd;
+
+  assert(!NKC_IsActive(inst));
+
+  inst->got_response = 0;
+
+  if (!client_credentials) {
+    DEBUG_LOG("Missing client credentials");
+    return 0;
+  }
+
+  /* Follow the bindacqaddress and bindacqdevice settings */
+  CNF_GetBindAcquisitionAddress(inst->address.ip_addr.family, &local_addr.ip_addr);
+  local_addr.port = 0;
+  iface = CNF_GetBindAcquisitionInterface();
+
+  /* Make a label containing both the address and name of the server */
+  if (snprintf(label, sizeof (label), "%s (%s)",
+               UTI_IPSockAddrToString(&inst->address), inst->name) >= sizeof (label))
+    ;
+
+  sock_fd = SCK_OpenTcpSocket(&inst->address, &local_addr, iface, 0);
+  if (sock_fd < 0) {
+    LOG(LOGS_ERR, "Could not connect to %s", label);
+    return 0;
+  }
+
+  /* Start an NTS-KE session */
+  if (!NKSN_StartSession(inst->session, sock_fd, label, client_credentials, CLIENT_TIMEOUT)) {
+    SCK_CloseSocket(sock_fd);
+    return 0;
+  }
+
+  /* Send a request */
+  if (!prepare_request(inst)) {
+    DEBUG_LOG("Could not prepare NTS-KE request");
+    NKSN_StopSession(inst->session);
+    return 0;
+  }
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NKC_IsActive(NKC_Instance inst)
+{
+  return !NKSN_IsStopped(inst->session) || inst->resolving_name;
+}
+
+/* ================================================== */
+
+int
+NKC_GetNtsData(NKC_Instance inst, NKE_Context *context,
+               NKE_Cookie *cookies, int *num_cookies, int max_cookies,
+               IPSockAddr *ntp_address)
+{
+  int i;
+
+  if (!inst->got_response || inst->resolving_name)
+    return 0;
+
+  *context = inst->context;
+
+  for (i = 0; i < inst->num_cookies && i < max_cookies; i++)
+    cookies[i] = inst->cookies[i];
+  *num_cookies = i;
+
+  *ntp_address = inst->ntp_address;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NKC_GetRetryFactor(NKC_Instance inst)
+{
+  return NKSN_GetRetryFactor(inst->session);
+}
--- a/nts_ke_client.h
+++ b/nts_ke_client.h
@@ -0,0 +1,56 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for the NTS-KE client
+  */
+
+#ifndef GOT_NTS_KE_CLIENT_H
+#define GOT_NTS_KE_CLIENT_H
+
+#include "addressing.h"
+#include "nts_ke.h"
+
+typedef struct NKC_Instance_Record *NKC_Instance;
+
+/* Create a client NTS-KE instance */
+extern NKC_Instance NKC_CreateInstance(IPSockAddr *address, const char *name);
+
+/* Destroy an instance */
+extern void NKC_DestroyInstance(NKC_Instance inst);
+
+/* Connect to the server, start an NTS-KE session, send an NTS-KE request, and
+   process the response (asynchronously) */
+extern int NKC_Start(NKC_Instance inst);
+
+/* Check if the client is still running */
+extern int NKC_IsActive(NKC_Instance inst);
+
+/* Get the NTS data if the session was successful */
+extern int NKC_GetNtsData(NKC_Instance inst, NKE_Context *context,
+                          NKE_Cookie *cookies, int *num_cookies, int max_cookies,
+                          IPSockAddr *ntp_address);
+
+/* Get a factor to calculate retry interval (in log2 seconds) */
+extern int NKC_GetRetryFactor(NKC_Instance inst);
+
+#endif
--- a/nts_ke_server.c
+++ b/nts_ke_server.c
@@ -0,0 +1,964 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  NTS-KE server
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include "nts_ke_server.h"
+
+#include "array.h"
+#include "conf.h"
+#include "clientlog.h"
+#include "local.h"
+#include "logging.h"
+#include "memory.h"
+#include "ntp_core.h"
+#include "nts_ke_session.h"
+#include "privops.h"
+#include "siv.h"
+#include "socket.h"
+#include "sched.h"
+#include "sys.h"
+#include "util.h"
+
+#define SERVER_TIMEOUT 2.0
+
+#define SERVER_COOKIE_SIV AEAD_AES_SIV_CMAC_256
+#define SERVER_COOKIE_NONCE_LENGTH 16
+
+#define KEY_ID_INDEX_BITS 2
+#define MAX_SERVER_KEYS (1U << KEY_ID_INDEX_BITS)
+#define FUTURE_KEYS 1
+
+#define DUMP_FILENAME "ntskeys"
+#define DUMP_IDENTIFIER "NKS0\n"
+
+#define INVALID_SOCK_FD (-7)
+
+typedef struct {
+  uint32_t key_id;
+  unsigned char nonce[SERVER_COOKIE_NONCE_LENGTH];
+} ServerCookieHeader;
+
+typedef struct {
+  uint32_t id;
+  unsigned char key[SIV_MAX_KEY_LENGTH];
+  SIV_Instance siv;
+} ServerKey;
+
+typedef struct {
+  uint32_t key_id;
+  unsigned char key[SIV_MAX_KEY_LENGTH];
+  IPAddr client_addr;
+  uint16_t client_port;
+  uint16_t _pad;
+} HelperRequest;
+
+/* ================================================== */
+
+static ServerKey server_keys[MAX_SERVER_KEYS];
+static int current_server_key;
+static double last_server_key_ts;
+static int key_rotation_interval;
+
+static int server_sock_fd4;
+static int server_sock_fd6;
+
+static int helper_sock_fd;
+static int is_helper;
+
+static int initialised = 0;
+
+/* Array of NKSN instances */
+static ARR_Instance sessions;
+static void *server_credentials;
+
+/* ================================================== */
+
+static int handle_message(void *arg);
+
+/* ================================================== */
+
+static int
+handle_client(int sock_fd, IPSockAddr *addr)
+{
+  NKSN_Instance inst, *instp;
+  int i;
+
+  /* Leave at least half of the descriptors which can handled by select()
+     to other use */
+  if (sock_fd > FD_SETSIZE / 2) {
+    DEBUG_LOG("Rejected connection from %s (%s)",
+              UTI_IPSockAddrToString(addr), "too many descriptors");
+    return 0;
+  }
+
+  /* Find an unused server slot or one with an already stopped session */
+  for (i = 0, inst = NULL; i < ARR_GetSize(sessions); i++) {
+    instp = ARR_GetElement(sessions, i);
+    if (!*instp) {
+      /* NULL handler arg will be replaced with the session instance */
+      inst = NKSN_CreateInstance(1, NULL, handle_message, NULL);
+      *instp = inst;
+      break;
+    } else if (NKSN_IsStopped(*instp)) {
+      inst = *instp;
+      break;
+    }
+  }
+
+  if (!inst) {
+    DEBUG_LOG("Rejected connection from %s (%s)",
+              UTI_IPSockAddrToString(addr), "too many connections");
+    return 0;
+  }
+
+  assert(server_credentials);
+
+  if (!NKSN_StartSession(inst, sock_fd, UTI_IPSockAddrToString(addr),
+                         server_credentials, SERVER_TIMEOUT))
+    return 0;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static void
+handle_helper_request(int fd, int event, void *arg)
+{
+  SCK_Message *message;
+  HelperRequest *req;
+  IPSockAddr client_addr;
+  int sock_fd;
+
+  /* Receive the helper request with the NTS-KE session socket.
+     With multiple helpers EAGAIN errors are expected here. */
+  message = SCK_ReceiveMessage(fd, SCK_FLAG_MSG_DESCRIPTOR);
+  if (!message)
+    return;
+
+  sock_fd = message->descriptor;
+  if (sock_fd < 0) {
+    /* Message with no descriptor is a shutdown command */
+    SCH_QuitProgram();
+    return;
+  }
+
+  if (!initialised) {
+    DEBUG_LOG("Uninitialised helper");
+    SCK_CloseSocket(sock_fd);
+    return;
+  }
+
+  if (message->length != sizeof (HelperRequest))
+    LOG_FATAL("Invalid helper request");
+
+  req = message->data;
+
+  /* Extract the current server key and client address from the request */
+  server_keys[current_server_key].id = ntohl(req->key_id);
+  assert(sizeof (server_keys[current_server_key].key) == sizeof (req->key));
+  memcpy(server_keys[current_server_key].key, req->key,
+         sizeof (server_keys[current_server_key].key));
+  UTI_IPNetworkToHost(&req->client_addr, &client_addr.ip_addr);
+  client_addr.port = ntohs(req->client_port);
+
+  if (!SIV_SetKey(server_keys[current_server_key].siv, server_keys[current_server_key].key,
+                  SIV_GetKeyLength(SERVER_COOKIE_SIV)))
+    LOG_FATAL("Could not set SIV key");
+
+  if (!handle_client(sock_fd, &client_addr)) {
+    SCK_CloseSocket(sock_fd);
+    return;
+  }
+
+  DEBUG_LOG("Accepted helper request fd=%d", sock_fd);
+}
+
+/* ================================================== */
+
+static void
+accept_connection(int listening_fd, int event, void *arg)
+{
+  SCK_Message message;
+  IPSockAddr addr;
+  int log_index, sock_fd;
+  struct timespec now;
+
+  sock_fd = SCK_AcceptConnection(listening_fd, &addr);
+  if (sock_fd < 0)
+    return;
+
+  if (!NCR_CheckAccessRestriction(&addr.ip_addr)) {
+    DEBUG_LOG("Rejected connection from %s (%s)",
+              UTI_IPSockAddrToString(&addr), "access denied");
+    SCK_CloseSocket(sock_fd);
+    return;
+  }
+
+  SCH_GetLastEventTime(&now, NULL, NULL);
+
+  log_index = CLG_LogServiceAccess(CLG_NTSKE, &addr.ip_addr, &now);
+  if (log_index >= 0 && CLG_LimitServiceRate(CLG_NTSKE, log_index)) {
+    DEBUG_LOG("Rejected connection from %s (%s)",
+              UTI_IPSockAddrToString(&addr), "rate limit");
+    SCK_CloseSocket(sock_fd);
+    return;
+  }
+
+  /* Pass the socket to a helper process if enabled.  Otherwise, handle the
+     client in the main process. */
+  if (helper_sock_fd != INVALID_SOCK_FD) {
+    HelperRequest req;
+
+    memset(&req, 0, sizeof (req));
+
+    /* Include the current server key and client address in the request */
+    req.key_id = htonl(server_keys[current_server_key].id);
+    assert(sizeof (req.key) == sizeof (server_keys[current_server_key].key));
+    memcpy(req.key, server_keys[current_server_key].key, sizeof (req.key));
+    UTI_IPHostToNetwork(&addr.ip_addr, &req.client_addr);
+    req.client_port = htons(addr.port);
+
+    SCK_InitMessage(&message, SCK_ADDR_UNSPEC);
+    message.data = &req;
+    message.length = sizeof (req);
+    message.descriptor = sock_fd;
+
+    errno = 0;
+    if (!SCK_SendMessage(helper_sock_fd, &message, SCK_FLAG_MSG_DESCRIPTOR)) {
+      /* If sending failed with EPIPE, it means all helpers closed their end of
+         the socket (e.g. due to a fatal error) */
+      if (errno == EPIPE)
+        LOG_FATAL("NTS-KE helpers failed");
+      SCK_CloseSocket(sock_fd);
+      return;
+    }
+
+    SCK_CloseSocket(sock_fd);
+  } else {
+    if (!handle_client(sock_fd, &addr)) {
+      SCK_CloseSocket(sock_fd);
+      return;
+    }
+  }
+
+  DEBUG_LOG("Accepted connection from %s fd=%d", UTI_IPSockAddrToString(&addr), sock_fd);
+}
+
+/* ================================================== */
+
+static int
+open_socket(int family)
+{
+  IPSockAddr local_addr;
+  int backlog, sock_fd;
+  char *iface;
+
+  if (!SCK_IsIpFamilyEnabled(family))
+    return INVALID_SOCK_FD;
+
+  CNF_GetBindAddress(family, &local_addr.ip_addr);
+  local_addr.port = CNF_GetNtsServerPort();
+  iface = CNF_GetBindNtpInterface();
+
+  sock_fd = SCK_OpenTcpSocket(NULL, &local_addr, iface, 0);
+  if (sock_fd < 0) {
+    LOG(LOGS_ERR, "Could not open NTS-KE socket on %s", UTI_IPSockAddrToString(&local_addr));
+    return INVALID_SOCK_FD;
+  }
+
+  /* Set the maximum number of waiting connections on the socket to the maximum
+     number of concurrent sessions */
+  backlog = MAX(CNF_GetNtsServerProcesses(), 1) * CNF_GetNtsServerConnections();
+
+  if (!SCK_ListenOnSocket(sock_fd, backlog)) {
+    SCK_CloseSocket(sock_fd);
+    return INVALID_SOCK_FD;
+  }
+
+  SCH_AddFileHandler(sock_fd, SCH_FILE_INPUT, accept_connection, NULL);
+
+  return sock_fd;
+}
+
+/* ================================================== */
+
+static void
+helper_signal(int x)
+{
+  SCH_QuitProgram();
+}
+
+/* ================================================== */
+
+static int
+prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_algorithm)
+{
+  NKE_Context context;
+  NKE_Cookie cookie;
+  char *ntp_server;
+  uint16_t datum;
+  int i;
+
+  DEBUG_LOG("NTS KE response: error=%d next=%d aead=%d", error, next_protocol, aead_algorithm);
+
+  NKSN_BeginMessage(session);
+
+  if (error >= 0) {
+    datum = htons(error);
+    if (!NKSN_AddRecord(session, 1, NKE_RECORD_ERROR, &datum, sizeof (datum)))
+      return 0;
+  } else if (next_protocol < 0) {
+    if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, NULL, 0))
+      return 0;
+  } else if (aead_algorithm < 0) {
+    datum = htons(next_protocol);
+    if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, &datum, sizeof (datum)))
+      return 0;
+    if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, NULL, 0))
+      return 0;
+  } else {
+    datum = htons(next_protocol);
+    if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, &datum, sizeof (datum)))
+      return 0;
+
+    datum = htons(aead_algorithm);
+    if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, &datum, sizeof (datum)))
+      return 0;
+
+    if (CNF_GetNTPPort() != NTP_PORT) {
+      datum = htons(CNF_GetNTPPort());
+      if (!NKSN_AddRecord(session, 1, NKE_RECORD_NTPV4_PORT_NEGOTIATION, &datum, sizeof (datum)))
+        return 0;
+    }
+
+    ntp_server = CNF_GetNtsNtpServer();
+    if (ntp_server) {
+      if (!NKSN_AddRecord(session, 1, NKE_RECORD_NTPV4_SERVER_NEGOTIATION,
+                          ntp_server, strlen(ntp_server)))
+        return 0;
+    }
+
+    context.algorithm = aead_algorithm;
+
+    if (!NKSN_GetKeys(session, aead_algorithm, &context.c2s, &context.s2c))
+      return 0;
+
+    for (i = 0; i < NKE_MAX_COOKIES; i++) {
+      if (!NKS_GenerateCookie(&context, &cookie))
+        return 0;
+      if (!NKSN_AddRecord(session, 0, NKE_RECORD_COOKIE, cookie.cookie, cookie.length))
+        return 0;
+    }
+  }
+
+  if (!NKSN_EndMessage(session))
+    return 0;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static int
+process_request(NKSN_Instance session)
+{
+  int next_protocol_records = 0, aead_algorithm_records = 0;
+  int next_protocol_values = 0, aead_algorithm_values = 0;
+  int next_protocol = -1, aead_algorithm = -1, error = -1;
+  int i, critical, type, length;
+  uint16_t data[NKE_MAX_RECORD_BODY_LENGTH / sizeof (uint16_t)];
+
+  assert(NKE_MAX_RECORD_BODY_LENGTH % sizeof (uint16_t) == 0);
+  assert(sizeof (uint16_t) == 2);
+
+  while (error < 0) {
+    if (!NKSN_GetRecord(session, &critical, &type, &length, &data, sizeof (data)))
+      break;
+
+    switch (type) {
+      case NKE_RECORD_NEXT_PROTOCOL:
+        if (!critical || length < 2 || length % 2 != 0) {
+          error = NKE_ERROR_BAD_REQUEST;
+          break;
+        }
+
+        next_protocol_records++;
+
+        for (i = 0; i < MIN(length, sizeof (data)) / 2; i++) {
+          next_protocol_values++;
+          if (ntohs(data[i]) == NKE_NEXT_PROTOCOL_NTPV4)
+            next_protocol = NKE_NEXT_PROTOCOL_NTPV4;
+        }
+        break;
+      case NKE_RECORD_AEAD_ALGORITHM:
+        if (length < 2 || length % 2 != 0) {
+          error = NKE_ERROR_BAD_REQUEST;
+          break;
+        }
+
+        aead_algorithm_records++;
+
+        for (i = 0; i < MIN(length, sizeof (data)) / 2; i++) {
+          aead_algorithm_values++;
+          if (ntohs(data[i]) == AEAD_AES_SIV_CMAC_256)
+            aead_algorithm = AEAD_AES_SIV_CMAC_256;
+        }
+        break;
+      case NKE_RECORD_ERROR:
+      case NKE_RECORD_WARNING:
+      case NKE_RECORD_COOKIE:
+        error = NKE_ERROR_BAD_REQUEST;
+        break;
+      default:
+        if (critical)
+          error = NKE_ERROR_UNRECOGNIZED_CRITICAL_RECORD;
+    }
+  }
+
+  if (error < 0) {
+    if (next_protocol_records != 1 || next_protocol_values < 1 ||
+        (next_protocol == NKE_NEXT_PROTOCOL_NTPV4 &&
+         (aead_algorithm_records != 1 || aead_algorithm_values < 1)))
+      error = NKE_ERROR_BAD_REQUEST;
+  }
+
+  if (!prepare_response(session, error, next_protocol, aead_algorithm))
+    return 0;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static int
+handle_message(void *arg)
+{
+  NKSN_Instance session = arg;
+
+  return process_request(session);
+}
+
+/* ================================================== */
+
+static void
+generate_key(int index)
+{
+  int key_length;
+
+  if (index < 0 || index >= MAX_SERVER_KEYS)
+    assert(0);
+
+  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
+  if (key_length > sizeof (server_keys[index].key))
+    assert(0);
+
+  UTI_GetRandomBytesUrandom(server_keys[index].key, key_length);
+
+  if (!server_keys[index].siv ||
+      !SIV_SetKey(server_keys[index].siv, server_keys[index].key, key_length))
+    LOG_FATAL("Could not set SIV key");
+
+  UTI_GetRandomBytes(&server_keys[index].id, sizeof (server_keys[index].id));
+
+  /* Encode the index in the lowest bits of the ID */
+  server_keys[index].id &= -1U << KEY_ID_INDEX_BITS;
+  server_keys[index].id |= index;
+
+  DEBUG_LOG("Generated server key %"PRIX32, server_keys[index].id);
+
+  last_server_key_ts = SCH_GetLastEventMonoTime();
+}
+
+/* ================================================== */
+
+static void
+save_keys(void)
+{
+  char buf[SIV_MAX_KEY_LENGTH * 2 + 1], *dump_dir;
+  int i, index, key_length;
+  double last_key_age;
+  FILE *f;
+
+  /* Don't save the keys if rotation is disabled to enable an external
+     management of the keys (e.g. share them with another server) */
+  if (key_rotation_interval == 0)
+    return;
+
+  dump_dir = CNF_GetNtsDumpDir();
+  if (!dump_dir)
+    return;
+
+  f = UTI_OpenFile(dump_dir, DUMP_FILENAME, ".tmp", 'w', 0600);
+  if (!f)
+    return;
+
+  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
+  last_key_age = SCH_GetLastEventMonoTime() - last_server_key_ts;
+
+  if (fprintf(f, "%s%d %.1f\n", DUMP_IDENTIFIER, SERVER_COOKIE_SIV, last_key_age) < 0)
+    goto error;
+
+  for (i = 0; i < MAX_SERVER_KEYS; i++) {
+    index = (current_server_key + i + 1 + FUTURE_KEYS) % MAX_SERVER_KEYS;
+
+    if (key_length > sizeof (server_keys[index].key) ||
+        !UTI_BytesToHex(server_keys[index].key, key_length, buf, sizeof (buf)) ||
+        fprintf(f, "%08"PRIX32" %s\n", server_keys[index].id, buf) < 0)
+      goto error;
+  }
+
+  fclose(f);
+
+  /* Rename the temporary file, or remove it if that fails */
+  if (!UTI_RenameTempFile(dump_dir, DUMP_FILENAME, ".tmp", NULL)) {
+    if (!UTI_RemoveFile(dump_dir, DUMP_FILENAME, ".tmp"))
+      ;
+  }
+
+  return;
+
+error:
+  DEBUG_LOG("Could not %s server keys", "save");
+  fclose(f);
+
+  if (!UTI_RemoveFile(dump_dir, DUMP_FILENAME, NULL))
+    ;
+}
+
+/* ================================================== */
+
+#define MAX_WORDS 2
+
+static int
+load_keys(void)
+{
+  char *dump_dir, line[1024], *words[MAX_WORDS];
+  unsigned char key[SIV_MAX_KEY_LENGTH];
+  int i, index, key_length, algorithm;
+  double key_age;
+  FILE *f;
+  uint32_t id;
+
+  dump_dir = CNF_GetNtsDumpDir();
+  if (!dump_dir)
+    return 0;
+
+  f = UTI_OpenFile(dump_dir, DUMP_FILENAME, NULL, 'r', 0);
+  if (!f)
+    return 0;
+
+  if (!fgets(line, sizeof (line), f) || strcmp(line, DUMP_IDENTIFIER) != 0 ||
+      !fgets(line, sizeof (line), f) || UTI_SplitString(line, words, MAX_WORDS) != 2 ||
+        sscanf(words[0], "%d", &algorithm) != 1 || algorithm != SERVER_COOKIE_SIV ||
+        sscanf(words[1], "%lf", &key_age) != 1)
+    goto error;
+
+  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
+  last_server_key_ts = SCH_GetLastEventMonoTime() - MAX(key_age, 0.0);
+
+  for (i = 0; i < MAX_SERVER_KEYS && fgets(line, sizeof (line), f); i++) {
+    if (UTI_SplitString(line, words, MAX_WORDS) != 2 ||
+        sscanf(words[0], "%"PRIX32, &id) != 1)
+      goto error;
+
+    if (UTI_HexToBytes(words[1], key, sizeof (key)) != key_length)
+      goto error;
+
+    index = id % MAX_SERVER_KEYS;
+
+    server_keys[index].id = id;
+    assert(sizeof (server_keys[index].key) == sizeof (key));
+    memcpy(server_keys[index].key, key, key_length);
+
+    if (!SIV_SetKey(server_keys[index].siv, server_keys[index].key, key_length))
+      LOG_FATAL("Could not set SIV key");
+
+    DEBUG_LOG("Loaded key %"PRIX32, id);
+
+    current_server_key = (index + MAX_SERVER_KEYS - FUTURE_KEYS) % MAX_SERVER_KEYS;
+  }
+
+  fclose(f);
+
+  return 1;
+
+error:
+  DEBUG_LOG("Could not %s server keys", "load");
+  fclose(f);
+
+  return 0;
+}
+
+/* ================================================== */
+
+static void
+key_timeout(void *arg)
+{
+  current_server_key = (current_server_key + 1) % MAX_SERVER_KEYS;
+  generate_key((current_server_key + FUTURE_KEYS) % MAX_SERVER_KEYS);
+  save_keys();
+
+  SCH_AddTimeoutByDelay(key_rotation_interval, key_timeout, NULL);
+}
+
+/* ================================================== */
+
+static void
+run_helper(uid_t uid, gid_t gid, int scfilter_level)
+{
+  LOG_Severity log_severity;
+
+  /* Finish minimal initialisation and run using the scheduler loop
+     similarly to the main process */
+
+  DEBUG_LOG("Helper started");
+
+  /* Suppress a log message about disabled clock control */
+  log_severity = LOG_GetMinSeverity();
+  LOG_SetMinSeverity(LOGS_ERR);
+
+  SYS_Initialise(0);
+  LOG_SetMinSeverity(log_severity);
+
+  if (!geteuid() && (uid || gid))
+    SYS_DropRoot(uid, gid, SYS_NTSKE_HELPER);
+
+  NKS_Initialise();
+
+  UTI_SetQuitSignalsHandler(helper_signal, 1);
+  if (scfilter_level != 0)
+    SYS_EnableSystemCallFilter(scfilter_level, SYS_NTSKE_HELPER);
+
+  SCH_MainLoop();
+
+  DEBUG_LOG("Helper exiting");
+
+  NKS_Finalise();
+  SCK_Finalise();
+  SYS_Finalise();
+  SCH_Finalise();
+  LCL_Finalise();
+  PRV_Finalise();
+  CNF_Finalise();
+  LOG_Finalise();
+
+  exit(0);
+}
+
+/* ================================================== */
+
+void
+NKS_PreInitialise(uid_t uid, gid_t gid, int scfilter_level)
+{
+  int i, processes, sock_fd1, sock_fd2;
+  char prefix[16];
+  pid_t pid;
+
+  helper_sock_fd = INVALID_SOCK_FD;
+  is_helper = 0;
+
+  if (!CNF_GetNtsServerCertFile() || !CNF_GetNtsServerKeyFile())
+    return;
+
+  processes = CNF_GetNtsServerProcesses();
+  if (processes <= 0)
+    return;
+
+  /* Start helper processes to perform (computationally expensive) NTS-KE
+     sessions with clients on sockets forwarded from the main process */
+
+  sock_fd1 = SCK_OpenUnixSocketPair(0, &sock_fd2);
+  if (sock_fd1 < 0)
+    LOG_FATAL("Could not open socket pair");
+
+  for (i = 0; i < processes; i++) {
+    pid = fork();
+
+    if (pid < 0)
+      LOG_FATAL("fork() failed : %s", strerror(errno));
+
+    if (pid > 0)
+      continue;
+
+    is_helper = 1;
+
+    snprintf(prefix, sizeof (prefix), "nks#%d:", i + 1);
+    LOG_SetDebugPrefix(prefix);
+    LOG_CloseParentFd();
+
+    SCK_CloseSocket(sock_fd1);
+    SCH_AddFileHandler(sock_fd2, SCH_FILE_INPUT, handle_helper_request, NULL);
+
+    run_helper(uid, gid, scfilter_level);
+  }
+
+  SCK_CloseSocket(sock_fd2);
+  helper_sock_fd = sock_fd1;
+}
+
+/* ================================================== */
+
+void
+NKS_Initialise(void)
+{
+  char *cert, *key;
+  double key_delay;
+  int i;
+
+  server_sock_fd4 = INVALID_SOCK_FD;
+  server_sock_fd6 = INVALID_SOCK_FD;
+
+  cert = CNF_GetNtsServerCertFile();
+  key = CNF_GetNtsServerKeyFile();
+
+  if (!cert || !key)
+    return;
+
+  if (helper_sock_fd == INVALID_SOCK_FD) {
+    server_credentials = NKSN_CreateCertCredentials(cert, key, NULL);
+    if (!server_credentials)
+      return;
+  } else {
+    server_credentials = NULL;
+  }
+
+  sessions = ARR_CreateInstance(sizeof (NKSN_Instance));
+  for (i = 0; i < CNF_GetNtsServerConnections(); i++)
+    *(NKSN_Instance *)ARR_GetNewElement(sessions) = NULL;
+
+  /* Generate random keys, even if they will be replaced by reloaded keys,
+     or unused (in the helper) */
+  for (i = 0; i < MAX_SERVER_KEYS; i++) {
+    server_keys[i].siv = SIV_CreateInstance(SERVER_COOKIE_SIV);
+    generate_key(i);
+  }
+
+  current_server_key = MAX_SERVER_KEYS - 1;
+
+  if (!is_helper) {
+    server_sock_fd4 = open_socket(IPADDR_INET4);
+    server_sock_fd6 = open_socket(IPADDR_INET6);
+
+    key_rotation_interval = MAX(CNF_GetNtsRotate(), 0);
+
+    /* Reload saved keys, or save the new keys */
+    if (!load_keys())
+      save_keys();
+
+    if (key_rotation_interval > 0) {
+      key_delay = key_rotation_interval - (SCH_GetLastEventMonoTime() - last_server_key_ts);
+      SCH_AddTimeoutByDelay(MAX(key_delay, 0.0), key_timeout, NULL);
+    }
+  }
+
+  initialised = 1;
+}
+
+/* ================================================== */
+
+void
+NKS_Finalise(void)
+{
+  int i;
+
+  if (!initialised)
+    return;
+
+  if (helper_sock_fd != INVALID_SOCK_FD) {
+    /* Send the helpers a request to exit */
+    for (i = 0; i < CNF_GetNtsServerProcesses(); i++) {
+      if (!SCK_Send(helper_sock_fd, "", 1, 0))
+        ;
+    }
+    SCK_CloseSocket(helper_sock_fd);
+  }
+  if (server_sock_fd4 != INVALID_SOCK_FD)
+    SCK_CloseSocket(server_sock_fd4);
+  if (server_sock_fd6 != INVALID_SOCK_FD)
+    SCK_CloseSocket(server_sock_fd6);
+
+  if (!is_helper)
+    save_keys();
+
+  for (i = 0; i < MAX_SERVER_KEYS; i++)
+    SIV_DestroyInstance(server_keys[i].siv);
+
+  for (i = 0; i < ARR_GetSize(sessions); i++) {
+    NKSN_Instance session = *(NKSN_Instance *)ARR_GetElement(sessions, i);
+    if (session)
+      NKSN_DestroyInstance(session);
+  }
+  ARR_DestroyInstance(sessions);
+
+  if (server_credentials)
+    NKSN_DestroyCertCredentials(server_credentials);
+}
+
+/* ================================================== */
+
+void
+NKS_DumpKeys(void)
+{
+  save_keys();
+}
+
+/* ================================================== */
+
+void
+NKS_ReloadKeys(void)
+{
+  /* Don't load the keys if they are expected to be generated by this server
+     instance (i.e. they are already loaded) to not delay the next rotation */
+  if (key_rotation_interval > 0)
+    return;
+
+  load_keys();
+}
+
+/* ================================================== */
+
+/* A server cookie consists of key ID, nonce, and encrypted C2S+S2C keys */
+
+int
+NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
+{
+  unsigned char plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
+  int plaintext_length, tag_length;
+  ServerCookieHeader *header;
+  ServerKey *key;
+
+  if (!initialised) {
+    DEBUG_LOG("NTS server disabled");
+    return 0;
+  }
+
+  /* The algorithm is hardcoded for now */
+  if (context->algorithm != AEAD_AES_SIV_CMAC_256) {
+    DEBUG_LOG("Unexpected SIV algorithm");
+    return 0;
+  }
+
+  if (context->c2s.length < 0 || context->c2s.length > NKE_MAX_KEY_LENGTH ||
+      context->s2c.length < 0 || context->s2c.length > NKE_MAX_KEY_LENGTH) {
+    DEBUG_LOG("Invalid key length");
+    return 0;
+  }
+
+  key = &server_keys[current_server_key];
+
+  header = (ServerCookieHeader *)cookie->cookie;
+
+  header->key_id = htonl(key->id);
+  UTI_GetRandomBytes(header->nonce, sizeof (header->nonce));
+
+  plaintext_length = context->c2s.length + context->s2c.length;
+  assert(plaintext_length <= sizeof (plaintext));
+  memcpy(plaintext, context->c2s.key, context->c2s.length);
+  memcpy(plaintext + context->c2s.length, context->s2c.key, context->s2c.length);
+
+  tag_length = SIV_GetTagLength(key->siv);
+  cookie->length = sizeof (*header) + plaintext_length + tag_length;
+  assert(cookie->length <= sizeof (cookie->cookie));
+  ciphertext = cookie->cookie + sizeof (*header);
+
+  if (!SIV_Encrypt(key->siv, header->nonce, sizeof (header->nonce),
+                   "", 0,
+                   plaintext, plaintext_length,
+                   ciphertext, plaintext_length + tag_length)) {
+    DEBUG_LOG("Could not encrypt cookie");
+    return 0;
+  }
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context)
+{
+  unsigned char plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
+  int ciphertext_length, plaintext_length, tag_length;
+  ServerCookieHeader *header;
+  ServerKey *key;
+  uint32_t key_id;
+
+  if (!initialised) {
+    DEBUG_LOG("NTS server disabled");
+    return 0;
+  }
+
+  if (cookie->length <= (int)sizeof (*header)) {
+    DEBUG_LOG("Invalid cookie length");
+    return 0;
+  }
+
+  header = (ServerCookieHeader *)cookie->cookie;
+  ciphertext = cookie->cookie + sizeof (*header);
+  ciphertext_length = cookie->length - sizeof (*header);
+
+  key_id = ntohl(header->key_id);
+  key = &server_keys[key_id % MAX_SERVER_KEYS];
+  if (key_id != key->id) {
+    DEBUG_LOG("Unknown key %"PRIX32, key_id);
+    return 0;
+  }
+
+  tag_length = SIV_GetTagLength(key->siv);
+  if (tag_length >= ciphertext_length) {
+    DEBUG_LOG("Invalid cookie length");
+    return 0;
+  }
+
+  plaintext_length = ciphertext_length - tag_length;
+  if (plaintext_length > sizeof (plaintext) || plaintext_length % 2 != 0) {
+    DEBUG_LOG("Invalid cookie length");
+    return 0;
+  }
+
+  if (!SIV_Decrypt(key->siv, header->nonce, sizeof (header->nonce),
+                   "", 0,
+                   ciphertext, ciphertext_length,
+                   plaintext, plaintext_length)) {
+    DEBUG_LOG("Could not decrypt cookie");
+    return 0;
+  }
+
+  context->algorithm = AEAD_AES_SIV_CMAC_256;
+
+  context->c2s.length = plaintext_length / 2;
+  context->s2c.length = plaintext_length / 2;
+  assert(context->c2s.length <= sizeof (context->c2s.key));
+
+  memcpy(context->c2s.key, plaintext, context->c2s.length);
+  memcpy(context->s2c.key, plaintext + context->c2s.length, context->s2c.length);
+
+  return 1;
+}
--- a/nts_ke_server.h
+++ b/nts_ke_server.h
@@ -0,0 +1,49 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for the NTS-KE server
+  */
+
+#ifndef GOT_NTS_KE_SERVER_H
+#define GOT_NTS_KE_SERVER_H
+
+#include "nts_ke.h"
+
+/* Init and fini functions */
+extern void NKS_PreInitialise(uid_t uid, gid_t gid, int scfilter_level);
+extern void NKS_Initialise(void);
+extern void NKS_Finalise(void);
+
+/* Save the current server keys */
+extern void NKS_DumpKeys(void);
+
+/* Reload the keys */
+extern void NKS_ReloadKeys(void);
+
+/* Generate an NTS cookie with a given context */
+extern int NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie);
+
+/* Validate a cookie and decode the context */
+extern int NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context);
+
+#endif
--- a/nts_ke_session.c
+++ b/nts_ke_session.c
@@ -0,0 +1,875 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  NTS-KE session used by server and client
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include "nts_ke_session.h"
+
+#include "conf.h"
+#include "local.h"
+#include "logging.h"
+#include "memory.h"
+#include "siv.h"
+#include "socket.h"
+#include "sched.h"
+#include "util.h"
+
+#include <gnutls/gnutls.h>
+#include <gnutls/x509.h>
+
+#define INVALID_SOCK_FD (-8)
+
+struct RecordHeader {
+  uint16_t type;
+  uint16_t body_length;
+};
+
+struct Message {
+  int length;
+  int sent;
+  int parsed;
+  int complete;
+  unsigned char data[NKE_MAX_MESSAGE_LENGTH];
+};
+
+typedef enum {
+  KE_WAIT_CONNECT,
+  KE_HANDSHAKE,
+  KE_SEND,
+  KE_RECEIVE,
+  KE_SHUTDOWN,
+  KE_STOPPED,
+} KeState;
+
+struct NKSN_Instance_Record {
+  int server;
+  char *server_name;
+  NKSN_MessageHandler handler;
+  void *handler_arg;
+
+  KeState state;
+  int sock_fd;
+  char *label;
+  gnutls_session_t tls_session;
+  SCH_TimeoutID timeout_id;
+  int retry_factor;
+
+  struct Message message;
+  int new_message;
+};
+
+/* ================================================== */
+
+static gnutls_priority_t priority_cache;
+
+static int credentials_counter = 0;
+
+static int clock_updates = 0;
+
+/* ================================================== */
+
+static void
+reset_message(struct Message *message)
+{
+  message->length = 0;
+  message->sent = 0;
+  message->parsed = 0;
+  message->complete = 0;
+}
+
+/* ================================================== */
+
+static int
+add_record(struct Message *message, int critical, int type, const void *body, int body_length)
+{
+  struct RecordHeader header;
+
+  assert(message->length <= sizeof (message->data));
+
+  if (body_length < 0 || body_length > 0xffff || type < 0 || type > 0x7fff ||
+      message->length + sizeof (header) + body_length > sizeof (message->data))
+    return 0;
+
+  header.type = htons(!!critical * NKE_RECORD_CRITICAL_BIT | type);
+  header.body_length = htons(body_length);
+
+  memcpy(&message->data[message->length], &header, sizeof (header));
+  message->length += sizeof (header);
+
+  if (body_length > 0) {
+    memcpy(&message->data[message->length], body, body_length);
+    message->length += body_length;
+  }
+
+  return 1;
+}
+
+/* ================================================== */
+
+static void
+reset_message_parsing(struct Message *message)
+{
+  message->parsed = 0;
+}
+
+/* ================================================== */
+
+static int
+get_record(struct Message *message, int *critical, int *type, int *body_length,
+           void *body, int buffer_length)
+{
+  struct RecordHeader header;
+  int blen, rlen;
+
+  if (message->length < message->parsed + sizeof (header) ||
+      buffer_length < 0)
+    return 0;
+
+  memcpy(&header, &message->data[message->parsed], sizeof (header));
+
+  blen = ntohs(header.body_length);
+  rlen = sizeof (header) + blen;
+  assert(blen >= 0 && rlen > 0);
+
+  if (message->length < message->parsed + rlen)
+    return 0;
+
+  if (critical)
+    *critical = !!(ntohs(header.type) & NKE_RECORD_CRITICAL_BIT);
+  if (type)
+    *type = ntohs(header.type) & ~NKE_RECORD_CRITICAL_BIT;
+  if (body)
+    memcpy(body, &message->data[message->parsed + sizeof (header)], MIN(buffer_length, blen));
+  if (body_length)
+    *body_length = blen;
+
+  message->parsed += rlen;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static int
+check_message_format(struct Message *message, int eof)
+{
+  int critical = 0, type = -1, length = -1, ends = 0;
+
+  reset_message_parsing(message);
+  message->complete = 0;
+
+  while (get_record(message, &critical, &type, &length, NULL, 0)) {
+    if (type == NKE_RECORD_END_OF_MESSAGE) {
+      if (!critical || length != 0 || ends > 0)
+        return 0;
+      ends++;
+    }
+  }
+
+  /* If the message cannot be fully parsed, but more data may be coming,
+     consider the format to be ok */
+  if (message->length == 0 || message->parsed < message->length)
+    return !eof;
+
+  if (type != NKE_RECORD_END_OF_MESSAGE)
+    return !eof;
+
+  message->complete = 1;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static gnutls_session_t
+create_tls_session(int server_mode, int sock_fd, const char *server_name,
+                   gnutls_certificate_credentials_t credentials,
+                   gnutls_priority_t priority)
+{
+  unsigned char alpn_name[sizeof (NKE_ALPN_NAME)];
+  gnutls_session_t session;
+  gnutls_datum_t alpn;
+  unsigned int flags;
+  int r;
+
+  r = gnutls_init(&session, GNUTLS_NONBLOCK | GNUTLS_NO_TICKETS |
+                  (server_mode ? GNUTLS_SERVER : GNUTLS_CLIENT));
+  if (r < 0) {
+    LOG(LOGS_ERR, "Could not %s TLS session : %s", "create", gnutls_strerror(r));
+    return NULL;
+  }
+
+  if (!server_mode) {
+    r = gnutls_server_name_set(session, GNUTLS_NAME_DNS, server_name, strlen(server_name));
+    if (r < 0)
+      goto error;
+
+    flags = 0;
+
+    if (clock_updates < CNF_GetNoCertTimeCheck()) {
+      flags |= GNUTLS_VERIFY_DISABLE_TIME_CHECKS | GNUTLS_VERIFY_DISABLE_TRUSTED_TIME_CHECKS;
+      DEBUG_LOG("Disabled time checks");
+    }
+
+    gnutls_session_set_verify_cert(session, server_name, flags);
+  }
+
+  r = gnutls_priority_set(session, priority);
+  if (r < 0)
+    goto error;
+
+  r = gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, credentials);
+  if (r < 0)
+    goto error;
+
+  memcpy(alpn_name, NKE_ALPN_NAME, sizeof (alpn_name));
+  alpn.data = alpn_name;
+  alpn.size = sizeof (alpn_name) - 1;
+
+  r = gnutls_alpn_set_protocols(session, &alpn, 1, 0);
+  if (r < 0)
+    goto error;
+
+  gnutls_transport_set_int(session, sock_fd);
+
+  return session;
+
+error:
+  LOG(LOGS_ERR, "Could not %s TLS session : %s", "set", gnutls_strerror(r));
+  gnutls_deinit(session);
+  return NULL;
+}
+
+/* ================================================== */
+
+static void
+stop_session(NKSN_Instance inst)
+{
+  if (inst->state == KE_STOPPED)
+    return;
+
+  inst->state = KE_STOPPED;
+
+  SCH_RemoveFileHandler(inst->sock_fd);
+  SCK_CloseSocket(inst->sock_fd);
+  inst->sock_fd = INVALID_SOCK_FD;
+
+  Free(inst->label);
+  inst->label = NULL;
+
+  gnutls_deinit(inst->tls_session);
+  inst->tls_session = NULL;
+
+  SCH_RemoveTimeout(inst->timeout_id);
+  inst->timeout_id = 0;
+}
+
+/* ================================================== */
+
+static void
+session_timeout(void *arg)
+{
+  NKSN_Instance inst = arg;
+
+  LOG(inst->server ? LOGS_DEBUG : LOGS_ERR, "NTS-KE session with %s timed out", inst->label);
+
+  inst->timeout_id = 0;
+  stop_session(inst);
+}
+
+/* ================================================== */
+
+static int
+check_alpn(NKSN_Instance inst)
+{
+  gnutls_datum_t alpn;
+
+  if (gnutls_alpn_get_selected_protocol(inst->tls_session, &alpn) < 0 ||
+      alpn.size != sizeof (NKE_ALPN_NAME) - 1 ||
+      memcmp(alpn.data, NKE_ALPN_NAME, sizeof (NKE_ALPN_NAME) - 1) != 0)
+    return 0;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static void
+set_input_output(NKSN_Instance inst, int output)
+{
+  SCH_SetFileHandlerEvent(inst->sock_fd, SCH_FILE_INPUT, !output);
+  SCH_SetFileHandlerEvent(inst->sock_fd, SCH_FILE_OUTPUT, output);
+}
+
+/* ================================================== */
+
+static void
+change_state(NKSN_Instance inst, KeState state)
+{
+  int output;
+
+  switch (state) {
+    case KE_HANDSHAKE:
+      output = !inst->server;
+      break;
+    case KE_WAIT_CONNECT:
+    case KE_SEND:
+    case KE_SHUTDOWN:
+      output = 1;
+      break;
+    case KE_RECEIVE:
+      output = 0;
+      break;
+    default:
+      assert(0);
+  }
+
+  set_input_output(inst, output);
+
+  inst->state = state;
+}
+
+/* ================================================== */
+
+static int
+handle_event(NKSN_Instance inst, int event)
+{
+  struct Message *message = &inst->message;
+  int r;
+
+  DEBUG_LOG("Session event %d fd=%d state=%d", event, inst->sock_fd, (int)inst->state);
+
+  switch (inst->state) {
+    case KE_WAIT_CONNECT:
+      /* Check if connect() succeeded */
+      if (event != SCH_FILE_OUTPUT)
+        return 0;
+
+      /* Get the socket error */
+      if (!SCK_GetIntOption(inst->sock_fd, SOL_SOCKET, SO_ERROR, &r))
+        r = EINVAL;
+
+      if (r != 0) {
+        LOG(LOGS_ERR, "Could not connect to %s : %s", inst->label, strerror(r));
+        stop_session(inst);
+        return 0;
+      }
+
+      DEBUG_LOG("Connected to %s", inst->label);
+
+      change_state(inst, KE_HANDSHAKE);
+      return 0;
+
+    case KE_HANDSHAKE:
+      r = gnutls_handshake(inst->tls_session);
+
+      if (r < 0) {
+        if (gnutls_error_is_fatal(r)) {
+          gnutls_datum_t cert_error;
+
+          /* Get a description of verification errors */
+          if (r != GNUTLS_E_CERTIFICATE_VERIFICATION_ERROR ||
+              gnutls_certificate_verification_status_print(
+                          gnutls_session_get_verify_cert_status(inst->tls_session),
+                          gnutls_certificate_type_get(inst->tls_session), &cert_error, 0) < 0)
+            cert_error.data = NULL;
+
+          LOG(inst->server ? LOGS_DEBUG : LOGS_ERR,
+              "TLS handshake with %s failed : %s%s%s", inst->label, gnutls_strerror(r),
+              cert_error.data ? " " : "", cert_error.data ? (const char *)cert_error.data : "");
+
+          if (cert_error.data)
+            gnutls_free(cert_error.data);
+
+          stop_session(inst);
+
+          /* Increase the retry interval if the handshake did not fail due
+             to the other end closing the connection */
+          if (r != GNUTLS_E_PULL_ERROR && r != GNUTLS_E_PREMATURE_TERMINATION)
+            inst->retry_factor = NKE_RETRY_FACTOR2_TLS;
+
+          return 0;
+        }
+
+        /* Disable output when the handshake is trying to receive data */
+        set_input_output(inst, gnutls_record_get_direction(inst->tls_session));
+        return 0;
+      }
+
+      inst->retry_factor = NKE_RETRY_FACTOR2_TLS;
+
+      if (DEBUG) {
+        char *description = gnutls_session_get_desc(inst->tls_session);
+        DEBUG_LOG("Handshake with %s completed %s",
+                  inst->label, description ? description : "");
+        gnutls_free(description);
+      }
+
+      if (!check_alpn(inst)) {
+        LOG(inst->server ? LOGS_DEBUG : LOGS_ERR, "NTS-KE not supported by %s", inst->label);
+        stop_session(inst);
+        return 0;
+      }
+
+      /* Client will send a request to the server */
+      change_state(inst, inst->server ? KE_RECEIVE : KE_SEND);
+      return 0;
+
+    case KE_SEND:
+      assert(inst->new_message && message->complete);
+      assert(message->length <= sizeof (message->data) && message->length > message->sent);
+
+      r = gnutls_record_send(inst->tls_session, &message->data[message->sent],
+                             message->length - message->sent);
+
+      if (r < 0) {
+        if (gnutls_error_is_fatal(r)) {
+          LOG(inst->server ? LOGS_DEBUG : LOGS_ERR,
+              "Could not send NTS-KE message to %s : %s", inst->label, gnutls_strerror(r));
+          stop_session(inst);
+        }
+        return 0;
+      }
+
+      DEBUG_LOG("Sent %d bytes to %s", r, inst->label);
+
+      message->sent += r;
+      if (message->sent < message->length)
+        return 0;
+
+      /* Client will receive a response */
+      change_state(inst, inst->server ? KE_SHUTDOWN : KE_RECEIVE);
+      reset_message(&inst->message);
+      inst->new_message = 0;
+      return 0;
+
+    case KE_RECEIVE:
+      do {
+        if (message->length >= sizeof (message->data)) {
+          DEBUG_LOG("Message is too long");
+          stop_session(inst);
+          return 0;
+        }
+
+        r = gnutls_record_recv(inst->tls_session, &message->data[message->length],
+                               sizeof (message->data) - message->length);
+
+        if (r < 0) {
+          /* Handle a renegotiation request on both client and server as
+             a protocol error */
+          if (gnutls_error_is_fatal(r) || r == GNUTLS_E_REHANDSHAKE) {
+            LOG(inst->server ? LOGS_DEBUG : LOGS_ERR,
+                "Could not receive NTS-KE message from %s : %s",
+                inst->label, gnutls_strerror(r));
+            stop_session(inst);
+          }
+          return 0;
+        }
+
+        DEBUG_LOG("Received %d bytes from %s", r, inst->label);
+
+        message->length += r;
+
+      } while (gnutls_record_check_pending(inst->tls_session) > 0);
+
+      if (!check_message_format(message, r == 0)) {
+        LOG(inst->server ? LOGS_DEBUG : LOGS_ERR,
+            "Received invalid NTS-KE message from %s", inst->label);
+        stop_session(inst);
+        return 0;
+      }
+
+      /* Wait for more data if the message is not complete yet */
+      if (!message->complete)
+        return 0;
+
+      /* Server will send a response to the client */
+      change_state(inst, inst->server ? KE_SEND : KE_SHUTDOWN);
+
+      /* Return success to process the received message */
+      return 1;
+
+    case KE_SHUTDOWN:
+      r = gnutls_bye(inst->tls_session, GNUTLS_SHUT_RDWR);
+
+      if (r < 0) {
+        if (gnutls_error_is_fatal(r)) {
+          DEBUG_LOG("Shutdown with %s failed : %s", inst->label, gnutls_strerror(r));
+          stop_session(inst);
+          return 0;
+        }
+
+        /* Disable output when the TLS shutdown is trying to receive data */
+        set_input_output(inst, gnutls_record_get_direction(inst->tls_session));
+        return 0;
+      }
+
+      SCK_ShutdownConnection(inst->sock_fd);
+      stop_session(inst);
+
+      DEBUG_LOG("Shutdown completed");
+      return 0;
+
+    default:
+      assert(0);
+      return 0;
+  }
+}
+
+/* ================================================== */
+
+static void
+read_write_socket(int fd, int event, void *arg)
+{
+  NKSN_Instance inst = arg;
+
+  if (!handle_event(inst, event))
+    return;
+
+  /* A valid message was received.  Call the handler to process the message,
+     and prepare a response if it is a server. */
+
+  reset_message_parsing(&inst->message);
+
+  if (!(inst->handler)(inst->handler_arg)) {
+    stop_session(inst);
+    return;
+  }
+}
+
+/* ================================================== */
+
+static time_t
+get_time(time_t *t)
+{
+  struct timespec now;
+
+  LCL_ReadCookedTime(&now, NULL);
+  if (t)
+    *t = now.tv_sec;
+
+  return now.tv_sec;
+}
+
+/* ================================================== */
+
+static void
+handle_step(struct timespec *raw, struct timespec *cooked, double dfreq,
+            double doffset, LCL_ChangeType change_type, void *anything)
+{
+  if (change_type != LCL_ChangeUnknownStep && clock_updates < INT_MAX)
+    clock_updates++;
+}
+
+/* ================================================== */
+
+static int gnutls_initialised = 0;
+
+static void
+init_gnutls(void)
+{
+  int r;
+
+  if (gnutls_initialised)
+    return;
+
+  r = gnutls_global_init();
+  if (r < 0)
+    LOG_FATAL("Could not initialise %s : %s", "gnutls", gnutls_strerror(r));
+
+  /* Prepare a priority cache for server and client NTS-KE sessions
+     (the NTS specification requires TLS1.3 or later) */
+  r = gnutls_priority_init2(&priority_cache,
+                            "-VERS-SSL3.0:-VERS-TLS1.0:-VERS-TLS1.1:-VERS-TLS1.2:-VERS-DTLS-ALL",
+                            NULL, GNUTLS_PRIORITY_INIT_DEF_APPEND);
+  if (r < 0)
+    LOG_FATAL("Could not initialise %s : %s", "priority cache", gnutls_strerror(r));
+
+  /* Use our clock instead of the system clock in certificate verification */
+  gnutls_global_set_time_function(get_time);
+
+  gnutls_initialised = 1;
+  DEBUG_LOG("Initialised");
+
+  LCL_AddParameterChangeHandler(handle_step, NULL);
+}
+
+/* ================================================== */
+
+static void
+deinit_gnutls(void)
+{
+  if (!gnutls_initialised || credentials_counter > 0)
+    return;
+
+  LCL_RemoveParameterChangeHandler(handle_step, NULL);
+
+  gnutls_priority_deinit(priority_cache);
+  gnutls_global_deinit();
+  gnutls_initialised = 0;
+  DEBUG_LOG("Deinitialised");
+}
+
+/* ================================================== */
+
+void *
+NKSN_CreateCertCredentials(char *cert, char *key, char *trusted_certs)
+{
+  gnutls_certificate_credentials_t credentials = NULL;
+  int r;
+
+  init_gnutls();
+
+  r = gnutls_certificate_allocate_credentials(&credentials);
+  if (r < 0)
+    goto error;
+
+  if (cert && key) {
+    r = gnutls_certificate_set_x509_key_file(credentials, cert, key,
+                                             GNUTLS_X509_FMT_PEM);
+    if (r < 0)
+      goto error;
+  } else {
+    if (!CNF_GetNoSystemCert()) {
+      r = gnutls_certificate_set_x509_system_trust(credentials);
+      if (r < 0)
+        goto error;
+    }
+
+    if (trusted_certs) {
+      r = gnutls_certificate_set_x509_trust_file(credentials, trusted_certs,
+                                                 GNUTLS_X509_FMT_PEM);
+      if (r < 0)
+        goto error;
+    }
+  }
+
+  credentials_counter++;
+
+  return credentials;
+
+error:
+  LOG(LOGS_ERR, "Could not set credentials : %s", gnutls_strerror(r));
+  if (credentials)
+    gnutls_certificate_free_credentials(credentials);
+  deinit_gnutls();
+  return NULL;
+}
+
+/* ================================================== */
+
+void
+NKSN_DestroyCertCredentials(void *credentials)
+{
+  gnutls_certificate_free_credentials(credentials);
+  credentials_counter--;
+  deinit_gnutls();
+}
+
+/* ================================================== */
+
+NKSN_Instance
+NKSN_CreateInstance(int server_mode, const char *server_name,
+                    NKSN_MessageHandler handler, void *handler_arg)
+{
+  NKSN_Instance inst;
+
+  inst = MallocNew(struct NKSN_Instance_Record);
+
+  inst->server = server_mode;
+  inst->server_name = server_name ? Strdup(server_name) : NULL;
+  inst->handler = handler;
+  inst->handler_arg = handler_arg;
+  /* Replace a NULL argument with the session itself */
+  if (!inst->handler_arg)
+    inst->handler_arg = inst;
+
+  inst->state = KE_STOPPED;
+  inst->sock_fd = INVALID_SOCK_FD;
+  inst->label = NULL;
+  inst->tls_session = NULL;
+  inst->timeout_id = 0;
+  inst->retry_factor = NKE_RETRY_FACTOR2_CONNECT;
+
+  return inst;
+}
+
+/* ================================================== */
+
+void
+NKSN_DestroyInstance(NKSN_Instance inst)
+{
+  stop_session(inst);
+
+  Free(inst->server_name);
+  Free(inst);
+}
+
+/* ================================================== */
+
+int
+NKSN_StartSession(NKSN_Instance inst, int sock_fd, const char *label,
+                  void *credentials, double timeout)
+{
+  assert(inst->state == KE_STOPPED);
+
+  inst->tls_session = create_tls_session(inst->server, sock_fd, inst->server_name,
+                                         credentials, priority_cache);
+  if (!inst->tls_session)
+    return 0;
+
+  inst->sock_fd = sock_fd;
+  SCH_AddFileHandler(sock_fd, SCH_FILE_INPUT, read_write_socket, inst);
+
+  inst->label = Strdup(label);
+  inst->timeout_id = SCH_AddTimeoutByDelay(timeout, session_timeout, inst);
+  inst->retry_factor = NKE_RETRY_FACTOR2_CONNECT;
+
+  reset_message(&inst->message);
+  inst->new_message = 0;
+
+  change_state(inst, inst->server ? KE_HANDSHAKE : KE_WAIT_CONNECT);
+
+  return 1;
+}
+
+/* ================================================== */
+
+void
+NKSN_BeginMessage(NKSN_Instance inst)
+{
+  reset_message(&inst->message);
+  inst->new_message = 1;
+}
+
+/* ================================================== */
+
+int
+NKSN_AddRecord(NKSN_Instance inst, int critical, int type, const void *body, int body_length)
+{
+  assert(inst->new_message && !inst->message.complete);
+  assert(type != NKE_RECORD_END_OF_MESSAGE);
+
+  return add_record(&inst->message, critical, type, body, body_length);
+}
+
+/* ================================================== */
+
+int
+NKSN_EndMessage(NKSN_Instance inst)
+{
+  assert(!inst->message.complete);
+
+  /* Terminate the message */
+  if (!add_record(&inst->message, 1, NKE_RECORD_END_OF_MESSAGE, NULL, 0))
+    return 0;
+
+  inst->message.complete = 1;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NKSN_GetRecord(NKSN_Instance inst, int *critical, int *type, int *body_length,
+               void *body, int buffer_length)
+{
+  int type2;
+
+  assert(inst->message.complete);
+
+  if (body_length)
+    *body_length = 0;
+
+  if (!get_record(&inst->message, critical, &type2, body_length, body, buffer_length))
+    return 0;
+
+  /* Hide the end-of-message record */
+  if (type2 == NKE_RECORD_END_OF_MESSAGE)
+    return 0;
+
+  if (type)
+    *type = type2;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NKSN_GetKeys(NKSN_Instance inst, SIV_Algorithm siv, NKE_Key *c2s, NKE_Key *s2c)
+{
+  int length = SIV_GetKeyLength(siv);
+
+  if (length <= 0 || length > sizeof (c2s->key) || length > sizeof (s2c->key)) {
+    DEBUG_LOG("Invalid algorithm");
+    return 0;
+  }
+
+  if (gnutls_prf_rfc5705(inst->tls_session,
+                         sizeof (NKE_EXPORTER_LABEL) - 1, NKE_EXPORTER_LABEL,
+                         sizeof (NKE_EXPORTER_CONTEXT_C2S) - 1, NKE_EXPORTER_CONTEXT_C2S,
+                         length, (char *)c2s->key) < 0 ||
+      gnutls_prf_rfc5705(inst->tls_session,
+                         sizeof (NKE_EXPORTER_LABEL) - 1, NKE_EXPORTER_LABEL,
+                         sizeof (NKE_EXPORTER_CONTEXT_S2C) - 1, NKE_EXPORTER_CONTEXT_S2C,
+                         length, (char *)s2c->key) < 0) {
+    DEBUG_LOG("Could not export key");
+    return 0;
+  }
+
+  c2s->length = length;
+  s2c->length = length;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NKSN_IsStopped(NKSN_Instance inst)
+{
+  return inst->state == KE_STOPPED;
+}
+
+/* ================================================== */
+
+void
+NKSN_StopSession(NKSN_Instance inst)
+{
+  stop_session(inst);
+}
+
+/* ================================================== */
+
+int
+NKSN_GetRetryFactor(NKSN_Instance inst)
+{
+  return inst->retry_factor;
+}
--- a/nts_ke_session.h
+++ b/nts_ke_session.h
@@ -0,0 +1,87 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for the NTS-KE session
+  */
+
+#ifndef GOT_NTS_KE_SESSION_H
+#define GOT_NTS_KE_SESSION_H
+
+#include "nts_ke.h"
+#include "siv.h"
+
+typedef struct NKSN_Instance_Record *NKSN_Instance;
+
+/* Handler for received NTS-KE messages.  A zero return code stops
+   the session. */
+typedef int (*NKSN_MessageHandler)(void *arg);
+
+/* Get client or server credentials using certificates of trusted CAs,
+   or a server certificate and key.  The credentials may be shared between
+   different clients or servers. */
+extern void *NKSN_CreateCertCredentials(char *cert, char *key, char *trusted_certs);
+
+/* Destroy the credentials */
+extern void NKSN_DestroyCertCredentials(void *credentials);
+
+/* Create an instance */
+extern NKSN_Instance NKSN_CreateInstance(int server_mode, const char *server_name,
+                                         NKSN_MessageHandler handler, void *handler_arg);
+
+/* Destroy an instance */
+extern void NKSN_DestroyInstance(NKSN_Instance inst);
+
+/* Start a new NTS-KE session */
+extern int NKSN_StartSession(NKSN_Instance inst, int sock_fd, const char *label,
+                             void *credentials, double timeout);
+
+/* Begin an NTS-KE message.  A request should be made right after starting
+   the session and response should be made in the message handler. */
+extern void NKSN_BeginMessage(NKSN_Instance inst);
+
+/* Add a record to the message */
+extern int NKSN_AddRecord(NKSN_Instance inst, int critical, int type,
+                          const void *body, int body_length);
+
+/* Terminate the message */
+extern int NKSN_EndMessage(NKSN_Instance inst);
+
+/* Get the next record from the received message.  This function should be
+   called from the message handler. */
+extern int NKSN_GetRecord(NKSN_Instance inst, int *critical, int *type, int *body_length,
+                          void *body, int buffer_length);
+
+/* Export NTS keys for a specified algorithm */
+extern int NKSN_GetKeys(NKSN_Instance inst, SIV_Algorithm siv, NKE_Key *c2s, NKE_Key *s2c);
+
+/* Check if the session has stopped */
+extern int NKSN_IsStopped(NKSN_Instance inst);
+
+/* Stop the session */
+extern void NKSN_StopSession(NKSN_Instance inst);
+
+/* Get a factor to calculate retry interval (in log2 seconds)
+   based on the session state or how it was terminated */
+extern int NKSN_GetRetryFactor(NKSN_Instance inst);
+
+#endif
--- a/nts_ntp.h
+++ b/nts_ntp.h
@@ -0,0 +1,41 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for the NTS-NTP protocol
+  */
+
+#ifndef GOT_NTS_NTP_H
+#define GOT_NTS_NTP_H
+
+#define NTP_EF_NTS_UNIQUE_IDENTIFIER    0x0104
+#define NTP_EF_NTS_COOKIE               0x0204
+#define NTP_EF_NTS_COOKIE_PLACEHOLDER   0x0304
+#define NTP_EF_NTS_AUTH_AND_EEF         0x0404
+
+#define NTP_KOD_NTS_NAK                 0x4e54534e
+
+#define NTS_MIN_UNIQ_ID_LENGTH          32
+#define NTS_MIN_UNPADDED_NONCE_LENGTH   16
+#define NTS_MAX_COOKIES                 8
+
+#endif
--- a/nts_ntp_auth.c
+++ b/nts_ntp_auth.c
@@ -0,0 +1,183 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  NTS Authenticator and Encrypted Extension Fields extension field
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include "nts_ntp_auth.h"
+
+#include "logging.h"
+#include "ntp_ext.h"
+#include "nts_ntp.h"
+#include "siv.h"
+#include "util.h"
+
+struct AuthHeader {
+  uint16_t nonce_length;
+  uint16_t ciphertext_length;
+};
+
+/* ================================================== */
+
+static int
+get_padding_length(int length)
+{
+  return length % 4U ? 4 - length % 4U : 0;
+}
+
+/* ================================================== */
+
+static int
+get_padded_length(int length)
+{
+  return length + get_padding_length(length);
+}
+
+/* ================================================== */
+
+int
+NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
+                   const unsigned char *nonce, int nonce_length,
+                   const unsigned char *plaintext, int plaintext_length,
+                   int min_ef_length)
+{
+  int auth_length, ciphertext_length, assoc_length;
+  int nonce_padding, ciphertext_padding, additional_padding;
+  unsigned char *ciphertext, *body;
+  struct AuthHeader *header;
+
+  assert(sizeof (*header) == 4);
+
+  if (nonce_length <= 0 || plaintext_length < 0) {
+    DEBUG_LOG("Invalid nonce/plaintext length");
+    return 0;
+  }
+
+  assoc_length = info->length;
+  ciphertext_length = SIV_GetTagLength(siv) + plaintext_length;
+  nonce_padding = get_padding_length(nonce_length);
+  ciphertext_padding = get_padding_length(ciphertext_length);
+  min_ef_length = get_padded_length(min_ef_length);
+
+  auth_length = sizeof (*header) + nonce_length + nonce_padding +
+                ciphertext_length + ciphertext_padding;
+  additional_padding = MAX(min_ef_length - auth_length - 4, 0);
+  additional_padding = MAX(NTS_MIN_UNPADDED_NONCE_LENGTH - nonce_length - nonce_padding,
+                           additional_padding);
+  auth_length += additional_padding;
+
+  if (!NEF_AddBlankField(packet, info, NTP_EF_NTS_AUTH_AND_EEF, auth_length,
+                         (void **)&header)) {
+    DEBUG_LOG("Could not add EF");
+    return 0;
+  }
+
+  header->nonce_length = htons(nonce_length);
+  header->ciphertext_length = htons(ciphertext_length);
+
+  body = (unsigned char *)(header + 1);
+  ciphertext = body + nonce_length + nonce_padding;
+
+  if ((unsigned char *)header + auth_length !=
+      ciphertext + ciphertext_length + ciphertext_padding + additional_padding)
+    assert(0);
+
+  memcpy(body, nonce, nonce_length);
+  memset(body + nonce_length, 0, nonce_padding);
+
+  if (!SIV_Encrypt(siv, nonce, nonce_length, packet, assoc_length,
+                   plaintext, plaintext_length, ciphertext, ciphertext_length)) {
+    DEBUG_LOG("SIV encrypt failed");
+    info->length = assoc_length;
+    return 0;
+  }
+
+  memset(ciphertext + ciphertext_length, 0, ciphertext_padding + additional_padding);
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, int ef_start,
+                  unsigned char *plaintext, int buffer_length, int *plaintext_length)
+{
+  unsigned int siv_tag_length, nonce_length, ciphertext_length;
+  unsigned char *nonce, *ciphertext;
+  int ef_type, ef_body_length;
+  void *ef_body;
+  struct AuthHeader *header;
+
+  if (buffer_length < 0)
+    return 0;
+
+  if (!NEF_ParseField(packet, info->length, ef_start,
+                      NULL, &ef_type, &ef_body, &ef_body_length))
+    return 0;
+
+  if (ef_type != NTP_EF_NTS_AUTH_AND_EEF || ef_body_length < sizeof (*header))
+    return 0;
+
+  header = ef_body;
+
+  nonce_length = ntohs(header->nonce_length);
+  ciphertext_length = ntohs(header->ciphertext_length);
+
+  if (get_padded_length(nonce_length) +
+      get_padded_length(ciphertext_length) > ef_body_length)
+    return 0;
+
+  nonce = (unsigned char *)(header + 1);
+  ciphertext = nonce + get_padded_length(nonce_length);
+
+  siv_tag_length = SIV_GetTagLength(siv);
+
+  if (nonce_length < 1 ||
+      ciphertext_length < siv_tag_length ||
+      ciphertext_length - siv_tag_length > buffer_length) {
+    DEBUG_LOG("Unexpected nonce/ciphertext length");
+    return 0;
+  }
+
+  if (ef_body_length < sizeof (*header) +
+        NTS_MIN_UNPADDED_NONCE_LENGTH + get_padded_length(ciphertext_length)) {
+    DEBUG_LOG("Missing padding");
+    return 0;
+  }
+
+  *plaintext_length = ciphertext_length - siv_tag_length;
+  assert(*plaintext_length >= 0);
+
+  if (!SIV_Decrypt(siv, nonce, nonce_length, packet, ef_start,
+                   ciphertext, ciphertext_length, plaintext, *plaintext_length)) {
+    DEBUG_LOG("SIV decrypt failed");
+    return 0;
+  }
+
+  return 1;
+}
--- a/nts_ntp_auth.h
+++ b/nts_ntp_auth.h
@@ -0,0 +1,43 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header for NTS Authenticator and Encrypted Extension Fields
+  extension field
+  */
+
+#ifndef GOT_NTS_NTP_AUTH_H
+#define GOT_NTS_NTP_AUTH_H
+
+#include "ntp.h"
+#include "siv.h"
+
+extern int NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
+                              const unsigned char *nonce, int nonce_length,
+                              const unsigned char *plaintext, int plaintext_length,
+                              int min_ef_length);
+
+extern int NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
+                             int ef_start, unsigned char *plaintext, int buffer_length,
+                             int *plaintext_length);
+
+#endif
--- a/nts_ntp_client.c
+++ b/nts_ntp_client.c
@@ -0,0 +1,703 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Client NTS-NTP authentication
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include "nts_ntp_client.h"
+
+#include "conf.h"
+#include "logging.h"
+#include "memory.h"
+#include "ntp.h"
+#include "ntp_ext.h"
+#include "ntp_sources.h"
+#include "nts_ke_client.h"
+#include "nts_ntp.h"
+#include "nts_ntp_auth.h"
+#include "sched.h"
+#include "siv.h"
+#include "util.h"
+
+/* Maximum length of all cookies to avoid IP fragmentation */
+#define MAX_TOTAL_COOKIE_LENGTH (8 * 108)
+
+/* Magic string of files containing keys and cookies */
+#define DUMP_IDENTIFIER "NNC0\n"
+
+struct NNC_Instance_Record {
+  const IPSockAddr *ntp_address;
+  IPSockAddr nts_address;
+  char *name;
+
+  NKC_Instance nke;
+  SIV_Instance siv;
+
+  int load_attempt;
+  int nke_attempts;
+  double next_nke_attempt;
+  double last_nke_success;
+
+  NKE_Context context;
+  unsigned int context_id;
+  NKE_Cookie cookies[NTS_MAX_COOKIES];
+  int num_cookies;
+  int cookie_index;
+  int auth_ready;
+  int nak_response;
+  int ok_response;
+  unsigned char nonce[NTS_MIN_UNPADDED_NONCE_LENGTH];
+  unsigned char uniq_id[NTS_MIN_UNIQ_ID_LENGTH];
+};
+
+/* ================================================== */
+
+static void save_cookies(NNC_Instance inst);
+static void load_cookies(NNC_Instance inst);
+
+/* ================================================== */
+
+static void
+reset_instance(NNC_Instance inst)
+{
+  if (inst->nke)
+    NKC_DestroyInstance(inst->nke);
+  inst->nke = NULL;
+  if (inst->siv)
+    SIV_DestroyInstance(inst->siv);
+  inst->siv = NULL;
+
+  inst->load_attempt = 0;
+  inst->nke_attempts = 0;
+  inst->next_nke_attempt = 0.0;
+  inst->last_nke_success = 0.0;
+
+  memset(&inst->context, 0, sizeof (inst->context));
+  inst->context_id = 0;
+  memset(inst->cookies, 0, sizeof (inst->cookies));
+  inst->num_cookies = 0;
+  inst->cookie_index = 0;
+  inst->auth_ready = 0;
+  inst->nak_response = 0;
+  inst->ok_response = 1;
+  memset(inst->nonce, 0, sizeof (inst->nonce));
+  memset(inst->uniq_id, 0, sizeof (inst->uniq_id));
+}
+
+/* ================================================== */
+
+NNC_Instance
+NNC_CreateInstance(IPSockAddr *nts_address, const char *name, const IPSockAddr *ntp_address)
+{
+  NNC_Instance inst;
+
+  inst = MallocNew(struct NNC_Instance_Record);
+
+  inst->ntp_address = ntp_address;
+  inst->nts_address = *nts_address;
+  inst->name = name ? Strdup(name) : NULL;
+  inst->siv = NULL;
+  inst->nke = NULL;
+
+  reset_instance(inst);
+
+  return inst;
+}
+
+/* ================================================== */
+
+void
+NNC_DestroyInstance(NNC_Instance inst)
+{
+  save_cookies(inst);
+
+  reset_instance(inst);
+
+  Free(inst->name);
+  Free(inst);
+}
+
+/* ================================================== */
+
+static int
+check_cookies(NNC_Instance inst)
+{
+  /* Force a new NTS-KE session if a NAK was received without a valid response,
+     or the keys encrypting the cookies need to be refreshed */
+  if (inst->num_cookies > 0 &&
+      ((inst->nak_response && !inst->ok_response) ||
+       SCH_GetLastEventMonoTime() - inst->last_nke_success > CNF_GetNtsRefresh())) {
+    inst->num_cookies = 0;
+    DEBUG_LOG("Dropped cookies");
+  }
+
+  return inst->num_cookies > 0;
+}
+
+/* ================================================== */
+
+static int
+set_ntp_address(NNC_Instance inst, NTP_Remote_Address *negotiated_address)
+{
+  NTP_Remote_Address old_address, new_address;
+
+  old_address = *inst->ntp_address;
+  new_address = *negotiated_address;
+
+  if (new_address.ip_addr.family == IPADDR_UNSPEC)
+    new_address.ip_addr = old_address.ip_addr;
+  if (new_address.port == 0)
+    new_address.port = old_address.port;
+
+  if (UTI_CompareIPs(&old_address.ip_addr, &new_address.ip_addr, NULL) == 0 &&
+      old_address.port == new_address.port)
+    /* Nothing to do */
+    return 1;
+
+  if (NSR_UpdateSourceNtpAddress(&old_address, &new_address) != NSR_Success) {
+    LOG(LOGS_ERR, "Could not change %s to negotiated address %s",
+        UTI_IPToString(&old_address.ip_addr), UTI_IPToString(&new_address.ip_addr));
+    return 0;
+  }
+
+  return 1;
+}
+
+/* ================================================== */
+
+static void
+update_next_nke_attempt(NNC_Instance inst, double now)
+{
+  int factor, interval;
+
+  if (!inst->nke)
+    return;
+
+  factor = NKC_GetRetryFactor(inst->nke);
+  interval = MIN(factor + inst->nke_attempts - 1, NKE_MAX_RETRY_INTERVAL2);
+  inst->next_nke_attempt = now + UTI_Log2ToDouble(interval);
+}
+
+/* ================================================== */
+
+static int
+get_cookies(NNC_Instance inst)
+{
+  NTP_Remote_Address ntp_address;
+  double now;
+  int got_data;
+
+  assert(inst->num_cookies == 0);
+
+  now = SCH_GetLastEventMonoTime();
+
+  /* Create and start a new NTS-KE session if not already present */
+  if (!inst->nke) {
+    if (now < inst->next_nke_attempt) {
+      DEBUG_LOG("Limiting NTS-KE request rate (%f seconds)",
+                inst->next_nke_attempt - now);
+      return 0;
+    }
+
+    if (!inst->name) {
+      LOG(LOGS_ERR, "Missing name of %s for NTS-KE",
+          UTI_IPToString(&inst->nts_address.ip_addr));
+      return 0;
+    }
+
+    inst->nke = NKC_CreateInstance(&inst->nts_address, inst->name);
+
+    inst->nke_attempts++;
+    update_next_nke_attempt(inst, now);
+
+    if (!NKC_Start(inst->nke))
+      return 0;
+  }
+
+  update_next_nke_attempt(inst, now);
+
+  /* Wait until the session stops */
+  if (NKC_IsActive(inst->nke))
+    return 0;
+
+  assert(sizeof (inst->cookies) / sizeof (inst->cookies[0]) == NTS_MAX_COOKIES);
+
+  /* Get the new keys, cookies and NTP address if the session was successful */
+  got_data = NKC_GetNtsData(inst->nke, &inst->context,
+                            inst->cookies, &inst->num_cookies, NTS_MAX_COOKIES,
+                            &ntp_address);
+
+  NKC_DestroyInstance(inst->nke);
+  inst->nke = NULL;
+
+  if (!got_data)
+    return 0;
+
+  if (inst->siv)
+    SIV_DestroyInstance(inst->siv);
+  inst->siv = NULL;
+
+  inst->context_id++;
+
+  /* Force a new session if the NTP address is used by another source, with
+     an expectation that it will eventually get a non-conflicting address */
+  if (!set_ntp_address(inst, &ntp_address)) {
+    inst->num_cookies = 0;
+    return 0;
+  }
+
+  inst->last_nke_success = now;
+  inst->cookie_index = 0;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NNC_PrepareForAuth(NNC_Instance inst)
+{
+  inst->auth_ready = 0;
+
+  /* Prepare data for the next request and invalidate any responses to the
+     previous request */
+  UTI_GetRandomBytes(inst->uniq_id, sizeof (inst->uniq_id));
+  UTI_GetRandomBytes(inst->nonce, sizeof (inst->nonce));
+
+  /* Try to reload saved keys and cookies (once for the NTS-KE address) */
+  if (!inst->load_attempt) {
+    load_cookies(inst);
+    inst->load_attempt = 1;
+  }
+
+  /* Get new cookies if there are not any, or they are no longer usable */
+  if (!check_cookies(inst)) {
+    if (!get_cookies(inst))
+      return 0;
+  }
+
+  inst->nak_response = 0;
+
+  if (!inst->siv)
+    inst->siv = SIV_CreateInstance(inst->context.algorithm);
+
+  if (!inst->siv ||
+      !SIV_SetKey(inst->siv, inst->context.c2s.key, inst->context.c2s.length)) {
+    DEBUG_LOG("Could not set SIV key");
+    return 0;
+  }
+
+  inst->auth_ready = 1;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NNC_GenerateRequestAuth(NNC_Instance inst, NTP_Packet *packet,
+                        NTP_PacketInfo *info)
+{
+  NKE_Cookie *cookie;
+  int i, req_cookies;
+  void *ef_body;
+
+  if (!inst->auth_ready)
+    return 0;
+
+  inst->auth_ready = 0;
+
+  if (inst->num_cookies <= 0 || !inst->siv)
+    return 0;
+
+  if (info->mode != MODE_CLIENT)
+    return 0;
+
+  cookie = &inst->cookies[inst->cookie_index];
+  inst->num_cookies--;
+  inst->cookie_index = (inst->cookie_index + 1) % NTS_MAX_COOKIES;
+
+  req_cookies = MIN(NTS_MAX_COOKIES - inst->num_cookies,
+                    MAX_TOTAL_COOKIE_LENGTH / (cookie->length + 4));
+
+  if (!NEF_AddField(packet, info, NTP_EF_NTS_UNIQUE_IDENTIFIER,
+                    inst->uniq_id, sizeof (inst->uniq_id)))
+    return 0;
+
+  if (!NEF_AddField(packet, info, NTP_EF_NTS_COOKIE,
+                    cookie->cookie, cookie->length))
+    return 0;
+
+  for (i = 0; i < req_cookies - 1; i++) {
+    if (!NEF_AddBlankField(packet, info, NTP_EF_NTS_COOKIE_PLACEHOLDER,
+                           cookie->length, &ef_body))
+      return 0;
+    memset(ef_body, 0, cookie->length);
+  }
+
+  if (!NNA_GenerateAuthEF(packet, info, inst->siv, inst->nonce, sizeof (inst->nonce),
+                          (const unsigned char *)"", 0, NTP_MAX_V4_MAC_LENGTH + 4))
+    return 0;
+
+  inst->ok_response = 0;
+
+  return 1;
+}
+
+/* ================================================== */
+
+static int
+parse_encrypted_efs(NNC_Instance inst, unsigned char *plaintext, int length)
+{
+  int ef_length, parsed;
+
+  for (parsed = 0; parsed < length; parsed += ef_length) {
+    if (!NEF_ParseSingleField(plaintext, length, parsed, &ef_length, NULL, NULL, NULL)) {
+      DEBUG_LOG("Could not parse encrypted EF");
+      return 0;
+    }
+  }
+
+  return 1;
+}
+
+/* ================================================== */
+
+static int
+extract_cookies(NNC_Instance inst, unsigned char *plaintext, int length)
+{
+  int ef_type, ef_body_length, ef_length, parsed, index, acceptable, saved;
+  void *ef_body;
+
+  acceptable = saved = 0;
+
+  for (parsed = 0; parsed < length; parsed += ef_length) {
+    if (!NEF_ParseSingleField(plaintext, length, parsed,
+                              &ef_length, &ef_type, &ef_body, &ef_body_length))
+      return 0;
+
+    if (ef_type != NTP_EF_NTS_COOKIE)
+      continue;
+
+    if (ef_length < NTP_MIN_EF_LENGTH || ef_body_length > sizeof (inst->cookies[0].cookie)) {
+      DEBUG_LOG("Unexpected cookie length %d", ef_body_length);
+      continue;
+    }
+
+    acceptable++;
+
+    if (inst->num_cookies >= NTS_MAX_COOKIES)
+      continue;
+
+    index = (inst->cookie_index + inst->num_cookies) % NTS_MAX_COOKIES;
+    assert(index >= 0 && index < NTS_MAX_COOKIES);
+    assert(sizeof (inst->cookies) / sizeof (inst->cookies[0]) == NTS_MAX_COOKIES);
+
+    memcpy(inst->cookies[index].cookie, ef_body, ef_body_length);
+    inst->cookies[index].length = ef_body_length;
+    inst->num_cookies++;
+
+    saved++;
+  }
+
+  DEBUG_LOG("Extracted %d cookies (saved %d)", acceptable, saved);
+
+  return acceptable > 0;
+}
+
+/* ================================================== */
+
+int
+NNC_CheckResponseAuth(NNC_Instance inst, NTP_Packet *packet,
+                      NTP_PacketInfo *info)
+{
+  int ef_type, ef_body_length, ef_length, parsed, plaintext_length;
+  int has_valid_uniq_id = 0, has_valid_auth = 0;
+  unsigned char plaintext[NTP_MAX_EXTENSIONS_LENGTH];
+  void *ef_body;
+
+  if (info->ext_fields == 0 || info->mode != MODE_SERVER)
+    return 0;
+
+  /* Accept at most one response per request */
+  if (inst->ok_response || inst->auth_ready)
+    return 0;
+
+  if (!inst->siv ||
+      !SIV_SetKey(inst->siv, inst->context.s2c.key, inst->context.s2c.length)) {
+    DEBUG_LOG("Could not set SIV key");
+    return 0;
+  }
+
+  for (parsed = NTP_HEADER_LENGTH; parsed < info->length; parsed += ef_length) {
+    if (!NEF_ParseField(packet, info->length, parsed,
+                        &ef_length, &ef_type, &ef_body, &ef_body_length))
+      /* This is not expected as the packet already passed NAU_ParsePacket() */
+      return 0;
+
+    switch (ef_type) {
+      case NTP_EF_NTS_UNIQUE_IDENTIFIER:
+        if (ef_body_length != sizeof (inst->uniq_id) ||
+            memcmp(ef_body, inst->uniq_id, sizeof (inst->uniq_id)) != 0) {
+          DEBUG_LOG("Invalid uniq id");
+          return 0;
+        }
+        has_valid_uniq_id = 1;
+        break;
+      case NTP_EF_NTS_COOKIE:
+        DEBUG_LOG("Unencrypted cookie");
+        break;
+      case NTP_EF_NTS_AUTH_AND_EEF:
+        if (parsed + ef_length != info->length) {
+          DEBUG_LOG("Auth not last EF");
+          return 0;
+        }
+
+        if (!NNA_DecryptAuthEF(packet, info, inst->siv, parsed,
+                               plaintext, sizeof (plaintext), &plaintext_length))
+          return 0;
+
+        if (!parse_encrypted_efs(inst, plaintext, plaintext_length))
+          return 0;
+
+        has_valid_auth = 1;
+        break;
+      default:
+        break;
+    }
+  }
+
+  if (!has_valid_uniq_id || !has_valid_auth) {
+    if (has_valid_uniq_id && packet->stratum == NTP_INVALID_STRATUM &&
+        ntohl(packet->reference_id) == NTP_KOD_NTS_NAK) {
+      DEBUG_LOG("NTS NAK");
+      inst->nak_response = 1;
+      return 0;
+    }
+
+    DEBUG_LOG("Missing NTS EF");
+    return 0;
+  }
+
+  if (!extract_cookies(inst, plaintext, plaintext_length))
+    return 0;
+
+  inst->ok_response = 1;
+
+  /* At this point we know the client interoperates with the server.  Allow a
+     new NTS-KE session to be started as soon as the cookies run out. */
+  inst->nke_attempts = 0;
+  inst->next_nke_attempt = 0.0;
+
+  return 1;
+}
+
+/* ================================================== */
+
+void
+NNC_ChangeAddress(NNC_Instance inst, IPAddr *address)
+{
+  save_cookies(inst);
+
+  inst->nts_address.ip_addr = *address;
+
+  reset_instance(inst);
+
+  DEBUG_LOG("NTS reset");
+}
+
+/* ================================================== */
+
+static void
+save_cookies(NNC_Instance inst)
+{
+  char buf[2 * NKE_MAX_COOKIE_LENGTH + 2], *dump_dir, *filename;
+  struct timespec now;
+  double context_time;
+  FILE *f;
+  int i;
+
+  if (inst->num_cookies < 1 || !inst->name || !UTI_IsIPReal(&inst->nts_address.ip_addr))
+    return;
+
+  dump_dir = CNF_GetNtsDumpDir();
+  if (!dump_dir)
+    return;
+
+  filename = UTI_IPToString(&inst->nts_address.ip_addr);
+
+  f = UTI_OpenFile(dump_dir, filename, ".tmp", 'w', 0600);
+  if (!f)
+    return;
+
+  SCH_GetLastEventTime(&now, NULL, NULL);
+  context_time = inst->last_nke_success - SCH_GetLastEventMonoTime();
+  context_time += UTI_TimespecToDouble(&now);
+
+  if (fprintf(f, "%s%s\n%.1f\n%s %d\n%u %d ",
+              DUMP_IDENTIFIER, inst->name, context_time,
+              UTI_IPToString(&inst->ntp_address->ip_addr), inst->ntp_address->port,
+              inst->context_id, (int)inst->context.algorithm) < 0 ||
+      !UTI_BytesToHex(inst->context.s2c.key, inst->context.s2c.length, buf, sizeof (buf)) ||
+      fprintf(f, "%s ", buf) < 0 ||
+      !UTI_BytesToHex(inst->context.c2s.key, inst->context.c2s.length, buf, sizeof (buf)) ||
+      fprintf(f, "%s\n", buf) < 0)
+    goto error;
+
+  for (i = 0; i < inst->num_cookies; i++) {
+    if (!UTI_BytesToHex(inst->cookies[i].cookie, inst->cookies[i].length, buf, sizeof (buf)) ||
+        fprintf(f, "%s\n", buf) < 0)
+      goto error;
+  }
+
+  fclose(f);
+
+  if (!UTI_RenameTempFile(dump_dir, filename, ".tmp", ".nts"))
+    ;
+  return;
+
+error:
+  DEBUG_LOG("Could not %s cookies for %s", "save", filename);
+  fclose(f);
+
+  if (!UTI_RemoveFile(dump_dir, filename, ".nts"))
+    ;
+}
+
+/* ================================================== */
+
+#define MAX_WORDS 4
+
+static void
+load_cookies(NNC_Instance inst)
+{
+  char line[2 * NKE_MAX_COOKIE_LENGTH + 2], *dump_dir, *filename, *words[MAX_WORDS];
+  unsigned int context_id;
+  int i, algorithm, port;
+  double context_time;
+  struct timespec now;
+  IPSockAddr ntp_addr;
+  FILE *f;
+
+  dump_dir = CNF_GetNtsDumpDir();
+  if (!dump_dir)
+    return;
+
+  filename = UTI_IPToString(&inst->nts_address.ip_addr);
+
+  f = UTI_OpenFile(dump_dir, filename, ".nts", 'r', 0);
+  if (!f)
+    return;
+
+  /* Don't load this file again */
+  if (!UTI_RemoveFile(dump_dir, filename, ".nts"))
+    ;
+
+  if (inst->siv)
+    SIV_DestroyInstance(inst->siv);
+  inst->siv = NULL;
+
+  if (!fgets(line, sizeof (line), f) || strcmp(line, DUMP_IDENTIFIER) != 0 ||
+      !fgets(line, sizeof (line), f) || UTI_SplitString(line, words, MAX_WORDS) != 1 ||
+        !inst->name || strcmp(words[0], inst->name) != 0 ||
+      !fgets(line, sizeof (line), f) || UTI_SplitString(line, words, MAX_WORDS) != 1 ||
+        sscanf(words[0], "%lf", &context_time) != 1 ||
+      !fgets(line, sizeof (line), f) || UTI_SplitString(line, words, MAX_WORDS) != 2 ||
+        !UTI_StringToIP(words[0], &ntp_addr.ip_addr) || sscanf(words[1], "%d", &port) != 1 ||
+      !fgets(line, sizeof (line), f) || UTI_SplitString(line, words, MAX_WORDS) != 4 ||
+        sscanf(words[0], "%u", &context_id) != 1 || sscanf(words[1], "%d", &algorithm) != 1)
+    goto error;
+
+  inst->context.algorithm = algorithm;
+  inst->context.s2c.length = UTI_HexToBytes(words[2], inst->context.s2c.key,
+                                            sizeof (inst->context.s2c.key));
+  inst->context.c2s.length = UTI_HexToBytes(words[3], inst->context.c2s.key,
+                                            sizeof (inst->context.c2s.key));
+
+  if (inst->context.s2c.length != SIV_GetKeyLength(algorithm) ||
+      inst->context.c2s.length != inst->context.s2c.length)
+    goto error;
+
+  for (i = 0; i < NTS_MAX_COOKIES && fgets(line, sizeof (line), f); i++) {
+    if (UTI_SplitString(line, words, MAX_WORDS) != 1)
+      goto error;
+
+    inst->cookies[i].length = UTI_HexToBytes(words[0], inst->cookies[i].cookie,
+                                             sizeof (inst->cookies[i].cookie));
+    if (inst->cookies[i].length == 0)
+      goto error;
+  }
+
+  inst->num_cookies = i;
+
+  ntp_addr.port = port;
+  if (!set_ntp_address(inst, &ntp_addr))
+    goto error;
+
+  SCH_GetLastEventTime(&now, NULL, NULL);
+  context_time -= UTI_TimespecToDouble(&now);
+  if (context_time > 0)
+    context_time = 0;
+  inst->last_nke_success = context_time + SCH_GetLastEventMonoTime();
+  inst->context_id = context_id;
+
+  DEBUG_LOG("Loaded %d cookies for %s", i, filename);
+  return;
+
+error:
+  DEBUG_LOG("Could not %s cookies for %s", "load", filename);
+  fclose(f);
+
+  memset(&inst->context, 0, sizeof (inst->context));
+  inst->num_cookies = 0;
+}
+
+/* ================================================== */
+
+void
+NNC_DumpData(NNC_Instance inst)
+{
+  save_cookies(inst);
+}
+
+/* ================================================== */
+
+void
+NNC_GetReport(NNC_Instance inst, RPT_AuthReport *report)
+{
+  report->key_id = inst->context_id;
+  report->key_type = inst->context.algorithm;
+  report->key_length = 8 * inst->context.s2c.length;
+  report->ke_attempts = inst->nke_attempts;
+  if (report->key_length > 0)
+    report->last_ke_ago = SCH_GetLastEventMonoTime() - inst->last_nke_success;
+  else
+    report->last_ke_ago = -1;
+  report->cookies = inst->num_cookies;
+  report->cookie_length = inst->num_cookies > 0 ? inst->cookies[inst->cookie_index].length : 0;
+  report->nak = inst->nak_response;
+}
--- a/nts_ntp_client.h
+++ b/nts_ntp_client.h
@@ -0,0 +1,51 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for client NTS-NTP authentication
+  */
+
+#ifndef GOT_NTS_NTP_CLIENT_H
+#define GOT_NTS_NTP_CLIENT_H
+
+#include "addressing.h"
+#include "ntp.h"
+#include "reports.h"
+
+typedef struct NNC_Instance_Record *NNC_Instance;
+
+extern NNC_Instance NNC_CreateInstance(IPSockAddr *nts_address, const char *name,
+                                                   const IPSockAddr *ntp_address);
+extern void NNC_DestroyInstance(NNC_Instance inst);
+extern int NNC_PrepareForAuth(NNC_Instance inst);
+extern int NNC_GenerateRequestAuth(NNC_Instance inst, NTP_Packet *packet,
+                                   NTP_PacketInfo *info);
+extern int NNC_CheckResponseAuth(NNC_Instance inst, NTP_Packet *packet,
+                                 NTP_PacketInfo *info);
+
+extern void NNC_ChangeAddress(NNC_Instance inst, IPAddr *address);
+
+extern void NNC_DumpData(NNC_Instance inst);
+
+extern void NNC_GetReport(NNC_Instance inst, RPT_AuthReport *report);
+
+#endif
--- a/nts_ntp_server.c
+++ b/nts_ntp_server.c
@@ -0,0 +1,281 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Server NTS-NTP authentication
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include "nts_ntp_server.h"
+
+#include "conf.h"
+#include "logging.h"
+#include "memory.h"
+#include "ntp.h"
+#include "ntp_ext.h"
+#include "nts_ke_server.h"
+#include "nts_ntp.h"
+#include "nts_ntp_auth.h"
+#include "siv.h"
+#include "util.h"
+
+#define SERVER_SIV AEAD_AES_SIV_CMAC_256
+
+struct NtsServer {
+  SIV_Instance siv;
+  unsigned char nonce[NTS_MIN_UNPADDED_NONCE_LENGTH];
+  NKE_Cookie cookies[NTS_MAX_COOKIES];
+  int num_cookies;
+  NTP_int64 req_tx;
+};
+
+/* The server instance handling all requests */
+struct NtsServer *server;
+
+/* ================================================== */
+
+void
+NNS_Initialise(void)
+{
+  /* Create an NTS-NTP server instance only if NTS-KE server is enabled */
+  if (!CNF_GetNtsServerCertFile() || !CNF_GetNtsServerKeyFile()) {
+    server = NULL;
+    return;
+  }
+
+  server = Malloc(sizeof (struct NtsServer));
+  server->siv = SIV_CreateInstance(SERVER_SIV);
+  if (!server->siv)
+    LOG_FATAL("Could not initialise SIV cipher");
+}
+
+/* ================================================== */
+
+void
+NNS_Finalise(void)
+{
+  if (!server)
+    return;
+
+  SIV_DestroyInstance(server->siv);
+  Free(server);
+  server = NULL;
+}
+
+/* ================================================== */
+
+int
+NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod)
+{
+  int ef_type, ef_body_length, ef_length, has_uniq_id = 0, has_auth = 0, has_cookie = 0;
+  int i, plaintext_length, parsed, requested_cookies, cookie_length = -1, auth_start = 0;
+  unsigned char plaintext[NTP_MAX_EXTENSIONS_LENGTH];
+  NKE_Context context;
+  NKE_Cookie cookie;
+  void *ef_body;
+
+  *kod = 0;
+
+  if (!server)
+    return 0;
+
+  server->num_cookies = 0;
+  server->req_tx = packet->transmit_ts;
+
+  if (info->ext_fields == 0 || info->mode != MODE_CLIENT)
+    return 0;
+
+  requested_cookies = 0;
+
+  for (parsed = NTP_HEADER_LENGTH; parsed < info->length; parsed += ef_length) {
+    if (!NEF_ParseField(packet, info->length, parsed,
+                        &ef_length, &ef_type, &ef_body, &ef_body_length))
+      /* This is not expected as the packet already passed NAU_ParsePacket() */
+      return 0;
+
+    switch (ef_type) {
+      case NTP_EF_NTS_UNIQUE_IDENTIFIER:
+        has_uniq_id = 1;
+        break;
+      case NTP_EF_NTS_COOKIE:
+        if (has_cookie || ef_body_length > sizeof (cookie.cookie)) {
+          DEBUG_LOG("Unexpected cookie/length");
+          return 0;
+        }
+        cookie.length = ef_body_length;
+        memcpy(cookie.cookie, ef_body, ef_body_length);
+        has_cookie = 1;
+        /* Fall through */
+      case NTP_EF_NTS_COOKIE_PLACEHOLDER:
+        requested_cookies++;
+
+        if (cookie_length >= 0 && cookie_length != ef_body_length) {
+          DEBUG_LOG("Invalid cookie/placeholder length");
+          return 0;
+        }
+        cookie_length = ef_body_length;
+        break;
+      case NTP_EF_NTS_AUTH_AND_EEF:
+        if (parsed + ef_length != info->length) {
+          DEBUG_LOG("Auth not last EF");
+          return 0;
+        }
+
+        auth_start = parsed;
+        has_auth = 1;
+        break;
+      default:
+        break;
+    }
+  }
+
+  if (!has_uniq_id || !has_cookie || !has_auth) {
+    DEBUG_LOG("Missing an NTS EF");
+    return 0;
+  }
+
+  if (!NKS_DecodeCookie(&cookie, &context)) {
+    *kod = NTP_KOD_NTS_NAK;
+    return 0;
+  }
+
+  if (context.algorithm != SERVER_SIV) {
+    DEBUG_LOG("Unexpected SIV");
+    return 0;
+  }
+
+  if (!SIV_SetKey(server->siv, context.c2s.key, context.c2s.length)) {
+    DEBUG_LOG("Could not set C2S key");
+    return 0;
+  }
+
+  if (!NNA_DecryptAuthEF(packet, info, server->siv, auth_start,
+                         plaintext, sizeof (plaintext), &plaintext_length)) {
+    *kod = NTP_KOD_NTS_NAK;
+    return 0;
+  }
+
+  for (parsed = 0; parsed < plaintext_length; parsed += ef_length) {
+    if (!NEF_ParseSingleField(plaintext, plaintext_length, parsed,
+                              &ef_length, &ef_type, &ef_body, &ef_body_length)) {
+      DEBUG_LOG("Could not parse encrypted EF");
+      return 0;
+    }
+
+    switch (ef_type) {
+      case NTP_EF_NTS_COOKIE_PLACEHOLDER:
+        if (cookie_length != ef_body_length) {
+          DEBUG_LOG("Invalid cookie/placeholder length");
+          return 0;
+        }
+        requested_cookies++;
+        break;
+      default:
+        break;
+    }
+  }
+
+  if (!SIV_SetKey(server->siv, context.s2c.key, context.s2c.length)) {
+    DEBUG_LOG("Could not set S2C key");
+    return 0;
+  }
+
+  /* Prepare data for NNS_GenerateResponseAuth() to minimise the time spent
+     there (when the TX timestamp is already set) */
+
+  UTI_GetRandomBytes(server->nonce, sizeof (server->nonce));
+
+  assert(sizeof (server->cookies) / sizeof (server->cookies[0]) == NTS_MAX_COOKIES);
+  for (i = 0; i < NTS_MAX_COOKIES && i < requested_cookies; i++)
+    if (!NKS_GenerateCookie(&context, &server->cookies[i]))
+      return 0;
+
+  server->num_cookies = i;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+NNS_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *req_info,
+                         NTP_Packet *response, NTP_PacketInfo *res_info,
+                         uint32_t kod)
+{
+  int i, ef_type, ef_body_length, ef_length, parsed;
+  void *ef_body;
+  unsigned char plaintext[NTP_MAX_EXTENSIONS_LENGTH];
+  int plaintext_length;
+
+  if (!server || req_info->mode != MODE_CLIENT || res_info->mode != MODE_SERVER)
+    return 0;
+
+  /* Make sure this is a response to the request from the last call
+     of NNS_CheckRequestAuth() */
+  if (UTI_CompareNtp64(&server->req_tx, &request->transmit_ts) != 0)
+    assert(0);
+
+  for (parsed = NTP_HEADER_LENGTH; parsed < req_info->length; parsed += ef_length) {
+    if (!NEF_ParseField(request, req_info->length, parsed,
+                        &ef_length, &ef_type, &ef_body, &ef_body_length))
+      /* This is not expected as the packet already passed NAU_ParsePacket() */
+      return 0;
+
+    switch (ef_type) {
+      case NTP_EF_NTS_UNIQUE_IDENTIFIER:
+        /* Copy the ID from the request */
+        if (!NEF_AddField(response, res_info, ef_type, ef_body, ef_body_length))
+          return 0;
+      default:
+        break;
+    }
+  }
+
+  /* NTS NAK response does not have any other fields */
+  if (kod)
+    return 1;
+
+  for (i = 0, plaintext_length = 0; i < server->num_cookies; i++) {
+    if (!NEF_SetField(plaintext, sizeof (plaintext), plaintext_length,
+                      NTP_EF_NTS_COOKIE, server->cookies[i].cookie,
+                      server->cookies[i].length, &ef_length))
+      return 0;
+
+    plaintext_length += ef_length;
+    assert(plaintext_length <= sizeof (plaintext));
+  }
+
+  server->num_cookies = 0;
+
+  /* Generate an authenticator field which will make the length
+     of the response equal to the length of the request */
+  if (!NNA_GenerateAuthEF(response, res_info, server->siv,
+                          server->nonce, sizeof (server->nonce),
+                          plaintext, plaintext_length,
+                          req_info->length - res_info->length))
+    return 0;
+
+  return 1;
+}
--- a/nts_ntp_server.h
+++ b/nts_ntp_server.h
@@ -0,0 +1,40 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for server NTS-NTP authentication
+  */
+
+#ifndef GOT_NTS_NTP_SERVER_H
+#define GOT_NTS_NTP_SERVER_H
+
+#include "ntp.h"
+
+extern void NNS_Initialise(void);
+extern void NNS_Finalise(void);
+
+extern int NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod);
+extern int NNS_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *req_info,
+                                    NTP_Packet *response, NTP_PacketInfo *res_info,
+                                    uint32_t kod);
+
+#endif
--- a/pktlength.c
+++ b/pktlength.c
@@ -110,16 +110,24 @@ static const struct request_length request_lengths[] = {
  REQ_LENGTH_ENTRY(smoothtime, null),           /* SMOOTHTIME */
  REQ_LENGTH_ENTRY(null, null),                 /* REFRESH */
  REQ_LENGTH_ENTRY(null, server_stats),         /* SERVER_STATS */
-  REQ_LENGTH_ENTRY(client_accesses_by_index,
-                   client_accesses_by_index),   /* CLIENT_ACCESSES_BY_INDEX2 */
+  { 0, 0 },                                     /* CLIENT_ACCESSES_BY_INDEX2 - not supported */
  REQ_LENGTH_ENTRY(local, null),                /* LOCAL2 */
  REQ_LENGTH_ENTRY(ntp_data, ntp_data),         /* NTP_DATA */
  { 0, 0 },                                     /* ADD_SERVER2 */
  { 0, 0 },                                     /* ADD_PEER2 */
-  REQ_LENGTH_ENTRY(ntp_source, null),           /* ADD_SERVER3 */
-  REQ_LENGTH_ENTRY(ntp_source, null),           /* ADD_PEER3 */
+  { 0, 0 },                                     /* ADD_SERVER3 */
+  { 0, 0 },                                     /* ADD_PEER3 */
  REQ_LENGTH_ENTRY(null, null),                 /* SHUTDOWN */
  REQ_LENGTH_ENTRY(null, null),                 /* ONOFFLINE */
+  REQ_LENGTH_ENTRY(ntp_source, null),           /* ADD_SOURCE */
+  REQ_LENGTH_ENTRY(ntp_source_name,
+                   ntp_source_name),            /* NTP_SOURCE_NAME */
+  REQ_LENGTH_ENTRY(null, null),                 /* RESET_SOURCES */
+  REQ_LENGTH_ENTRY(auth_data, auth_data),       /* AUTH_DATA */
+  REQ_LENGTH_ENTRY(client_accesses_by_index,
+                   client_accesses_by_index),   /* CLIENT_ACCESSES_BY_INDEX3 */
+  REQ_LENGTH_ENTRY(select_data, select_data),   /* SELECT_DATA */
+  REQ_LENGTH_ENTRY(null, null),                 /* RELOAD_SOURCES */
 };

 static const uint16_t reply_lengths[] = {
@@ -137,11 +145,16 @@ static const uint16_t reply_lengths[] = {
  0,                                            /* MANUAL_LIST - not supported */
  RPY_LENGTH_ENTRY(activity),                   /* ACTIVITY */
  RPY_LENGTH_ENTRY(smoothing),                  /* SMOOTHING */
-  RPY_LENGTH_ENTRY(server_stats),               /* SERVER_STATS */
-  RPY_LENGTH_ENTRY(client_accesses_by_index),   /* CLIENT_ACCESSES_BY_INDEX2 */
+  0,                                            /* SERVER_STATS - not supported */
+  0,                                            /* CLIENT_ACCESSES_BY_INDEX2 - not supported */
  RPY_LENGTH_ENTRY(ntp_data),                   /* NTP_DATA */
  RPY_LENGTH_ENTRY(manual_timestamp),           /* MANUAL_TIMESTAMP2 */
  RPY_LENGTH_ENTRY(manual_list),                /* MANUAL_LIST2 */
+  RPY_LENGTH_ENTRY(ntp_source_name),            /* NTP_SOURCE_NAME */
+  RPY_LENGTH_ENTRY(auth_data),                  /* AUTH_DATA */
+  RPY_LENGTH_ENTRY(client_accesses_by_index),   /* CLIENT_ACCESSES_BY_INDEX3 */
+  RPY_LENGTH_ENTRY(server_stats),               /* SERVER_STATS2 */
+  RPY_LENGTH_ENTRY(select_data),                /* SELECT_DATA */
 };

 /* ================================================== */
--- a/privops.c
+++ b/privops.c
@@ -33,6 +33,7 @@
 #include "nameserv.h"
 #include "logging.h"
 #include "privops.h"
+#include "socket.h"
 #include "util.h"

 #define OP_ADJUSTTIME     1024
@@ -158,7 +159,7 @@ res_fatal(PrvResponse *res, const char *fmt, ...)
 static int
 send_response(int fd, const PrvResponse *res)
 {
-  if (send(fd, res, sizeof (*res), 0) != sizeof (*res))
+  if (SCK_Send(fd, res, sizeof (*res), 0) != sizeof (*res))
    return 0;

  return 1;
@@ -170,37 +171,23 @@ send_response(int fd, const PrvResponse *res)
 static int
 receive_from_daemon(int fd, PrvRequest *req)
 {
-  struct msghdr msg;
-  struct cmsghdr *cmsg;
-  struct iovec iov;
-  char cmsgbuf[256];
+  SCK_Message *message;

-  iov.iov_base = req;
-  iov.iov_len = sizeof (*req);
-
-  msg.msg_name = NULL;
-  msg.msg_namelen = 0;
-  msg.msg_iov = &iov;
-  msg.msg_iovlen = 1;
-  msg.msg_control = (void *)cmsgbuf;
-  msg.msg_controllen = sizeof (cmsgbuf);
-  msg.msg_flags = MSG_WAITALL;
-
-  /* read the data */
-  if (recvmsg(fd, &msg, 0) != sizeof (*req))
+  message = SCK_ReceiveMessage(fd, SCK_FLAG_MSG_DESCRIPTOR);
+  if (!message || message->length != sizeof (*req))
    return 0;

+  memcpy(req, message->data, sizeof (*req));
+
  if (req->op == OP_BINDSOCKET) {
-    /* extract transferred descriptor */
-    req->data.bind_socket.sock = -1;
-    for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
-      if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS)
-        memcpy(&req->data.bind_socket.sock, CMSG_DATA(cmsg), sizeof (int));
-    }
+    req->data.bind_socket.sock = message->descriptor;

    /* return error if valid descriptor not found */
    if (req->data.bind_socket.sock < 0)
      return 0;
+  } else if (message->descriptor >= 0) {
+    SCK_CloseSocket(message->descriptor);
+    return 0;
  }

  return 1;
@@ -257,8 +244,7 @@ do_set_time(const ReqSetTime *req, PrvResponse *res)
 static void
 do_bind_socket(ReqBindSocket *req, PrvResponse *res)
 {
-  unsigned short port;
-  IPAddr ip;
+  IPSockAddr ip_saddr;
  int sock_fd;
  struct sockaddr *sa;
  socklen_t sa_len;
@@ -267,10 +253,11 @@ do_bind_socket(ReqBindSocket *req, PrvResponse *res)
  sa_len = req->sa_len;
  sock_fd = req->sock;

-  UTI_SockaddrToIPAndPort(sa, &ip, &port);
-  if (port && port != CNF_GetNTPPort() && port != CNF_GetAcquisitionPort()) {
-    close(sock_fd);
-    res_fatal(res, "Invalid port %d", port);
+  SCK_SockaddrToIPSockAddr(sa, sa_len, &ip_saddr);
+  if (ip_saddr.port != 0 && ip_saddr.port != CNF_GetNTPPort() &&
+      ip_saddr.port != CNF_GetAcquisitionPort()) {
+    SCK_CloseSocket(sock_fd);
+    res_fatal(res, "Invalid port %d", ip_saddr.port);
    return;
  }

@@ -279,7 +266,7 @@ do_bind_socket(ReqBindSocket *req, PrvResponse *res)
    res->res_errno = errno;

  /* sock is still open on daemon side, but we're done with it in the helper */
-  close(sock_fd);
+  SCK_CloseSocket(sock_fd);
 }
 #endif

@@ -373,7 +360,7 @@ helper_main(int fd)
    send_response(fd, &res);
  }

-  close(fd);
+  SCK_CloseSocket(fd);
  exit(0);
 }

@@ -386,7 +373,7 @@ receive_response(PrvResponse *res)
 {
  int resp_len;

-  resp_len = recv(helper_fd, res, sizeof (*res), 0);
+  resp_len = SCK_Receive(helper_fd, res, sizeof (*res), 0);
  if (resp_len < 0)
    LOG_FATAL("Could not read from helper : %s", strerror(errno));
  if (resp_len != sizeof (*res))
@@ -409,41 +396,22 @@ receive_response(PrvResponse *res)
 static void
 send_request(PrvRequest *req)
 {
-  struct msghdr msg;
-  struct iovec iov;
-  char cmsgbuf[256];
+  SCK_Message message;
+  int flags;

-  iov.iov_base = req;
-  iov.iov_len = sizeof (*req);
+  SCK_InitMessage(&message, SCK_ADDR_UNSPEC);

-  msg.msg_name = NULL;
-  msg.msg_namelen = 0;
-  msg.msg_iov = &iov;
-  msg.msg_iovlen = 1;
-  msg.msg_control = NULL;
-  msg.msg_controllen = 0;
-  msg.msg_flags = 0;
+  message.data = req;
+  message.length = sizeof (*req);
+  flags = 0;

  if (req->op == OP_BINDSOCKET) {
    /* send file descriptor as a control message */
-    struct cmsghdr *cmsg;
-    int *ptr_send_fd;
-
-    msg.msg_control = cmsgbuf;
-    msg.msg_controllen = CMSG_SPACE(sizeof (int));
-
-    cmsg = CMSG_FIRSTHDR(&msg);
-    memset(cmsg, 0, CMSG_SPACE(sizeof (int)));
-
-    cmsg->cmsg_level = SOL_SOCKET;
-    cmsg->cmsg_type = SCM_RIGHTS;
-    cmsg->cmsg_len = CMSG_LEN(sizeof (int));
-
-    ptr_send_fd = (int *)CMSG_DATA(cmsg);
-    *ptr_send_fd = req->data.bind_socket.sock;
+    message.descriptor = req->data.bind_socket.sock;
+    flags |= SCK_FLAG_MSG_DESCRIPTOR;
  }

-  if (sendmsg(helper_fd, &msg, 0) < 0) {
+  if (!SCK_SendMessage(helper_fd, &message, flags)) {
    /* don't try to send another request from exit() */
    helper_fd = -1;
    LOG_FATAL("Could not send to helper : %s", strerror(errno));
@@ -573,13 +541,13 @@ PRV_SetTime(const struct timeval *tp, const struct timezone *tzp)
 int
 PRV_BindSocket(int sock, struct sockaddr *address, socklen_t address_len)
 {
+  IPSockAddr ip_saddr;
  PrvRequest req;
  PrvResponse res;
-  IPAddr ip;
-  unsigned short port;

-  UTI_SockaddrToIPAndPort(address, &ip, &port);
-  if (port && port != CNF_GetNTPPort() && port != CNF_GetAcquisitionPort())
+  SCK_SockaddrToIPSockAddr(address, address_len, &ip_saddr);
+  if (ip_saddr.port != 0 && ip_saddr.port != CNF_GetNTPPort() &&
+      ip_saddr.port != CNF_GetAcquisitionPort())
    assert(0);

  if (!have_helper())
@@ -589,6 +557,7 @@ PRV_BindSocket(int sock, struct sockaddr *address, socklen_t address_len)
  req.op = OP_BINDSOCKET;
  req.data.bind_socket.sock = sock;
  req.data.bind_socket.sa_len = address_len;
+  assert(address_len <= sizeof (req.data.bind_socket.sa));
  memcpy(&req.data.bind_socket.sa.u, address, address_len);

  submit_request(&req, &res);
@@ -616,7 +585,6 @@ PRV_Name2IPAddress(const char *name, IPAddr *ip_addrs, int max_addrs)
  req.op = OP_NAME2IPADDRESS;
  if (snprintf(req.data.name_to_ipaddress.name, sizeof (req.data.name_to_ipaddress.name),
               "%s", name) >= sizeof (req.data.name_to_ipaddress.name)) {
-    DEBUG_LOG("Name too long");
    return DNS_Failure;
  }

@@ -670,20 +638,14 @@ void
 PRV_StartHelper(void)
 {
  pid_t pid;
-  int fd, sock_pair[2];
+  int fd, sock_fd1, sock_fd2;

  if (have_helper())
    LOG_FATAL("Helper already running");

-  if (
-#ifdef SOCK_SEQPACKET
-      socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sock_pair) &&
-#endif
-      socketpair(AF_UNIX, SOCK_DGRAM, 0, sock_pair))
-    LOG_FATAL("socketpair() failed : %s", strerror(errno));
-
-  UTI_FdSetCloexec(sock_pair[0]);
-  UTI_FdSetCloexec(sock_pair[1]);
+  sock_fd1 = SCK_OpenUnixSocketPair(SCK_FLAG_BLOCK, &sock_fd2);
+  if (sock_fd1 < 0)
+    LOG_FATAL("Could not open socket pair");

  pid = fork();
  if (pid < 0)
@@ -691,23 +653,24 @@ PRV_StartHelper(void)

  if (pid == 0) {
    /* child process */
-    close(sock_pair[0]);
+    SCK_CloseSocket(sock_fd1);

-    /* close other descriptors inherited from the parent process */
-    for (fd = 0; fd < 1024; fd++) {
-      if (fd != sock_pair[1])
+    /* close other descriptors inherited from the parent process, except
+       stdin, stdout, and stderr */
+    for (fd = STDERR_FILENO + 1; fd < 1024; fd++) {
+      if (fd != sock_fd2)
        close(fd);
    }

    /* ignore signals, the process will exit on OP_QUIT request */
    UTI_SetQuitSignalsHandler(SIG_IGN, 1);

-    helper_main(sock_pair[1]);
+    helper_main(sock_fd2);

  } else {
    /* parent process */
-    close(sock_pair[1]);
-    helper_fd = sock_pair[0];
+    SCK_CloseSocket(sock_fd2);
+    helper_fd = sock_fd1;
    helper_pid = pid;

    /* stop the helper even when not exiting cleanly from the main function */
--- a/refclock.c
+++ b/refclock.c
@@ -181,7 +181,7 @@ RCL_AddRefclock(RefclockParameters *params)
    LOG_FATAL("refclock tai option requires leapsectz");

  inst->data = NULL;
-  inst->driver_parameter = params->driver_parameter;
+  inst->driver_parameter = Strdup(params->driver_parameter);
  inst->driver_parameter_length = 0;
  inst->driver_poll = params->driver_poll;
  inst->poll = params->poll;
@@ -253,15 +253,14 @@ RCL_AddRefclock(RefclockParameters *params)
  inst->filter = SPF_CreateInstance(MIN(params->filter_length, 4), params->filter_length,
                                    params->max_dispersion, 0.6);

-  inst->source = SRC_CreateNewInstance(inst->ref_id, SRC_REFCLOCK, params->sel_options, NULL,
-                                       params->min_samples, params->max_samples, 0.0, 0.0);
+  inst->source = SRC_CreateNewInstance(inst->ref_id, SRC_REFCLOCK, 0, params->sel_options,
+                                       NULL, params->min_samples, params->max_samples,
+                                       0.0, 0.0);

  DEBUG_LOG("refclock %s refid=%s poll=%d dpoll=%d filter=%d",
      params->driver_name, UTI_RefidToString(inst->ref_id),
      inst->poll, inst->driver_poll, params->filter_length);

-  Free(params->driver_name);
-
  return 1;
 }

@@ -415,7 +414,6 @@ accumulate_sample(RCL_Instance instance, struct timespec *sample_time, double of
  sample.root_delay = instance->delay;
  sample.peer_dispersion = dispersion;
  sample.root_dispersion = dispersion;
-  sample.leap = instance->leap_status;

  /* Handle special case when PPS is used with the local reference */
  if (instance->pps_active && instance->lock_ref == -1)
@@ -704,6 +702,7 @@ poll_timeout(void *arg)

    if (SPF_GetFilteredSample(inst->filter, &sample)) {
      SRC_UpdateReachability(inst->source, 1);
+      SRC_SetLeapStatus(inst->source, inst->leap_status);
      SRC_AccumulateSample(inst->source, &sample);
      SRC_SelectSource(inst->source);

--- a/refclock_sock.c
+++ b/refclock_sock.c
@@ -33,6 +33,7 @@
 #include "logging.h"
 #include "util.h"
 #include "sched.h"
+#include "socket.h"

 #define SOCK_MAGIC 0x534f434b

@@ -97,7 +98,6 @@ static void read_sample(int sockfd, int event, void *anything)

 static int sock_initialise(RCL_Instance instance)
 {
-  struct sockaddr_un s;
  int sockfd;
  char *path;

@@ -105,25 +105,9 @@ static int sock_initialise(RCL_Instance instance)

  path = RCL_GetDriverParameter(instance);
 
-  s.sun_family = AF_UNIX;
-  if (snprintf(s.sun_path, sizeof (s.sun_path), "%s", path) >= sizeof (s.sun_path)) {
-    LOG_FATAL("Path %s too long", path);
-    return 0;
-  }
-
-  sockfd = socket(AF_UNIX, SOCK_DGRAM, 0);
-  if (sockfd < 0) {
-    LOG_FATAL("socket() failed");
-    return 0;
-  }
-
-  UTI_FdSetCloexec(sockfd);
-
-  unlink(path);
-  if (bind(sockfd, (struct sockaddr *)&s, sizeof (s)) < 0) {
-    LOG_FATAL("bind(%s) failed : %s", path, strerror(errno));
-    return 0;
-  }
+  sockfd = SCK_OpenUnixDatagramSocket(NULL, path, 0);
+  if (sockfd < 0)
+    LOG_FATAL("Could not open socket %s", path);

  RCL_SetDriverData(instance, (void *)(long)sockfd);
  SCH_AddFileHandler(sockfd, SCH_FILE_INPUT, read_sample, instance);
@@ -136,7 +120,8 @@ static void sock_finalise(RCL_Instance instance)

  sockfd = (long)RCL_GetDriverData(instance);
  SCH_RemoveFileHandler(sockfd);
-  close(sockfd);
+  SCK_RemoveSocket(sockfd);
+  SCK_CloseSocket(sockfd);
 }

 RefclockDriver RCL_SOCK_driver = {
--- a/reference.c
+++ b/reference.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2009-2018
+ * Copyright (C) Miroslav Lichvar  2009-2018, 2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -42,11 +42,18 @@
 /* The minimum allowed skew */
 #define MIN_SKEW 1.0e-12

+/* The update interval of the reference in the local reference mode */
+#define LOCAL_REF_UPDATE_INTERVAL 64.0
+
+/* Interval between updates of the drift file */
+#define MAX_DRIFTFILE_AGE 3600.0
+
 static int are_we_synchronised;
 static int enable_local_stratum;
 static int local_stratum;
 static int local_orphan;
 static double local_distance;
+static struct timespec local_ref_time;
 static NTP_Leap our_leap_status;
 static int our_leap_sec;
 static int our_tai_offset;
@@ -58,6 +65,8 @@ static double our_skew;
 static double our_residual_freq;
 static double our_root_delay;
 static double our_root_dispersion;
+static double our_offset_sd;
+static double our_frequency_sd;

 static double max_update_skew;

@@ -103,6 +112,9 @@ static void update_drift_file(double, double);
 /* Leap second handling mode */
 static REF_LeapMode leap_mode;

+/* Time of UTC midnight of the upcoming or previous leap second */
+static time_t leap_when;
+
 /* Flag indicating the clock was recently corrected for leap second and it may
   not have correct time yet (missing 23:59:60 in the UTC time scale) */
 static int leap_in_progress;
@@ -134,8 +146,8 @@ static struct fb_drift *fb_drifts = NULL;
 static int next_fb_drift;
 static SCH_TimeoutID fb_drift_timeout_id;

-/* Timestamp of last reference update */
-static struct timespec last_ref_update;
+/* Monotonic timestamp of the last reference update */
+static double last_ref_update;
 static double last_ref_update_interval;

 /* ================================================== */
@@ -160,9 +172,8 @@ handle_slew(struct timespec *raw,
    UTI_AdjustTimespec(&our_ref_time, cooked, &our_ref_time, &delta, dfreq, doffset);

  if (change_type == LCL_ChangeUnknownStep) {
-    UTI_ZeroTimespec(&last_ref_update);
-  } else if (last_ref_update.tv_sec) {
-    UTI_AdjustTimespec(&last_ref_update, cooked, &last_ref_update, &delta, dfreq, doffset);
+    last_ref_update = 0.0;
+    REF_SetUnsynchronised();
  }

  /* When the clock was stepped, check if that doesn't change our leap status
@@ -194,12 +205,14 @@ REF_Initialise(void)
  our_frequency_ppm = 0.0;
  our_skew = 1.0; /* i.e. rather bad */
  our_residual_freq = 0.0;
+  our_frequency_sd = 0.0;
+  our_offset_sd = 0.0;
  drift_file_age = 0.0;

  /* Now see if we can get the drift file opened */
  drift_file = CNF_GetDriftFile();
  if (drift_file) {
-    in = fopen(drift_file, "r");
+    in = UTI_OpenFile(NULL, drift_file, NULL, 'r', 0);
    if (in) {
      if (fscanf(in, "%lf%lf", &file_freq_ppm, &file_skew_ppm) == 2) {
        /* We have read valid data */
@@ -234,7 +247,9 @@ REF_Initialise(void)
  correction_time_ratio = CNF_GetCorrectionTimeRatio();

  enable_local_stratum = CNF_AllowLocalReference(&local_stratum, &local_orphan, &local_distance);
+  UTI_ZeroTimespec(&local_ref_time);

+  leap_when = 0;
  leap_timeout_id = 0;
  leap_in_progress = 0;
  leap_mode = CNF_GetLeapSecMode();
@@ -269,7 +284,7 @@ REF_Initialise(void)
  }

  UTI_ZeroTimespec(&our_ref_time);
-  UTI_ZeroTimespec(&last_ref_update);
+  last_ref_update = 0.0;
  last_ref_update_interval = 0.0;

  LCL_AddParameterChangeHandler(handle_slew, NULL);
@@ -289,6 +304,8 @@ REF_Finalise(void)
    update_drift_file(LCL_ReadAbsoluteFrequency(), our_skew);
  }

+  LCL_RemoveParameterChangeHandler(handle_slew, NULL);
+
  Free(fb_drifts);

  initialised = 0;
@@ -331,61 +348,20 @@ REF_GetLeapMode(void)
 static void
 update_drift_file(double freq_ppm, double skew)
 {
-  struct stat buf;
-  char *temp_drift_file;
  FILE *out;
-  int r1, r2;

  /* Create a temporary file with a '.tmp' extension. */
-
-  temp_drift_file = (char*) Malloc(strlen(drift_file)+8);
-
-  if(!temp_drift_file) {
+  out = UTI_OpenFile(NULL, drift_file, ".tmp", 'w', 0644);
+  if (!out)
    return;
-  }
-
-  strcpy(temp_drift_file,drift_file);
-  strcat(temp_drift_file,".tmp");
-
-  out = fopen(temp_drift_file, "w");
-  if (!out) {
-    Free(temp_drift_file);
-    LOG(LOGS_WARN, "Could not open temporary driftfile %s.tmp for writing",
-        drift_file);
-    return;
-  }

  /* Write the frequency and skew parameters in ppm */
-  r1 = fprintf(out, "%20.6f %20.6f\n", freq_ppm, 1.0e6 * skew);
-  r2 = fclose(out);
-  if (r1 < 0 || r2) {
-    Free(temp_drift_file);
-    LOG(LOGS_WARN, "Could not write to temporary driftfile %s.tmp",
-        drift_file);
-    return;
-  }
+  fprintf(out, "%20.6f %20.6f\n", freq_ppm, 1.0e6 * skew);
+  fclose(out);

-  /* Clone the file attributes from the existing file if there is one. */
-
-  if (!stat(drift_file,&buf)) {
-    if (chown(temp_drift_file,buf.st_uid,buf.st_gid) ||
-        chmod(temp_drift_file,buf.st_mode & 0777)) {
-      LOG(LOGS_WARN, "Could not change ownership or permissions of temporary driftfile %s.tmp",
-          drift_file);
-    }
-  }
-
-  /* Rename the temporary file to the correct location (see rename(2) for details). */
-
-  if (rename(temp_drift_file,drift_file)) {
-    unlink(temp_drift_file);
-    Free(temp_drift_file);
-    LOG(LOGS_WARN, "Could not replace old driftfile %s with new one %s.tmp",
-        drift_file,drift_file);
-    return;
-  }
-
-  Free(temp_drift_file);
+  /* Rename the temporary file to the correct location */
+  if (!UTI_RenameTempFile(NULL, drift_file, ".tmp", NULL))
+    ;
 }

 /* ================================================== */
@@ -451,16 +427,16 @@ fb_drift_timeout(void *arg)
 /* ================================================== */

 static void
-schedule_fb_drift(struct timespec *now)
+schedule_fb_drift(void)
 {
  int i, c, secs;
-  double unsynchronised;
-  struct timespec when;
+  double unsynchronised, now;

  if (fb_drift_timeout_id)
    return; /* already scheduled */

-  unsynchronised = UTI_DiffTimespecsToDouble(now, &last_ref_update);
+  now = SCH_GetLastEventMonoTime();
+  unsynchronised = now - last_ref_update;

  for (c = secs = 0, i = fb_drift_min; i <= fb_drift_max; i++) {
    secs = 1 << i;
@@ -482,8 +458,7 @@ schedule_fb_drift(struct timespec *now)

  if (i <= fb_drift_max) {
    next_fb_drift = i;
-    UTI_AddDoubleToTimespec(now, secs - unsynchronised, &when);
-    fb_drift_timeout_id = SCH_AddTimeout(&when, fb_drift_timeout, NULL);
+    fb_drift_timeout_id = SCH_AddTimeoutByDelay(secs - unsynchronised, fb_drift_timeout, NULL);
    DEBUG_LOG("Fallback drift %d scheduled", i);
  }
 }
@@ -516,8 +491,7 @@ maybe_log_offset(double offset, time_t now)
  abs_offset = fabs(offset);

  if (abs_offset > log_change_threshold) {
-    LOG(LOGS_WARN, "System clock wrong by %.6f seconds, adjustment started",
-        -offset);
+    LOG(LOGS_WARN, "System clock wrong by %.6f seconds", -offset);
  }

  if (do_mail_change &&
@@ -583,8 +557,7 @@ is_offset_ok(double offset)
    return 1;
  }

-  offset = fabs(offset);
-  if (offset > max_offset) {
+  if (fabs(offset) > max_offset) {
    LOG(LOGS_WARN, 
        "Adjustment of %.3f seconds exceeds the allowed maximum of %.3f seconds (%s) ",
        -offset, max_offset, !max_offset_ignore ? "exiting" : "ignored");
@@ -751,10 +724,12 @@ set_leap_timeout(time_t now)
  if (!our_leap_sec)
    return;

+  leap_when = (now / (24 * 3600) + 1) * (24 * 3600);
+
  /* Insert leap second at 0:00:00 UTC, delete at 23:59:59 UTC.  If the clock
     will be corrected by the system, timeout slightly sooner to be sure it
     will happen before the system correction. */
-  when.tv_sec = (now / (24 * 3600) + 1) * (24 * 3600);
+  when.tv_sec = leap_when;
  when.tv_nsec = 0;
  if (our_leap_sec < 0)
    when.tv_sec--;
@@ -798,7 +773,7 @@ update_leap_status(NTP_Leap leap, time_t now, int reset)
  }
  
  if ((leap_sec != our_leap_sec || tai_offset != our_tai_offset)
-      && !REF_IsLeapSecondClose()) {
+      && !REF_IsLeapSecondClose(NULL, 0.0)) {
    our_leap_sec = leap_sec;
    our_tai_offset = tai_offset;

@@ -837,6 +812,20 @@ get_root_dispersion(struct timespec *ts)

 /* ================================================== */

+static void
+update_sync_status(struct timespec *now)
+{
+  double elapsed;
+
+  elapsed = fabs(UTI_DiffTimespecsToDouble(now, &our_ref_time));
+
+  LCL_SetSyncStatus(are_we_synchronised,
+                    our_offset_sd + elapsed * our_frequency_sd,
+                    our_root_delay / 2.0 + get_root_dispersion(now));
+}
+
+/* ================================================== */
+
 static void
 write_log(struct timespec *now, int combined_sources, double freq,
          double offset, double offset_sd, double uncorrected_offset,
@@ -959,6 +948,18 @@ get_clock_estimates(int manual,

 /* ================================================== */

+static void
+fuzz_ref_time(struct timespec *ts)
+{
+  uint32_t rnd;
+
+  /* Add a random value from interval [-1.0, 0.0] */
+  UTI_GetRandomBytes(&rnd, sizeof (rnd));
+  UTI_AddDoubleToTimespec(ts, -(double)rnd / (uint32_t)-1, ts);
+}
+
+/* ================================================== */
+
 void
 REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
                 uint32_t ref_id, IPAddr *ref_ip, struct timespec *ref_time,
@@ -968,9 +969,8 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
 {
  double uncorrected_offset, accumulate_offset, step_offset;
  double residual_frequency, local_abs_frequency;
-  double elapsed, update_interval, correction_rate, orig_root_distance;
+  double elapsed, mono_now, update_interval, correction_rate, orig_root_distance;
  struct timespec now, raw_now;
-  NTP_int64 ref_fuzz;
  int manual;

  assert(initialised);
@@ -983,17 +983,16 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,

  manual = leap == LEAP_Unsynchronised;

+  mono_now = SCH_GetLastEventMonoTime();
  LCL_ReadRawTime(&raw_now);
  LCL_GetOffsetCorrection(&raw_now, &uncorrected_offset, NULL);
  UTI_AddDoubleToTimespec(&raw_now, uncorrected_offset, &now);

  elapsed = UTI_DiffTimespecsToDouble(&now, ref_time);
  offset += elapsed * frequency;
-  offset_sd += elapsed * frequency_sd;

-  if (last_ref_update.tv_sec) {
-    update_interval = UTI_DiffTimespecsToDouble(&now, &last_ref_update);
-    update_interval = MAX(update_interval, 0.0);
+  if (last_ref_update != 0.0) {
+    update_interval = mono_now - last_ref_update;
  } else {
    update_interval = 0.0;
  }
@@ -1019,7 +1018,9 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
  our_residual_freq = residual_frequency;
  our_root_delay = root_delay;
  our_root_dispersion = root_dispersion;
-  last_ref_update = now;
+  our_frequency_sd = frequency_sd;
+  our_offset_sd = offset_sd;
+  last_ref_update = mono_now;
  last_ref_update_interval = update_interval;
  last_offset = offset;

@@ -1051,7 +1052,6 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
  /* Adjust the clock */
  LCL_AccumulateFrequencyAndOffset(frequency, accumulate_offset, correction_rate);
    
-  update_leap_status(leap, raw_now.tv_sec, 0);
  maybe_log_offset(offset, raw_now.tv_sec);

  if (step_offset != 0.0) {
@@ -1059,17 +1059,13 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
      LOG(LOGS_WARN, "System clock was stepped by %.6f seconds", -step_offset);
  }

-  LCL_SetSyncStatus(are_we_synchronised, offset_sd,
-                    root_delay / 2.0 + get_root_dispersion(&now));
+  update_leap_status(leap, raw_now.tv_sec, 0);
+  update_sync_status(&now);

  /* Add a random error of up to one second to the reference time to make it
     less useful when disclosed to NTP and cmdmon clients for estimating
     receive timestamps in the interleaved symmetric NTP mode */
-  UTI_GetNtp64Fuzz(&ref_fuzz, 0);
-  UTI_TimespecToNtp64(&our_ref_time, &ref_fuzz, &ref_fuzz);
-  UTI_Ntp64ToTimespec(&ref_fuzz, &our_ref_time);
-  if (UTI_CompareTimespecs(&our_ref_time, ref_time) >= 0)
-    our_ref_time.tv_sec--;
+  fuzz_ref_time(&our_ref_time);

  local_abs_frequency = LCL_ReadAbsoluteFrequency();

@@ -1079,7 +1075,7 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
  if (drift_file) {
    /* Update drift file at most once per hour */
    drift_file_age += update_interval;
-    if (drift_file_age < 0.0 || drift_file_age > 3600.0) {
+    if (drift_file_age >= MAX_DRIFTFILE_AGE) {
      update_drift_file(local_abs_frequency, our_skew);
      drift_file_age = 0.0;
    }
@@ -1088,7 +1084,7 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
  /* Update fallback drifts */
  if (fb_drifts && are_we_synchronised) {
    update_fb_drifts(local_abs_frequency, update_interval);
-    schedule_fb_drift(&now);
+    schedule_fb_drift();
  }

  /* Update the moving average of squares of offset, quickly on start */
@@ -1141,7 +1137,7 @@ REF_SetUnsynchronised(void)
  UTI_AddDoubleToTimespec(&now_raw, uncorrected_offset, &now);

  if (fb_drifts) {
-    schedule_fb_drift(&now);
+    schedule_fb_drift();
  }

  update_leap_status(LEAP_Unsynchronised, 0, 0);
@@ -1158,6 +1154,25 @@ REF_SetUnsynchronised(void)

 /* ================================================== */

+void
+REF_UpdateLeapStatus(NTP_Leap leap)
+{
+  struct timespec raw_now, now;
+
+  /* Wait for a full reference update if not already synchronised */
+  if (!are_we_synchronised)
+    return;
+
+  SCH_GetLastEventTime(&now, NULL, &raw_now);
+
+  update_leap_status(leap, raw_now.tv_sec, 0);
+
+  /* Update also the synchronisation status */
+  update_sync_status(&now);
+}
+
+/* ================================================== */
+
 void
 REF_GetReferenceParams
 (
@@ -1171,7 +1186,7 @@ REF_GetReferenceParams
 double *root_dispersion
 )
 {
-  double dispersion;
+  double dispersion, delta;

  assert(initialised);

@@ -1203,13 +1218,17 @@ REF_GetReferenceParams

    *stratum = local_stratum;
    *ref_id = NTP_REFID_LOCAL;
-    /* Make the reference time be now less a second - this will
-       scarcely affect the client, but will ensure that the transmit
-       timestamp cannot come before this (which would cause test 7 to
-       fail in the client's read routine) if the local system clock's
-       read routine is broken in any way. */
-    *ref_time = *local_time;
-    --ref_time->tv_sec;
+
+    /* Keep the reference timestamp up to date.  Adjust the timestamp to make
+       sure that the transmit timestamp cannot come before this (which might
+       fail a test of an NTP client). */
+    delta = UTI_DiffTimespecsToDouble(local_time, &local_ref_time);
+    if (delta > LOCAL_REF_UPDATE_INTERVAL || delta < 1.0) {
+      UTI_AddDoubleToTimespec(local_time, -1.0, &local_ref_time);
+      fuzz_ref_time(&local_ref_time);
+    }
+
+    *ref_time = local_ref_time;

    /* Not much else we can do for leap second bits - maybe need to
       have a way for the administrator to feed leap bits in */
@@ -1311,22 +1330,24 @@ REF_DisableLocal(void)

 #define LEAP_SECOND_CLOSE 5

-int REF_IsLeapSecondClose(void)
+static int
+is_leap_close(time_t t)
+{
+  return t >= leap_when - LEAP_SECOND_CLOSE && t < leap_when + LEAP_SECOND_CLOSE;
+}
+
+/* ================================================== */
+
+int REF_IsLeapSecondClose(struct timespec *ts, double offset)
 {
  struct timespec now, now_raw;
-  time_t t;
-
-  if (!our_leap_sec)
-    return 0;

  SCH_GetLastEventTime(&now, NULL, &now_raw);

-  t = now.tv_sec > 0 ? now.tv_sec : -now.tv_sec;
-  if ((t + LEAP_SECOND_CLOSE) % (24 * 3600) < 2 * LEAP_SECOND_CLOSE)
+  if (is_leap_close(now.tv_sec) || is_leap_close(now_raw.tv_sec))
    return 1;

-  t = now_raw.tv_sec > 0 ? now_raw.tv_sec : -now_raw.tv_sec;
-  if ((t + LEAP_SECOND_CLOSE) % (24 * 3600) < 2 * LEAP_SECOND_CLOSE)
+  if (ts && (is_leap_close(ts->tv_sec) || is_leap_close(ts->tv_sec + offset)))
    return 1;

  return 0;
--- a/reference.h
+++ b/reference.h
@@ -162,6 +162,9 @@ extern void REF_SetManualReference
 extern void
 REF_SetUnsynchronised(void);

+/* Announce a leap second before the full reference update */
+extern void REF_UpdateLeapStatus(NTP_Leap leap);
+
 /* Return the current stratum of this host or 16 if the host is not
   synchronised */
 extern int REF_GetOurStratum(void);
@@ -181,9 +184,9 @@ extern void REF_ModifyMakestep(int limit, double threshold);
 extern void REF_EnableLocal(int stratum, double distance, int orphan);
 extern void REF_DisableLocal(void);

-/* Check if current raw or cooked time is close to a leap second
-   and is better to discard any measurements */
-extern int REF_IsLeapSecondClose(void);
+/* Check if either of the current raw and cooked time, and optionally a
+   provided timestamp with an offset, is close to a leap second */
+extern int REF_IsLeapSecondClose(struct timespec *ts, double offset);

 /* Return TAI-UTC offset corresponding to a time in UTC if available */
 extern int REF_GetTaiOffset(struct timespec *ts);
--- a/reports.h
+++ b/reports.h
@@ -36,8 +36,14 @@ typedef struct {
  int stratum;
  int poll;
  enum {RPT_NTP_CLIENT, RPT_NTP_PEER, RPT_LOCAL_REFERENCE} mode;
-  enum {RPT_SYNC, RPT_UNREACH, RPT_FALSETICKER, RPT_JITTERY, RPT_CANDIDATE, RPT_OUTLIER} state;
-  int sel_options;
+  enum {
+    RPT_NONSELECTABLE,
+    RPT_FALSETICKER,
+    RPT_JITTERY,
+    RPT_SELECTABLE,
+    RPT_UNSELECTED,
+    RPT_SELECTED,
+  } state;

  int reachability;
  unsigned long latest_meas_ago; /* seconds */
@@ -78,8 +84,8 @@ typedef struct {

 typedef struct {
  struct timespec ref_time;
-  unsigned short n_samples;
-  unsigned short n_runs;
+  unsigned long n_samples;
+  unsigned long n_runs;
  unsigned long span_seconds;
  double rtc_seconds_fast;
  double rtc_gain_rate_ppm;
@@ -88,22 +94,29 @@ typedef struct {
 typedef struct {
  IPAddr ip_addr;
  uint32_t ntp_hits;
+  uint32_t nke_hits;
  uint32_t cmd_hits;
  uint16_t ntp_drops;
+  uint16_t nke_drops;
  uint16_t cmd_drops;
  int8_t ntp_interval;
+  int8_t nke_interval;
  int8_t cmd_interval;
  int8_t ntp_timeout_interval;
  uint32_t last_ntp_hit_ago;
+  uint32_t last_nke_hit_ago;
  uint32_t last_cmd_hit_ago;
 } RPT_ClientAccessByIndex_Report;

 typedef struct {
  uint32_t ntp_hits;
+  uint32_t nke_hits;
  uint32_t cmd_hits;
  uint32_t ntp_drops;
+  uint32_t nke_drops;
  uint32_t cmd_drops;
  uint32_t log_drops;
+  uint32_t ntp_auth_hits;
 } RPT_ServerStatsReport;

 typedef struct {
@@ -160,4 +173,30 @@ typedef struct {
  uint32_t total_valid_count;
 } RPT_NTPReport;

+typedef struct {
+  NTP_AuthMode mode;
+  uint32_t key_id;
+  int key_type;
+  int key_length;
+  int ke_attempts;
+  uint32_t last_ke_ago;
+  int cookies;
+  int cookie_length;
+  int nak;
+} RPT_AuthReport;
+
+typedef struct {
+  uint32_t ref_id;
+  IPAddr ip_addr;
+  char state_char;
+  int authentication;
+  NTP_Leap leap;
+  int conf_options;
+  int eff_options;
+  uint32_t last_sample_ago;
+  double score;
+  double lo_limit;
+  double hi_limit;
+} RPT_SelectReport;
+
 #endif /* GOT_REPORTS_H */
--- a/rtc.c
+++ b/rtc.c
@@ -160,7 +160,7 @@ RTC_Initialise(int initial_set)
 void
 RTC_Finalise(void)
 {
-  if (driver.fini) {
+  if (driver_initialised) {
    (driver.fini)();
  }
 }
--- a/rtc_linux.c
+++ b/rtc_linux.c
@@ -390,12 +390,9 @@ read_hwclock_file(const char *hwclock_file)
  if (!hwclock_file || !hwclock_file[0])
    return;

-  in = fopen(hwclock_file, "r");
-  if (!in) {
-    LOG(LOGS_WARN, "Could not open %s : %s",
-        hwclock_file, strerror(errno));
+  in = UTI_OpenFile(NULL, hwclock_file, NULL, 'r', 0);
+  if (!in)
    return;
-  }

  /* Read third line from the file. */
  for (i = 0; i < 3; i++) {
@@ -445,7 +442,8 @@ read_coefs_from_file(void)

    tried_to_load_coefs = 1;

-    if (coefs_file_name && (in = fopen(coefs_file_name, "r"))) {
+    if (coefs_file_name &&
+        (in = UTI_OpenFile(NULL, coefs_file_name, NULL, 'r', 0))) {
      if (fscanf(in, "%d%ld%lf%lf",
                 &valid_coefs_from_file,
                 &file_ref_time,
@@ -466,67 +464,40 @@ read_coefs_from_file(void)
 static int
 write_coefs_to_file(int valid,time_t ref_time,double offset,double rate)
 {
-  struct stat buf;
-  char *temp_coefs_file_name;
  FILE *out;
-  int r1, r2;

  /* Create a temporary file with a '.tmp' extension. */
-
-  temp_coefs_file_name = (char*) Malloc(strlen(coefs_file_name)+8);
-
-  if(!temp_coefs_file_name) {
+  out = UTI_OpenFile(NULL, coefs_file_name, ".tmp", 'w', 0644);
+  if (!out)
    return RTC_ST_BADFILE;
-  }
-
-  strcpy(temp_coefs_file_name,coefs_file_name);
-  strcat(temp_coefs_file_name,".tmp");
-
-  out = fopen(temp_coefs_file_name, "w");
-  if (!out) {
-    Free(temp_coefs_file_name);
-    LOG(LOGS_WARN, "Could not open temporary RTC file %s.tmp for writing",
-        coefs_file_name);
-    return RTC_ST_BADFILE;
-  }

  /* Gain rate is written out in ppm */
-  r1 = fprintf(out, "%1d %ld %.6f %.3f\n",
-               valid, ref_time, offset, 1.0e6 * rate);
-  r2 = fclose(out);
-  if (r1 < 0 || r2) {
-    Free(temp_coefs_file_name);
-    LOG(LOGS_WARN, "Could not write to temporary RTC file %s.tmp",
-        coefs_file_name);
+  fprintf(out, "%1d %ld %.6f %.3f\n", valid, ref_time, offset, 1.0e6 * rate);
+  fclose(out);
+
+  /* Rename the temporary file to the correct location */
+  if (!UTI_RenameTempFile(NULL, coefs_file_name, ".tmp", NULL))
    return RTC_ST_BADFILE;
-  }
-
-  /* Clone the file attributes from the existing file if there is one. */
-
-  if (!stat(coefs_file_name,&buf)) {
-    if (chown(temp_coefs_file_name,buf.st_uid,buf.st_gid) ||
-        chmod(temp_coefs_file_name,buf.st_mode & 0777)) {
-      LOG(LOGS_WARN,
-          "Could not change ownership or permissions of temporary RTC file %s.tmp",
-          coefs_file_name);
-    }
-  }
-
-  /* Rename the temporary file to the correct location (see rename(2) for details). */
-
-  if (rename(temp_coefs_file_name,coefs_file_name)) {
-    unlink(temp_coefs_file_name);
-    Free(temp_coefs_file_name);
-    LOG(LOGS_WARN, "Could not replace old RTC file %s.tmp with new one %s",
-        coefs_file_name, coefs_file_name);
-    return RTC_ST_BADFILE;
-  }
-
-  Free(temp_coefs_file_name);

  return RTC_ST_OK;
 }

+/* ================================================== */
+
+static int
+switch_interrupts(int on_off)
+{
+  if (ioctl(fd, on_off ? RTC_UIE_ON : RTC_UIE_OFF, 0) < 0) {
+    LOG(LOGS_ERR, "Could not %s RTC interrupt : %s",
+        on_off ? "enable" : "disable", strerror(errno));
+    return 0;
+  }
+
+  if (on_off)
+    skip_interrupts = 1;
+
+  return 1;
+}

 /* ================================================== */
 /* file_name is the name of the file where we save the RTC params
@@ -536,6 +507,23 @@ write_coefs_to_file(int valid,time_t ref_time,double offset,double rate)
 int
 RTC_Linux_Initialise(void)
 {
+  /* Try to open the device */
+  fd = open(CNF_GetRtcDevice(), O_RDWR);
+  if (fd < 0) {
+    LOG(LOGS_ERR, "Could not open RTC device %s : %s",
+        CNF_GetRtcDevice(), strerror(errno));
+    return 0;
+  }
+
+  /* Make sure the RTC supports interrupts */
+  if (!switch_interrupts(1) || !switch_interrupts(0)) {
+    close(fd);
+    return 0;
+  }
+
+  /* Close on exec */
+  UTI_FdSetCloexec(fd);
+
  rtc_sec = MallocArray(time_t, MAX_SAMPLES);
  rtc_trim = MallocArray(double, MAX_SAMPLES);
  system_times = MallocArray(struct timespec, MAX_SAMPLES);
@@ -546,18 +534,6 @@ RTC_Linux_Initialise(void)
  /* In case it didn't get done by pre-init */
  coefs_file_name = CNF_GetRtcFile();

-  /* Try to open device */
-
-  fd = open (CNF_GetRtcDevice(), O_RDWR);
-  if (fd < 0) {
-    LOG(LOGS_ERR, "Could not open RTC device %s : %s",
-        CNF_GetRtcDevice(), strerror(errno));
-    return 0;
-  }
-
-  /* Close on exec */
-  UTI_FdSetCloexec(fd);
-
  n_samples = 0;
  n_samples_since_regression = 0;
  n_runs = 0;
@@ -590,12 +566,17 @@ RTC_Linux_Finalise(void)
  /* Remove input file handler */
  if (fd >= 0) {
    SCH_RemoveFileHandler(fd);
+    switch_interrupts(0);
    close(fd);

    /* Save the RTC data */
    (void) RTC_Linux_WriteParameters();

  }
+
+  if (rtc_sec)
+    LCL_RemoveParameterChangeHandler(slew_samples, NULL);
+
  Free(rtc_sec);
  Free(rtc_trim);
  Free(system_times);
@@ -603,29 +584,6 @@ RTC_Linux_Finalise(void)

 /* ================================================== */

-static void
-switch_interrupts(int onoff)
-{
-  int status;
-
-  if (onoff) {
-    status = ioctl(fd, RTC_UIE_ON, 0);
-    if (status < 0) {
-      LOG(LOGS_ERR, "Could not %s RTC interrupt : %s", "enable", strerror(errno));
-      return;
-    }
-    skip_interrupts = 1;
-  } else {
-    status = ioctl(fd, RTC_UIE_OFF, 0);
-    if (status < 0) {
-      LOG(LOGS_ERR, "Could not %s RTC interrupt : %s", "disable", strerror(errno));
-      return;
-    }
-  }
-}    
-
-/* ================================================== */
-
 static void
 measurement_timeout(void *any)
 {
--- a/samplefilt.c
+++ b/samplefilt.c
@@ -267,7 +267,7 @@ select_samples(SPF_Instance filter)
    }
  }

-  for (i = j = 0, k = -1; i < filter->used; i++) {
+  for (i = j = 0; i < filter->used; i++) {
    if (selected[i] != -1)
      selected[j++] = (selected[i] + filter->used - o) % filter->used;
  }
@@ -387,7 +387,6 @@ combine_selected_samples(SPF_Instance filter, int n, NTP_Sample *result)
  result->peer_delay = mean_peer_delay;
  result->root_delay = mean_root_delay;
  result->stratum = last_sample->stratum;
-  result->leap = last_sample->leap;

  return 1;
 }
--- a/sched.c
+++ b/sched.c
@@ -65,6 +65,12 @@ static ARR_Instance file_handlers;
 static struct timespec last_select_ts, last_select_ts_raw;
 static double last_select_ts_err;

+#define TS_MONO_PRECISION_NS 10000000U
+
+/* Monotonic low-precision timestamp measuring interval since the start */
+static double last_select_ts_mono;
+static uint32_t last_select_ts_mono_ns;
+
 /* ================================================== */

 /* Variables to handler the timer queue */
@@ -136,6 +142,8 @@ SCH_Initialise(void)

  LCL_ReadRawTime(&last_select_ts_raw);
  last_select_ts = last_select_ts_raw;
+  last_select_ts_mono = 0.0;
+  last_select_ts_mono_ns = 0;

  initialised = 1;
 }
@@ -147,6 +155,8 @@ void
 SCH_Finalise(void) {
  ARR_DestroyInstance(file_handlers);

+  LCL_RemoveParameterChangeHandler(handle_slew, NULL);
+
  initialised = 0;
 }

@@ -247,6 +257,14 @@ SCH_GetLastEventTime(struct timespec *cooked, double *err, struct timespec *raw)

 /* ================================================== */

+double
+SCH_GetLastEventMonoTime(void)
+{
+  return last_select_ts_mono;
+}
+
+/* ================================================== */
+
 #define TQE_ALLOC_QUANTUM 32

 static TimerQueueEntry *
@@ -706,6 +724,31 @@ check_current_time(struct timespec *prev_raw, struct timespec *raw, int timeout,

 /* ================================================== */

+static void
+update_monotonic_time(struct timespec *now, struct timespec *before)
+{
+  struct timespec diff;
+
+  /* Avoid frequent floating-point operations and handle small
+     increments to a large value */
+
+  UTI_DiffTimespecs(&diff, now, before);
+  if (diff.tv_sec == 0) {
+    last_select_ts_mono_ns += diff.tv_nsec;
+  } else {
+    last_select_ts_mono += fabs(UTI_TimespecToDouble(&diff) +
+                                last_select_ts_mono_ns / 1.0e9);
+    last_select_ts_mono_ns = 0;
+  }
+
+  if (last_select_ts_mono_ns > TS_MONO_PRECISION_NS) {
+    last_select_ts_mono += last_select_ts_mono_ns / 1.0e9;
+    last_select_ts_mono_ns = 0;
+  }
+}
+
+/* ================================================== */
+
 void
 SCH_MainLoop(void)
 {
@@ -756,6 +799,8 @@ SCH_MainLoop(void)
    LCL_ReadRawTime(&now);
    LCL_CookTime(&now, &cooked, &err);

+    update_monotonic_time(&now, &last_select_ts_raw);
+
    /* Check if the time didn't jump unexpectedly */
    if (!check_current_time(&saved_now, &now, status == 0, &saved_tv, ptv)) {
      /* Cook the time again after handling the step */
--- a/sched.h
+++ b/sched.h
@@ -65,6 +65,9 @@ extern void SCH_SetFileHandlerEvent(int fd, int event, int enable);
 /* Get the time stamp taken after a file descriptor became ready or a timeout expired */
 extern void SCH_GetLastEventTime(struct timespec *cooked, double *err, struct timespec *raw);

+/* Get a low-precision monotonic timestamp (starting at 0.0) */
+extern double SCH_GetLastEventMonoTime(void);
+
 /* This queues a timeout to elapse at a given (raw) local time */
 extern SCH_TimeoutID SCH_AddTimeout(struct timespec *ts, SCH_TimeoutHandler handler, SCH_ArbitraryArgument arg);

--- a/siv.h
+++ b/siv.h
@@ -0,0 +1,70 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2019
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for Synthetic Initialization Vector (SIV) ciphers.
+
+  */
+
+#ifndef GOT_SIV_H
+#define GOT_SIV_H
+
+/* Maximum key length of all supported SIVs */
+#define SIV_MAX_KEY_LENGTH 32
+
+/* Maximum difference between lengths of ciphertext and plaintext */
+#define SIV_MAX_TAG_LENGTH 16
+
+/* Identifiers of SIV algorithms following the IANA AEAD registry */
+typedef enum {
+  AEAD_AES_SIV_CMAC_256 = 15,
+  AEAD_AES_SIV_CMAC_384 = 16,
+  AEAD_AES_SIV_CMAC_512 = 17,
+  AEAD_AES_128_GCM_SIV = 30,
+  AEAD_AES_256_GCM_SIV = 31,
+} SIV_Algorithm;
+
+typedef struct SIV_Instance_Record *SIV_Instance;
+
+extern SIV_Instance SIV_CreateInstance(SIV_Algorithm algorithm);
+
+extern void SIV_DestroyInstance(SIV_Instance instance);
+
+extern int SIV_GetKeyLength(SIV_Algorithm algorithm);
+
+extern int SIV_SetKey(SIV_Instance instance, const unsigned char *key, int length);
+
+extern int SIV_GetTagLength(SIV_Instance instance);
+
+extern int SIV_Encrypt(SIV_Instance instance,
+                       const unsigned char *nonce, int nonce_length,
+                       const void *assoc, int assoc_length,
+                       const void *plaintext, int plaintext_length,
+                       unsigned char *ciphertext, int ciphertext_length);
+
+extern int SIV_Decrypt(SIV_Instance instance,
+                       const unsigned char *nonce, int nonce_length,
+                       const void *assoc, int assoc_length,
+                       const unsigned char *ciphertext, int ciphertext_length,
+                       void *plaintext, int plaintext_length);
+
+#endif
--- a/siv_gnutls.c
+++ b/siv_gnutls.c
@@ -0,0 +1,256 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2020
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  SIV ciphers using the GnuTLS library
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include <gnutls/crypto.h>
+
+#include "logging.h"
+#include "memory.h"
+#include "siv.h"
+
+struct SIV_Instance_Record {
+  gnutls_cipher_algorithm_t algorithm;
+  gnutls_aead_cipher_hd_t cipher;
+};
+
+/* ================================================== */
+
+static int instance_counter = 0;
+static int gnutls_initialised = 0;
+
+/* ================================================== */
+
+static void
+init_gnutls(void)
+{
+  int r;
+
+  if (gnutls_initialised)
+    return;
+
+  r = gnutls_global_init();
+  if (r < 0)
+    LOG_FATAL("Could not initialise %s : %s", "gnutls", gnutls_strerror(r));
+
+  DEBUG_LOG("Initialised");
+  gnutls_initialised = 1;
+}
+
+/* ================================================== */
+
+static void
+deinit_gnutls(void)
+{
+  assert(gnutls_initialised);
+  gnutls_global_deinit();
+  gnutls_initialised = 0;
+  DEBUG_LOG("Deinitialised");
+}
+
+/* ================================================== */
+
+static gnutls_cipher_algorithm_t
+get_cipher_algorithm(SIV_Algorithm algorithm)
+{
+  switch (algorithm) {
+    case AEAD_AES_SIV_CMAC_256:
+      return GNUTLS_CIPHER_AES_128_SIV;
+    default:
+      return 0;
+  }
+}
+
+/* ================================================== */
+
+SIV_Instance
+SIV_CreateInstance(SIV_Algorithm algorithm)
+{
+  gnutls_cipher_algorithm_t calgo;
+  SIV_Instance instance;
+
+  calgo = get_cipher_algorithm(algorithm);
+  if (calgo == 0)
+    return NULL;
+
+  if (instance_counter == 0)
+    init_gnutls();
+
+  /* Check if the cipher is actually supported */
+  if (gnutls_cipher_get_tag_size(calgo) == 0)
+    return NULL;
+
+  instance = MallocNew(struct SIV_Instance_Record);
+  instance->algorithm = calgo;
+  instance->cipher = NULL;
+
+  instance_counter++;
+
+  return instance;
+}
+
+/* ================================================== */
+
+void
+SIV_DestroyInstance(SIV_Instance instance)
+{
+  if (instance->cipher)
+    gnutls_aead_cipher_deinit(instance->cipher);
+  Free(instance);
+
+  instance_counter--;
+  if (instance_counter == 0)
+    deinit_gnutls();
+}
+
+/* ================================================== */
+
+int
+SIV_GetKeyLength(SIV_Algorithm algorithm)
+{
+  gnutls_cipher_algorithm_t calgo = get_cipher_algorithm(algorithm);
+  int len;
+
+  if (calgo == 0)
+    return 0;
+
+  len = gnutls_cipher_get_key_size(calgo);
+
+  if (len < 1 || len > SIV_MAX_KEY_LENGTH)
+    LOG_FATAL("Invalid key length");
+
+  return len;
+}
+
+/* ================================================== */
+
+int
+SIV_SetKey(SIV_Instance instance, const unsigned char *key, int length)
+{
+  gnutls_aead_cipher_hd_t cipher;
+  gnutls_datum_t datum;
+  int r;
+
+  if (length <= 0 || length != gnutls_cipher_get_key_size(instance->algorithm))
+    return 0;
+
+  datum.data = (unsigned char *)key;
+  datum.size = length;
+
+  /* Initialise a new cipher with the provided key (gnutls does not seem to
+     have a function to change the key directly) */
+  r = gnutls_aead_cipher_init(&cipher, instance->algorithm, &datum);
+  if (r < 0) {
+    DEBUG_LOG("Could not initialise %s : %s", "cipher", gnutls_strerror(r));
+    return 0;
+  }
+
+  /* Replace the previous cipher */
+  if (instance->cipher)
+    gnutls_aead_cipher_deinit(instance->cipher);
+  instance->cipher = cipher;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+SIV_GetTagLength(SIV_Instance instance)
+{
+  int len;
+
+  len = gnutls_cipher_get_tag_size(instance->algorithm);
+
+  if (len < 1 || len > SIV_MAX_TAG_LENGTH)
+    LOG_FATAL("Invalid tag length");
+
+  return len;
+}
+
+/* ================================================== */
+
+int
+SIV_Encrypt(SIV_Instance instance,
+            const unsigned char *nonce, int nonce_length,
+            const void *assoc, int assoc_length,
+            const void *plaintext, int plaintext_length,
+            unsigned char *ciphertext, int ciphertext_length)
+{
+  size_t clen = ciphertext_length;
+
+  if (!instance->cipher)
+    return 0;
+
+  if (nonce_length < 1 || assoc_length < 0 ||
+      plaintext_length < 0 || ciphertext_length < 0)
+    return 0;
+
+  assert(assoc && plaintext);
+
+  if (gnutls_aead_cipher_encrypt(instance->cipher,
+                                 nonce, nonce_length, assoc, assoc_length, 0,
+                                 plaintext, plaintext_length, ciphertext, &clen) < 0)
+    return 0;
+
+  if (clen != ciphertext_length)
+    return 0;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+SIV_Decrypt(SIV_Instance instance,
+            const unsigned char *nonce, int nonce_length,
+            const void *assoc, int assoc_length,
+            const unsigned char *ciphertext, int ciphertext_length,
+            void *plaintext, int plaintext_length)
+{
+  size_t plen = plaintext_length;
+
+  if (!instance->cipher)
+    return 0;
+
+  if (nonce_length < 1 || assoc_length < 0 ||
+      plaintext_length < 0 || ciphertext_length < 0)
+    return 0;
+
+  assert(assoc && plaintext);
+
+  if (gnutls_aead_cipher_decrypt(instance->cipher,
+                                 nonce, nonce_length, assoc, assoc_length, 0,
+                                 ciphertext, ciphertext_length, plaintext, &plen) < 0)
+    return 0;
+
+  if (plen != plaintext_length)
+    return 0;
+
+  return 1;
+}
--- a/siv_nettle.c
+++ b/siv_nettle.c
@@ -0,0 +1,156 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2019
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  SIV ciphers using the Nettle library
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#ifdef HAVE_NETTLE_SIV_CMAC
+#include <nettle/siv-cmac.h>
+#else
+#include "siv_nettle_int.c"
+#endif
+
+#include "memory.h"
+#include "siv.h"
+
+struct SIV_Instance_Record {
+  struct siv_cmac_aes128_ctx siv;
+  int key_set;
+};
+
+/* ================================================== */
+
+SIV_Instance
+SIV_CreateInstance(SIV_Algorithm algorithm)
+{
+  SIV_Instance instance;
+
+  if (algorithm != AEAD_AES_SIV_CMAC_256)
+    return NULL;
+
+  instance = MallocNew(struct SIV_Instance_Record);
+  instance->key_set = 0;
+
+  return instance;
+}
+
+/* ================================================== */
+
+void
+SIV_DestroyInstance(SIV_Instance instance)
+{
+  Free(instance);
+}
+
+/* ================================================== */
+
+int
+SIV_GetKeyLength(SIV_Algorithm algorithm)
+{
+  assert(32 <= SIV_MAX_KEY_LENGTH);
+
+  if (algorithm == AEAD_AES_SIV_CMAC_256)
+    return 32;
+  return 0;
+}
+
+/* ================================================== */
+
+int
+SIV_SetKey(SIV_Instance instance, const unsigned char *key, int length)
+{
+  if (length != 32)
+    return 0;
+
+  siv_cmac_aes128_set_key(&instance->siv, key);
+
+  instance->key_set = 1;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+SIV_GetTagLength(SIV_Instance instance)
+{
+  assert(SIV_DIGEST_SIZE <= SIV_MAX_TAG_LENGTH);
+
+  return SIV_DIGEST_SIZE;
+}
+
+/* ================================================== */
+
+int
+SIV_Encrypt(SIV_Instance instance,
+            const unsigned char *nonce, int nonce_length,
+            const void *assoc, int assoc_length,
+            const void *plaintext, int plaintext_length,
+            unsigned char *ciphertext, int ciphertext_length)
+{
+  if (!instance->key_set)
+    return 0;
+
+  if (nonce_length < SIV_MIN_NONCE_SIZE || assoc_length < 0 ||
+      plaintext_length < 0 || plaintext_length > ciphertext_length ||
+      plaintext_length + SIV_DIGEST_SIZE != ciphertext_length)
+    return 0;
+
+  assert(assoc && plaintext);
+
+  siv_cmac_aes128_encrypt_message(&instance->siv, nonce_length, nonce,
+                                  assoc_length, assoc,
+                                  ciphertext_length, ciphertext, plaintext);
+  return 1;
+}
+
+/* ================================================== */
+
+int
+SIV_Decrypt(SIV_Instance instance,
+            const unsigned char *nonce, int nonce_length,
+            const void *assoc, int assoc_length,
+            const unsigned char *ciphertext, int ciphertext_length,
+            void *plaintext, int plaintext_length)
+{
+  if (!instance->key_set)
+    return 0;
+
+  if (nonce_length < SIV_MIN_NONCE_SIZE || assoc_length < 0 ||
+      plaintext_length < 0 || plaintext_length > ciphertext_length ||
+      plaintext_length + SIV_DIGEST_SIZE != ciphertext_length)
+    return 0;
+
+  assert(assoc && plaintext);
+
+  if (!siv_cmac_aes128_decrypt_message(&instance->siv, nonce_length, nonce,
+                                       assoc_length, assoc,
+                                       plaintext_length, plaintext, ciphertext))
+    return 0;
+
+  return 1;
+}
--- a/siv_nettle_int.c
+++ b/siv_nettle_int.c
@@ -0,0 +1,452 @@
+/* This is a single-file implementation of AES-SIV-CMAC-256 based on
+   a patch for GNU Nettle by Nikos Mavrogiannopoulos */
+
+/*
+   AES-CMAC-128 (rfc 4493)
+   Copyright (C) Stefan Metzmacher 2012
+   Copyright (C) Jeremy Allison 2012
+   Copyright (C) Michael Adam 2012
+   Copyright (C) 2017, Red Hat Inc.
+
+   This file is part of GNU Nettle.
+
+   GNU Nettle is free software: you can redistribute it and/or
+   modify it under the terms of either:
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at your
+       option) any later version.
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at your
+       option) any later version.
+
+   or both in parallel, as here.
+
+   GNU Nettle is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see http://www.gnu.org/licenses/.
+*/
+/* siv-aes128.c, siv-cmac.c, siv.h
+
+   AES-SIV, RFC5297
+   SIV-CMAC, RFC5297
+
+   Copyright (C) 2017 Nikos Mavrogiannopoulos
+
+   This file is part of GNU Nettle.
+
+   GNU Nettle is free software: you can redistribute it and/or
+   modify it under the terms of either:
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at your
+       option) any later version.
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at your
+       option) any later version.
+
+   or both in parallel, as here.
+
+   GNU Nettle is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see http://www.gnu.org/licenses/.
+*/
+/* cmac.h, siv-cmac.h, cmac-aes128.c
+
+   CMAC mode, as specified in RFC4493
+   SIV-CMAC mode, as specified in RFC5297
+   CMAC using AES128 as the underlying cipher.
+
+   Copyright (C) 2017 Red Hat, Inc.
+
+   Contributed by Nikos Mavrogiannopoulos
+
+   This file is part of GNU Nettle.
+
+   GNU Nettle is free software: you can redistribute it and/or
+   modify it under the terms of either:
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at your
+       option) any later version.
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at your
+       option) any later version.
+
+   or both in parallel, as here.
+
+   GNU Nettle is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see http://www.gnu.org/licenses/.
+*/
+
+# include "config.h"
+
+#include <assert.h>
+#include <string.h>
+
+#include "nettle/aes.h"
+#include "nettle/ctr.h"
+#include "nettle/macros.h"
+#include "nettle/memxor.h"
+#include "nettle/memops.h"
+
+#include "nettle/nettle-types.h"
+
+/* For SIV, the block size of the block cipher shall be 128 bits. */
+#define SIV_BLOCK_SIZE  16
+#define SIV_DIGEST_SIZE 16
+#define SIV_MIN_NONCE_SIZE 1
+
+/*
+ * SIV mode requires the aad and plaintext when building the IV, which
+ * prevents streaming processing and it incompatible with the AEAD API.
+ */
+
+/* AES_SIV_CMAC_256 */
+struct siv_cmac_aes128_ctx {
+    struct aes128_ctx         cipher;
+    uint8_t s2vk[AES128_KEY_SIZE];
+};
+
+struct cmac128_ctx
+{
+  /* Key */
+  union nettle_block16 K1;
+  union nettle_block16 K2;
+
+  /* MAC state */
+  union nettle_block16 X;
+
+  /* Block buffer */
+  union nettle_block16 block;
+  size_t index;
+};
+
+/* shift one and XOR with 0x87. */
+static void
+_cmac128_block_mulx(union nettle_block16 *dst,
+	   const union nettle_block16 *src)
+{
+  uint64_t b1 = READ_UINT64(src->b);
+  uint64_t b2 = READ_UINT64(src->b+8);
+
+  b1 = (b1 << 1) | (b2 >> 63);
+  b2 <<= 1;
+
+  if (src->b[0] & 0x80)
+    b2 ^= 0x87;
+
+  WRITE_UINT64(dst->b, b1);
+  WRITE_UINT64(dst->b+8, b2);
+}
+
+static void
+cmac128_set_key(struct cmac128_ctx *ctx, const void *cipher,
+		nettle_cipher_func *encrypt)
+{
+  static const uint8_t const_zero[] = {
+    0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00
+  };
+  union nettle_block16 *L = &ctx->block;
+  memset(ctx, 0, sizeof(*ctx));
+
+  /* step 1 - generate subkeys k1 and k2 */
+  encrypt(cipher, 16, L->b, const_zero);
+
+  _cmac128_block_mulx(&ctx->K1, L);
+  _cmac128_block_mulx(&ctx->K2, &ctx->K1);
+}
+
+#define MIN(x,y) ((x)<(y)?(x):(y))
+
+static void
+cmac128_update(struct cmac128_ctx *ctx, const void *cipher,
+	       nettle_cipher_func *encrypt,
+	       size_t msg_len, const uint8_t *msg)
+{
+  union nettle_block16 Y;
+  /*
+   * check if we expand the block
+   */
+  if (ctx->index < 16)
+    {
+      size_t len = MIN(16 - ctx->index, msg_len);
+      memcpy(&ctx->block.b[ctx->index], msg, len);
+      msg += len;
+      msg_len -= len;
+      ctx->index += len;
+    }
+
+  if (msg_len == 0) {
+    /* if it is still the last block, we are done */
+    return;
+  }
+
+  /*
+   * now checksum everything but the last block
+   */
+  memxor3(Y.b, ctx->X.b, ctx->block.b, 16);
+  encrypt(cipher, 16, ctx->X.b, Y.b);
+
+  while (msg_len > 16)
+    {
+      memxor3(Y.b, ctx->X.b, msg, 16);
+      encrypt(cipher, 16, ctx->X.b, Y.b);
+      msg += 16;
+      msg_len -= 16;
+    }
+
+  /*
+   * copy the last block, it will be processed in
+   * cmac128_digest().
+   */
+  memcpy(ctx->block.b, msg, msg_len);
+  ctx->index = msg_len;
+}
+
+static void
+cmac128_digest(struct cmac128_ctx *ctx, const void *cipher,
+	       nettle_cipher_func *encrypt,
+	       unsigned length,
+	       uint8_t *dst)
+{
+  union nettle_block16 Y;
+
+  memset(ctx->block.b+ctx->index, 0, sizeof(ctx->block.b)-ctx->index);
+
+  /* re-use ctx->block for memxor output */
+  if (ctx->index < 16)
+    {
+      ctx->block.b[ctx->index] = 0x80;
+      memxor(ctx->block.b, ctx->K2.b, 16);
+    }
+  else
+    {
+      memxor(ctx->block.b, ctx->K1.b, 16);
+    }
+
+  memxor3(Y.b, ctx->block.b, ctx->X.b, 16);
+
+  assert(length <= 16);
+  if (length == 16)
+    {
+      encrypt(cipher, 16, dst, Y.b);
+    }
+  else
+    {
+      encrypt(cipher, 16, ctx->block.b, Y.b);
+      memcpy(dst, ctx->block.b, length);
+    }
+
+  /* reset state for re-use */
+  memset(&ctx->X, 0, sizeof(ctx->X));
+  ctx->index = 0;
+}
+
+
+#define CMAC128_CTX(type) \
+  { struct cmac128_ctx ctx; type cipher; }
+
+/* NOTE: Avoid using NULL, as we don't include anything defining it. */
+#define CMAC128_SET_KEY(self, set_key, encrypt, cmac_key)	\
+  do {								\
+    (set_key)(&(self)->cipher, (cmac_key));			\
+    if (0) (encrypt)(&(self)->cipher, ~(size_t) 0,		\
+		     (uint8_t *) 0, (const uint8_t *) 0);	\
+    cmac128_set_key(&(self)->ctx, &(self)->cipher,		\
+		(nettle_cipher_func *) (encrypt));		\
+  } while (0)
+
+#define CMAC128_UPDATE(self, encrypt, length, src)		\
+  cmac128_update(&(self)->ctx, &(self)->cipher,			\
+	      (nettle_cipher_func *)encrypt, (length), (src))
+
+#define CMAC128_DIGEST(self, encrypt, length, digest)		\
+  (0 ? (encrypt)(&(self)->cipher, ~(size_t) 0,			\
+		 (uint8_t *) 0, (const uint8_t *) 0)		\
+     : cmac128_digest(&(self)->ctx, &(self)->cipher,		\
+		  (nettle_cipher_func *) (encrypt),		\
+		  (length), (digest)))
+
+struct cmac_aes128_ctx CMAC128_CTX(struct aes128_ctx);
+
+static void
+cmac_aes128_set_key(struct cmac_aes128_ctx *ctx, const uint8_t *key)
+{
+  CMAC128_SET_KEY(ctx, aes128_set_encrypt_key, aes128_encrypt, key);
+}
+
+static void
+cmac_aes128_update (struct cmac_aes128_ctx *ctx,
+		   size_t length, const uint8_t *data)
+{
+  CMAC128_UPDATE (ctx, aes128_encrypt, length, data);
+}
+
+static void
+cmac_aes128_digest(struct cmac_aes128_ctx *ctx,
+		  size_t length, uint8_t *digest)
+{
+  CMAC128_DIGEST(ctx, aes128_encrypt, length, digest);
+}
+
+static const uint8_t const_one[] = {
+	0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x01
+};
+
+static const uint8_t const_zero[] = {
+	0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00
+};
+
+static
+void _siv_s2v(nettle_set_key_func *cmac_set_key,
+	      nettle_hash_update_func *cmac_update,
+	      nettle_hash_digest_func *cmac_digest,
+	      size_t cmac_ctx_size,
+	      const uint8_t *s2vk, size_t alength, const uint8_t *adata,
+              size_t nlength, const uint8_t *nonce,
+              size_t plength, const uint8_t *pdata,
+              uint8_t *v)
+{
+  uint8_t ctx[sizeof(struct cmac128_ctx)+sizeof(struct aes_ctx)];
+  union nettle_block16 D, S, T;
+
+  assert(cmac_ctx_size <= sizeof (ctx));
+
+  cmac_set_key(ctx, s2vk);
+
+  if (nlength == 0 && alength == 0) {
+    cmac_update(ctx, 16, const_one);
+    cmac_digest(ctx, 16, v);
+    return;
+  }
+
+  cmac_update(ctx, 16, const_zero);
+  cmac_digest(ctx, 16, D.b);
+
+  if (1) {
+    _cmac128_block_mulx(&D, &D);
+    cmac_update(ctx, alength, adata);
+    cmac_digest(ctx, 16, S.b);
+
+    memxor(D.b, S.b, 16);
+  }
+
+  if (nlength > 0) {
+    _cmac128_block_mulx(&D, &D);
+    cmac_update(ctx, nlength, nonce);
+    cmac_digest(ctx, 16, S.b);
+
+    memxor(D.b, S.b, 16);
+  }
+
+  /* Sn */
+  if (plength >= 16) {
+    cmac_update(ctx, plength-16, pdata);
+
+    pdata += plength-16;
+
+    memxor3(T.b, pdata, D.b, 16);
+  } else {
+    union nettle_block16 pad;
+
+    _cmac128_block_mulx(&T, &D);
+    memcpy(pad.b, pdata, plength);
+    pad.b[plength] = 0x80;
+    if (plength+1 < 16)
+      memset(&pad.b[plength+1], 0, 16-plength-1);
+
+    memxor(T.b, pad.b, 16);
+  }
+
+  cmac_update(ctx, 16, T.b);
+  cmac_digest(ctx, 16, v);
+}
+
+static void
+siv_cmac_aes128_set_key(struct siv_cmac_aes128_ctx *ctx, const uint8_t *key)
+{
+  memcpy(ctx->s2vk, key, 16);
+  aes128_set_encrypt_key(&ctx->cipher, key+16);
+}
+
+static void
+siv_cmac_aes128_encrypt_message(struct siv_cmac_aes128_ctx *ctx,
+				size_t nlength, const uint8_t *nonce,
+				size_t alength, const uint8_t *adata,
+				size_t clength, uint8_t *dst, const uint8_t *src)
+{
+  union nettle_block16 siv;
+  size_t slength;
+
+  assert (clength >= SIV_DIGEST_SIZE);
+  slength = clength - SIV_DIGEST_SIZE;
+
+  /* create CTR nonce */
+  _siv_s2v((nettle_set_key_func*)cmac_aes128_set_key,
+	   (nettle_hash_update_func*)cmac_aes128_update,
+	   (nettle_hash_digest_func*)cmac_aes128_digest,
+	   sizeof(struct cmac_aes128_ctx), ctx->s2vk, alength, adata,
+	   nlength, nonce, slength, src, siv.b);
+  memcpy(dst, siv.b, SIV_DIGEST_SIZE);
+  siv.b[8] &= ~0x80;
+  siv.b[12] &= ~0x80;
+
+  ctr_crypt(&ctx->cipher, (nettle_cipher_func *)aes128_encrypt, AES_BLOCK_SIZE,
+            siv.b, slength, dst+SIV_DIGEST_SIZE, src);
+}
+
+static int
+siv_cmac_aes128_decrypt_message(struct siv_cmac_aes128_ctx *ctx,
+				size_t nlength, const uint8_t *nonce,
+				size_t alength, const uint8_t *adata,
+				size_t mlength, uint8_t *dst, const uint8_t *src)
+{
+  union nettle_block16 siv;
+  union nettle_block16 ctr;
+
+  memcpy(ctr.b, src, SIV_DIGEST_SIZE);
+  ctr.b[8] &= ~0x80;
+  ctr.b[12] &= ~0x80;
+
+  ctr_crypt(&ctx->cipher, (nettle_cipher_func *)aes128_encrypt, AES_BLOCK_SIZE,
+            ctr.b, mlength, dst, src+SIV_DIGEST_SIZE);
+
+  /* create CTR nonce */
+  _siv_s2v((nettle_set_key_func*)cmac_aes128_set_key,
+	   (nettle_hash_update_func*)cmac_aes128_update,
+	   (nettle_hash_digest_func*)cmac_aes128_digest,
+	   sizeof(struct cmac_aes128_ctx), ctx->s2vk, alength, adata,
+	   nlength, nonce, mlength, dst, siv.b);
+
+  return memeql_sec(siv.b, src, SIV_DIGEST_SIZE);
+}
+
--- a/smooth.c
+++ b/smooth.c
@@ -272,6 +272,10 @@ void SMT_Initialise(void)

 void SMT_Finalise(void)
 {
+  if (!enabled)
+    return;
+
+  LCL_RemoveParameterChangeHandler(handle_slew, NULL);
 }

 int SMT_IsEnabled(void)
--- a/socket.c
+++ b/socket.c
--- a/socket.h
+++ b/socket.h
@@ -0,0 +1,147 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2019
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  This is the header file for socket operations.
+
+  */
+
+#ifndef GOT_SOCKET_H
+#define GOT_SOCKET_H
+
+#include "addressing.h"
+
+/* Flags for opening sockets */
+#define SCK_FLAG_BLOCK 1
+#define SCK_FLAG_BROADCAST 2
+#define SCK_FLAG_RX_DEST_ADDR 4
+#define SCK_FLAG_ALL_PERMISSIONS 8
+#define SCK_FLAG_PRIV_BIND 16
+
+/* Flags for receiving and sending messages */
+#define SCK_FLAG_MSG_ERRQUEUE 1
+#define SCK_FLAG_MSG_DESCRIPTOR 2
+
+typedef enum {
+  SCK_ADDR_UNSPEC = 0,
+  SCK_ADDR_IP,
+  SCK_ADDR_UNIX
+} SCK_AddressType;
+
+typedef struct {
+  void *data;
+  int length;
+  SCK_AddressType addr_type;
+  int if_index;
+
+  union {
+    IPSockAddr ip;
+    const char *path;
+  } remote_addr;
+
+  union {
+    IPAddr ip;
+  } local_addr;
+
+  struct {
+    struct timespec kernel;
+    struct timespec hw;
+    int if_index;
+    int l2_length;
+    int tx_flags;
+  } timestamp;
+
+  int descriptor;
+} SCK_Message;
+
+/* Initialisation function (the specified IP family is enabled,
+   or all if IPADDR_UNSPEC) */
+extern void SCK_Initialise(int family);
+
+/* Finalisation function */
+extern void SCK_Finalise(void);
+
+/* Check if support for the IP family is enabled */
+extern int SCK_IsIpFamilyEnabled(int family);
+
+/* Get the 0.0.0.0/::0 or 127.0.0.1/::1 address */
+extern void SCK_GetAnyLocalIPAddress(int family, IPAddr *local_addr);
+extern void SCK_GetLoopbackIPAddress(int family, IPAddr *local_addr);
+
+/* Check if an IP address is a link-local address */
+extern int SCK_IsLinkLocalIPAddress(IPAddr *addr);
+
+/* Specify a bind()-like function for binding sockets to privileged ports when
+   running in a restricted process (e.g. after dropping root privileges) */
+extern void SCK_SetPrivBind(int (*function)(int sock_fd, struct sockaddr *address,
+                                            socklen_t address_len));
+
+/* Open a socket (addresses and iface may be NULL) */
+extern int SCK_OpenUdpSocket(IPSockAddr *remote_addr, IPSockAddr *local_addr,
+                             const char *iface, int flags);
+extern int SCK_OpenTcpSocket(IPSockAddr *remote_addr, IPSockAddr *local_addr,
+                             const char *iface, int flags);
+extern int SCK_OpenUnixDatagramSocket(const char *remote_addr, const char *local_addr,
+                                      int flags);
+extern int SCK_OpenUnixStreamSocket(const char *remote_addr, const char *local_addr,
+                                    int flags);
+extern int SCK_OpenUnixSocketPair(int flags, int *other_fd);
+
+/* Set and get a socket option of int size */
+extern int SCK_SetIntOption(int sock_fd, int level, int name, int value);
+extern int SCK_GetIntOption(int sock_fd, int level, int name, int *value);
+
+/* Enable RX timestamping socket option */
+extern int SCK_EnableKernelRxTimestamping(int sock_fd);
+
+/* Operate on a stream socket - listen()/accept()/shutdown() wrappers */
+extern int SCK_ListenOnSocket(int sock_fd, int backlog);
+extern int SCK_AcceptConnection(int sock_fd, IPSockAddr *remote_addr);
+extern int SCK_ShutdownConnection(int sock_fd);
+
+/* Receive and send data on connected sockets - recv()/send() wrappers */
+extern int SCK_Receive(int sock_fd, void *buffer, int length, int flags);
+extern int SCK_Send(int sock_fd, const void *buffer, int length, int flags);
+
+/* Receive a single message or multiple messages.  The functions return
+   a pointer to static buffers, or NULL on error.  The buffers are valid until
+   another call of the functions and can be reused for sending messages. */
+extern SCK_Message *SCK_ReceiveMessage(int sock_fd, int flags);
+extern SCK_Message *SCK_ReceiveMessages(int sock_fd, int flags, int *num_messages);
+
+/* Initialise a new message (e.g. before sending) */
+extern void SCK_InitMessage(SCK_Message *message, SCK_AddressType addr_type);
+
+/* Send a message */
+extern int SCK_SendMessage(int sock_fd, SCK_Message *message, int flags);
+
+/* Remove bound Unix socket */
+extern int SCK_RemoveSocket(int sock_fd);
+
+/* Close the socket */
+extern void SCK_CloseSocket(int sock_fd);
+
+/* Convert between IPSockAddr and sockaddr_in/in6 */
+extern void SCK_SockaddrToIPSockAddr(struct sockaddr *sa, int sa_length, IPSockAddr *ip_sa);
+extern int SCK_IPSockAddrToSockaddr(IPSockAddr *ip_sa, struct sockaddr *sa, int sa_length);
+
+#endif
--- a/sources.c
+++ b/sources.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2011-2016, 2018
+ * Copyright (C) Miroslav Lichvar  2011-2016, 2018, 2020
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -54,7 +54,6 @@ static int initialised = 0;
 /* ================================================== */
 /* Structure used to hold info for selecting between sources */
 struct SelectInfo {
-  NTP_Leap leap;
  int stratum;
  int select_ok;
  double std_dev;
@@ -119,13 +118,25 @@ struct SRC_Instance_Record {
  /* Type of the source */
  SRC_Type type;

-  /* Options used when selecting sources */ 
+  /* Flag indicating that the source is authenticated */
+  int authenticated;
+
+  /* Configured selection options */
+  int conf_sel_options;
+
+  /* Effective selection options */
  int sel_options;

  /* Score against currently selected source */
  double sel_score;

  struct SelectInfo sel_info;
+
+  /* Latest leap status */
+  NTP_Leap leap;
+
+  /* Flag indicating the source has a leap second vote */
+  int leap_vote;
 };

 /* ================================================== */
@@ -167,13 +178,11 @@ static double combine_limit;
 /* ================================================== */
 /* Forward prototype */

-static void
-slew_sources(struct timespec *raw, struct timespec *cooked, double dfreq,
-             double doffset, LCL_ChangeType change_type, void *anything);
-static void
-add_dispersion(double dispersion, void *anything);
-static char *
-source_to_string(SRC_Instance inst);
+static void update_sel_options(void);
+static void slew_sources(struct timespec *raw, struct timespec *cooked, double dfreq,
+                         double doffset, LCL_ChangeType change_type, void *anything);
+static void add_dispersion(double dispersion, void *anything);
+static char *source_to_string(SRC_Instance inst);

 /* ================================================== */
 /* Initialisation function */
@@ -213,9 +222,9 @@ void SRC_Finalise(void)
 /* Function to create a new instance.  This would be called by one of
   the individual source-type instance creation routines. */

-SRC_Instance SRC_CreateNewInstance(uint32_t ref_id, SRC_Type type, int sel_options,
-                                   IPAddr *addr, int min_samples, int max_samples,
-                                   double min_delay, double asymmetry)
+SRC_Instance SRC_CreateNewInstance(uint32_t ref_id, SRC_Type type, int authenticated,
+                                   int sel_options, IPAddr *addr, int min_samples,
+                                   int max_samples, double min_delay, double asymmetry)
 {
  SRC_Instance result;

@@ -248,13 +257,18 @@ SRC_Instance SRC_CreateNewInstance(uint32_t ref_id, SRC_Type type, int sel_optio

  result->index = n_sources;
  result->type = type;
+  result->authenticated = authenticated;
+  result->conf_sel_options = sel_options;
  result->sel_options = sel_options;
+  result->active = 0;

  SRC_SetRefid(result, ref_id, addr);
  SRC_ResetInstance(result);

  n_sources++;

+  update_sel_options();
+
  return result;
 }

@@ -279,6 +293,8 @@ void SRC_DestroyInstance(SRC_Instance instance)
  --n_sources;
  Free(instance);

+  update_sel_options();
+
  /* If this was the previous reference source, we have to reselect! */
  if (selected_source_index == dead_index)
    SRC_ReselectSource();
@@ -291,13 +307,16 @@ void SRC_DestroyInstance(SRC_Instance instance)
 void
 SRC_ResetInstance(SRC_Instance instance)
 {
-  instance->active = 0;
  instance->updates = 0;
  instance->reachability = 0;
  instance->reachability_size = 0;
  instance->distant = 0;
  instance->status = SRC_BAD_STATS;
  instance->sel_score = 1.0;
+  instance->leap = LEAP_Unsynchronised;
+  instance->leap_vote = 0;
+
+  memset(&instance->sel_info, 0, sizeof (instance->sel_info));

  SST_ResetInstance(instance->stats);
 }
@@ -323,6 +342,48 @@ SRC_GetSourcestats(SRC_Instance instance)

 /* ================================================== */

+static NTP_Leap
+get_leap_status(void)
+{
+  int i, leap_votes, leap_ins, leap_del;
+
+  /* Accept a leap second if more than half of the sources with a vote agree */
+
+  for (i = leap_ins = leap_del = leap_votes = 0; i < n_sources; i++) {
+    if (!sources[i]->leap_vote)
+      continue;
+
+    leap_votes++;
+    if (sources[i]->leap == LEAP_InsertSecond)
+      leap_ins++;
+    else if (sources[i]->leap == LEAP_DeleteSecond)
+      leap_del++;
+  }
+
+  if (leap_ins > leap_votes / 2)
+    return LEAP_InsertSecond;
+  else if (leap_del > leap_votes / 2)
+    return LEAP_DeleteSecond;
+  else
+    return LEAP_Normal;
+}
+
+/* ================================================== */
+
+void
+SRC_SetLeapStatus(SRC_Instance inst, NTP_Leap leap)
+{
+  if (REF_IsLeapSecondClose(NULL, 0.0))
+    return;
+
+  inst->leap = leap;
+
+  if (inst->leap_vote)
+    REF_UpdateLeapStatus(get_leap_status());
+}
+
+/* ================================================== */
+
 /* This function is called by one of the source drivers when it has
   a new sample that is to be accumulated.

@@ -337,11 +398,11 @@ SRC_AccumulateSample(SRC_Instance inst, NTP_Sample *sample)

  assert(initialised);

-  DEBUG_LOG("ip=[%s] t=%s ofs=%f del=%f disp=%f str=%d",
+  DEBUG_LOG("src=%s ts=%s offset=%e delay=%e disp=%e stratum=%d",
            source_to_string(inst), UTI_TimespecToString(&sample->time), -sample->offset,
            sample->root_delay, sample->root_dispersion, sample->stratum);

-  if (REF_IsLeapSecondClose()) {
+  if (REF_IsLeapSecondClose(&sample->time, sample->offset)) {
    LOG(LOGS_INFO, "Dropping sample around leap second");
    return;
  }
@@ -378,7 +439,7 @@ special_mode_end(void)
      if (!sources[i]->active)
        continue;

-      /* Don't expect more updates than from an offline iburst NTP source */
+      /* Don't expect more updates than the initial burst of an NTP source */
      if (sources[i]->reachability_size >= SOURCE_REACH_BITS - 1)
        continue;

@@ -434,7 +495,76 @@ SRC_ResetReachability(SRC_Instance inst)
 /* ================================================== */

 static void
-log_selection_message(char *format, char *arg)
+update_sel_options(void)
+{
+  int options, auth_ntp_options, unauth_ntp_options, refclk_options;
+  int i, auth_ntp_sources, unauth_ntp_sources;
+
+  auth_ntp_sources = unauth_ntp_sources = 0;
+
+  for (i = 0; i < n_sources; i++) {
+    if (sources[i]->conf_sel_options & SRC_SELECT_NOSELECT)
+      continue;
+    if (sources[i]->type != SRC_NTP)
+      continue;
+    if (sources[i]->authenticated)
+      auth_ntp_sources++;
+    else
+      unauth_ntp_sources++;
+  }
+
+  auth_ntp_options = unauth_ntp_options = refclk_options = 0;
+
+  /* Determine which selection options need to be added to authenticated NTP
+     sources, unauthenticated NTP sources, and refclocks, to follow the
+     configured selection mode */
+  switch (CNF_GetAuthSelectMode()) {
+    case SRC_AUTHSELECT_IGNORE:
+      break;
+    case SRC_AUTHSELECT_MIX:
+      if (auth_ntp_sources > 0 && unauth_ntp_sources > 0)
+        auth_ntp_options = refclk_options = SRC_SELECT_REQUIRE | SRC_SELECT_TRUST;
+      break;
+    case SRC_AUTHSELECT_PREFER:
+      if (auth_ntp_sources > 0)
+        unauth_ntp_options = SRC_SELECT_NOSELECT;
+      break;
+    case SRC_AUTHSELECT_REQUIRE:
+      unauth_ntp_options = SRC_SELECT_NOSELECT;
+      break;
+    default:
+      assert(0);
+  }
+
+  for (i = 0; i < n_sources; i++) {
+    options = sources[i]->conf_sel_options;
+
+    if (options & SRC_SELECT_NOSELECT)
+      continue;
+
+    switch (sources[i]->type) {
+      case SRC_NTP:
+        options |= sources[i]->authenticated ? auth_ntp_options : unauth_ntp_options;
+        break;
+      case SRC_REFCLOCK:
+        options |= refclk_options;
+        break;
+      default:
+        assert(0);
+    }
+
+    if (sources[i]->sel_options != options) {
+      DEBUG_LOG("changing %s from %x to %x", source_to_string(sources[i]),
+                (unsigned int)sources[i]->sel_options, (unsigned int)options);
+      sources[i]->sel_options = options;
+    }
+  }
+}
+
+/* ================================================== */
+
+static void
+log_selection_message(const char *format, const char *arg)
 {
  if (REF_GetMode() != REF_ModeNormal)
    return;
@@ -443,6 +573,24 @@ log_selection_message(char *format, char *arg)

 /* ================================================== */

+static void
+log_selection_source(const char *format, SRC_Instance inst)
+{
+  char buf[320], *name, *ntp_name;
+
+  name = source_to_string(inst);
+  ntp_name = inst->type == SRC_NTP ? NSR_GetName(inst->ip_addr) : NULL;
+
+  if (ntp_name && strcmp(name, ntp_name) != 0)
+    snprintf(buf, sizeof (buf), "%s (%s)", name, ntp_name);
+  else
+    snprintf(buf, sizeof (buf), "%s", name);
+
+  log_selection_message(format, buf);
+}
+
+/* ================================================== */
+
 static int
 compare_sort_elements(const void *a, const void *b)
 {
@@ -480,6 +628,20 @@ source_to_string(SRC_Instance inst)

 /* ================================================== */

+static void
+mark_source(SRC_Instance inst, SRC_Status status)
+{
+  inst->status = status;
+
+  DEBUG_LOG("%s status=%d options=%x reach=%o/%d updates=%d distant=%d leap=%d vote=%d lo=%f hi=%f",
+            source_to_string(inst), (int)inst->status, (unsigned int)inst->sel_options,
+            (unsigned int)inst->reachability, inst->reachability_size, inst->updates,
+            inst->distant, (int)inst->leap, inst->leap_vote,
+            inst->sel_info.lo_limit, inst->sel_info.hi_limit);
+}
+
+/* ================================================== */
+
 static void
 mark_ok_sources(SRC_Status status)
 {
@@ -488,7 +650,7 @@ mark_ok_sources(SRC_Status status)
  for (i = 0; i < n_sources; i++) {
    if (sources[i]->status != SRC_OK)
      continue;
-    sources[i]->status = status;
+    mark_source(sources[i], status);
  }
 }

@@ -539,12 +701,12 @@ combine_sources(int n_sel_sources, struct timespec *ref_time, double *offset,
    }

    if (sources[index]->distant) {
-      sources[index]->status = SRC_DISTANT;
+      mark_source(sources[index], SRC_DISTANT);
      continue;
    }

    if (sources[index]->status == SRC_OK)
-      sources[index]->status = SRC_UNSELECTED;
+      mark_source(sources[index], SRC_UNSELECTED);

    elapsed = UTI_DiffTimespecsToDouble(ref_time, &src_ref_time);
    src_offset += elapsed * src_frequency;
@@ -593,12 +755,13 @@ SRC_SelectSource(SRC_Instance updated_inst)
  struct timespec now, ref_time;
  int i, j, j1, j2, index, sel_prefer, n_endpoints, n_sel_sources, sel_req_source;
  int n_badstats_sources, max_sel_reach, max_sel_reach_size, max_badstat_reach;
-  int depth, best_depth, trust_depth, best_trust_depth;
+  int depth, best_depth, trust_depth, best_trust_depth, n_sel_trust_sources;
  int combined, stratum, min_stratum, max_score_index;
-  int orphan_stratum, orphan_source, leap_votes, leap_ins, leap_del;
+  int orphan_stratum, orphan_source;
  double src_offset, src_offset_sd, src_frequency, src_frequency_sd, src_skew;
  double src_root_delay, src_root_dispersion;
  double best_lo, best_hi, distance, sel_src_distance, max_score;
+  double best_trust_lo, best_trust_hi;
  double first_sample_ago, max_reach_sample_ago;
  NTP_Leap leap_status;

@@ -620,7 +783,7 @@ SRC_SelectSource(SRC_Instance updated_inst)
  /* Step 1 - build intervals about each source */

  n_endpoints = 0;
-  n_sel_sources = 0;
+  n_sel_sources = n_sel_trust_sources = 0;
  n_badstats_sources = 0;
  sel_req_source = 0;
  max_sel_reach = max_badstat_reach = 0;
@@ -630,6 +793,9 @@ SRC_SelectSource(SRC_Instance updated_inst)
  for (i = 0; i < n_sources; i++) {
    assert(sources[i]->status != SRC_OK);

+    /* Don't allow the source to vote on leap seconds unless it's selectable */
+    sources[i]->leap_vote = 0;
+
    /* If some sources are specified with the require option, at least one
       of them will have to be selectable in order to update the clock */
    if (sources[i]->sel_options & SRC_SELECT_REQUIRE)
@@ -637,19 +803,19 @@ SRC_SelectSource(SRC_Instance updated_inst)

    /* Ignore sources which were added with the noselect option */
    if (sources[i]->sel_options & SRC_SELECT_NOSELECT) {
-      sources[i]->status = SRC_UNSELECTABLE;
+      mark_source(sources[i], SRC_UNSELECTABLE);
      continue;
    }

    si = &sources[i]->sel_info;
-    SST_GetSelectionData(sources[i]->stats, &now, &si->stratum, &si->leap,
+    SST_GetSelectionData(sources[i]->stats, &now, &si->stratum,
                         &si->lo_limit, &si->hi_limit, &si->root_distance,
                         &si->std_dev, &first_sample_ago,
                         &si->last_sample_ago, &si->select_ok);

    if (!si->select_ok) {
      ++n_badstats_sources;
-      sources[i]->status = SRC_BAD_STATS;
+      mark_source(sources[i], SRC_BAD_STATS);
      if (max_badstat_reach < sources[i]->reachability)
        max_badstat_reach = sources[i]->reachability;
      continue;
@@ -665,15 +831,16 @@ SRC_SelectSource(SRC_Instance updated_inst)
      si->hi_limit += extra_disp;
    }

-    /* Require the root distance to be below the allowed maximum */
-    if (si->root_distance > max_distance) {
-      sources[i]->status = SRC_BAD_DISTANCE;
+    /* Require the root distance to be below the allowed maximum and the
+       endpoints to be in the right order (i.e. a non-negative distance) */
+    if (!(si->root_distance <= max_distance && si->lo_limit <= si->hi_limit)) {
+      mark_source(sources[i], SRC_BAD_DISTANCE);
      continue;
    }

    /* And the same applies for the estimated standard deviation */
    if (si->std_dev > max_jitter) {
-      sources[i]->status = SRC_JITTERY;
+      mark_source(sources[i], SRC_JITTERY);
      continue;
    }

@@ -702,7 +869,7 @@ SRC_SelectSource(SRC_Instance updated_inst)
       can still be selected if its newest sample is not older than the oldest
       sample from reachable sources. */
    if (!sources[i]->reachability && max_reach_sample_ago < si->last_sample_ago) {
-      sources[i]->status = SRC_STALE;
+      mark_source(sources[i], SRC_STALE);
      continue;
    }

@@ -724,7 +891,7 @@ SRC_SelectSource(SRC_Instance updated_inst)
       local unsychronised time and others are synchronised to it. */

    if (si->stratum >= orphan_stratum && sources[i]->type == SRC_NTP) {
-      sources[i]->status = SRC_ORPHAN;
+      mark_source(sources[i], SRC_ORPHAN);

      if (si->stratum == orphan_stratum && sources[i]->reachability &&
          (orphan_source == INVALID_SOURCE ||
@@ -754,6 +921,9 @@ SRC_SelectSource(SRC_Instance updated_inst)
    if (sources[i]->status != SRC_OK)
      continue;

+    if (sources[i]->sel_options & SRC_SELECT_TRUST)
+      n_sel_trust_sources++;
+
    si = &sources[i]->sel_info;

    j1 = n_endpoints;
@@ -770,7 +940,7 @@ SRC_SelectSource(SRC_Instance updated_inst)
    n_endpoints += 2;
  }

-  DEBUG_LOG("badstat=%d sel=%d badstat_reach=%x sel_reach=%x size=%d max_reach_ago=%f",
+  DEBUG_LOG("badstat=%d sel=%d badstat_reach=%o sel_reach=%o size=%d max_reach_ago=%f",
            n_badstats_sources, n_sel_sources, (unsigned int)max_badstat_reach,
            (unsigned int)max_sel_reach, max_sel_reach_size, max_reach_sample_ago);

@@ -826,7 +996,7 @@ SRC_SelectSource(SRC_Instance updated_inst)

  trust_depth = best_trust_depth = 0;
  depth = best_depth = 0;
-  best_lo = best_hi = 0.0;
+  best_lo = best_hi = best_trust_lo = best_trust_hi = 0.0;

  for (i = 0; i < n_endpoints; i++) {
    switch (sort_list[i].tag) {
@@ -836,14 +1006,20 @@ SRC_SelectSource(SRC_Instance updated_inst)
          trust_depth++;
        if (trust_depth > best_trust_depth ||
            (trust_depth == best_trust_depth && depth > best_depth)) {
-          best_trust_depth = trust_depth;
+          if (trust_depth > best_trust_depth) {
+            best_trust_depth = trust_depth;
+            best_trust_lo = sort_list[i].offset;
+          }
          best_depth = depth;
          best_lo = sort_list[i].offset;
        }
        break;
      case HIGH:
-        if (trust_depth == best_trust_depth && depth == best_depth)
-          best_hi = sort_list[i].offset;
+        if (trust_depth == best_trust_depth) {
+          if (depth == best_depth)
+            best_hi = sort_list[i].offset;
+          best_trust_hi = sort_list[i].offset;
+        }
        if (sources[sort_list[i].index]->sel_options & SRC_SELECT_TRUST)
          trust_depth--;
        depth--;
@@ -851,11 +1027,16 @@ SRC_SelectSource(SRC_Instance updated_inst)
      default:
        assert(0);
    }
+    assert(trust_depth <= depth);
+    assert(trust_depth >= 0);
  }

-  if (best_depth <= n_sel_sources / 2 && !best_trust_depth) {
-    /* Could not even get half the reachable sources to agree and there
-       are no trusted sources - clearly we can't synchronise */
+  assert(depth == 0 && trust_depth == 0);
+  assert(2 * n_sel_sources == n_endpoints);
+
+  if ((best_trust_depth == 0 && best_depth <= n_sel_sources / 2) ||
+      (best_trust_depth > 0 && best_trust_depth <= n_sel_trust_sources / 2)) {
+    /* Could not even get half the reachable (trusted) sources to agree */

    if (selected_source_index != INVALID_SOURCE) {
      log_selection_message("Can't synchronise: no majority", NULL);
@@ -882,24 +1063,28 @@ SRC_SelectSource(SRC_Instance updated_inst)
      continue;

    /* Check if source's interval contains the best interval, or is wholly
-       contained within it.  If there are any trusted sources the first
-       condition is applied only to them to not allow non-trusted sources to
-       move the final offset outside the interval. */
-    if (((!best_trust_depth || sources[i]->sel_options & SRC_SELECT_TRUST) &&
-         sources[i]->sel_info.lo_limit <= best_lo &&
+       contained within it.  If there are any trusted sources, other sources
+       are required to be wholly contained within the best interval of the
+       trusted sources to not allow non-trusted sources to move the final
+       offset outside the trusted interval. */
+    if ((sources[i]->sel_info.lo_limit <= best_lo &&
         sources[i]->sel_info.hi_limit >= best_hi) ||
        (sources[i]->sel_info.lo_limit >= best_lo &&
         sources[i]->sel_info.hi_limit <= best_hi)) {

+      if (!(best_trust_depth == 0 || (sources[i]->sel_options & SRC_SELECT_TRUST) ||
+            (sources[i]->sel_info.lo_limit >= best_trust_lo &&
+             sources[i]->sel_info.hi_limit <= best_trust_hi))) {
+        mark_source(sources[i], SRC_UNTRUSTED);
+        continue;
+      }
+
      sel_sources[n_sel_sources++] = i;

      if (sources[i]->sel_options & SRC_SELECT_REQUIRE)
        sel_req_source = 0;
-    } else if (sources[i]->sel_info.lo_limit <= best_lo &&
-               sources[i]->sel_info.hi_limit >= best_hi) {
-      sources[i]->status = SRC_UNTRUSTED;
    } else {
-      sources[i]->status = SRC_FALSETICKER;
+      mark_source(sources[i], SRC_FALSETICKER);
    }
  }

@@ -914,26 +1099,15 @@ SRC_SelectSource(SRC_Instance updated_inst)
    return;
  }

-  /* Accept leap second status if more than half of selectable (and trusted
-     if there are any) sources agree */
-  for (i = leap_ins = leap_del = leap_votes = 0; i < n_sel_sources; i++) {
+  /* Enable the selectable sources (and trusted if there are any) to
+     vote on leap seconds */
+  for (i = 0; i < n_sel_sources; i++) {
    index = sel_sources[i];
    if (best_trust_depth && !(sources[index]->sel_options & SRC_SELECT_TRUST))
      continue;
-    leap_votes++;
-    if (sources[index]->sel_info.leap == LEAP_InsertSecond)
-      leap_ins++;
-    else if (sources[index]->sel_info.leap == LEAP_DeleteSecond)
-      leap_del++;
+    sources[index]->leap_vote = 1;
  }

-  if (leap_ins > leap_votes / 2)
-    leap_status = LEAP_InsertSecond;
-  else if (leap_del > leap_votes / 2)
-    leap_status = LEAP_DeleteSecond;
-  else
-    leap_status = LEAP_Normal;
-
  /* If there are any sources with prefer option, reduce the list again
     only to the preferred sources */
  for (i = 0; i < n_sel_sources; i++) {
@@ -943,7 +1117,7 @@ SRC_SelectSource(SRC_Instance updated_inst)
  if (i < n_sel_sources) {
    for (i = j = 0; i < n_sel_sources; i++) {
      if (!(sources[sel_sources[i]]->sel_options & SRC_SELECT_PREFER))
-        sources[sel_sources[i]]->status = SRC_NONPREFERRED;
+        mark_source(sources[sel_sources[i]], SRC_NONPREFERRED);
      else
        sel_sources[j++] = sel_sources[i];
    }
@@ -1007,10 +1181,8 @@ SRC_SelectSource(SRC_Instance updated_inst)
      sources[i]->sel_score = 1.0 / distance;
    }

-    DEBUG_LOG("select score=%f refid=%"PRIx32" match_refid=%"PRIx32" status=%u dist=%f",
-              sources[i]->sel_score, sources[i]->ref_id,
-              updated_inst ? updated_inst->ref_id : 0,
-              sources[i]->status, distance);
+    DEBUG_LOG("%s score=%f dist=%f",
+              source_to_string(sources[i]), sources[i]->sel_score, distance);

    if (max_score < sources[i]->sel_score) {
      max_score = sources[i]->sel_score;
@@ -1031,13 +1203,11 @@ SRC_SelectSource(SRC_Instance updated_inst)
    if (sources[max_score_index]->updates == 0) {
      selected_source_index = INVALID_SOURCE;
      mark_ok_sources(SRC_WAITS_UPDATE);
-      DEBUG_LOG("best source has no updates");
      return;
    }

    selected_source_index = max_score_index;
-    log_selection_message("Selected source %s",
-                          source_to_string(sources[selected_source_index]));
+    log_selection_source("Selected source %s", sources[selected_source_index]);

    /* New source has been selected, reset all scores */
    for (i = 0; i < n_sources; i++) {
@@ -1046,7 +1216,7 @@ SRC_SelectSource(SRC_Instance updated_inst)
    }
  }

-  sources[selected_source_index]->status = SRC_SELECTED;
+  mark_source(sources[selected_source_index], SRC_SELECTED);

  /* Don't update reference when the selected source has no new samples */

@@ -1056,8 +1226,7 @@ SRC_SelectSource(SRC_Instance updated_inst)
    for (i = 0; i < n_sel_sources; i++) {
      index = sel_sources[i];
      if (sources[index]->status == SRC_OK)
-        sources[index]->status = sources[index]->distant ?
-                                 SRC_DISTANT : SRC_UNSELECTED;
+        mark_source(sources[index], sources[index]->distant ? SRC_DISTANT : SRC_UNSELECTED);
    }
    return;
  }
@@ -1065,6 +1234,8 @@ SRC_SelectSource(SRC_Instance updated_inst)
  for (i = 0; i < n_sources; i++)
    sources[i]->updates = 0;

+  leap_status = get_leap_status();
+
  /* Now just use the statistics of the selected source combined with
     the other selectable sources for trimming the local clock */

@@ -1128,7 +1299,7 @@ slew_sources(struct timespec *raw, struct timespec *cooked, double dfreq,
  }

  if (change_type == LCL_ChangeUnknownStep) {
-    /* After resetting no source is selectable, set reference unsynchronised */
+    /* Update selection status */
    SRC_SelectSource(NULL);
  }
 }
@@ -1150,34 +1321,23 @@ add_dispersion(double dispersion, void *anything)
 /* ================================================== */

 static
-FILE *open_dumpfile(SRC_Instance inst, const char *mode)
+FILE *open_dumpfile(SRC_Instance inst, char mode)
 {
-  FILE *f;
-  char filename[1024], *dumpdir;
+  char filename[64], *dumpdir;

  dumpdir = CNF_GetDumpDir();
-  if (dumpdir[0] == '\0') {
-    LOG(LOGS_WARN, "dumpdir not specified");
+  if (!dumpdir)
    return NULL;
-  }

  /* Include IP address in the name for NTP sources, or reference ID in hex */
-  if ((inst->type == SRC_NTP &&
-       snprintf(filename, sizeof (filename), "%s/%s.dat", dumpdir,
-                source_to_string(inst)) >= sizeof (filename)) ||
-      (inst->type != SRC_NTP &&
-       snprintf(filename, sizeof (filename), "%s/refid:%08"PRIx32".dat",
-                dumpdir, inst->ref_id) >= sizeof (filename))) {
-    LOG(LOGS_WARN, "dumpdir too long");
+  if (inst->type == SRC_NTP && UTI_IsIPReal(inst->ip_addr))
+    snprintf(filename, sizeof (filename), "%s", source_to_string(inst));
+  else if (inst->type == SRC_REFCLOCK)
+    snprintf(filename, sizeof (filename), "refid:%08"PRIx32, inst->ref_id);
+  else
    return NULL;
-  }

-  f = fopen(filename, mode);
-  if (!f && mode[0] != 'r')
-    LOG(LOGS_WARN, "Could not open dump file for %s",
-        source_to_string(inst));
-
-  return f;
+  return UTI_OpenFile(dumpdir, filename, ".dat", mode, 0644);
 }

 /* ================================================== */
@@ -1190,7 +1350,7 @@ SRC_DumpSources(void)
  int i;

  for (i = 0; i < n_sources; i++) {
-    out = open_dumpfile(sources[i], "w");
+    out = open_dumpfile(sources[i], 'w');
    if (!out)
      continue;
    SST_SaveToFile(sources[i]->stats, out);
@@ -1207,7 +1367,7 @@ SRC_ReloadSources(void)
  int i;

  for (i = 0; i < n_sources; i++) {
-    in = open_dumpfile(sources[i], "r");
+    in = open_dumpfile(sources[i], 'r');
    if (!in)
      continue;
    if (!SST_LoadFromFile(sources[i]->stats, in))
@@ -1225,13 +1385,13 @@ SRC_ReloadSources(void)
 void
 SRC_RemoveDumpFiles(void)
 {
-  char pattern[1024], name[64], *dumpdir, *s;
+  char pattern[PATH_MAX], name[64], *dumpdir, *s;
  IPAddr ip_addr;
  glob_t gl;
  size_t i;

  dumpdir = CNF_GetDumpDir();
-  if (dumpdir[0] == '\0' ||
+  if (!dumpdir ||
      snprintf(pattern, sizeof (pattern), "%s/*.dat", dumpdir) >= sizeof (pattern))
    return;

@@ -1252,8 +1412,8 @@ SRC_RemoveDumpFiles(void)
    if (strncmp(name, "refid:", 6) && !UTI_StringToIP(name, &ip_addr))
      continue;

-    DEBUG_LOG("Removing %s", gl.gl_pathv[i]);
-    unlink(gl.gl_pathv[i]);
+    if (!UTI_RemoveFile(NULL, gl.gl_pathv[i], NULL))
+      ;
  }

  globfree(&gl);
@@ -1261,6 +1421,17 @@ SRC_RemoveDumpFiles(void)

 /* ================================================== */

+void
+SRC_ResetSources(void)
+{
+  int i;
+
+  for (i = 0; i < n_sources; i++)
+    SRC_ResetInstance(sources[i]);
+}
+
+/* ================================================== */
+
 int
 SRC_IsSyncPeer(SRC_Instance inst)
 {
@@ -1328,26 +1499,24 @@ SRC_ReportSource(int index, RPT_SourceReport *report, struct timespec *now)
      case SRC_JITTERY:
        report->state = RPT_JITTERY;
        break;
-      case SRC_UNTRUSTED:
      case SRC_WAITS_SOURCES:
      case SRC_NONPREFERRED:
      case SRC_WAITS_UPDATE:
      case SRC_DISTANT:
      case SRC_OUTLIER:
-        report->state = RPT_OUTLIER;
+        report->state = RPT_SELECTABLE;
        break;
      case SRC_UNSELECTED:
-        report->state = RPT_CANDIDATE;
+        report->state = RPT_UNSELECTED;
        break;
      case SRC_SELECTED:
-        report->state = RPT_SYNC;
+        report->state = RPT_SELECTED;
        break;
      default:
-        report->state = RPT_UNREACH;
+        report->state = RPT_NONSELECTABLE;
        break;
    }

-    report->sel_options = src->sel_options;
    report->reachability = src->reachability;

    /* Call stats module to fill out estimates */
@@ -1381,6 +1550,79 @@ SRC_ReportSourcestats(int index, RPT_SourcestatsReport *report, struct timespec

 /* ================================================== */

+static char
+get_status_char(SRC_Status status)
+{
+  switch (status) {
+    case SRC_UNSELECTABLE:
+      return 'N';
+    case SRC_BAD_STATS:
+      return 'M';
+    case SRC_BAD_DISTANCE:
+      return 'd';
+    case SRC_JITTERY:
+      return '~';
+    case SRC_WAITS_STATS:
+      return 'w';
+    case SRC_STALE:
+      return 'S';
+    case SRC_ORPHAN:
+      return 'O';
+    case SRC_UNTRUSTED:
+      return 'T';
+    case SRC_FALSETICKER:
+      return 'x';
+    case SRC_WAITS_SOURCES:
+      return 'W';
+    case SRC_NONPREFERRED:
+      return 'P';
+    case SRC_WAITS_UPDATE:
+      return 'U';
+    case SRC_DISTANT:
+      return 'D';
+    case SRC_OUTLIER:
+      return 'L';
+    case SRC_UNSELECTED:
+      return '+';
+    case SRC_SELECTED:
+      return '*';
+    default:
+      return '?';
+  }
+}
+
+/* ================================================== */
+
+int
+SRC_GetSelectReport(int index, RPT_SelectReport *report)
+{
+  SRC_Instance inst;
+
+  if (index >= n_sources || index < 0)
+    return 0;
+
+  inst = sources[index];
+
+  report->ref_id = inst->ref_id;
+  if (inst->ip_addr)
+    report->ip_addr = *inst->ip_addr;
+  else
+    report->ip_addr.family = IPADDR_UNSPEC;
+  report->state_char = get_status_char(inst->status);
+  report->authentication = inst->authenticated;
+  report->leap = inst->leap;
+  report->conf_options = inst->conf_sel_options;
+  report->eff_options = inst->sel_options;
+  report->last_sample_ago = inst->sel_info.last_sample_ago;
+  report->score = inst->sel_score;
+  report->lo_limit = inst->sel_info.lo_limit;
+  report->hi_limit = inst->sel_info.hi_limit;
+
+  return 1;
+}
+
+/* ================================================== */
+
 SRC_Type
 SRC_GetType(int index)
 {
--- a/sources.h
+++ b/sources.h
@@ -51,6 +51,14 @@ extern void SRC_Initialise(void);
 /* Finalisation function */
 extern void SRC_Finalise(void);

+/* Modes for selecting NTP sources based on their authentication status */
+typedef enum {
+  SRC_AUTHSELECT_IGNORE,
+  SRC_AUTHSELECT_MIX,
+  SRC_AUTHSELECT_PREFER,
+  SRC_AUTHSELECT_REQUIRE,
+} SRC_AuthSelectMode;
+
 typedef enum {
  SRC_NTP,                      /* NTP client/peer */
  SRC_REFCLOCK                  /* Rerefence clock */
@@ -59,9 +67,9 @@ typedef enum {
 /* Function to create a new instance.  This would be called by one of
   the individual source-type instance creation routines. */

-extern SRC_Instance SRC_CreateNewInstance(uint32_t ref_id, SRC_Type type, int sel_options,
-                                          IPAddr *addr, int min_samples, int max_samples,
-                                          double min_delay, double asymmetry);
+extern SRC_Instance SRC_CreateNewInstance(uint32_t ref_id, SRC_Type type, int authenticated,
+                                          int sel_options, IPAddr *addr, int min_samples,
+                                          int max_samples, double min_delay, double asymmetry);

 /* Function to get rid of a source when it is being unconfigured.
   This may cause the current reference source to be reselected, if this
@@ -79,8 +87,10 @@ extern void SRC_SetRefid(SRC_Instance instance, uint32_t ref_id, IPAddr *addr);
 /* Function to get access to the sourcestats instance */
 extern SST_Stats SRC_GetSourcestats(SRC_Instance instance);

-/* This function is called by one of the source drivers when it has
-   a new sample that is to be accumulated */
+/* Function to set the current leap status according to the source */
+extern void SRC_SetLeapStatus(SRC_Instance instance, NTP_Leap leap);
+
+/* Function to accumulate a new sample from the source */
 extern void SRC_AccumulateSample(SRC_Instance instance, NTP_Sample *sample);

 /* This routine sets the source as receiving reachability updates */
@@ -114,13 +124,16 @@ extern void SRC_DumpSources(void);
 extern void SRC_ReloadSources(void);
 extern void SRC_RemoveDumpFiles(void);

+extern void SRC_ResetSources(void);
+
 extern int SRC_IsSyncPeer(SRC_Instance inst);
 extern int SRC_IsReachable(SRC_Instance inst);
 extern int SRC_ReadNumberOfSources(void);
 extern int SRC_ActiveSources(void);
-extern int SRC_ReportSource(int index, RPT_SourceReport *report, struct timespec *now);

+extern int SRC_ReportSource(int index, RPT_SourceReport *report, struct timespec *now);
 extern int SRC_ReportSourcestats(int index, RPT_SourcestatsReport *report, struct timespec *now);
+extern int SRC_GetSelectReport(int index, RPT_SelectReport *report);

 extern SRC_Type SRC_GetType(int index);

--- a/sourcestats.c
+++ b/sourcestats.c
@@ -54,6 +54,9 @@
 /* The minimum standard deviation */
 #define MIN_STDDEV 1.0e-9

+/* The worst case bound on an unknown standard deviation of the offset */
+#define WORST_CASE_STDDEV_BOUND 4.0
+
 /* The asymmetry of network jitter when all jitter is in one direction */
 #define MAX_ASYMMETRY 0.5

@@ -177,9 +180,6 @@ struct SST_Stats_Record {

  /* The stratum from the last accumulated sample */
  int stratum;
-
-  /* The leap status from the last accumulated sample */
-  NTP_Leap leap;
 };

 /* ================================================== */
@@ -249,13 +249,12 @@ SST_ResetInstance(SST_Stats inst)
  inst->estimated_frequency_sd = WORST_CASE_FREQ_BOUND;
  inst->skew = WORST_CASE_FREQ_BOUND;
  inst->estimated_offset = 0.0;
-  inst->estimated_offset_sd = 86400.0; /* Assume it's at least within a day! */
+  inst->estimated_offset_sd = WORST_CASE_STDDEV_BOUND;
  UTI_ZeroTimespec(&inst->offset_time);
-  inst->std_dev = 4.0;
+  inst->std_dev = WORST_CASE_STDDEV_BOUND;
  inst->nruns = 0;
  inst->asymmetry_run = 0;
  inst->asymmetry = 0.0;
-  inst->leap = LEAP_Unsynchronised;
 }

 /* ================================================== */
@@ -323,7 +322,6 @@ SST_AccumulateSample(SST_Stats inst, NTP_Sample *sample)
  inst->root_delays[m] = sample->root_delay;
  inst->root_dispersions[m] = sample->root_dispersion;
  inst->stratum = sample->stratum;
-  inst->leap = sample->leap;
 
  if (inst->peer_delays[n] < inst->fixed_min_delay)
    inst->peer_delays[n] = 2.0 * inst->fixed_min_delay - inst->peer_delays[n];
@@ -603,9 +601,20 @@ SST_DoNewRegression(SST_Stats inst)
    times_back_start = inst->runs_samples + best_start;
    prune_register(inst, best_start);
  } else {
-    inst->estimated_frequency = 0.0;
    inst->estimated_frequency_sd = WORST_CASE_FREQ_BOUND;
    inst->skew = WORST_CASE_FREQ_BOUND;
+    inst->estimated_offset_sd = WORST_CASE_STDDEV_BOUND;
+    inst->std_dev = WORST_CASE_STDDEV_BOUND;
+    inst->nruns = 0;
+
+    if (inst->n_samples > 0) {
+      inst->estimated_offset = inst->offsets[inst->last_sample];
+      inst->offset_time = inst->sample_times[inst->last_sample];
+    } else {
+      inst->estimated_offset = 0.0;
+      UTI_ZeroTimespec(&inst->offset_time);
+    }
+
    times_back_start = 0;
  }

@@ -641,7 +650,7 @@ SST_GetFrequencyRange(SST_Stats inst,

 void
 SST_GetSelectionData(SST_Stats inst, struct timespec *now,
-                     int *stratum, NTP_Leap *leap,
+                     int *stratum,
                     double *offset_lo_limit,
                     double *offset_hi_limit,
                     double *root_distance,
@@ -662,7 +671,6 @@ SST_GetSelectionData(SST_Stats inst, struct timespec *now,
  j = get_buf_index(inst, inst->best_single_sample);

  *stratum = inst->stratum;
-  *leap = inst->leap;
  *std_dev = inst->std_dev;

  sample_elapsed = fabs(UTI_DiffTimespecsToDouble(now, &inst->sample_times[i]));
@@ -694,6 +702,13 @@ SST_GetSelectionData(SST_Stats inst, struct timespec *now,

  *select_ok = inst->regression_ok;

+  /* If maxsamples is too small to have a successful regression, enable the
+     selection as a special case for a fast update/print-once reference mode */
+  if (!*select_ok && inst->n_samples < 3 && inst->n_samples == inst->max_samples) {
+    *std_dev = CNF_GetMaxJitter();
+    *select_ok = 1;
+  }
+
  DEBUG_LOG("n=%d off=%f dist=%f sd=%f first_ago=%f last_ago=%f selok=%d",
            inst->n_samples, offset, *root_distance, *std_dev,
            *first_sample_ago, *last_sample_ago, *select_ok);
@@ -993,31 +1008,24 @@ SST_DoSourcestatsReport(SST_Stats inst, RPT_SourcestatsReport *report, struct ti
 {
  double dspan;
  double elapsed, sample_elapsed;
-  int li, lj, bi, bj;
+  int bi, bj;

  report->n_samples = inst->n_samples;
  report->n_runs = inst->nruns;

-  if (inst->n_samples > 1) {
-    li = get_runsbuf_index(inst, inst->n_samples - 1);
-    lj = get_buf_index(inst, inst->n_samples - 1);
-    dspan = UTI_DiffTimespecsToDouble(&inst->sample_times[li],
-        &inst->sample_times[get_runsbuf_index(inst, 0)]);
-    report->span_seconds = (unsigned long) (dspan + 0.5);
+  if (inst->n_samples > 0) {
+    bi = get_runsbuf_index(inst, inst->best_single_sample);
+    bj = get_buf_index(inst, inst->best_single_sample);

-    if (inst->n_samples > 3) {
-      elapsed = UTI_DiffTimespecsToDouble(now, &inst->offset_time);
-      bi = get_runsbuf_index(inst, inst->best_single_sample);
-      bj = get_buf_index(inst, inst->best_single_sample);
-      sample_elapsed = UTI_DiffTimespecsToDouble(now, &inst->sample_times[bi]);
-      report->est_offset = inst->estimated_offset + elapsed * inst->estimated_frequency;
-      report->est_offset_err = (inst->estimated_offset_sd +
-                 sample_elapsed * inst->skew +
-                 (0.5*inst->root_delays[bj] + inst->root_dispersions[bj]));
-    } else {
-      report->est_offset = inst->offsets[li];
-      report->est_offset_err = 0.5*inst->root_delays[lj] + inst->root_dispersions[lj];
-    }
+    dspan = UTI_DiffTimespecsToDouble(&inst->sample_times[inst->last_sample],
+                                      &inst->sample_times[get_runsbuf_index(inst, 0)]);
+    elapsed = UTI_DiffTimespecsToDouble(now, &inst->offset_time);
+    sample_elapsed = UTI_DiffTimespecsToDouble(now, &inst->sample_times[bi]);
+
+    report->span_seconds = round(dspan);
+    report->est_offset = inst->estimated_offset + elapsed * inst->estimated_frequency;
+    report->est_offset_err = inst->estimated_offset_sd + sample_elapsed * inst->skew +
+                             (0.5 * inst->root_delays[bj] + inst->root_dispersions[bj]);
  } else {
    report->span_seconds = 0;
    report->est_offset = 0;
--- a/sourcestats.h
+++ b/sourcestats.h
@@ -69,7 +69,7 @@ extern void SST_GetFrequencyRange(SST_Stats inst, double *lo, double *hi);
 /* Get data needed for selection */
 extern void
 SST_GetSelectionData(SST_Stats inst, struct timespec *now,
-                     int *stratum, NTP_Leap *leap,
+                     int *stratum,
                     double *offset_lo_limit,
                     double *offset_hi_limit,
                     double *root_distance,
--- a/srcparams.h
+++ b/srcparams.h
@@ -52,6 +52,8 @@ typedef struct {
  int filter_length;
  int interleaved;
  int sel_options;
+  int nts;
+  int nts_port;
  uint32_t authkey;
  double max_delay;
  double max_delay_ratio;
@@ -74,6 +76,7 @@ typedef struct {
 #define SRC_DEFAULT_MINSAMPLES (-1)
 #define SRC_DEFAULT_MAXSAMPLES (-1)
 #define SRC_DEFAULT_ASYMMETRY 1.0
+#define SRC_DEFAULT_NTSPORT 4460
 #define INACTIVE_AUTHKEY 0

 /* Flags for source selection */
--- a/stubs.c
+++ b/stubs.c
@@ -28,6 +28,7 @@
 #include "config.h"

 #include "clientlog.h"
+#include "cmac.h"
 #include "cmdmon.h"
 #include "keys.h"
 #include "logging.h"
@@ -39,12 +40,16 @@
 #include "ntp_io.h"
 #include "ntp_sources.h"
 #include "ntp_signd.h"
+#include "nts_ke_client.h"
+#include "nts_ke_server.h"
+#include "nts_ntp_client.h"
+#include "nts_ntp_server.h"
 #include "privops.h"
 #include "refclock.h"
 #include "sched.h"
 #include "util.h"

-#ifndef FEAT_ASYNCDNS
+#if defined(FEAT_NTP) && !defined(FEAT_ASYNCDNS)

 /* This is a blocking implementation used when asynchronous resolving is not available */

@@ -107,7 +112,7 @@ DNS_Name2IPAddressAsync(const char *name, DNS_NameResolveHandler handler, void *
 #ifndef FEAT_CMDMON

 void
-CAM_Initialise(int family)
+CAM_Initialise(void)
 {
 }

@@ -142,7 +147,7 @@ MNL_Finalise(void)
 #ifndef FEAT_NTP

 void
-NCR_AddBroadcastDestination(IPAddr *addr, unsigned short port, int interval)
+NCR_AddBroadcastDestination(NTP_Remote_Address *addr, int interval)
 {
 }

@@ -169,7 +174,7 @@ NCR_CheckAccessRestriction(IPAddr *ip_addr)
 }

 void
-NIO_Initialise(int family)
+NIO_Initialise(void)
 {
 }

@@ -189,22 +194,30 @@ NSR_Finalise(void)
 }

 NSR_Status
-NSR_AddSource(NTP_Remote_Address *remote_addr, NTP_Source_Type type, SourceParameters *params)
+NSR_AddSource(NTP_Remote_Address *remote_addr, NTP_Source_Type type,
+              SourceParameters *params, uint32_t *conf_id)
 {
  return NSR_TooManySources;
 }

-void
-NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type, SourceParameters *params)
+NSR_Status
+NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,
+                    SourceParameters *params, uint32_t *conf_id)
 {
+  return NSR_TooManySources;
 }

 NSR_Status
-NSR_RemoveSource(NTP_Remote_Address *remote_addr)
+NSR_RemoveSource(IPAddr *address)
 {
  return NSR_NoSuchSource;
 }

+void
+NSR_RemoveSourcesById(uint32_t conf_id)
+{
+}
+
 void
 NSR_RemoveAllSources(void)
 {
@@ -220,6 +233,12 @@ NSR_RefreshAddresses(void)
 {
 }

+char *
+NSR_GetName(IPAddr *address)
+{
+  return NULL;
+}
+
 void
 NSR_SetSourceResolvingEndHandler(NSR_SourceResolvingEndHandler handler)
 {
@@ -307,6 +326,12 @@ NSR_ReportSource(RPT_SourceReport *report, struct timespec *now)
  memset(report, 0, sizeof (*report));
 }
  
+int
+NSR_GetAuthReport(IPAddr *address, RPT_AuthReport *report)
+{
+  return 0;
+}
+
 int
 NSR_GetNTPReport(RPT_NTPReport *report)
 {
@@ -319,6 +344,11 @@ NSR_GetActivityReport(RPT_ActivityReport *report)
  memset(report, 0, sizeof (*report));
 }

+void
+NSR_DumpAuthData(void)
+{
+}
+
 #ifndef FEAT_CMDMON

 void
@@ -398,15 +428,139 @@ NSD_Finalise(void)
 }

 int
-NSD_GetAuthDelay(uint32_t key_id)
-{
-  return 0;
-}
-
-int
-NSD_SignAndSendPacket(uint32_t key_id, NTP_Packet *packet, NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr, int length)
+NSD_SignAndSendPacket(uint32_t key_id, NTP_Packet *packet, NTP_PacketInfo *info,
+                      NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr)
 {
  return 0;
 }

 #endif /* !FEAT_SIGND */
+
+#ifndef HAVE_CMAC
+
+int
+CMC_GetKeyLength(CMC_Algorithm algorithm)
+{
+  return 0;
+}
+
+CMC_Instance
+CMC_CreateInstance(CMC_Algorithm algorithm, const unsigned char *key, int length)
+{
+  return NULL;
+}
+
+int
+CMC_Hash(CMC_Instance inst, const void *in, int in_len, unsigned char *out, int out_len)
+{
+  return 0;
+}
+
+void
+CMC_DestroyInstance(CMC_Instance inst)
+{
+}
+
+#endif /* !HAVE_CMAC */
+
+#ifndef FEAT_NTS
+
+void
+NNS_Initialise(void)
+{
+}
+
+void
+NNS_Finalise(void)
+{
+}
+
+int
+NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod)
+{
+  *kod = 0;
+  return 0;
+}
+
+int
+NNS_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *req_info,
+                         NTP_Packet *response, NTP_PacketInfo *res_info,
+                         uint32_t kod)
+{
+  return 0;
+}
+
+NNC_Instance
+NNC_CreateInstance(IPSockAddr *nts_address, const char *name, const IPSockAddr *ntp_address)
+{
+  return NULL;
+}
+
+void
+NNC_DestroyInstance(NNC_Instance inst)
+{
+}
+
+int
+NNC_PrepareForAuth(NNC_Instance inst)
+{
+  return 1;
+}
+
+int
+NNC_GenerateRequestAuth(NNC_Instance inst, NTP_Packet *packet, NTP_PacketInfo *info)
+{
+  static int logged = 0;
+
+  LOG(logged ? LOGS_DEBUG : LOGS_WARN, "Missing NTS support");
+  logged = 1;
+  return 0;
+}
+
+int
+NNC_CheckResponseAuth(NNC_Instance inst, NTP_Packet *packet, NTP_PacketInfo *info)
+{
+  return 0;
+}
+
+void
+NNC_ChangeAddress(NNC_Instance inst, IPAddr *address)
+{
+}
+
+void
+NNC_DumpData(NNC_Instance inst)
+{
+}
+
+void
+NNC_GetReport(NNC_Instance inst, RPT_AuthReport *report)
+{
+}
+
+void
+NKS_PreInitialise(uid_t uid, gid_t gid, int scfilter_level)
+{
+}
+
+void
+NKS_Initialise(void)
+{
+}
+
+void
+NKS_Finalise(void)
+{
+}
+
+void
+NKS_DumpKeys(void)
+{
+}
+
+void
+NKS_ReloadKeys(void)
+{
+}
+
+#endif /* !FEAT_NTS */
--- a/sys.c
+++ b/sys.c
@@ -97,16 +97,16 @@ SYS_Finalise(void)

 /* ================================================== */

-void SYS_DropRoot(uid_t uid, gid_t gid)
+void SYS_DropRoot(uid_t uid, gid_t gid, SYS_ProcessContext context)
 {
 #if defined(LINUX) && defined (FEAT_PRIVDROP)
-  SYS_Linux_DropRoot(uid, gid, !null_driver);
+  SYS_Linux_DropRoot(uid, gid, context, !null_driver);
 #elif defined(SOLARIS) && defined(FEAT_PRIVDROP)
-  SYS_Solaris_DropRoot(uid, gid);
+  SYS_Solaris_DropRoot(uid, gid, context);
 #elif (defined(NETBSD) || defined(FREEBSD)) && defined(FEAT_PRIVDROP)
-  SYS_NetBSD_DropRoot(uid, gid);
+  SYS_NetBSD_DropRoot(uid, gid, context, !null_driver);
 #elif defined(MACOSX) && defined(FEAT_PRIVDROP)
-  SYS_MacOSX_DropRoot(uid, gid);
+  SYS_MacOSX_DropRoot(uid, gid, context);
 #else
  LOG_FATAL("dropping root privileges not supported");
 #endif
@@ -114,10 +114,10 @@ void SYS_DropRoot(uid_t uid, gid_t gid)

 /* ================================================== */

-void SYS_EnableSystemCallFilter(int level)
+void SYS_EnableSystemCallFilter(int level, SYS_ProcessContext context)
 {
 #if defined(LINUX) && defined(FEAT_SCFILTER)
-  SYS_Linux_EnableSystemCallFilter(level);
+  SYS_Linux_EnableSystemCallFilter(level, context);
 #else
  LOG_FATAL("system call filter not supported");
 #endif
--- a/sys.h
+++ b/sys.h
@@ -35,12 +35,17 @@ extern void SYS_Initialise(int clock_control);
 /* Called at the end of the run to do final clean-up */
 extern void SYS_Finalise(void);

-/* Drop root privileges to the specified user and group */
-extern void SYS_DropRoot(uid_t uid, gid_t gid);
+typedef enum {
+  SYS_MAIN_PROCESS,
+  SYS_NTSKE_HELPER,
+} SYS_ProcessContext;
+
+/* Switch to the specified user and group in given context */
+extern void SYS_DropRoot(uid_t uid, gid_t gid, SYS_ProcessContext context);

 /* Enable a system call filter to allow only system calls
   which chronyd normally needs after initialization */
-extern void SYS_EnableSystemCallFilter(int level);
+extern void SYS_EnableSystemCallFilter(int level, SYS_ProcessContext context);

 extern void SYS_SetScheduler(int SchedPriority);
 extern void SYS_LockMemory(void);
--- a/sys_generic.c
+++ b/sys_generic.c
@@ -417,6 +417,8 @@ SYS_Generic_Finalise(void)

  LCL_ReadRawTime(&now);
  stop_fastslew(&now);
+
+  LCL_RemoveParameterChangeHandler(handle_step, NULL);
 }

 /* ================================================== */
--- a/sys_linux.c
+++ b/sys_linux.c
@@ -426,7 +426,7 @@ SYS_Linux_Finalise(void)

 #ifdef FEAT_PRIVDROP
 void
-SYS_Linux_DropRoot(uid_t uid, gid_t gid, int clock_control)
+SYS_Linux_DropRoot(uid_t uid, gid_t gid, SYS_ProcessContext context, int clock_control)
 {
  char cap_text[256];
  cap_t cap;
@@ -437,13 +437,23 @@ SYS_Linux_DropRoot(uid_t uid, gid_t gid, int clock_control)
  
  UTI_DropRoot(uid, gid);

-  /* Keep CAP_NET_BIND_SERVICE only if a server NTP port can be opened
-     and keep CAP_SYS_TIME only if the clock control is enabled */
-  if (snprintf(cap_text, sizeof (cap_text), "%s %s",
-               CNF_GetNTPPort() ? "cap_net_bind_service=ep" : "",
+  /* Keep CAP_NET_BIND_SERVICE if the NTP server sockets may need to be bound
+     to a privileged port.
+     Keep CAP_NET_RAW if an NTP socket may need to be bound to a device on
+     kernels before 5.7.
+     Keep CAP_SYS_TIME if the clock control is enabled. */
+  if (snprintf(cap_text, sizeof (cap_text), "%s %s %s",
+               (CNF_GetNTPPort() > 0 && CNF_GetNTPPort() < 1024) ?
+                 "cap_net_bind_service=ep" : "",
+               (CNF_GetBindNtpInterface() || CNF_GetBindAcquisitionInterface()) &&
+                 !SYS_Linux_CheckKernelVersion(5, 7) ? "cap_net_raw=ep" : "",
               clock_control ? "cap_sys_time=ep" : "") >= sizeof (cap_text))
    assert(0);

+  /* Helpers don't need any capabilities */
+  if (context != SYS_MAIN_PROCESS)
+    cap_text[0] = '\0';
+
  if ((cap = cap_from_text(cap_text)) == NULL) {
    LOG_FATAL("cap_from_text() failed");
  }
@@ -474,39 +484,127 @@ void check_seccomp_applicability(void)
 /* ================================================== */

 void
-SYS_Linux_EnableSystemCallFilter(int level)
+SYS_Linux_EnableSystemCallFilter(int level, SYS_ProcessContext context)
 {
  const int syscalls[] = {
    /* Clock */
-    SCMP_SYS(adjtimex), SCMP_SYS(clock_gettime), SCMP_SYS(gettimeofday),
-    SCMP_SYS(settimeofday), SCMP_SYS(time),
+    SCMP_SYS(adjtimex),
+    SCMP_SYS(clock_adjtime),
+#ifdef __NR_clock_adjtime64
+    SCMP_SYS(clock_adjtime64),
+#endif
+    SCMP_SYS(clock_gettime),
+#ifdef __NR_clock_gettime64
+    SCMP_SYS(clock_gettime64),
+#endif
+    SCMP_SYS(gettimeofday),
+    SCMP_SYS(settimeofday),
+    SCMP_SYS(time),
+
    /* Process */
-    SCMP_SYS(clone), SCMP_SYS(exit), SCMP_SYS(exit_group), SCMP_SYS(getpid),
-    SCMP_SYS(getrlimit), SCMP_SYS(rt_sigaction), SCMP_SYS(rt_sigreturn),
-    SCMP_SYS(rt_sigprocmask), SCMP_SYS(set_tid_address), SCMP_SYS(sigreturn),
-    SCMP_SYS(wait4), SCMP_SYS(waitpid),
+    SCMP_SYS(clone),
+    SCMP_SYS(exit),
+    SCMP_SYS(exit_group),
+    SCMP_SYS(getpid),
+    SCMP_SYS(getrlimit),
+    SCMP_SYS(getuid),
+    SCMP_SYS(rt_sigaction),
+    SCMP_SYS(rt_sigreturn),
+    SCMP_SYS(rt_sigprocmask),
+    SCMP_SYS(set_tid_address),
+    SCMP_SYS(sigreturn),
+    SCMP_SYS(wait4),
+    SCMP_SYS(waitpid),
+
    /* Memory */
-    SCMP_SYS(brk), SCMP_SYS(madvise), SCMP_SYS(mmap), SCMP_SYS(mmap2),
-    SCMP_SYS(mprotect), SCMP_SYS(mremap), SCMP_SYS(munmap), SCMP_SYS(shmdt),
+    SCMP_SYS(brk),
+    SCMP_SYS(madvise),
+    SCMP_SYS(mmap),
+    SCMP_SYS(mmap2),
+    SCMP_SYS(mprotect),
+    SCMP_SYS(mremap),
+    SCMP_SYS(munmap),
+    SCMP_SYS(shmdt),
+
    /* Filesystem */
-    SCMP_SYS(_llseek), SCMP_SYS(access), SCMP_SYS(chmod), SCMP_SYS(chown),
-    SCMP_SYS(chown32), SCMP_SYS(faccessat), SCMP_SYS(fchmodat), SCMP_SYS(fchownat),
-    SCMP_SYS(fstat), SCMP_SYS(fstat64), SCMP_SYS(getdents), SCMP_SYS(getdents64),
-    SCMP_SYS(lseek), SCMP_SYS(newfstatat), SCMP_SYS(rename), SCMP_SYS(renameat),
-    SCMP_SYS(stat), SCMP_SYS(stat64), SCMP_SYS(statfs), SCMP_SYS(statfs64),
-    SCMP_SYS(unlink), SCMP_SYS(unlinkat),
+    SCMP_SYS(_llseek),
+    SCMP_SYS(access),
+    SCMP_SYS(chmod),
+    SCMP_SYS(chown),
+    SCMP_SYS(chown32),
+    SCMP_SYS(faccessat),
+    SCMP_SYS(fchmodat),
+    SCMP_SYS(fchownat),
+    SCMP_SYS(fstat),
+    SCMP_SYS(fstat64),
+    SCMP_SYS(getdents),
+    SCMP_SYS(getdents64),
+    SCMP_SYS(lseek),
+    SCMP_SYS(lstat),
+    SCMP_SYS(lstat64),
+    SCMP_SYS(newfstatat),
+    SCMP_SYS(readlink),
+    SCMP_SYS(readlinkat),
+    SCMP_SYS(rename),
+    SCMP_SYS(renameat),
+    SCMP_SYS(renameat2),
+    SCMP_SYS(stat),
+    SCMP_SYS(stat64),
+    SCMP_SYS(statfs),
+    SCMP_SYS(statfs64),
+    SCMP_SYS(unlink),
+    SCMP_SYS(unlinkat),
+
    /* Socket */
-    SCMP_SYS(bind), SCMP_SYS(connect), SCMP_SYS(getsockname), SCMP_SYS(getsockopt),
-    SCMP_SYS(recv), SCMP_SYS(recvfrom), SCMP_SYS(recvmmsg), SCMP_SYS(recvmsg),
-    SCMP_SYS(send), SCMP_SYS(sendmmsg), SCMP_SYS(sendmsg), SCMP_SYS(sendto),
+    SCMP_SYS(accept),
+    SCMP_SYS(bind),
+    SCMP_SYS(connect),
+    SCMP_SYS(getsockname),
+    SCMP_SYS(getsockopt),
+    SCMP_SYS(recv),
+    SCMP_SYS(recvfrom),
+    SCMP_SYS(recvmmsg),
+#ifdef __NR_recvmmsg_time64
+    SCMP_SYS(recvmmsg_time64),
+#endif
+    SCMP_SYS(recvmsg),
+    SCMP_SYS(send),
+    SCMP_SYS(sendmmsg),
+    SCMP_SYS(sendmsg),
+    SCMP_SYS(sendto),
+    SCMP_SYS(shutdown),
    /* TODO: check socketcall arguments */
    SCMP_SYS(socketcall),
+
    /* General I/O */
-    SCMP_SYS(_newselect), SCMP_SYS(close), SCMP_SYS(open), SCMP_SYS(openat), SCMP_SYS(pipe),
-    SCMP_SYS(pipe2), SCMP_SYS(poll), SCMP_SYS(ppoll), SCMP_SYS(pselect6), SCMP_SYS(read),
-    SCMP_SYS(futex), SCMP_SYS(select), SCMP_SYS(set_robust_list), SCMP_SYS(write),
+    SCMP_SYS(_newselect),
+    SCMP_SYS(close),
+    SCMP_SYS(open),
+    SCMP_SYS(openat),
+    SCMP_SYS(pipe),
+    SCMP_SYS(pipe2),
+    SCMP_SYS(poll),
+    SCMP_SYS(ppoll),
+#ifdef __NR_ppoll_time64
+    SCMP_SYS(ppoll_time64),
+#endif
+    SCMP_SYS(pselect6),
+#ifdef __NR_pselect6_time64
+    SCMP_SYS(pselect6_time64),
+#endif
+    SCMP_SYS(read),
+    SCMP_SYS(futex),
+#ifdef __NR_futex_time64
+    SCMP_SYS(futex_time64),
+#endif
+    SCMP_SYS(select),
+    SCMP_SYS(set_robust_list),
+    SCMP_SYS(write),
+
    /* Miscellaneous */
-    SCMP_SYS(getrandom), SCMP_SYS(sysinfo), SCMP_SYS(uname),
+    SCMP_SYS(getrandom),
+    SCMP_SYS(sysinfo),
+    SCMP_SYS(uname),
  };

  const int socket_domains[] = {
@@ -522,13 +620,16 @@ SYS_Linux_EnableSystemCallFilter(int level)
    { SOL_IPV6, IPV6_V6ONLY }, { SOL_IPV6, IPV6_RECVPKTINFO },
 #endif
    { SOL_SOCKET, SO_BROADCAST }, { SOL_SOCKET, SO_REUSEADDR },
+#ifdef SO_REUSEPORT
+    { SOL_SOCKET, SO_REUSEPORT },
+#endif
    { SOL_SOCKET, SO_TIMESTAMP }, { SOL_SOCKET, SO_TIMESTAMPNS },
 #ifdef HAVE_LINUX_TIMESTAMPING
    { SOL_SOCKET, SO_SELECT_ERR_QUEUE }, { SOL_SOCKET, SO_TIMESTAMPING },
 #endif
  };

-  const static int fcntls[] = { F_GETFD, F_SETFD, F_SETFL };
+  const static int fcntls[] = { F_GETFD, F_SETFD, F_GETFL, F_SETFL };

  const static unsigned long ioctls[] = {
    FIONREAD, TCGETS,
@@ -558,14 +659,16 @@ SYS_Linux_EnableSystemCallFilter(int level)
  scmp_filter_ctx *ctx;
  int i;

-  /* Check if the chronyd configuration is supported */
-  check_seccomp_applicability();
+  if (context == SYS_MAIN_PROCESS) {
+    /* Check if the chronyd configuration is supported */
+    check_seccomp_applicability();

-  /* Start the helper process, which will run without any seccomp filter.  It
-     will be used for getaddrinfo(), for which it's difficult to maintain a
-     list of required system calls (with glibc it depends on what NSS modules
-     are installed and enabled on the system). */
-  PRV_StartHelper();
+    /* Start the helper process, which will run without any seccomp filter.  It
+       will be used for getaddrinfo(), for which it's difficult to maintain a
+       list of required system calls (with glibc it depends on what NSS modules
+       are installed and enabled on the system). */
+    PRV_StartHelper();
+  }

  ctx = seccomp_init(level > 0 ? SCMP_ACT_KILL : SCMP_ACT_TRAP);
  if (ctx == NULL)
@@ -577,42 +680,44 @@ SYS_Linux_EnableSystemCallFilter(int level)
      goto add_failed;
  }

-  /* Allow sockets to be created only in selected domains */
-  for (i = 0; i < sizeof (socket_domains) / sizeof (*socket_domains); i++) {
-    if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
-                         SCMP_A0(SCMP_CMP_EQ, socket_domains[i])) < 0)
-      goto add_failed;
-  }
+  if (context == SYS_MAIN_PROCESS) {
+    /* Allow opening sockets in selected domains */
+    for (i = 0; i < sizeof (socket_domains) / sizeof (*socket_domains); i++) {
+      if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(socket), 1,
+                           SCMP_A0(SCMP_CMP_EQ, socket_domains[i])) < 0)
+        goto add_failed;
+    }

-  /* Allow setting only selected sockets options */
-  for (i = 0; i < sizeof (socket_options) / sizeof (*socket_options); i++) {
-    if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(setsockopt), 3,
-                         SCMP_A1(SCMP_CMP_EQ, socket_options[i][0]),
-                         SCMP_A2(SCMP_CMP_EQ, socket_options[i][1]),
-                         SCMP_A4(SCMP_CMP_LE, sizeof (int))) < 0)
-      goto add_failed;
-  }
+    /* Allow selected socket options */
+    for (i = 0; i < sizeof (socket_options) / sizeof (*socket_options); i++) {
+      if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(setsockopt), 3,
+                           SCMP_A1(SCMP_CMP_EQ, socket_options[i][0]),
+                           SCMP_A2(SCMP_CMP_EQ, socket_options[i][1]),
+                           SCMP_A4(SCMP_CMP_LE, sizeof (int))) < 0)
+        goto add_failed;
+    }

-  /* Allow only selected fcntl calls */
-  for (i = 0; i < sizeof (fcntls) / sizeof (*fcntls); i++) {
-    if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fcntl), 1,
-                         SCMP_A1(SCMP_CMP_EQ, fcntls[i])) < 0 ||
-        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fcntl64), 1,
-                         SCMP_A1(SCMP_CMP_EQ, fcntls[i])) < 0)
-      goto add_failed;
-  }
+    /* Allow selected fcntl calls */
+    for (i = 0; i < sizeof (fcntls) / sizeof (*fcntls); i++) {
+      if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fcntl), 1,
+                           SCMP_A1(SCMP_CMP_EQ, fcntls[i])) < 0 ||
+          seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fcntl64), 1,
+                           SCMP_A1(SCMP_CMP_EQ, fcntls[i])) < 0)
+        goto add_failed;
+    }

-  /* Allow only selected ioctls */
-  for (i = 0; i < sizeof (ioctls) / sizeof (*ioctls); i++) {
-    if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(ioctl), 1,
-                         SCMP_A1(SCMP_CMP_EQ, ioctls[i])) < 0)
-      goto add_failed;
+    /* Allow selected ioctls */
+    for (i = 0; i < sizeof (ioctls) / sizeof (*ioctls); i++) {
+      if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(ioctl), 1,
+                           SCMP_A1(SCMP_CMP_EQ, ioctls[i])) < 0)
+        goto add_failed;
+    }
  }

  if (seccomp_load(ctx) < 0)
    LOG_FATAL("Failed to load seccomp rules");

-  LOG(LOGS_INFO, "Loaded seccomp filter");
+  LOG(context == SYS_MAIN_PROCESS ? LOGS_INFO : LOGS_DEBUG, "Loaded seccomp filter");
  seccomp_release(ctx);
  return;

--- a/Show More
+++ b/Show More