doc: update NEWS

doc: update README
ntp: fix address in error message
2025-12-03 18:45:07 -05:00 · 2021-04-22 10:44:50 +02:00 · 2021-04-22 10:20:31 +02:00 · 2021-04-22 10:20:31 +02:00 · 2021-04-22 10:20:31 +02:00 · 2021-04-22 10:20:31 +02:00
233 changed files with 24014 additions and 5861 deletions
--- a/.gitignore
+++ b/.gitignore
@@ -1,9 +1,12 @@
 .deps
 .vimrc
+*.gcda
+*.gcno
 *.o
 *.swp
 *.dSYM
 *.DS_Store
+core.*
 tags
 /RELEASES
 /Makefile
--- 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 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)
@@ -70,7 +68,9 @@ distclean : clean
 	-rm -f Makefile config.h config.log

 clean :
-	-rm -f *.o *.s chronyc chronyd core *~
+	$(MAKE) -C test/unit clean
+	-rm -f *.o *.s chronyc chronyd core.* *~
+	-rm -f *.gcda *.gcno
 	-rm -rf .deps
 	-rm -rf *.dSYM

@@ -112,10 +112,15 @@ install-docs :
 quickcheck : chronyd chronyc
 	$(MAKE) -C test/unit check
 	cd test/simulation && ./run
+	cd test/system && ./run

 check : chronyd chronyc
 	$(MAKE) -C test/unit check
 	cd test/simulation && ./run -i 20 -m 2
+	cd test/system && ./run
+
+print-chronyd-objects :
+	@echo $(OBJS)

 Makefile : Makefile.in configure
 	@echo
@@ -129,4 +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/146
+++ b/146
@@ -1,3 +1,149 @@
+New in version 4.1
+==================
+
+Enhancements
+------------
+* Add support for NTS servers specified by IP address (matching
+  Subject Alternative Name in server certificate)
+* Add source-specific configuration of trusted certificates
+* Allow multiple files and directories with trusted certificates
+* Allow multiple pairs of server keys and certificates
+* Add copy option to server/pool directive
+* Increase PPS lock limit to 40% of pulse interval
+* Perform source selection immediately after loading dump files
+* Reload dump files for addresses negotiated by NTS-KE server
+* Update seccomp filter
+* Restart ongoing name resolution on online command
+
+Bug fixes
+---------
+* Fix responding to IPv4 command requests on FreeBSD
+* Fix dump files to not include uncorrected offset
+* Fix initstepslew to accept time from own NTP clients
+* Reset NTP address and port when no longer negotiated by NTS-KE server
+
+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
+==================
+
+Enhancements
+------------
+* Add support for more accurate reading of PHC on Linux 5.0
+* Add support for hardware timestamping on interfaces with read-only
+  timestamping configuration
+* Add support for memory locking and real-time priority on FreeBSD,
+  NetBSD, Solaris
+* Update seccomp filter to work on more architectures
+* Validate refclock driver options
+
+Bug fixes
+---------
+* Fix bindaddress directive on FreeBSD
+* Fix transposition of hardware RX timestamp on Linux 4.13 and later
+* Fix building on non-glibc systems
+
+New in version 3.4
+==================
+
+Enhancements
+------------
+* Add filter option to server/pool/peer directive
+* Add minsamples and maxsamples options to hwtimestamp directive
+* Add support for faster frequency adjustments in Linux 4.19
+* Change default pidfile to /var/run/chrony/chronyd.pid to allow
+  chronyd without root privileges to remove it on exit
+* Disable sub-second polling intervals for distant NTP sources
+* Extend range of supported sub-second polling intervals
+* Get/set IPv4 destination/source address of NTP packets on FreeBSD
+* Make burst options and command useful with short polling intervals
+* Modify auto_offline option to activate when sending request failed
+* Respond from interface that received NTP request if possible
+* Add onoffline command to switch between online and offline state
+  according to current system network configuration
+* Improve example NetworkManager dispatcher script
+
+Bug fixes
+---------
+* Avoid waiting in Linux getrandom system call
+* Fix PPS support on FreeBSD and NetBSD
+
+New in version 3.3
+==================
+
+Enhancements
+------------
+* Add burst option to server/pool directive
+* Add stratum and tai options to refclock directive
+* Add support for Nettle crypto library
+* Add workaround for missing kernel receive timestamps on Linux
+* Wait for late hardware transmit timestamps
+* Improve source selection with unreachable sources
+* Improve protection against replay attacks on symmetric mode
+* Allow PHC refclock to use socket in /var/run/chrony
+* Add shutdown command to stop chronyd
+* Simplify format of response to manual list command
+* Improve handling of unknown responses in chronyc
+
+Bug fixes
+---------
+* Respond to NTPv1 client requests with zero mode
+* Fix -x option to not require CAP_SYS_TIME under non-root user
+* Fix acquisitionport directive to work with privilege separation
+* Fix handling of socket errors on Linux to avoid high CPU usage
+* Fix chronyc to not get stuck in infinite loop after clock step
+
 New in version 3.2
 ==================

--- a/170
+++ b/170
@@ -29,28 +29,22 @@ 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?
 ===================

 The file INSTALL gives instructions.  On supported systems the
-compilation process should be automatic.
-
-You will need an ANSI C compiler -- gcc is recommended.
-
-The manual (in texinfo and text formats) describes how to set the
-software up for the less straightforward cases.
+compilation process should be automatic.  You will need a C compiler,
+e.g. gcc or clang.

 What documentation is there?
 ============================

-A manual is supplied in Texinfo format (chrony.texi) and
-ready-formatted plain text (chrony.txt) in the distribution.
+The distribution includes manual pages and a document containing
+Frequently Asked Questions (FAQ).

-There is also information available on the chrony web pages, accessible
+The documentation is also available on the chrony web pages, accessible
 through the URL 

    https://chrony.tuxfamily.org/
@@ -59,24 +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
@@ -84,12 +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
 =======

@@ -104,135 +88,73 @@ 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>
-    Patch to add tab-completion to chronyc
-
 Benny Lyne Amorsen <benny@amorsen.dk>
-    Patch to add minstratum option
-
 Andrew Bishop <amb@gedanken.demon.co.uk>
-    Fixes for bugs in logging when in daemon mode
-    Fixes for compiler warnings
-    Robustness improvements for drift file
-    Improve installation (directory checking etc)
-    Entries in contrib directory
-    Improvements to 'sources' and 'sourcestats' output from chronyc
-    Improvements to documentation
-    Investigation of required dosynctodr behaviour for various Solaris
-      versions.
-
+Vincent Blut <vincent.debian@free.fr>
 Stephan I. Boettcher <stephan@nevis1.columbia.edu>
-    Entries in contrib directory
-
+David Bohman <debohman@gmail.com>
+Goswin Brederlow <brederlo@informatik.uni-tuebingen.de>
+Leigh Brown <leigh@solinno.co.uk>
 Erik Bryer <ebryer@spots.ab.ca>
-    Entries in contrib directory
-
+Jonathan Cameron <jic23@cam.ac.uk>
 Bryan Christianson <bryan@whatroute.net>
-    Support for macOS
-    Support for privilege separation
-    Entries in contrib directory
-
 Juliusz Chroboczek <jch@pps.jussieu.fr>
-    Fix install rule in Makefile if chronyd file is in use.
-
+Kamil Dudka <kdudka@redhat.com>
+Christian Ehrhardt <christian.ehrhardt@canonical.com>
 Paul Elliott <pelliott@io.com>
-    DNSchrony (in contrib directory), a tool for handling NTP servers
-    with variable IP addresses.
-
+Robert Fairley <rfairley@redhat.com>
+Stefan R. Filipek <srfilipek@gmail.com>
 Mike Fleetwood <mike@rockover.demon.co.uk>
-    Fixes for compiler warnings
-
 Alexander Gretencord <arutha@gmx.de>
-    Changes to installation directory system to make it easier for
-    package builders.
-
 Andrew Griffiths <agriffit@redhat.com>
-    Patch to add support for seccomp filter
-
 Walter Haidinger <walter.haidinger@gmx.at>
-    Providing me with login access to a Linux installation where v1.12
-    wouldn't compile, so I could develop the fixes for v1.13.  Also, for
-    providing the disc space so I can keep an independent backup of the
-    sources.
-
 Juergen Hannken-Illjes <hannken@eis.cs.tu-bs.de>
-    Port to NetBSD
-
 John Hasler <john@dhh.gt.org>
-    Project and website at tuxfamily.org
-    Changes to support 64 bit machines (i.e. those where
-      sizeof(unsigned long) > 4)
-    Bug fix to initstepslew directive
-    Fix to remove potential buffer overrun errors.
-    Memory locking and real-time scheduler support
-    Fix fault where chronyd enters an endless loop
-
 Tjalling Hattink <t.hattink@fugro.nl>
-    Fix scheduler to allow stepping clock from timeout handler
-    Patch to take leap second in PPS refclock from locked source
-    Patch to make reading of RTC for initial trim more reliable
-
 Liam Hatton <me@liamhatton.com>
-    Advice on configuring for Linux on PPC
-
 Jachym Holecek <jakym@volny.cz>
-    Patch to make Linux real time clock work with devfs
-
 Håkan Johansson <f96hajo@chalmers.se>
-    Patch to avoid large values in sources and sourcestats output
-
 Jim Knoble <jmknoble@pobox.com>
-    Fixes for compiler warnings
-
 Antti Jrvinen <costello@iki.fi>
-    Advice on configuring for BSD/386
-
+Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
+Eric Lammerts <eric@lammerts.org>
+Stefan Lucke <stefan@lucke.in-berlin.de>
+Victor Lum <viclum@vanu.com>
+Kevin Lyda <kevin@ie.suberic.net>
+Paul Menzel <paulepanter@users.sourceforge.net>
+Vladimir Michl <vladimir.michl@seznam.cz>
 Victor Moroz <vim@prv.adlum.ru>
-    Patch to support Linux with HZ!=100
-
 Kalle Olavi Niemitalo  <tosi@stekt.oulu.fi>
-    acquisitionport support
-
 Frank Otto <sandwichmacher@web.de>
-    Handling arbitrary HZ values
-
 Denny Page <dennypage@me.com>
-    Advice on support for hardware timestamping
-
+Chris Perl <cperl@janestreet.com>
 Gautier PHILIPPON <gautier.philippon@ensimag.grenoble-inp.fr>
-    Patch to add refresh command to chronyc
-
 Andreas Piesk <apiesk@virbus.de>
-    Patch to make chronyc use the readline library if available
-
+Baruch Siach <baruch@tkos.co.il>
+Foster Snowhill <forst@forstwoof.ru>
+Andreas Steinmetz <ast@domdv.de>
+NAKAMURA Takumi <takumi@ps.sakura.ne.jp>
 Timo Teras <timo.teras@iki.fi>
-    Patch to reply correctly on multihomed hosts
-
 Bill Unruh <unruh@physics.ubc.ca>
-    Advice on statistics
-
 Stephen Wadeley <swadeley@redhat.com>
-    Improvements to man pages
-
+Bernhard Weiss <lisnablagh@web.de>
 Wolfgang Weisselberg <weissel@netcologne.de>
-    Entries in contrib directory
-
+Bernhard M. Wiedemann <bwiedemann@suse.de>
+Joachim Wiedorn <ad_debian@joonet.de>
 Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
-    Many robustness and security improvements
-    
-Ulrich Windl <ulrich.windl@rz.uni-regensburg.de> for the
-    Providing me with information about the Linux 2.2 kernel
-    functionality compared to 2.0.
-
+Ulrich Windl <ulrich.windl@rz.uni-regensburg.de>
+Michael Witten <mfwitten@gmail.com>
 Doug Woodward <dougw@whistler.com>
-    Advice on configuring for Solaris 2.8 on x86
+Thomas Zajic <zlatko@zlatko.fdns.net>

 Many other people have contributed bug reports and suggestions.  We are sorry
 we cannot identify all of you individually.
--- 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
@@ -99,7 +99,17 @@
 #define REQ_ADD_PEER2 59
 #define REQ_ADD_SERVER3 60
 #define REQ_ADD_PEER3 61
-#define N_REQUEST_TYPES 62
+#define REQ_SHUTDOWN 62
+#define REQ_ONOFFLINE 63
+#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 REQ_DOFFSET2 71
+#define N_REQUEST_TYPES 72

 /* Structure used to exchange timespecs independent of time_t size */
 typedef struct {
@@ -243,6 +253,11 @@ 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
@@ -252,9 +267,13 @@ typedef struct {
 #define REQ_ADDSRC_TRUST 0x20
 #define REQ_ADDSRC_REQUIRE 0x40
 #define REQ_ADDSRC_INTERLEAVED 0x80
+#define REQ_ADDSRC_BURST 0x100
+#define REQ_ADDSRC_NTS 0x200
+#define REQ_ADDSRC_COPY 0x400

 typedef struct {
-  IPAddr ip_addr;
+  uint32_t type;
+  uint8_t name[256];
  uint32_t port;
  int32_t minpoll;
  int32_t maxpoll;
@@ -266,6 +285,7 @@ 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;
@@ -273,7 +293,9 @@ typedef struct {
  Float asymmetry;
  Float offset;
  uint32_t flags;
-  uint32_t reserved[4];
+  int32_t filter_length;
+  uint32_t cert_set;
+  uint32_t reserved[2];
  int32_t EOR;
 } REQ_NTP_Source;

@@ -288,8 +310,7 @@ typedef struct {
 } REQ_Dfreq;

 typedef struct {
-  int32_t sec;
-  int32_t usec;
+  Float doffset;
  int32_t EOR;
 } REQ_Doffset;

@@ -305,6 +326,8 @@ typedef struct {
 typedef struct {
  uint32_t first_index;
  uint32_t n_clients;
+  uint32_t min_hits;
+  uint32_t reset;
  int32_t EOR;
 } REQ_ClientAccessesByIndex;

@@ -331,6 +354,21 @@ 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
@@ -367,9 +405,10 @@ typedef struct {
   domain socket.

   Version 6 (no authentication) : changed format of client accesses by index
-   (using new request/reply types) and manual timestamp, new fields and flags
-   in NTP source request and report, new commands: ntpdata, refresh,
-   serverstats
+   (two times), delta offset, and manual timestamp, added new fields and
+   flags to NTP source request and report, made length of manual list constant,
+   added new commands: authdata, ntpdata, onoffline, refresh, reset,
+   selectdata, serverstats, shutdown, sourcename
 */

 #define PROTO_VERSION_NUMBER 6
@@ -383,8 +422,8 @@ 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

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

@@ -433,6 +472,9 @@ 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
@@ -468,7 +510,13 @@ typedef struct {
 #define RPY_CLIENT_ACCESSES_BY_INDEX2 15
 #define RPY_NTP_DATA 16
 #define RPY_MANUAL_TIMESTAMP2 17
-#define N_REPLY_TYPES 18
+#define RPY_MANUAL_LIST2 18
+#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
@@ -492,6 +540,7 @@ typedef struct {
 #define STT_INVALIDAF 17
 #define STT_BADPKTVERSION 18
 #define STT_BADPKTLENGTH 19
+#define STT_INVALIDNAME 21

 typedef struct {
  int32_t EOR;
@@ -506,17 +555,12 @@ 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;
@@ -585,14 +629,17 @@ 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;

@@ -606,10 +653,13 @@ 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;

@@ -683,6 +733,50 @@ 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;
@@ -712,6 +806,9 @@ 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
--- 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
@@ -48,9 +48,10 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
  src->port = SRC_DEFAULT_PORT;
  src->params.minpoll = SRC_DEFAULT_MINPOLL;
  src->params.maxpoll = SRC_DEFAULT_MAXPOLL;
-  src->params.online = 1;
+  src->params.connectivity = SRC_ONLINE;
  src->params.auto_offline = 0;
  src->params.presend_minpoll = SRC_DEFAULT_PRESEND_MINPOLL;
+  src->params.burst = 0;
  src->params.iburst = 0;
  src->params.min_stratum = SRC_DEFAULT_MINSTRATUM;
  src->params.poll_target = SRC_DEFAULT_POLLTARGET;
@@ -58,9 +59,14 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
  src->params.max_sources = SRC_DEFAULT_MAXSOURCES;
  src->params.min_samples = SRC_DEFAULT_MINSAMPLES;
  src->params.max_samples = SRC_DEFAULT_MAXSAMPLES;
+  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.copy = 0;
  src->params.authkey = INACTIVE_AUTHKEY;
+  src->params.cert_set = SRC_DEFAULT_CERTSET;
  src->params.max_delay = SRC_DEFAULT_MAXDELAY;
  src->params.max_delay_ratio = SRC_DEFAULT_MAXDELAYRATIO;
  src->params.max_delay_dev_ratio = SRC_DEFAULT_MAXDELAYDEVRATIO;
@@ -84,10 +90,14 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)

    if (!strcasecmp(cmd, "auto_offline")) {
      src->params.auto_offline = 1;
+    } else if (!strcasecmp(cmd, "burst")) {
+      src->params.burst = 1;
+    } else if (!strcasecmp(cmd, "copy")) {
+      src->params.copy = 1;
    } else if (!strcasecmp(cmd, "iburst")) {
      src->params.iburst = 1;
    } else if (!strcasecmp(cmd, "offline")) {
-      src->params.online = 0;
+      src->params.connectivity = SRC_OFFLINE;
    } else if (!strcasecmp(cmd, "noselect")) {
      src->params.sel_options |= SRC_SELECT_NOSELECT;
    } else if (!strcasecmp(cmd, "prefer")) {
@@ -96,6 +106,9 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
      src->params.sel_options |= SRC_SELECT_REQUIRE;
    } else if (!strcasecmp(cmd, "trust")) {
      src->params.sel_options |= SRC_SELECT_TRUST;
+    } else if (!strcasecmp(cmd, "certset")) {
+      if (sscanf(line, "%"SCNu32"%n", &src->params.cert_set, &n) != 1)
+        return 0;
    } else if (!strcasecmp(cmd, "key")) {
      if (sscanf(line, "%"SCNu32"%n", &src->params.authkey, &n) != 1 ||
          src->params.authkey == INACTIVE_AUTHKEY)
@@ -103,6 +116,9 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
    } else if (!strcasecmp(cmd, "asymmetry")) {
      if (sscanf(line, "%lf%n", &src->params.asymmetry, &n) != 1)
        return 0;
+    } else if (!strcasecmp(cmd, "filter")) {
+      if (sscanf(line, "%d%n", &src->params.filter_length, &n) != 1)
+        return 0;
    } else if (!strcasecmp(cmd, "maxdelay")) {
      if (sscanf(line, "%lf%n", &src->params.max_delay, &n) != 1)
        return 0;
@@ -133,11 +149,16 @@ 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)
@@ -254,7 +275,7 @@ 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;

@@ -271,10 +292,10 @@ 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);
@@ -128,6 +140,8 @@ typedef enum {
 typedef struct {
  char *name;
  int minpoll;
+  int min_samples;
+  int max_samples;
  int nocrossts;
  CNF_HwTs_RxFilter rxfilter;
  double precision;
@@ -137,4 +151,16 @@ typedef struct {

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

+extern char *CNF_GetNtsDumpDir(void);
+extern char *CNF_GetNtsNtpServer(void);
+extern int CNF_GetNtsServerCertAndKeyFiles(const char ***certs, const char ***keys);
+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 int CNF_GetNtsTrustedCertsPaths(const char ***paths, uint32_t **ids);
+extern int CNF_GetNoSystemCert(void);
+extern int CNF_GetNoCertTimeCheck(void);
+
 #endif /* GOT_CONF_H */
--- a/354
+++ b/354
@@ -5,7 +5,8 @@
 #
 # Copyright (C) Richard P. Curnow  1997-2003
 # Copyright (C) Bryan Christianson  2016
-# Copyright (C) Miroslav Lichvar  2009, 2012-2016
+# Copyright (C) Miroslav Lichvar  2009, 2012-2020
+# Copyright (C) Stefan R. Filipek  2019
 #
 # =======================================================================

@@ -32,13 +33,13 @@ test_code () {
    echo "int main(int argc, char **argv) {"
    echo "$code"
    echo "return 0; }"
-  ) > docheck.c
+  ) > conftest.c

-  echo "docheck.c:" >> config.log
-  cat docheck.c >> config.log
-  echo $MYCC $MYCFLAGS $MYCPPFLAGS $cflags -o docheck docheck.c $ldflags \
+  echo "conftest.c:" >> config.log
+  cat conftest.c >> config.log
+  echo $MYCC $MYCFLAGS $MYCPPFLAGS $cflags -o conftest conftest.c $ldflags \
    $MYLDFLAGS >> config.log
-  $MYCC $MYCFLAGS $MYCPPFLAGS $cflags -o docheck docheck.c $ldflags \
+  $MYCC $MYCFLAGS $MYCPPFLAGS $cflags -o conftest conftest.c $ldflags \
    $MYLDFLAGS >> config.log 2>&1

  if [ $? -eq 0 ]
@@ -49,11 +50,39 @@ test_code () {
    echo "No"
    result=1
  fi
-  rm -f docheck.c docheck
+  rm -f conftest.c conftest
  echo >> config.log
  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
@@ -79,14 +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
@@ -107,7 +135,7 @@ For better control, use the options below.
                         since 1970-01-01 [50*365 days ago]
  --with-user=USER       Specify default chronyd user [root]
  --with-hwclockfile=PATH Specify default path to hwclock(8) adjtime file
-  --with-pidfile=PATH    Specify default pidfile [/var/run/chronyd.pid]
+  --with-pidfile=PATH    Specify default pidfile [/var/run/chrony/chronyd.pid]
  --with-rtcdevice=PATH  Specify default path to RTC device [/dev/rtc]
  --with-sendmail=PATH   Path to sendmail binary [/usr/lib/sendmail]
  --enable-debug         Enable debugging support
@@ -135,6 +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.
@@ -152,13 +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
@@ -184,22 +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
@@ -208,9 +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
@@ -225,9 +250,10 @@ feat_timestamping=1
 try_timestamping=0
 feat_ntp_signd=0
 ntp_era_split=""
+use_pthread=0
 default_user="root"
 default_hwclockfile=""
-default_pidfile="/var/run/chronyd.pid"
+default_pidfile="/var/run/chrony/chronyd.pid"
 default_rtcdevice="/dev/rtc"
 mail_program="/usr/lib/sendmail"

@@ -240,21 +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/[^=]*=//;'`
    ;;
@@ -360,12 +374,21 @@ do
    --disable-sechash )
      feat_sechash=0
    ;;
+    --without-nettle )
+      try_nettle=0
+    ;;
    --without-nss )
      try_nss=0
    ;;
    --without-tomcrypt )
      try_tomcrypt=0
    ;;
+    --disable-nts )
+      feat_nts=0
+    ;;
+    --without-gnutls )
+      try_gnutls=0
+    ;;
    --host-system=* )
      OPERATINGSYSTEM=`echo $option | sed -e 's/^.*=//;'`
    ;;
@@ -390,7 +413,7 @@ SYSTEM=${OPERATINGSYSTEM}-${MACHINE}

 case $OPERATINGSYSTEM in
    Linux)
-        EXTRA_OBJECTS="sys_generic.o sys_linux.o sys_timex.o"
+        EXTRA_OBJECTS="sys_generic.o sys_linux.o sys_timex.o sys_posix.o"
        [ $try_libcap != "0" ] && try_libcap=1
        try_rtc=1
        [ $try_seccomp != "0" ] && try_seccomp=1
@@ -405,7 +428,9 @@ case $OPERATINGSYSTEM in
        # recvmmsg() seems to be broken on FreeBSD 11.0 and it's just
        # a wrapper around recvmsg()
        try_recvmmsg=0
-        EXTRA_OBJECTS="sys_generic.o sys_netbsd.o sys_timex.o"
+        EXTRA_OBJECTS="sys_generic.o sys_netbsd.o sys_timex.o sys_posix.o"
+        try_setsched=1
+        try_lockmem=1
        add_def FREEBSD
        if [ $feat_droproot = "1" ]; then
          add_def FEAT_PRIVDROP
@@ -414,15 +439,16 @@ case $OPERATINGSYSTEM in
        echo "Configuring for $SYSTEM"
    ;;
    NetBSD)
-        EXTRA_OBJECTS="sys_generic.o sys_netbsd.o sys_timex.o"
+        EXTRA_OBJECTS="sys_generic.o sys_netbsd.o sys_timex.o sys_posix.o"
        try_clockctl=1
+        try_setsched=1
+        try_lockmem=1
        add_def NETBSD
        echo "Configuring for $SYSTEM"
    ;;
    Darwin)
        EXTRA_OBJECTS="sys_macosx.o"
-        EXTRA_LIBS="-lresolv"
-        EXTRA_CLI_LIBS="-lresolv"
+        LIBS="$LIBS -lresolv"
        add_def MACOSX
        if [ $feat_droproot = "1" ]; then
          add_def FEAT_PRIVDROP
@@ -440,9 +466,10 @@ case $OPERATINGSYSTEM in
        echo "Configuring for macOS (" $SYSTEM "macOS version" $VERSION ")"
    ;;
    SunOS)
-        EXTRA_OBJECTS="sys_generic.o sys_solaris.o sys_timex.o"
-        EXTRA_LIBS="-lsocket -lnsl -lresolv"
-        EXTRA_CLI_LIBS="-lsocket -lnsl -lresolv"
+        EXTRA_OBJECTS="sys_generic.o sys_solaris.o sys_timex.o sys_posix.o"
+        LIBS="$LIBS -lsocket -lnsl -lresolv"
+        try_setsched=1
+        try_lockmem=1
        add_def SOLARIS
        # These are needed to have msg_control in struct msghdr
        add_def __EXTENSIONS__
@@ -472,7 +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"
@@ -540,6 +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" $PKG_CONFIG --version; then
+  try_nettle=0
+  try_nss=0
+  try_gnutls=0
+fi
+
 if test_code '64-bit time_t' 'time.h' '' '' '
  char x[sizeof(time_t) > 4 ? 1 : -1] = {0};
  return x[0];'
@@ -550,7 +587,11 @@ then
    split_seconds=$ntp_era_split
    split_days=0
  else
-    split_seconds=`date '+%s'`
+    if [ "x$SOURCE_DATE_EPOCH" != "x" ]; then
+      split_seconds=$SOURCE_DATE_EPOCH
+    else
+      split_seconds=`date '+%s'`
+    fi
    if [ "x$split_seconds" = "x" ]; then
      echo "error: could not get current time, --with-ntp-era option is needed"
      exit 1
@@ -575,25 +616,15 @@ 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
  fi
 fi
  
-if test_code '<stdint.h>' 'stdint.h' '' '' ''; then
-  add_def HAVE_STDINT_H
-fi
-
-if test_code '<inttypes.h>' 'inttypes.h' '' '' ''; then
-  add_def HAVE_INTTYPES_H
-fi
-
 if test_code 'struct in_pktinfo' 'sys/socket.h netinet/in.h' '' '' '
  struct in_pktinfo ipi;
  return sizeof (ipi.ipi_spec_dst.s_addr) + IP_PKTINFO;'
@@ -602,10 +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
@@ -623,6 +655,20 @@ then
  fi
 fi

+if ! test_code 'O_NOFOLLOW flag' 'sys/types.h sys/stat.h fcntl.h' '' "$LIBS" \
+  'return open("/dev/null", O_NOFOLLOW);'
+then
+  if test_code 'O_NOFOLLOW flag with _GNU_SOURCE' 'sys/types.h sys/stat.h fcntl.h' \
+    '-D_GNU_SOURCE' "$LIBS" \
+    'return open("/dev/null", O_NOFOLLOW);'
+  then
+    add_def _GNU_SOURCE
+  else
+    echo "error: open() does not support O_NOFOLLOW flag"
+    exit 1
+  fi
+fi
+
 if [ $try_clock_gettime = "1" ]; then
  if test_code 'clock_gettime()' 'time.h' '' '' \
    'clock_gettime(CLOCK_REALTIME, NULL);'
@@ -638,40 +684,42 @@ 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
+  echo "error: getaddrinfo() not found"
+  exit 1
 fi

 if [ $feat_asyncdns = "1" ] && \
-  test_code 'pthread' 'pthread.h' '-pthread' '' \
-    'return pthread_create((void *)1, NULL, (void *)1, NULL);'
+  test_code 'pthread' 'pthread.h' '-pthread' '' '
+    pthread_t thread;
+    return (int)pthread_create(&thread, NULL, (void *)1, NULL);'
 then
  add_def FEAT_ASYNCDNS
  add_def USE_PTHREAD_ASYNCDNS
  EXTRA_OBJECTS="$EXTRA_OBJECTS nameserv_async.o"
-  MYCFLAGS="$MYCFLAGS -pthread"
+  use_pthread=1
 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
@@ -696,6 +744,7 @@ then
    struct scm_ts_pktinfo pktinfo;
    pktinfo.if_index = pktinfo.pkt_length = 0;
    return pktinfo.if_index + pktinfo.pkt_length + HWTSTAMP_FILTER_NTP_ALL +
+           SCM_TIMESTAMPING_PKTINFO +
           SOF_TIMESTAMPING_OPT_PKTINFO + SOF_TIMESTAMPING_OPT_TX_SWHW;'; then
    add_def HAVE_LINUX_TIMESTAMPING_RXFILTER_NTP 1
    add_def HAVE_LINUX_TIMESTAMPING_OPT_PKTINFO 1
@@ -705,11 +754,11 @@ fi

 timepps_h=""
 if [ $feat_refclock = "1" ] && [ $feat_pps = "1" ]; then
-  if test_code '<sys/timepps.h>' 'sys/timepps.h' '' '' ''; then
+  if test_code '<sys/timepps.h>' 'inttypes.h time.h sys/timepps.h' '' '' ''; then
    timepps_h="sys/timepps.h"
    add_def HAVE_SYS_TIMEPPS_H
  else
-    if test_code '<timepps.h>' 'timepps.h' '' '' ''; then
+    if test_code '<timepps.h>' 'inttypes.h time.h timepps.h' '' '' ''; then
      timepps_h="timepps.h"
      add_def HAVE_TIMEPPS_H
    fi
@@ -717,10 +766,11 @@ if [ $feat_refclock = "1" ] && [ $feat_pps = "1" ]; then
 fi

 if [ "x$timepps_h" != "x" ] && \
-  test_code 'PPSAPI' "string.h $timepps_h" '' '' '
+  test_code 'PPSAPI' "inttypes.h string.h time.h $timepps_h" '' '' '
    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
@@ -749,10 +799,12 @@ 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

@@ -784,25 +836,34 @@ fi

 if [ $try_setsched = "1" ] && \
  test_code \
-    'sched_setscheduler()' \
-    'sched.h' '' '' '
+    'pthread_setschedparam()' \
+    'pthread.h sched.h' '-pthread' '' '
     struct sched_param sched;
     sched_get_priority_max(SCHED_FIFO);
-     sched_setscheduler(0, SCHED_FIFO, &sched);'
+     pthread_setschedparam(pthread_self(), SCHED_FIFO, &sched);'
 then
-  add_def HAVE_SCHED_SETSCHEDULER
+  add_def HAVE_PTHREAD_SETSCHEDPARAM
+  use_pthread=1
 fi

 if [ $try_lockmem = "1" ] && \
  test_code \
    'mlockall()' \
-    'sys/mman.h sys/resource.h' '' '' '
-     struct rlimit rlim;
-     setrlimit(RLIMIT_MEMLOCK, &rlim);
+    'sys/mman.h' '' '' '
     mlockall(MCL_CURRENT|MCL_FUTURE);'
 then
  add_def HAVE_MLOCKALL
 fi
+if [ $try_lockmem = "1" ] && \
+  test_code \
+    '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
+fi

 if [ $feat_forcednsretry = "1" ]
 then
@@ -812,37 +873,11 @@ 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

@@ -852,16 +887,37 @@ fi
 HASH_OBJ="hash_intmd5.o"
 HASH_LINK=""

-if [ $feat_sechash = "1" ] && [ $try_nss = "1" ]; then
+if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ]  && [ $try_nettle = "1" ]; then
+  test_cflags="`pkg_config --cflags nettle`"
+  test_link="`pkg_config --libs nettle`"
+  if test_code 'nettle' 'nettle/nettle-meta.h nettle/sha2.h' \
+    "$test_cflags" "$test_link" \
+    'return nettle_hashes[0]->context_size;'
+  then
+    HASH_OBJ="hash_nettle.o"
+    HASH_LINK="$test_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
@@ -873,12 +929,62 @@ 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
+
 SYSCONFDIR=/etc
 if [ "x$SETSYSCONFDIR" != "x" ]; then
  SYSCONFDIR=$SETSYSCONFDIR
@@ -942,9 +1048,9 @@ add_def DEFAULT_USER "\"$default_user\""
 add_def DEFAULT_COMMAND_SOCKET "\"$CHRONYRUNDIR/chronyd.sock\""
 add_def MAIL_PROGRAM "\"$mail_program\""

-common_features="`get_features IPV6 DEBUG`"
+common_features="`get_features SECHASH IPV6 DEBUG`"
 chronyc_features="`get_features READLINE`"
-chronyd_features="`get_features CMDMON NTP REFCLOCK RTC PRIVDROP SCFILTER SECHASH 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 $common_features"
@@ -960,15 +1066,15 @@ add_def CHRONY_VERSION "\"${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
--- 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 +77,17 @@ 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 original hostnames or IP addresses of NTP
+sources that were specified in the configuration file, or *chronyc* commands.
+Without the *-n* and *-N* option, the printed hostnames are obtained from
+reverse DNS lookups and can be different from the specified hostnames.
+
 *-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 +117,14 @@ 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 +184,12 @@ 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 +295,18 @@ 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 +320,23 @@ 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.
@@ -338,8 +357,9 @@ register has 8 bits and is updated on every received or missed packet from
 the source. A value of 377 indicates that a valid reply was received for all
 from the last eight transmissions.
 *LastRx*:::
-This column shows how long ago the last sample was received from the source.
-This is normally in seconds. The letters _m_, _h_, _d_ or _y_ indicate
+This column shows how long ago the last good sample (which is shown in the next
+column) was received from the source. Measurements that failed some tests are
+ignored. This is normally in seconds. The letters _m_, _h_, _d_ or _y_ indicate
 minutes, hours, days, or years.
 *Last sample*:::
 This column shows the offset between the local clock and the source at the
@@ -352,18 +372,21 @@ 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
@@ -399,6 +422,98 @@ 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
@@ -439,10 +554,82 @@ 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)
@@ -525,15 +712,13 @@ 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.
 +
@@ -541,15 +726,27 @@ 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:
 +
@@ -600,7 +797,7 @@ 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.
@@ -687,7 +884,8 @@ 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.
 +
@@ -722,6 +920,14 @@ particular source or sources has been restored.
 +
 The syntax is identical to that of the <<offline,*offline*>> command.

+[[onoffline]]
+*onoffline*::
+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 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
 current set of sources. It is equivalent to the *polltarget* option in the
@@ -736,6 +942,20 @@ 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]]
@@ -772,7 +992,7 @@ 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
@@ -843,10 +1063,17 @@ 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:
 +
@@ -871,20 +1098,22 @@ 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
@@ -892,6 +1121,9 @@ 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_]::
@@ -901,11 +1133,8 @@ The effect of the allow command is identical to the
 The syntax is illustrated in the following examples:
 +
 ----
-allow foo.example.net
-allow all 1.2
-allow 3.4.5
-allow 6.7.8/22
-allow 6.7.8.9/22
+allow 1.2.3.4
+allow all 3.4.5.0/24
 allow 2001:db8:789a::/48
 allow 0/0
 allow ::/0
@@ -920,11 +1149,8 @@ The effect of the allow command is identical to the
 The syntax is illustrated in the following examples:
 +
 ----
-deny foo.example.net
-deny all 1.2
-deny 3.4.5
-deny 6.7.8/22
-deny 6.7.8.9/22
+deny 1.2.3.4
+deny all 3.4.5.0/24
 deny 2001:db8:789a::/48
 deny 0/0
 deny ::/0
@@ -1077,7 +1303,7 @@ 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
@@ -1110,23 +1336,38 @@ 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.
+
+[[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.

 === Client commands

@@ -1176,10 +1417,10 @@ 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:
 +
@@ -1189,7 +1430,13 @@ 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
@@ -81,9 +93,9 @@ started without root privileges.

 *-r*::
 This option will try to reload and then delete files containing sample
-histories for each of the servers and reference clocks being used. These
-histories are created by using the <<chronyc.adoc#dump,*dump*>> command in
-*chronyc*, or by setting the <<chrony.conf.adoc#dumponexit,*dumponexit*>>
+histories for each of the servers and reference clocks being used. The
+files are expected to be in the directory specified by the
+<<chrony.conf.adoc#dumpdir,*dumpdir*>>
 directive in the configuration file. This option is useful if you want to stop
 and restart *chronyd* briefly for any reason, e.g. to install a new version.
 However, it should be used only on systems where the kernel can maintain clock
@@ -125,47 +137,62 @@ 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 SYSSIG
-signal is thrown instead and in level 0 the filter is disabled (default 0).
+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. 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.
 This mode is only supported on Linux.

 *-x*::
-This option disables the control of the system clock. *chronyd* will not make
-any adjustments of the clock, but it will still track its offset and frequency
-relative to the estimated true time, and be able to operate as an NTP server.
-This allows *chronyd* to run without the capability to adjust or set the system
-clock (e.g. in some containers).
+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 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`
@@ -46,9 +49,11 @@ website.

 First, the client needs to know which NTP servers it should ask for the current
 time. They are specified by the `server` or `pool` directive. The `pool`
-directive can be used for names that resolve to multiple addresses. For good
-reliability the client should have at least three servers. The `iburst` option
-speeds up the initial synchronisation.
+directive is used with names that resolve to multiple addresses of different
+servers. For reliable operation, the client should have at least three servers.
+
+The `iburst` option enables a burst of requests to speed up the initial
+synchronisation.

 To stabilise the initial synchronisation on the next start, the estimated drift
 of the system clock is saved to a file specified by the `driftfile` directive.
@@ -59,13 +64,13 @@ 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
+If you wanted to use public NTP servers from the
+https://www.pool.ntp.org/[pool.ntp.org] project, the minimal _chrony.conf_ file
 could be:

 ----
@@ -75,52 +80,43 @@ 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.
+By default, `chronyd` does not operate as an NTP server. You need to add an
+`allow` directive to the _chrony.conf_ file in order for `chronyd` to open the
+server NTP port and respond to client requests.

-=== I have several computers on a LAN. Should be all clients of an external server?
+----
+allow 192.168.1.0/24
+----

-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
+An `allow` directive with no specified subnet allows access from all IPv4 and
+IPv6 addresses.
+
+=== Should all computers on a LAN be clients of an external server?
+
+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
@@ -133,29 +129,144 @@ 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 make the system clock more secure?
+
+An NTP client synchronising the system clock to an NTP server is susceptible to
+various attacks, which can break applications and network protocols relying on
+accuracy of the clock (e.g. DNSSEC, Kerberos, TLS, WireGuard).
+
+Generally, a man-in-the-middle (MITM) attacker between the client and server
+can
+
+* make fake responses, or modify real responses from the server, to create an
+  arbitrarily large time and frequency offset, make the server appear more
+  accurate, insert a leap second, etc.
+* delay the requests and/or responses to create a limited time offset and
+  temporarily also a limited frequency offset
+* drop the requests or responses to prevent updates of the clock with new
+  measurements
+* redirect the requests to a different server
+
+The attacks can be combined for a greater effect. The attacker can delay
+packets to create a significant frequency offset first and then drop all
+subsequent packets to let the clock quickly drift away from the true time.
+The attacker might also be able to control the server's clock.
+
+Some attacks cannot be prevented. Monitoring is needed for detection, e.g. the
+reachability register in the `sources` report shows missing packets. The extent
+to which the attacker can control the client's clock depends on its
+configuration.
+
+Enable authentication to prevent `chronyd` from accepting modified, fake, or
+redirected packets. It can be enabled with a symmetric key specified by the
+`key` option, or Network Time Security (NTS) by the `nts` option (supported
+since `chrony` version 4.0). The server needs to support the selected
+authentication mechanism. Symmetric keys have to be configured on both client
+and server, and each client must have its own key (one per server).
+
+The maximum offset that the attacker can insert in an NTP measurement by
+delaying packets can be limited by the `maxdelay` option. The default value is
+3 seconds. The measured delay is reported as the peer delay in the `ntpdata`
+report and `measurements` log. Set the `maxdelay` option to a value larger than
+the maximum value that is normally observed. Note that the delay can increase
+significantly even when not under an attack, e.g. when the network is congested
+or the routing has changed.
+
+The maximum accepted change in time offset between clock updates can be limited
+by the `maxchange` directive. Larger changes in the offset will be ignored or
+cause `chronyd` to exit. Note that the attacker can get around this limit by
+splitting the offset into multiple smaller offsets and/or creating a large
+frequency offset. When this directive is used, `chronyd` will have to be
+restarted after a successful attack. It will not be able to recover on its own.
+It must not be restarted automatically (e.g. by the service manager).
+
+The impact of a large accepted time offset can be reduced by disabling clock
+steps, i.e. by not using the `makestep` and `initstepslew` directives. The
+offset will be slowly corrected by speeding up or slowing down the clock at a
+rate which can be limited by the `maxslewrate` directive. Disabling clock steps
+completely is practical only if the clock cannot gain a larger error on its
+own, e.g. when the computer is shut down or suspended, and the `maxslewrate`
+limit is large enough to correct an expected error in an acceptable time. The
+`rtcfile` directive with the `-s` option can be used to compensate for the RTC
+drift.
+
+A more practical approach is to enable `makestep` for a limited number of clock
+updates (the 2nd argument of the directive) and limit the offset change in all
+updates by the `maxchange` directive. The attacker will be able to make only a
+limited step and only if the attack starts in a short window after booting the
+computer, or when `chronyd` is restarted without the `-R` option.
+
+The frequency offset can be limited by the `maxdrift` directive. The measured
+frequency offset is reported in the drift file, `tracking` report, and
+`tracking` log. Set `maxdrift` to a value larger than the maximum absolute
+value that is normally observed. Note that the frequency of the clock can
+change due to aging of the crystal, differences in calibration of the clock
+source between reboots, migrated virtual machine, etc. A typical computer clock
+has a drift smaller than 100 parts per million (ppm), but much larger drifts
+are possible (e.g. in some virtual machines).
+
+Use only trusted servers, which you expect to be well configured and managed,
+using authentication for their own servers, etc. Use multiple servers, ideally
+in different locations. The attacker will have to deal with a majority of the
+servers in order to pass the source selection and update the clock with a large
+offset. Use the `minsources` directive to increase the required number of
+selectable sources to make the selection more robust.
+
+Do not specify servers as peers. The symmetric mode is less secure than the
+client/server mode. If not authenticated, it is vulnerable to off-path
+denial-of-service attacks, and even when it is authenticated, it is still
+susceptible to replay attacks.
+
+Mixing of authenticated and unauthenticated servers should generally be
+avoided. If mixing is necessary (e.g. for a more accurate and stable
+synchronisation to a closer server which does not support authentication), the
+authenticated servers should be configured as trusted and required to not allow
+the unauthenticated servers to override the authenticated servers in the source
+selection. Since `chrony` version 4.0, the selection options are enabled in
+such a case automatically. This behaviour can be disabled or modified by the
+`authselmode` directive.
+
+An example of a client configuration limiting the impact of the attacks could
+be
+
+----
+server foo.example.net iburst nts maxdelay 0.1
+server bar.example.net iburst nts maxdelay 0.2
+server baz.example.net iburst nts maxdelay 0.05
+server qux.example.net iburst nts maxdelay 0.1
+server quux.example.net iburst nts maxdelay 0.1
+minsources 3
+maxchange 100 0 0
+makestep 0.001 1
+maxdrift 100
+maxslewrate 100
+driftfile /var/lib/chrony/drift
+ntsdumpdir /var/lib/chrony
+rtcsync
+----
+
 === 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
-should make local receive and transmit timestamps of NTP packets much more
-accurate.
+can be enabled by the `hwtimestamp` directive. It should make local receive and
+transmit timestamps of NTP packets much more stable and accurate.

-There are also useful options which can be set in the `server` directive, they
-are `minpoll`, `maxpoll`, `polltarget`, `maxdelay`, `maxdelayratio`,
-`maxdelaydevratio`, and `xleave`.
+The `server` directive has some useful options: `minpoll`, `maxpoll`,
+`polltarget`, `maxdelay`, `maxdelayratio`, `maxdelaydevratio`, `xleave`,
+`filter`.

 The first three options set the minimum and maximum allowed polling interval,
 and how should be the actual interval adjusted in the specified range. Their
@@ -163,14 +274,19 @@ 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
 temperature sensitivity of the crystal oscillator and the maximum rate of the
 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 might work better.
+
 An example of the directive for an NTP server on the Internet that you are
 allowed to poll frequently could be

@@ -178,15 +294,15 @@ allowed to poll frequently could be
 server foo.example.net minpoll 4 maxpoll 6 polltarget 16
 ----

-An example using very short polling intervals for a server located in the same
+An example using shorter polling intervals with a server located in the same
 LAN could be

 ----
 server ntp.local minpoll 2 maxpoll 4 polltarget 30
 ----

-The maxdelay options are useful to ignore measurements with larger delay (e.g.
-due to congestion in the network) and improve the stability of the
+The maxdelay options are useful to ignore measurements with an unusually large
+delay (e.g. due to congestion in the network) and improve the stability of the
 synchronisation. The `maxdelaydevratio` option could be added to the example
 with local NTP server

@@ -194,28 +310,179 @@ with local NTP server
 server ntp.local minpoll 2 maxpoll 4 polltarget 30 maxdelaydevratio 2
 ----

-If your server supports the interleaved mode, the `xleave` option should be
-added to the `server` directive in order to allow the server to send the
-client more accurate hardware or kernel transmit timestamps. When combined with
-local hardware timestamping, sub-microsecond accuracy may be possible. An
-example could be
+If your server supports the interleaved mode (e.g. it is running `chronyd`),
+the `xleave` option should be added to the `server` directive to enable the
+server to provide the client with more accurate transmit timestamps (kernel or
+preferably hardware). For example:

 ----
-server ntp.local minpoll 2 maxpoll 2 xleave
+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 might be possible. For example:
+
+----
+server ntp.local minpoll 0 maxpoll 0 xleave
 hwtimestamp eth0
 ----

+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. 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 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:
+
+----
+server ntp.local minpoll -6 maxpoll -6 filter 15 xleave
+hwtimestamp eth0 minpoll -6
+----
+
 === Does `chronyd` have an ntpdate mode?

 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 since `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` 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
+`corrtimeratio` directives reduce the maximum frequency error due to an offset
+correction and the `maxdrift` directive reduces the maximum assumed frequency
+error of the clock. The `makestep` directive enables a step threshold and the
+`maxchange` directive enables a panic threshold. The `maxclockerror` directive
+increases the minimum dispersion rate.
+
+----
+minsamples 32
+maxslewrate 500
+corrtimeratio 100
+maxdrift 500
+makestep 0.128 -1
+maxchange 1000 1 1
+maxclockerror 15
+----
+
+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 a computer at the
+same time. One can operate primarily as an NTP client to synchronise the system
+clock and another as a server for other computers. If they use the same
+filesystem, they need to be configured with different pidfiles, Unix domain
+command sockets, and any other file or directory specified in the configuration
+file. If they run in the same network namespace, they need to use different NTP
+and command ports, or bind the ports to different addresses or interfaces.
+
+The server instance should be started with the `-x` option to prevent it from
+adjusting the system clock and interfering with the client instance. It can be
+configured as a client to synchronise its NTP clock to other servers, or the
+client instance running on the same computer. In the latter case, the `copy`
+option (added in `chrony` version 4.1) can be used to assume the reference ID
+and stratum of the client instance, which enables detection of synchronisation
+loops with its own clients.
+
+On Linux, starting with `chrony` version 4.0, it is possible to run multiple
+server instances sharing a port to better utilise multiple cores of the CPU.
+Note that for rate limiting and client/server interleaved mode to work well
+it is necessary that all packets received from the same address are handled by
+the same server instance.
+
+An example configuration of the client instance could be
+
+----
+pool pool.ntp.org iburst
+allow 127.0.0.1
+port 11123
+driftfile /var/lib/chrony/drift
+makestep 1 3
+rtcsync
+----
+
+and configuration of the first server instance could be
+
+----
+server 127.0.0.1 port 11123 minpoll 0 maxpoll 0 copy
+allow
+cmdport 11323
+bindcmdaddress /var/run/chrony/chronyd-server1.sock
+pidfile /var/run/chronyd-server1.pid
+driftfile /var/lib/chrony/drift-server1
+----
+
+=== 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 other 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
@@ -232,18 +499,17 @@ 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
 this:

 ----
-210 Number of sources = 3
 MS Name/IP address         Stratum Poll Reach LastRx Last sample
 ===============================================================================
 ^* foo.example.net               2   6   377    34   +484us[ -157us] +/-   30ms
@@ -253,9 +519,10 @@ 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
@@ -266,6 +533,19 @@ currently online and offline. For example:
 0 sources with unknown address
 ----

+=== Is name resolution working correctly?
+
+NTP servers specified by their hostname (instead of an IP address) have to have
+their names resolved before `chronyd` can send any requests to them. If the
+`activity` command prints a non-zero number of sources with unknown address,
+there is an issue with the resolution. Typically, a DNS server is specified in
+_/etc/resolv.conf_. Make sure it is working correctly.
+
+Since `chrony` version 4.0, you can run `chronyc -N sources -a` command to
+print all sources, even those that do not have a known address yet, with their
+names as they were specified in the configuration. This can be useful to verify
+that the names specified in the configuration are used as expected.
+
 === Is `chronyd` allowed to step the system clock?

 By default, `chronyd` adjusts the clock gradually by slowing it down or
@@ -282,9 +562,9 @@ 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

@@ -292,6 +572,139 @@ to
 makestep 1 -1
 ----

+=== Using NTS?
+
+The Network Time Security (NTS) mechanism uses Transport Layer Security (TLS)
+to establish the keys needed for authentication of NTP packets.
+
+Run the `authdata` command to check whether the key establishment was
+successful:
+
+----
+# chronyc -N authdata
+Name/IP address             Mode KeyID Type KLen Last Atmp  NAK Cook CLen
+=========================================================================
+foo.example.net              NTS     1   15  256  33m    0    0    8  100
+bar.example.net              NTS     1   15  256  33m    0    0    8  100
+baz.example.net              NTS     1   15  256  33m    0    0    8  100
+----
+
+The KeyID, Type, and KLen columns should have non-zero values. If they are
+zero, check the system log for error messages from `chronyd`. One possible
+cause of failure is a firewall blocking the client's connection to the server's
+TCP port 4460.
+
+Another possible cause of failure is a certificate that is failing to verify
+because the client's clock is wrong. This is a chicken-and-egg problem with NTS.
+You might need to manually correct the date, or temporarily disable NTS, in
+order to get NTS working. If your computer has an RTC and it is backed up by a
+good battery, this operation should be needed only once, assuming the RTC will
+be set periodically with the `rtcsync` directive, or compensated with the
+`rtcfile` directive and the `-s` option.
+
+If the computer does not have an RTC or battery, you can use the `-s` option
+without `rtcfile` directive to restore time of the last shutdown or reboot from
+the drift file. The clock will start behind the true time, but if the computer
+was not shut down for too long and the server's certificate was not renewed too
+close to its expiration, it should be sufficient for the time checks to
+succeed.
+
+As a last resort, you can disable the time checks by the `nocerttimecheck`
+directive. This has some important security implications. To reduce the
+security risk, you can use the `nosystemcert` and `ntstrustedcerts` directives
+to disable the system's default trusted certificate authorities and trust only
+a minimal set of selected authorities needed to validate the certificates of
+used NTP servers.
+
+=== Using a Windows NTP server?
+
+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 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.
+
+The `maxdistance` value needs to be increased in _chrony.conf_ to enable
+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
+determine which second of UTC corresponds to each pulse. If it is another
+reference clock specified with the `lock` option in the `refclock` directive,
+the offset between the two reference clocks must be smaller than 0.2 seconds in
+order for the PPS reference clock to work. With NMEA reference clocks it is
+common to have a larger offset. It needs to be corrected with the `offset`
+option.
+
+One approach to find out a good value of the `offset` option is to configure
+the reference clocks with the `noselect` option and compare them to an NTP
+server. For example, if the `sourcestats` command showed
+
+----
+Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
+==============================================================================
+PPS0                        0   0     0     +0.000   2000.000     +0ns  4000ms
+NMEA                       58  30   231    -96.494     38.406   +504ms  6080us
+foo.example.net             7   3   200     -2.991     16.141   -107us   492us
+----
+
+the offset of the NMEA source would need to be increased by about 0.504
+seconds. It does not have to be very accurate. As long as the offset of the
+NMEA reference clock stays below 0.2 seconds, the PPS reference clock should be
+able to determine the seconds corresponding to the pulses and allow the samples
+to be used for synchronisation.
+
 == Issues with `chronyc`

 === I keep getting the error `506 Cannot talk to daemon`
@@ -299,31 +712,33 @@ makestep 1 -1
 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
@@ -347,12 +762,12 @@ 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
 `rtcsync` directive, which tells `chronyd` to enable a kernel mode which sets
-the RTC from the system clock every 11 minutes. `chronyd` itself won't touch
+the RTC from the system clock every 11 minutes. `chronyd` itself will not touch
 the RTC. If the computer is not turned off for a long time, the RTC should
 still be close to the true time when the system clock will be initialised from
 it on the next boot.
@@ -362,17 +777,17 @@ 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
+The `hwclock` program is run by default in the boot and/or shutdown
+scripts in some 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 do that, it will overwrite 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.
@@ -391,24 +806,53 @@ 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.
+
+=== When I start `chronyd`, the log says `Could not enable RTC interrupt : Invalid argument` (or it may say `disable`)
+
+Your real-time clock hardware might not support the required ioctl requests:
+
+* `RTC_UIE_ON`
+* `RTC_UIE_OFF`
+
+A possible solution could be to build the Linux kernel with support for software
+emulation instead; try enabling the following configuration option when building
+the Linux kernel:
+
+* `CONFIG_RTC_INTF_DEV_UIE_EMUL`
+
+=== What if my computer does not have an RTC or backup battery?
+
+In this case you can still use the `-s` option to set the system clock to the
+last modification time of the drift file, which should correspond to the system
+time when `chronyd` was previously stopped. The initial system time will be
+increasing across reboots and applications started after `chronyd` will not
+observe backward steps.

 == NTP-specific issues

-=== Can `chronyd` be driven from broadcast NTP servers?
+=== Can `chronyd` be driven from broadcast/multicast NTP servers?

-No, the broadcast client mode is not supported and there is currently no plan
-to implement it. The broadcast and multicast modes are inherently less
-accurate and less secure (even with authentication) than the ordinary
-server/client mode and they are not as useful as they used to be. Even with
-very modest hardware a single NTP server can serve time to hundreds of
-thousands of clients using the ordinary mode.
+No, the broadcast/multicast client mode is not supported and there is currently
+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.
+
+When configuring a large number of clients in a network, it is recommended to
+use the `pool` directive with a DNS name which resolves to addresses of
+multiple NTP servers. The clients will automatically replace the servers when
+they become unreachable, or otherwise unsuitable for synchronisation, with new
+servers from the pool.
+
+Even with very modest hardware, an NTP server can serve time to hundreds of
+thousands of clients using the ordinary client/server mode.

 === Can `chronyd` transmit broadcast NTP packets?

 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?

@@ -424,9 +868,21 @@ 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 is enabled
+by the `xleave` option. Otherwise, `chronyd` will use different transmit
+timestamps (e.g. daemon timestamp vs kernel timestamp) for serving time and
+synchronisation of its own clock, which will cause the other computer to
+measure a significant offset.
+
 == Operating systems

 === Does `chrony` support Windows?
--- a/doc/installation.adoc
+++ b/doc/installation.adoc
@@ -22,6 +22,26 @@ 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.

+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:
+
+* 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

 ----
@@ -29,8 +49,8 @@ After unpacking the source code, change directory into it, and type
 ----

 This is a shell script that automatically determines the system type. There is
-a single optional parameter, `--prefix` which indicates the directory tree
-where the software should be installed. For example,
+an optional parameter `--prefix`, which indicates the directory tree where the
+software should be installed. For example,

 ----
 ./configure --prefix=/opt/free
@@ -40,11 +60,11 @@ will install the `chronyd` daemon into `/opt/free/sbin` and the `chronyc`
 control program into `/opt/free/bin`. The default value for the prefix is
 `/usr/local`.

-The configure script assumes you want to use gcc as your compiler. If you want
-to use a different compiler, you can configure this way:
+The `configure` script assumes you want to use `gcc` as your compiler. If you
+want to use a different compiler, you can configure this way:

 ----
-CC=cc CFLAGS=-O ./configure --prefix=/opt/free
+CC=cc ./configure --prefix=/opt/free
 ----

 for Bourne-family shells, or
@@ -63,11 +83,26 @@ shown. Otherwise, `Makefile` will be generated.
 On Linux, if development files for the libcap library are available, `chronyd`
 will be built with support for dropping root privileges. On other systems no
 extra library is needed. The default user which `chronyd` should run as can be
-specified with the `--with-user` option of the configure script.
+specified with the `--with-user` option of the `configure` script.

-If development files for the editline or readline library are available,
+If development files for the POSIX threads library are available, `chronyd`
+will be built with support for asynchronous resolving of hostnames specified in
+the `server`, `peer`, and `pool` directives. This allows `chronyd` operating as
+a server to respond to client requests when resolving a hostname. If you don't
+want to enable the support, specify the `--disable-asyncdns` flag to
+`configure`.
+
+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
+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 library are available,
 `chronyc` will be built with line editing support. If you don't want this,
-specify the `--disable-readline` flag to configure.
+specify the `--disable-readline` flag to `configure`.

 If a `timepps.h` header is available (e.g. from the
 http://linuxpps.org[LinuxPPS project]), `chronyd` will be built with PPS API
@@ -75,6 +110,9 @@ reference clock driver. If the header is installed in a location that isn't
 normally searched by the compiler, you can add it to the searched locations by
 setting the `CPPFLAGS` variable to `-I/path/to/timepps`.

+The `--help` option can be specified to `configure` to print all options
+supported by the script.
+
 Now type

 ----
@@ -122,51 +160,24 @@ unprivileged user for `chronyd` and specify it with the `-u` command-line
 option or the `user` directive in the configuration file, or set the default
 user with the `--with-user` configure option before building.

-== Support for line editing libraries
+== Support for system call filtering

-`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.
+`chronyd` can be built with support for the Linux secure computing (seccomp)
+facility. This requires development files for the
+https://github.com/seccomp/libseccomp[libseccomp] library and the
+`--enable-scfilter` option specified to `configure`. The `-F` option of
+`chronyd` will enable a system call filter, which should significantly reduce
+the kernel attack surface and possibly prevent kernel exploits from `chronyd`
+if it is compromised.

 == Extra options for package builders

-The configure and make procedures have some extra options that may be useful if
-you are building a distribution package for chrony.
+The `configure` and `make` procedures have some extra options that may be
+useful if you are building a distribution package for `chrony`.

-The `--mandir=DIR` option to configure specifies an install directory for the
-man pages. This overrides the `man` subdirectory of the argument to the
--prefix option.
+The `--mandir=DIR` option to `configure` specifies an installation directory
+for the man pages. This overrides the `man` subdirectory of the argument to the
+`--prefix` option.

 ----
 ./configure --prefix=/usr --mandir=/usr/share/man
@@ -174,8 +185,8 @@ man pages. This overrides the `man` subdirectory of the argument to the

 to set both options together.

-The final option is the `DESTDIR` option to the make command. For example, you
-could use the commands
+The final option is the `DESTDIR` option to the `make` command. For example,
+you could use the commands

 ----
 ./configure --prefix=/usr --mandir=/usr/share/man
--- 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
@@ -95,7 +124,7 @@ driftfile /var/lib/chrony/drift
 # still running and bail out.  If you want to change the path to the PID
 # file, uncomment this line and edit it.  The default path is shown.

-! pidfile /var/run/chronyd.pid
+! pidfile /var/run/chrony/chronyd.pid

 # If the system timezone database is kept up to date and includes the
 # right/UTC timezone, chronyd can use it to determine the current
@@ -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.keys.example
+++ b/examples/chrony.keys.example
@@ -1,6 +1,7 @@
-# This is an example chrony keys file.  It is used for NTP authentication with
-# symmetric keys.  It should be readable only by root or the user to which
-# chronyd is configured to switch to after start.
+# This is an example chrony keys file.  It enables authentication of NTP
+# packets with symmetric keys when its location is specified by the keyfile
+# directive in chrony.conf(5).  It should be readable only by root and the
+# user under which chronyd is running.
 #
 # Don't use the example keys!  It's recommended to generate random keys using
 # the chronyc keygen command.
--- a/examples/chrony.nm-dispatcher
+++ b/examples/chrony.nm-dispatcher
@@ -1,35 +0,0 @@
-#!/bin/sh
-# This is a NetworkManager dispatcher script for chronyd to set its NTP sources
-# online or offline when a network interface is configured or removed
-
-export LC_ALL=C
-
-# Check if there is a default route
-
-if /sbin/ip route list 2> /dev/null | grep -q '^default'; then
-  chronyc online > /dev/null 2>&1
-  exit 0
-fi
-
-sources=$(chronyc -c -n sources 2> /dev/null)
-
-[ $? -ne 0 ] && exit 0
-
-# Check each configured source if it has a route
-
-echo "$sources" | while IFS=, read mode state address rest; do
-  [ "$mode" != '^' ] && [ "$mode" != '=' ] && continue
-
-  /sbin/ip route get "$address" > /dev/null 2>&1 && command="online" || command="offline"
-
-  # Set priority of sources so that the selected source is set as
-  # last if offline to avoid unnecessary reselection
-  [ "$state" != '*' ] && priority=1 || priority=2
-
-  echo "$priority $command $address"
-
-done | sort | while read priority command address; do
-  echo "$command $address"
-done | chronyc > /dev/null 2>&1
-
-exit 0
--- 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
@@ -0,0 +1,17 @@
+#!/bin/sh
+# This is a NetworkManager dispatcher / networkd-dispatcher script for
+# chronyd to set its NTP sources online or offline when a network interface
+# is configured or removed
+
+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
+
+exit 0
--- a/examples/chrony.spec
+++ b/examples/chrony.spec
@@ -1,46 +0,0 @@
-%global chrony_version @@VERSION@@
-%if 0%(echo %{chrony_version} | grep -q pre && echo 1)
-%global prerelease %(echo %{chrony_version} | sed 's/.*-//')
-%endif
-Summary: An NTP client/server
-Name: chrony
-Version: %(echo %{chrony_version} | sed 's/-.*//')
-Release: %{!?prerelease:1}%{?prerelease:0.1.%{prerelease}}
-Source: chrony-%{version}%{?prerelease:-%{prerelease}}.tar.gz
-License: GPLv2
-Group: Applications/Utilities
-BuildRoot: %{_tmppath}/%{name}-%{version}-root-%(id -u -n)
-
-%description
-chrony is a client and server for the Network Time Protocol (NTP).
-This program keeps your computer's clock accurate. It was specially
-designed to support systems with intermittent Internet connections,
-but it also works well in permanently connected environments. It can
-also use hardware reference clocks, the system real-time clock, or
-manual input as time references.
-
-%prep
-%setup -q -n %{name}-%{version}%{?prerelease:-%{prerelease}}
-
-%build
-./configure \
-	--prefix=%{_prefix} \
-	--bindir=%{_bindir} \
-	--sbindir=%{_sbindir} \
-	--mandir=%{_mandir}
-make
-
-%install
-rm -rf $RPM_BUILD_ROOT
-make install DESTDIR=$RPM_BUILD_ROOT
-
-%files
-%{_sbindir}/chronyd
-%{_bindir}/chronyc
-%{_mandir}/man1/chronyc.1.gz
-%{_mandir}/man5/chrony.conf.5.gz
-%{_mandir}/man8/chronyd.8.gz
-%doc README FAQ NEWS COPYING
-%doc examples/chrony.conf.example*
-%doc examples/chrony.keys.example
-
--- a/examples/chronyd.service
+++ b/examples/chronyd.service
@@ -7,7 +7,7 @@ ConditionCapability=CAP_SYS_TIME

 [Service]
 Type=forking
-PIDFile=/var/run/chronyd.pid
+PIDFile=/run/chrony/chronyd.pid
 EnvironmentFile=-/etc/sysconfig/chronyd
 ExecStart=/usr/sbin/chronyd $OPTIONS
 PrivateTmp=yes
--- 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
@@ -29,27 +29,27 @@
 #include "sysincl.h"
 #include "hash.h"
 #include "memory.h"
+#include "util.h"

 #include "md5.c"

 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 (out_len < 16)
+  if (in1_len < 0 || in2_len < 0 || out_len < 0)
    return 0;

  MD5Init(&ctx);
@@ -58,9 +58,11 @@ HSH_Hash(int id, const unsigned char *in1, unsigned int in1_len,
    MD5Update(&ctx, in2, in2_len);
  MD5Final(&ctx);

-  memcpy(out, ctx.digest, 16);
+  out_len = MIN(out_len, 16);

-  return 16;
+  memcpy(out, ctx.digest, out_len);
+
+  return out_len;
 }

 void
--- a/hash_nettle.c
+++ b/hash_nettle.c
@@ -0,0 +1,121 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2018
+ * 
+ * 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.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Routines implementing crypto hashing using the nettle library.
+
+  */
+
+#include "config.h"
+
+#include "sysincl.h"
+
+#include <nettle/nettle-meta.h>
+
+#include "hash.h"
+#include "memory.h"
+
+struct hash {
+  const HSH_Algorithm algorithm;
+  const char *int_name;
+  const struct nettle_hash *nettle_hash;
+  void *context;
+};
+
+static struct hash hashes[] = {
+  { 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(HSH_Algorithm algorithm)
+{
+  int id, nid;
+
+  for (id = 0; hashes[id].algorithm != 0; id++) {
+    if (hashes[id].algorithm == algorithm)
+      break;
+  }
+
+  if (hashes[id].algorithm == 0)
+    return -1;
+
+  if (hashes[id].context)
+    return id;
+
+  for (nid = 0; nettle_hashes[nid]; nid++) {
+    if (!strcmp(hashes[id].int_name, nettle_hashes[nid]->name))
+      break;
+  }
+
+  if (!nettle_hashes[nid] || !nettle_hashes[nid]->context_size || !nettle_hashes[nid]->init)
+    return -1;
+
+  hashes[id].nettle_hash = nettle_hashes[nid];
+  hashes[id].context = Malloc(hashes[id].nettle_hash->context_size);
+
+  return id;
+}
+
+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;
+
+  if (out_len > hash->digest_size)
+    out_len = hash->digest_size;
+
+  hash->init(context);
+  hash->update(context, in1_len, in1);
+  if (in2)
+    hash->update(context, in2_len, in2);
+  hash->digest(context, out_len, out);
+
+  return out_len;
+}
+
+void
+HSH_Finalise(void)
+{
+  int 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
@@ -32,35 +32,36 @@
 #include <nsslowhash.h>

 #include "hash.h"
+#include "util.h"

 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()))
@@ -73,18 +74,24 @@ 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 int ret;
+  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)
    NSSLOWHASH_Update(hashes[id].context, in2, in2_len);
-  NSSLOWHASH_End(hashes[id].context, out, &ret, out_len);
+  NSSLOWHASH_End(hashes[id].context, buf, &ret, sizeof (buf));
+
+  ret = MIN(ret, out_len);
+  memcpy(out, buf, ret);

  return ret;
 }
@@ -94,7 +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
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2012
+ * Copyright (C) Miroslav Lichvar  2012, 2018
 * 
 * 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
@@ -29,59 +29,54 @@

 #include "config.h"
 #include "hash.h"
+#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
+  { 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);
@@ -94,24 +89,31 @@ 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;

-  len = out_len;
+  if (in1_len < 0 || in2_len < 0 || out_len < 0)
+    return 0;
+
+  len = sizeof (buf);
  if (in2)
-    r = hash_memory_multi(id, out, &len,
-        in1, (unsigned long)in1_len, in2, (unsigned long)in2_len, NULL, 0);
+    r = hash_memory_multi(id, buf, &len,
+                          in1, (unsigned long)in1_len,
+                          in2, (unsigned long)in2_len, NULL, 0);
  else
-    r = hash_memory(id, in1, in1_len, out, &len);
+    r = hash_memory(id, in1, in1_len, buf, &len);

  if (r != CRYPT_OK)
    return 0;

+  len = MIN(len, out_len);
+  memcpy(out, buf, len);
+
  return len;
 }

--- a/hwclock.c
+++ b/hwclock.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2016-2017
+ * Copyright (C) Miroslav Lichvar  2016-2018
 * 
 * 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
@@ -36,8 +36,9 @@
 #include "regress.h"
 #include "util.h"

-/* Maximum number of samples per clock */
-#define MAX_SAMPLES 16
+/* Minimum and maximum number of samples per clock */
+#define MIN_SAMPLES 2
+#define MAX_SAMPLES 64

 /* Maximum acceptable frequency offset of the clock */
 #define MAX_FREQ_OFFSET (2.0 / 3.0)
@@ -49,10 +50,12 @@ struct HCL_Instance_Record {

  /* Samples stored as intervals (uncorrected for frequency error)
     relative to local_ref and hw_ref */
-  double x_data[MAX_SAMPLES];
-  double y_data[MAX_SAMPLES];
+  double *x_data;
+  double *y_data;

-  /* Number of samples */
+  /* Minimum, maximum and current number of samples */
+  int min_samples;
+  int max_samples;
  int n_samples;

  /* Maximum error of the last sample */
@@ -89,13 +92,21 @@ handle_slew(struct timespec *raw, struct timespec *cooked, double dfreq,
 /* ================================================== */

 HCL_Instance
-HCL_CreateInstance(double min_separation)
+HCL_CreateInstance(int min_samples, int max_samples, double min_separation)
 {
  HCL_Instance clock;

+  min_samples = CLAMP(MIN_SAMPLES, min_samples, MAX_SAMPLES);
+  max_samples = CLAMP(MIN_SAMPLES, max_samples, MAX_SAMPLES);
+  max_samples = MAX(min_samples, max_samples);
+
  clock = MallocNew(struct HCL_Instance_Record);
-  clock->x_data[MAX_SAMPLES - 1] = 0.0;
-  clock->y_data[MAX_SAMPLES - 1] = 0.0;
+  clock->x_data = MallocArray(double, max_samples);
+  clock->y_data = MallocArray(double, max_samples);
+  clock->x_data[max_samples - 1] = 0.0;
+  clock->y_data[max_samples - 1] = 0.0;
+  clock->min_samples = min_samples;
+  clock->max_samples = max_samples;
  clock->n_samples = 0;
  clock->valid_coefs = 0;
  clock->min_separation = min_separation;
@@ -110,6 +121,8 @@ HCL_CreateInstance(double min_separation)
 void HCL_DestroyInstance(HCL_Instance clock)
 {
  LCL_RemoveParameterChangeHandler(handle_slew, clock);
+  Free(clock->y_data);
+  Free(clock->x_data);
  Free(clock);
 }

@@ -138,7 +151,7 @@ HCL_AccumulateSample(HCL_Instance clock, struct timespec *hw_ts,

  /* Shift old samples */
  if (clock->n_samples) {
-    if (clock->n_samples >= MAX_SAMPLES)
+    if (clock->n_samples >= clock->max_samples)
      clock->n_samples--;

    hw_delta = UTI_DiffTimespecsToDouble(hw_ts, &clock->hw_ref);
@@ -149,7 +162,7 @@ HCL_AccumulateSample(HCL_Instance clock, struct timespec *hw_ts,
      DEBUG_LOG("HW clock reset interval=%f", local_delta);
    }

-    for (i = MAX_SAMPLES - clock->n_samples; i < MAX_SAMPLES; i++) {
+    for (i = clock->max_samples - clock->n_samples; i < clock->max_samples; i++) {
      clock->y_data[i - 1] = clock->y_data[i] - hw_delta;
      clock->x_data[i - 1] = clock->x_data[i] - local_delta;
    }
@@ -162,8 +175,8 @@ HCL_AccumulateSample(HCL_Instance clock, struct timespec *hw_ts,

  /* Get new coefficients */
  clock->valid_coefs =
-    RGR_FindBestRobustRegression(clock->x_data + MAX_SAMPLES - clock->n_samples,
-                                 clock->y_data + MAX_SAMPLES - clock->n_samples,
+    RGR_FindBestRobustRegression(clock->x_data + clock->max_samples - clock->n_samples,
+                                 clock->y_data + clock->max_samples - clock->n_samples,
                                 clock->n_samples, 1.0e-10, &clock->offset, &raw_freq,
                                 &n_runs, &best_start);

@@ -175,7 +188,8 @@ HCL_AccumulateSample(HCL_Instance clock, struct timespec *hw_ts,
  clock->frequency = raw_freq / local_freq;

  /* Drop unneeded samples */
-  clock->n_samples -= best_start;
+  if (clock->n_samples > clock->min_samples)
+    clock->n_samples -= MIN(best_start, clock->n_samples - clock->min_samples);

  /* If the fit doesn't cross the error interval of the last sample,
     or the frequency is not sane, drop all samples and start again */
--- a/hwclock.h
+++ b/hwclock.h
@@ -29,7 +29,8 @@
 typedef struct HCL_Instance_Record *HCL_Instance;

 /* Create a new HW clock instance */
-extern HCL_Instance HCL_CreateInstance(double min_separation);
+extern HCL_Instance HCL_CreateInstance(int min_samples, int max_samples,
+                                       double min_separation);

 /* Destroy a HW clock instance */
 extern void HCL_DestroyInstance(HCL_Instance clock);
--- 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;
@@ -98,60 +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;
-
-  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;
@@ -183,11 +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();
@@ -198,7 +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;
@@ -211,26 +195,56 @@ KEY_Reload(void)
    if (!*line)
      continue;

-    if (!CPS_ParseKey(line, &key_id, &hashname, &keyval)) {
-      LOG(LOGS_WARN, "Could not parse key at line %d in file %s", line_number, key_file);
+    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);
  }

@@ -249,9 +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);
 }

 /* ================================================== */
@@ -307,21 +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)
 {
@@ -333,7 +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;
+  }
 }

 /* ================================================== */
@@ -348,39 +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;

@@ -389,14 +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;
@@ -406,6 +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);
 }

 /* ================================================== */
@@ -509,7 +505,7 @@ LCL_AccumulateDeltaFrequency(double dfreq)

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

-void
+int
 LCL_AccumulateOffset(double offset, double corr_rate)
 {
  struct timespec raw, cooked;
@@ -521,12 +517,14 @@ LCL_AccumulateOffset(double offset, double corr_rate)
  LCL_CookTime(&raw, &cooked, NULL);

  if (!check_offset(&cooked, offset))
-      return;
+    return 0;

  (*drv_accrue_offset)(offset, corr_rate);

  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(&raw, &cooked, 0.0, offset, LCL_ChangeAdjust);
+
+  return 1;
 }

 /* ================================================== */
@@ -590,7 +588,7 @@ LCL_NotifyLeap(int leap)

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

-void
+int
 LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate)
 {
  struct timespec raw, cooked;
@@ -602,7 +600,7 @@ LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate)
  LCL_CookTime(&raw, &cooked, NULL);

  if (!check_offset(&cooked, doffset))
-      return;
+    return 0;

  old_freq_ppm = current_freq_ppm;

@@ -624,6 +622,8 @@ LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate)

  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(&raw, &cooked, dfreq, doffset, LCL_ChangeAdjust);
+
+  return 1;
 }

 /* ================================================== */
@@ -691,6 +691,19 @@ LCL_MakeStep(void)

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

+void
+LCL_CancelOffsetCorrection(void)
+{
+  struct timespec raw;
+  double correction;
+
+  LCL_ReadRawTime(&raw);
+  LCL_GetOffsetCorrection(&raw, &correction, NULL);
+  LCL_AccumulateOffset(correction, 0.0);
+}
+
+/* ================================================== */
+
 int
 LCL_CanSystemLeap(void)
 {
--- a/local.h
+++ b/local.h
@@ -149,7 +149,7 @@ extern void LCL_AccumulateDeltaFrequency(double dfreq);
   forwards (i.e. it is currently slow of true time).  Provided is also
   a suggested correction rate (correction time * offset). */

-extern void LCL_AccumulateOffset(double offset, double corr_rate);
+extern int LCL_AccumulateOffset(double offset, double corr_rate);

 /* Routine to apply an immediate offset by doing a sudden step if
   possible. (Intended for use after an initial estimate of offset has
@@ -171,7 +171,7 @@ extern void LCL_NotifyLeap(int leap);

 /* Perform the combination of modifying the frequency and applying
   a slew, in one easy step */
-extern void LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate);
+extern int LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate);

 /* Routine to read the system precision as a log to base 2 value. */
 extern int LCL_GetSysPrecisionAsLog(void);
@@ -197,6 +197,9 @@ extern void LCL_Finalise(void);
   to a timezone problem. */
 extern int LCL_MakeStep(void);

+/* Routine to cancel the outstanding system clock correction */
+extern void LCL_CancelOffsetCorrection(void);
+
 /* Check if the system driver supports leap seconds, i.e. LCL_SetSystemLeap
   does something */
 extern int LCL_CanSystemLeap(void);
--- a/logging.c
+++ b/logging.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2011-2014
+ * 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);
 }

 /* ================================================== */
@@ -79,14 +82,16 @@ LOG_Initialise(void)
 void
 LOG_Finalise(void)
 {
-  if (system_log) {
+  if (system_log)
    closelog();
-  } else {
+
+  if (file_log)
    fclose(file_log);
-  }

  LOG_CycleLogFiles();

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

@@ -116,7 +121,7 @@ static void log_message(int fatal, LOG_Severity severity, const char *message)
        assert(0);
    }
    syslog(priority, fatal ? "Fatal error : %s" : "%s", message);
-  } else {
+  } else if (file_log) {
    fprintf(file_log, fatal ? "Fatal error : %s\n" : "%s\n", message);
  }
 }
@@ -132,17 +137,21 @@ void LOG_Message(LOG_Severity severity,
  char buf[2048];
  va_list other_args;
  time_t t;
-  struct tm stm;
+  struct tm *tm;

-  if (!system_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);
-    stm = *gmtime(&t);
-    strftime(buf, sizeof(buf), "%Y-%m-%dT%H:%M:%SZ", &stm);
-    fprintf(file_log, "%s ", buf);
+    tm = gmtime(&t);
+    if (tm) {
+      strftime(buf, sizeof (buf), "%Y-%m-%dT%H:%M:%SZ", tm);
+      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
  }

@@ -155,22 +164,23 @@ 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);

-      /* With syslog, send the message also to the grandparent
-         process or write it to stderr if not detached */
-      if (system_log) {
-        if (parent_fd > 0) {
-          if (write(parent_fd, buf, strlen(buf) + 1) < 0)
-            ; /* Not much we can do here */
-        } else if (parent_fd == 0) {
-          system_log = 0;
-          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 */
+      if (parent_fd > 0) {
+        if (write(parent_fd, buf, strlen(buf) + 1) < 0)
+          ; /* Not much we can do here */
+      } else if (system_log && parent_fd == 0) {
+        system_log = 0;
+        log_message(1, severity, buf);
      }
+      exit(1);
      break;
    default:
      assert(0);
@@ -184,13 +194,18 @@ LOG_OpenFileLog(const char *log_file)
 {
  FILE *f;

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

  /* Enable line buffering */
  setvbuf(f, NULL, _IOLBF, BUFSIZ);

+  if (file_log && file_log != stderr)
+    fclose(file_log);
+
  file_log = f;
 }

@@ -206,12 +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);
 }

 /* ================================================== */
@@ -220,6 +250,8 @@ void
 LOG_SetParentFd(int fd)
 {
  parent_fd = fd;
+  if (file_log == stderr)
+    file_log = NULL;
 }

 /* ================================================== */
@@ -237,7 +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;
@@ -259,24 +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();
@@ -284,7 +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);

@@ -92,20 +92,24 @@ 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);

-/* Log messages to a file instead of stderr */
+/* 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);

 /* Log messages to syslog instead of stderr */
 extern void LOG_OpenSystemLog(void);

-/* Send fatal message also to the foreground process */
+/* Stop using stderr and send fatal message to the foreground process */
 extern void LOG_SetParentFd(int fd);

 /* Close the pipe to the foreground process so it can exit */
--- 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  2012-2017
+ * 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 +104,8 @@ MAI_CleanupAndExit(void)
 {
  if (!initialised) exit(exit_status);
  
-  if (CNF_GetDumpDir()[0] != '\0') {
-    SRC_DumpSources();
-  }
+  LCL_CancelOffsetCorrection();
+  SRC_DumpSources();

  /* Don't update clock when removing sources */
  REF_SetMode(REF_ModeIgnore);
@@ -112,18 +114,23 @@ 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 +149,6 @@ MAI_CleanupAndExit(void)
 static void
 signal_cleanup(int x)
 {
-  if (!initialised) exit(0);
  SCH_QuitProgram();
 }

@@ -178,7 +184,7 @@ ntp_source_resolving_end(void)
  NSR_AutoStartSources();

  /* Special modes can end only when sources update their reachability.
-     Give up immediatelly if there are no active sources. */
+     Give up immediately if there are no active sources. */
  if (ref_mode != REF_ModeNormal && !SRC_ActiveSources()) {
    REF_SetUnsynchronised();
  }
@@ -253,7 +259,10 @@ 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;

@@ -278,20 +287,18 @@ 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);
 }

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

+#define DEV_NULL "/dev/null"
+
 static void
 go_daemon(void)
 {
@@ -352,6 +359,13 @@ go_daemon(void)
      }

      LOG_SetParentFd(pipefd[1]);
+
+      /* Open /dev/null as new stdin/out/err */
+      errno = 0;
+      if (open(DEV_NULL, O_RDONLY) != STDIN_FILENO ||
+          open(DEV_NULL, O_WRONLY) != STDOUT_FILENO ||
+          open(DEV_NULL, O_RDWR) != STDERR_FILENO)
+        LOG_FATAL("Could not open %s : %s", DEV_NULL, strerror(errno));
    }
  }
 }
@@ -361,8 +375,34 @@ 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);
 }

 /* ================================================== */
@@ -395,16 +435,16 @@ 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);
@@ -418,7 +458,7 @@ 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':
@@ -438,12 +478,22 @@ 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;
+        log_severity = LOGS_WARN;
+        break;
      case 'P':
        sched_priority = parse_int_arg(optarg);
        break;
@@ -457,6 +507,7 @@ int main
        ref_mode = REF_ModePrintOnce;
        nofork = 1;
        client_only = 1;
+        user_check = 0;
        clock_control = 0;
        system_log = 0;
        break;
@@ -475,6 +526,9 @@ int main
      case 'u':
        user = optarg;
        break;
+      case 'U':
+        user_check = 0;
+        break;
      case 'v':
        print_version();
        return 0;
@@ -487,7 +541,7 @@ int main
    }
  }

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

  /* Turn into a daemon */
@@ -501,13 +555,15 @@ 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;
@@ -518,15 +574,33 @@ 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();

-  /* Write our pidfile to prevent other chronyds running */
+  if (!user)
+    user = CNF_GetUser();
+
+  pw = getpwnam(user);
+  if (!pw)
+    LOG_FATAL("Could not get user/group ID of %s", user);
+
+  /* Create directories for sockets, log files, and dump files */
+  CNF_CreateDirs(pw->pw_uid, pw->pw_gid);
+
+  /* Write our pidfile to prevent other instances from running */
  write_pidfile();

  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();
@@ -534,8 +608,8 @@ 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();

@@ -551,24 +625,19 @@ int main
    SYS_LockMemory();
  }

-  if (!user) {
-    user = CNF_GetUser();
-  }
-
-  if ((pw = getpwnam(user)) == NULL)
-    LOG_FATAL("Could not get %s uid/gid", user);
-
-  /* Create all directories before dropping root */
-  CNF_CreateDirs(pw->pw_uid, pw->pw_gid);
-
  /* 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);
+
+  if (!geteuid())
+    LOG(LOGS_WARN, "Running with root privileges");

  REF_Initialise();
  SST_Initialise();
  NSR_Initialise();
  NSD_Initialise();
+  NNS_Initialise();
+  NKS_Initialise();
  CLG_Initialise();
  MNL_Initialise();
  TMC_Initialise();
@@ -577,12 +646,12 @@ int main
  /* From now on, it is safe to do finalisation on exit */
  initialised = 1;

-  UTI_SetQuitSignalsHandler(signal_cleanup);
+  UTI_SetQuitSignalsHandler(signal_cleanup, 1);

  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;
@@ -591,7 +660,7 @@ 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/2
+++ b/2
@@ -36,8 +36,6 @@ cd RELEASES/$subdir || exit 1

 echo $version > version.txt

-sed -i -e "s%@@VERSION@@%${version}%" examples/chrony.spec
-
 ./configure && make -C doc man txt || exit 1

 iconv -f utf-8 -t ascii//TRANSLIT < doc/installation.txt > INSTALL
--- a/manual.c
+++ b/manual.c
@@ -92,6 +92,7 @@ MNL_Initialise(void)
 void
 MNL_Finalise(void)
 {
+  LCL_RemoveParameterChangeHandler(slew_samples, NULL);
 }

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

+#include "sysincl.h"
+
 /* Wrappers checking for errors */
 extern void *Malloc(size_t size);
 extern void *Realloc(void *ptr, size_t size);
--- a/nameserv.c
+++ b/nameserv.c
@@ -30,7 +30,11 @@

 #include "sysincl.h"

+#include <netdb.h>
+#include <resolv.h>
+
 #include "nameserv.h"
+#include "socket.h"
 #include "util.h"

 /* ================================================== */
@@ -46,15 +50,39 @@ DNS_SetAddressFamily(int family)
 DNS_Status 
 DNS_Name2IPAddress(const char *name, IPAddr *ip_addrs, int max_addrs)
 {
-#ifdef HAVE_GETADDRINFO
  struct addrinfo hints, *res, *ai;
  int i, result;
+  IPAddr ip;

  max_addrs = MIN(max_addrs, DNS_MAX_ADDRESSES);

+  for (i = 0; i < max_addrs; i++)
+    ip_addrs[i].family = IPADDR_UNSPEC;
+
+  /* Avoid calling getaddrinfo() if the name is an IP address */
+  if (UTI_StringToIP(name, &ip)) {
+    if (address_family != IPADDR_UNSPEC && ip.family != address_family)
+      return DNS_Failure;
+    if (max_addrs >= 1)
+      ip_addrs[0] = ip;
+    return DNS_Success;
+  }
+
  memset(&hints, 0, sizeof (hints));
-  hints.ai_family = AF_UNSPEC;
-  hints.ai_socktype = SOCK_STREAM;
+
+  switch (address_family) {
+    case IPADDR_INET4:
+      hints.ai_family = AF_INET;
+      break;
+#ifdef FEAT_IPV6
+    case IPADDR_INET6:
+      hints.ai_family = AF_INET6;
+      break;
+#endif
+    default:
+      hints.ai_family = AF_UNSPEC;
+  }
+  hints.ai_socktype = SOCK_DGRAM;

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

@@ -79,6 +107,9 @@ 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));
@@ -88,48 +119,9 @@ DNS_Name2IPAddress(const char *name, IPAddr *ip_addrs, int max_addrs)
    }
  }

-  for (; i < max_addrs; i++)
-        ip_addrs[i].family = IPADDR_UNSPEC;
-
  freeaddrinfo(res);

  return !max_addrs || ip_addrs[0].family != IPADDR_UNSPEC ? DNS_Success : DNS_Failure;
-#else
-  struct hostent *host;
-  int i;
-  
-  if (address_family != IPADDR_UNSPEC && address_family != IPADDR_INET4)
-    return DNS_Failure;
-
-  max_addrs = MIN(max_addrs, DNS_MAX_ADDRESSES);
-
-  host = gethostbyname(name);
-
-  if (host == NULL) {
-    if (h_errno == TRY_AGAIN)
-      return DNS_TryAgain;
-  } else {
-    if (host->h_addrtype != AF_INET || !host->h_addr_list[0])
-      return DNS_Failure;
-
-    for (i = 0; host->h_addr_list[i] && i < max_addrs; i++) {
-      ip_addrs[i].family = IPADDR_INET4;
-      ip_addrs[i].addr.in4 = ntohl(*(uint32_t *)host->h_addr_list[i]);
-    }
-
-    for (; i < max_addrs; i++)
-      ip_addrs[i].family = IPADDR_UNSPEC;
-
-    return DNS_Success;
-  }
-
-#ifdef FORCE_DNSRETRY
-  return DNS_TryAgain;
-#else
-  return DNS_Failure;
-#endif
-
-#endif
 }

 /* ================================================== */
@@ -138,35 +130,21 @@ int
 DNS_IPAddress2Name(IPAddr *ip_addr, char *name, int len)
 {
  char *result = NULL;
-
 #ifdef FEAT_IPV6
-  struct sockaddr_in6 in6;
+  struct sockaddr_in6 saddr;
+#else
+  struct sockaddr_in saddr;
+#endif
+  IPSockAddr ip_saddr;
  socklen_t slen;
  char hbuf[NI_MAXHOST];

-  slen = UTI_IPAndPortToSockaddr(ip_addr, 0, (struct sockaddr *)&in6);
-  if (!getnameinfo((struct sockaddr *)&in6, slen, hbuf, sizeof (hbuf), NULL, 0, 0))
-    result = hbuf;
-#else
-  struct hostent *host;
-  uint32_t addr;
+  ip_saddr.ip_addr = *ip_addr;
+  ip_saddr.port = 0;

-  switch (ip_addr->family) {
-    case IPADDR_INET4:
-      addr = htonl(ip_addr->addr.in4);
-      host = gethostbyaddr((const char *) &addr, sizeof (ip_addr), AF_INET);
-      break;
-#ifdef FEAT_IPV6
-    case IPADDR_INET6:
-      host = gethostbyaddr((const void *) ip_addr->addr.in6, sizeof (ip_addr->addr.in6), AF_INET6);
-      break;
-#endif
-    default:
-      host = NULL;
-  }
-  if (host)
-    result = host->h_name;
-#endif
+  slen = SCK_IPSockAddrToSockaddr(&ip_saddr, (struct sockaddr *)&saddr, sizeof (saddr));
+  if (!getnameinfo((struct sockaddr *)&saddr, slen, hbuf, sizeof (hbuf), NULL, 0, 0))
+    result = hbuf;

  if (result == NULL)
    result = UTI_IPToString(ip_addr);
--- 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)
@@ -121,4 +113,45 @@ 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
+   source).  root_delay/root_dispersion include peer_delay/peer_dispersion. */
+typedef struct {
+  struct timespec time;
+  double offset;
+  double peer_delay;
+  double peer_dispersion;
+  double root_delay;
+  double root_dispersion;
+} NTP_Sample;
+
 #endif /* GOT_NTP_H */
--- a/ntp_auth.c
+++ b/ntp_auth.c
@@ -0,0 +1,495 @@
+/*
+  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, uint32_t cert_set,
+                      uint16_t ntp_port)
+{
+  NAU_Instance instance = create_instance(NTP_AUTH_NTS);
+
+  instance->nts = NNC_CreateInstance(nts_address, name, cert_set, ntp_port);
+
+  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,
+                                          uint32_t cert_set, uint16_t ntp_port);
+
+/* 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 */
@@ -99,12 +101,9 @@ extern void NCR_ProcessTxUnknown(NTP_Remote_Address *remote_addr, NTP_Local_Addr
 /* Slew receive and transmit times in instance records */
 extern void NCR_SlewTimes(NCR_Instance inst, struct timespec *when, double dfreq, double doffset);

-/* Take a particular source online (i.e. start sampling it) */
-extern void NCR_TakeSourceOnline(NCR_Instance inst);
-
-/* Take a particular source offline (i.e. stop sampling it, without
-   marking it unreachable in the source selection stuff) */
-extern void NCR_TakeSourceOffline(NCR_Instance inst);
+/* Take a particular source online (i.e. start sampling it) or offline
+   (i.e. stop sampling it) */
+extern void NCR_SetConnectivity(NCR_Instance inst, SRC_Connectivity connectivity);

 extern void NCR_ModifyMinpoll(NCR_Instance inst, int new_minpoll);

@@ -123,6 +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);
@@ -137,6 +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
+ * 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 */
@@ -105,6 +67,9 @@ static int separate_client_sockets;
   disabled */
 static int permanent_server_sockets;

+/* Flag indicating the server IPv4 socket is bound to an address */
+static int bound_server_sock_fd4;
+
 /* Flag indicating that we have been initialised */
 static int initialised=0;

@@ -116,155 +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);
-
-  /* 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);
-
-      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
-    /* We want the local IP info on server sockets */
-    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");
-      /* Don't quit - we might survive anyway */
-    }
-#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);

@@ -274,40 +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);
 }

 /* ================================================== */
@@ -318,46 +151,27 @@ close_socket(int sock_fd)
  if (sock_fd == INVALID_SOCK_FD)
    return;

+#ifdef HAVE_LINUX_TIMESTAMPING
+  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
@@ -368,12 +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();

@@ -386,47 +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");
  }
 }
@@ -440,14 +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();
@@ -462,25 +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;
    }
@@ -497,20 +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;
  }
@@ -538,16 +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);
  }
 }
@@ -558,119 +329,76 @@ 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;
+}
+
+/* ================================================== */
+
+int
+NIO_IsServerConnectable(NTP_Remote_Address *remote_addr)
+{
+  int sock_fd;
+
+  sock_fd = open_separate_client_socket(remote_addr);
+  if (sock_fd == INVALID_SOCK_FD)
+    return 0;
+
+  close_socket(sock_fd);
+
+  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;
-    }
-#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=%d 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);
 }

 /* ================================================== */
@@ -678,49 +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 */
+  SCK_Message *messages;
+  int i, received, flags = 0;

-  struct MessageHeader *hdr;
-  unsigned int i, n;
-  int status, flags = 0;
-
-  hdr = ARR_GetElements(recv_headers);
-  n = ARR_GetSize(recv_headers);
-  assert(n >= 1);
+#ifdef HAVE_LINUX_TIMESTAMPING
+  if (NIO_Linux_ProcessEvent(sock_fd, event))
+    return;
+#endif

  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) {
-    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);
 }

 /* ================================================== */
@@ -730,102 +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);
-  }
-#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 !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 +53,12 @@ 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);
+
 /* Function to transmit a packet */
 extern int NIO_SendPacket(NTP_Packet *packet, NTP_Remote_Address *remote_addr,
                          NTP_Local_Address *local_addr, int length, int process_tx);
--- a/ntp_io_linux.c
+++ b/ntp_io_linux.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2016-2017
+ * Copyright (C) Miroslav Lichvar  2016-2019
 * 
 * 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
@@ -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;
@@ -94,6 +86,27 @@ static int ts_tx_flags;
 /* Flag indicating the socket options can't be changed in control messages */
 static int permanent_ts_options;

+/* When sending client requests to a close and fast server, it is possible that
+   a response will be received before the HW transmit timestamp of the request
+   itself.  To avoid processing of the response without the HW timestamp, we
+   monitor events returned by select() and suspend reading of packets from the
+   receive queue for up to 200 microseconds.  As the requests are normally
+   separated by at least 200 milliseconds, it is sufficient to monitor and
+   suspend one socket at a time. */
+static int monitored_socket;
+static int suspended_socket;
+static SCH_TimeoutID resume_timeout_id;
+
+#define RESUME_TIMEOUT 200.0e-6
+
+/* Unbound socket keeping the kernel RX timestamping permanently enabled
+   in order to avoid a race condition between receiving a server response
+   and the kernel actually starting to timestamp received packets after
+   enabling the timestamping and sending a request */
+static int dummy_rxts_socket;
+
+#define INVALID_SOCK_FD -3
+
 /* ================================================== */

 static int
@@ -102,7 +115,7 @@ add_interface(CNF_HwTsInterface *conf_iface)
  struct ethtool_ts_info ts_info;
  struct hwtstamp_config ts_config;
  struct ifreq req;
-  int sock_fd, if_index, phc_fd, req_hwts_flags;
+  int sock_fd, if_index, phc_fd, req_hwts_flags, rx_filter;
  unsigned int i;
  struct Interface *iface;

@@ -112,7 +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;

@@ -121,13 +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;
  }

@@ -138,7 +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;
  }

@@ -146,47 +159,65 @@ 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;
  }

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

  switch (conf_iface->rxfilter) {
    case CNF_HWTS_RXFILTER_ANY:
 #ifdef HAVE_LINUX_TIMESTAMPING_RXFILTER_NTP
      if (ts_info.rx_filters & (1 << HWTSTAMP_FILTER_NTP_ALL))
-        ts_config.rx_filter = HWTSTAMP_FILTER_NTP_ALL;
+        rx_filter = HWTSTAMP_FILTER_NTP_ALL;
      else
 #endif
      if (ts_info.rx_filters & (1 << HWTSTAMP_FILTER_ALL))
-        ts_config.rx_filter = HWTSTAMP_FILTER_ALL;
+        rx_filter = HWTSTAMP_FILTER_ALL;
      else
-        ts_config.rx_filter = HWTSTAMP_FILTER_NONE;
+        rx_filter = HWTSTAMP_FILTER_NONE;
      break;
    case CNF_HWTS_RXFILTER_NONE:
-      ts_config.rx_filter = HWTSTAMP_FILTER_NONE;
+      rx_filter = HWTSTAMP_FILTER_NONE;
      break;
 #ifdef HAVE_LINUX_TIMESTAMPING_RXFILTER_NTP
    case CNF_HWTS_RXFILTER_NTP:
-      ts_config.rx_filter = HWTSTAMP_FILTER_NTP_ALL;
+      rx_filter = HWTSTAMP_FILTER_NTP_ALL;
      break;
 #endif
    default:
-      ts_config.rx_filter = HWTSTAMP_FILTER_ALL;
+      rx_filter = HWTSTAMP_FILTER_ALL;
      break;
  }

+  ts_config.flags = 0;
+  ts_config.tx_type = HWTSTAMP_TX_ON;
+  ts_config.rx_filter = rx_filter;
  req.ifr_data = (char *)&ts_config;

  if (ioctl(sock_fd, SIOCSHWTSTAMP, &req)) {
-    DEBUG_LOG("ioctl(%s) failed : %s", "SIOCSHWTSTAMP", strerror(errno));
-    close(sock_fd);
-    return 0;
+    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
+       as requested */
+    req.ifr_data = (char *)&ts_config;
+#ifdef SIOCGHWTSTAMP
+    if (ioctl(sock_fd, SIOCGHWTSTAMP, &req) ||
+        ts_config.tx_type != HWTSTAMP_TX_ON || ts_config.rx_filter != rx_filter)
+#endif
+    {
+      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)
@@ -209,7 +240,8 @@ add_interface(CNF_HwTsInterface *conf_iface)
  iface->tx_comp = conf_iface->tx_comp;
  iface->rx_comp = conf_iface->rx_comp;

-  iface->clock = HCL_CreateInstance(UTI_Log2ToDouble(MAX(conf_iface->minpoll, MIN_PHC_POLL)));
+  iface->clock = HCL_CreateInstance(conf_iface->min_samples, conf_iface->max_samples,
+                                    UTI_Log2ToDouble(MAX(conf_iface->minpoll, MIN_PHC_POLL)));

  LOG(LOGS_INFO, "Enabled HW timestamping %son %s",
      ts_config.rx_filter == HWTSTAMP_FILTER_NONE ? "(TX only) " : "", iface->name);
@@ -252,9 +284,9 @@ update_interface_speed(struct Interface *iface)
 {
  struct ethtool_cmd cmd;
  struct ifreq req;
-  int sock_fd;
+  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;

@@ -267,13 +299,18 @@ 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);

-  iface->link_speed = ethtool_cmd_speed(&cmd);
+  link_speed = ethtool_cmd_speed(&cmd);
+
+  if (iface->link_speed != link_speed) {
+    iface->link_speed = link_speed;
+    DEBUG_LOG("Updated speed of %s to %d Mb/s", iface->name, link_speed);
+  }
 }

 /* ================================================== */
@@ -284,23 +321,41 @@ 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", 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

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

+static int
+open_dummy_socket(void)
+{
+  int sock_fd, events = 0;
+
+  sock_fd = SCK_OpenUdpSocket(NULL, NULL, NULL, 0);
+  if (sock_fd < 0)
+    return INVALID_SOCK_FD;
+
+  if (!NIO_Linux_SetTimestampSocketOptions(sock_fd, 1, &events)) {
+    SCK_CloseSocket(sock_fd);
+    return INVALID_SOCK_FD;
+  }
+
+  return sock_fd;
+}
+
+/* ================================================== */
+
 void
 NIO_Linux_Initialise(void)
 {
@@ -350,6 +405,10 @@ NIO_Linux_Initialise(void)

  /* Kernels before 4.7 ignore timestamping flags set in control messages */
  permanent_ts_options = !SYS_Linux_CheckKernelVersion(4, 7);
+
+  monitored_socket = INVALID_SOCK_FD;
+  suspended_socket = INVALID_SOCK_FD;
+  dummy_rxts_socket = INVALID_SOCK_FD;
 }

 /* ================================================== */
@@ -360,6 +419,9 @@ NIO_Linux_Finalise(void)
  struct Interface *iface;
  unsigned int i;

+  if (dummy_rxts_socket != INVALID_SOCK_FD)
+    SCK_CloseSocket(dummy_rxts_socket);
+
  for (i = 0; i < ARR_GetSize(interfaces); i++) {
    iface = ARR_GetElement(interfaces, i);
    HCL_DestroyInstance(iface->clock);
@@ -388,14 +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;
  }
@@ -406,6 +466,73 @@ NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events)

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

+static void
+resume_socket(int sock_fd)
+{
+  if (monitored_socket == sock_fd)
+    monitored_socket = INVALID_SOCK_FD;
+
+  if (sock_fd == INVALID_SOCK_FD || sock_fd != suspended_socket)
+    return;
+
+  suspended_socket = INVALID_SOCK_FD;
+
+  SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_INPUT, 1);
+
+  DEBUG_LOG("Resumed RX processing %s timeout fd=%d",
+            resume_timeout_id ? "before" : "on", sock_fd);
+
+  if (resume_timeout_id) {
+    SCH_RemoveTimeout(resume_timeout_id);
+    resume_timeout_id = 0;
+  }
+}
+
+/* ================================================== */
+
+static void
+resume_timeout(void *arg)
+{
+  resume_timeout_id = 0;
+  resume_socket(suspended_socket);
+}
+
+/* ================================================== */
+
+static void
+suspend_socket(int sock_fd)
+{
+  resume_socket(suspended_socket);
+
+  suspended_socket = sock_fd;
+
+  SCH_SetFileHandlerEvent(suspended_socket, SCH_FILE_INPUT, 0);
+  resume_timeout_id = SCH_AddTimeoutByDelay(RESUME_TIMEOUT, resume_timeout, NULL);
+
+  DEBUG_LOG("Suspended RX processing fd=%d", sock_fd);
+}
+
+/* ================================================== */
+
+int
+NIO_Linux_ProcessEvent(int sock_fd, int event)
+{
+  if (sock_fd != monitored_socket)
+    return 0;
+
+  if (event == SCH_FILE_INPUT) {
+    suspend_socket(monitored_socket);
+    monitored_socket = INVALID_SOCK_FD;
+
+    /* Don't process the message yet */
+    return 1;
+  }
+
+  return 0;
+}
+
+/* ================================================== */
+
 static struct Interface *
 get_interface(int if_index)
 {
@@ -454,7 +581,11 @@ process_hw_timestamp(struct Interface *iface, struct timespec *hw_ts,
  if (rx_ntp_length && iface->link_speed) {
    if (!l2_length)
      l2_length = (family == IPADDR_INET4 ? iface->l2_udp4_ntp_start :
-                   iface->l2_udp6_ntp_start) + rx_ntp_length + 4;
+                   iface->l2_udp6_ntp_start) + rx_ntp_length;
+
+    /* Include the frame check sequence (FCS) */
+    l2_length += 4;
+
    rx_correction = l2_length / (1.0e6 / 8 * iface->link_speed);

    UTI_AddDoubleToTimespec(hw_ts, rx_correction, hw_ts);
@@ -488,7 +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;
@@ -511,19 +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 */
@@ -555,16 +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);
@@ -575,67 +705,47 @@ 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 (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 (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 (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 the kernel is slow with enabling RX timestamping, open a dummy
+     socket to keep the kernel RX timestamping permanently enabled */
+  if (!is_tx && local_ts->source == NTP_TS_DAEMON && ts_flags) {
+    DEBUG_LOG("Missing kernel RX timestamp");
+    if (dummy_rxts_socket == INVALID_SOCK_FD)
+      dummy_rxts_socket = open_dummy_socket();
  }

  /* Return the message if it's not received from the error queue */
@@ -645,19 +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=%d",
-            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 */
@@ -666,38 +776,39 @@ 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;
+
+  /* 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
+     without the HW timestamp of the request */
+  if (ts_tx_flags & SOF_TIMESTAMPING_TX_HARDWARE && !NIO_IsServerSocket(sock_fd))
+    monitored_socket = 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 = (struct cmsghdr *)((char *)CMSG_FIRSTHDR(msg) + 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;
+}
+
+/* ================================================== */
+
+void
+NIO_Linux_NotifySocketClosing(int sock_fd)
+{
+  resume_socket(sock_fd);
 }
--- a/ntp_io_linux.h
+++ b/ntp_io_linux.h
@@ -24,13 +24,24 @@
  This is the header file for the Linux-specific NTP socket I/O bits.
  */

+#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);

 extern int NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events);

-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_ProcessEvent(int sock_fd, int event);

-extern int NIO_Linux_RequestTxTimestamp(struct msghdr *msg, int cmsglen, int sock_fd);
+extern int NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
+                                    NTP_Local_Timestamp *local_ts, int event);
+
+extern void NIO_Linux_RequestTxTimestamp(SCK_Message *message, int sock_fd);
+
+extern void NIO_Linux_NotifySocketClosing(int sock_fd);
+
+#endif
--- 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 */
@@ -235,7 +210,7 @@ read_write_socket(int sock_fd, int event, void *anything)
      return;

    /* Disable output and wait for a response */
-    SCH_SetFileHandlerEvents(sock_fd, SCH_FILE_INPUT);
+    SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_OUTPUT, 0);
  }

  if (event == SCH_FILE_INPUT) {
@@ -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))
@@ -283,7 +252,7 @@ read_write_socket(int sock_fd, int event, void *anything)
    /* Move the head and enable output for the next packet */
    queue_head = NEXT_QUEUE_INDEX(queue_head);
    if (!IS_QUEUE_EMPTY())
-      SCH_SetFileHandlerEvents(sock_fd, SCH_FILE_INPUT | SCH_FILE_OUTPUT);
+      SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_OUTPUT, 1);
  }
 }

@@ -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));
@@ -365,11 +327,11 @@ 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())
-    SCH_SetFileHandlerEvents(sock_fd, SCH_FILE_INPUT | SCH_FILE_OUTPUT);
+    SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_OUTPUT, 1);

  queue_tail = NEXT_QUEUE_INDEX(queue_tail);

--- 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 +91,18 @@ 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.  The update may be
+   postponed. */
+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 as it was specified (it may be
+   an IP 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);
@@ -102,14 +119,9 @@ extern void NSR_Initialise(void);
 extern void NSR_Finalise(void);

 /* This routine is used to indicate that sources whose IP addresses
-   match a particular subnet should be set online again.  Returns a
-   flag indicating whether any hosts matched the address */
-extern int NSR_TakeSourcesOnline(IPAddr *mask, IPAddr *address);
-
-/* This routine is used to indicate that sources whose IP addresses
-   match a particular subnet should be set offline.  Returns a flag
-   indicating whether any hosts matched the address */
-extern int NSR_TakeSourcesOffline(IPAddr *mask, IPAddr *address);
+   match a particular subnet should be set online or offline.  It returns
+   a flag indicating whether any hosts matched the address. */
+extern int NSR_SetConnectivity(IPAddr *mask, IPAddr *address, SRC_Connectivity connectivity);

 extern int NSR_ModifyMinpoll(IPAddr *address, int new_minpoll);

@@ -129,8 +141,12 @@ 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 +1,434 @@
+/*
+  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_Credentials credentials;
+  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 + 2];
+  IPSockAddr ntp_address;
+};
+
+/* ================================================== */
+
+static NKSN_Credentials default_credentials = NULL;
+static int default_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)) {
+      int length = strlen(inst->server_name);
+
+      /* Add a trailing dot if not present to force the name to be
+         resolved as a fully qualified domain name */
+      if (length < 1 || length + 1 >= sizeof (inst->server_name))
+        return 0;
+      if (inst->server_name[length - 1] != '.') {
+        inst->server_name[length] = '.';
+        inst->server_name[length + 1] = '\0';
+      }
+
+      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, uint32_t cert_set)
+{
+  const char **trusted_certs;
+  uint32_t *certs_ids;
+  NKC_Instance inst;
+  int n_certs;
+
+  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;
+
+  n_certs = CNF_GetNtsTrustedCertsPaths(&trusted_certs, &certs_ids);
+
+  /* Share the credentials among clients using the default set of trusted
+     certificates, which likely contains most certificates */
+  if (cert_set == 0) {
+    if (!default_credentials)
+      default_credentials = NKSN_CreateClientCertCredentials(trusted_certs, certs_ids,
+                                                             n_certs, cert_set);
+    inst->credentials = default_credentials;
+    if (default_credentials)
+      default_credentials_refs++;
+  } else {
+    inst->credentials = NKSN_CreateClientCertCredentials(trusted_certs, certs_ids,
+                                                         n_certs, cert_set);
+  }
+
+  return inst;
+}
+
+/* ================================================== */
+
+void
+NKC_DestroyInstance(NKC_Instance inst)
+{
+  NKSN_DestroyInstance(inst->session);
+
+  Free(inst->name);
+
+  if (inst->credentials) {
+    if (inst->credentials == default_credentials) {
+      default_credentials_refs--;
+      if (default_credentials_refs <= 0) {
+        NKSN_DestroyCertCredentials(default_credentials);
+        default_credentials = NULL;
+      }
+    } else {
+      NKSN_DestroyCertCredentials(inst->credentials);
+    }
+  }
+
+  /* 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 (!inst->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, inst->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, uint32_t cert_set);
+
+/* 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 +1,963 @@
+/*
+  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 NKSN_Credentials 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;
+  const char **certs, **keys;
+  char prefix[16];
+  pid_t pid;
+
+  helper_sock_fd = INVALID_SOCK_FD;
+  is_helper = 0;
+
+  if (CNF_GetNtsServerCertAndKeyFiles(&certs, &keys) <= 0)
+    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)
+{
+  const char **certs, **keys;
+  int i, n_certs_keys;
+  double key_delay;
+
+  server_sock_fd4 = INVALID_SOCK_FD;
+  server_sock_fd6 = INVALID_SOCK_FD;
+
+  n_certs_keys = CNF_GetNtsServerCertAndKeyFiles(&certs, &keys);
+  if (n_certs_keys <= 0)
+    return;
+
+  if (helper_sock_fd == INVALID_SOCK_FD) {
+    server_credentials = NKSN_CreateServerCertCredentials(certs, keys, n_certs_keys);
+    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 +1,920 @@
+/*
+  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) {
+    assert(server_name);
+
+    if (!UTI_IsStringIP(server_name)) {
+      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");
+}
+
+/* ================================================== */
+
+static NKSN_Credentials
+create_credentials(const char **certs, const char **keys, int n_certs_keys,
+                   const char **trusted_certs, uint32_t *trusted_certs_ids,
+                   int n_trusted_certs, uint32_t trusted_cert_set)
+{
+  gnutls_certificate_credentials_t credentials = NULL;
+  int i, r;
+
+  init_gnutls();
+
+  r = gnutls_certificate_allocate_credentials(&credentials);
+  if (r < 0)
+    goto error;
+
+  if (certs && keys) {
+    if (trusted_certs || trusted_certs_ids)
+      assert(0);
+
+    for (i = 0; i < n_certs_keys; i++) {
+      r = gnutls_certificate_set_x509_key_file(credentials, certs[i], keys[i],
+                                               GNUTLS_X509_FMT_PEM);
+      if (r < 0)
+        goto error;
+    }
+  } else {
+    if (certs || keys || n_certs_keys > 0)
+      assert(0);
+
+    if (trusted_cert_set == 0 && !CNF_GetNoSystemCert()) {
+      r = gnutls_certificate_set_x509_system_trust(credentials);
+      if (r < 0)
+        goto error;
+    }
+
+    if (trusted_certs && trusted_certs_ids) {
+      for (i = 0; i < n_trusted_certs; i++) {
+        struct stat buf;
+
+        if (trusted_certs_ids[i] != trusted_cert_set)
+          continue;
+
+        if (stat(trusted_certs[i], &buf) == 0 && S_ISDIR(buf.st_mode))
+          r = gnutls_certificate_set_x509_trust_dir(credentials, trusted_certs[i],
+                                                    GNUTLS_X509_FMT_PEM);
+        else
+          r = gnutls_certificate_set_x509_trust_file(credentials, trusted_certs[i],
+                                                     GNUTLS_X509_FMT_PEM);
+        if (r < 0)
+          goto error;
+
+        DEBUG_LOG("Added %d trusted certs from %s", r, trusted_certs[i]);
+      }
+    }
+  }
+
+  credentials_counter++;
+
+  return (NKSN_Credentials)credentials;
+
+error:
+  LOG(LOGS_ERR, "Could not set credentials : %s", gnutls_strerror(r));
+  if (credentials)
+    gnutls_certificate_free_credentials(credentials);
+  deinit_gnutls();
+  return NULL;
+}
+
+/* ================================================== */
+
+NKSN_Credentials
+NKSN_CreateServerCertCredentials(const char **certs, const char **keys, int n_certs_keys)
+{
+  return create_credentials(certs, keys, n_certs_keys, NULL, NULL, 0, 0);
+}
+
+/* ================================================== */
+
+NKSN_Credentials
+NKSN_CreateClientCertCredentials(const char **certs, uint32_t *ids,
+                                 int n_certs_ids, uint32_t trusted_cert_set)
+{
+  return create_credentials(NULL, NULL, 0, certs, ids, n_certs_ids, trusted_cert_set);
+}
+
+/* ================================================== */
+
+void
+NKSN_DestroyCertCredentials(NKSN_Credentials credentials)
+{
+  gnutls_certificate_free_credentials((gnutls_certificate_credentials_t)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,
+                  NKSN_Credentials credentials, double timeout)
+{
+  assert(inst->state == KE_STOPPED);
+
+  inst->tls_session = create_tls_session(inst->server, sock_fd, inst->server_name,
+                                         (gnutls_certificate_credentials_t)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 +1,93 @@
+/*
+  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_Credentials_Record *NKSN_Credentials;
+
+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 server or client credentials using a server certificate and key,
+   or certificates of trusted CAs.  The credentials may be shared between
+   different clients or servers. */
+extern NKSN_Credentials NKSN_CreateServerCertCredentials(const char **certs, const char **keys,
+                                                         int n_certs_keys);
+extern NKSN_Credentials NKSN_CreateClientCertCredentials(const char **certs, uint32_t *ids,
+                                                         int n_certs_ids,
+                                                         uint32_t trusted_cert_set);
+
+/* Destroy the credentials */
+extern void NKSN_DestroyCertCredentials(NKSN_Credentials 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,
+                             NKSN_Credentials 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 +1,707 @@
+/*
+  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 {
+  /* Address of NTS-KE server */
+  IPSockAddr nts_address;
+  /* Hostname or IP address for certificate verification */
+  char *name;
+  /* ID of trusted certificates */
+  uint32_t cert_set;
+  /* Configured NTP port */
+  uint16_t default_ntp_port;
+  /* Address of NTP server (can be negotiated in NTS-KE) */
+  IPSockAddr ntp_address;
+
+  NKC_Instance nke;
+  SIV_Instance siv;
+
+  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->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, uint32_t cert_set, uint16_t ntp_port)
+{
+  NNC_Instance inst;
+
+  inst = MallocNew(struct NNC_Instance_Record);
+
+  inst->nts_address = *nts_address;
+  inst->name = Strdup(name);
+  inst->cert_set = cert_set;
+  inst->default_ntp_port = ntp_port;
+  inst->ntp_address.ip_addr = nts_address->ip_addr;
+  inst->ntp_address.port = ntp_port;
+  inst->siv = NULL;
+  inst->nke = NULL;
+
+  reset_instance(inst);
+
+  /* Try to reload saved keys and cookies */
+  load_cookies(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 = inst->nts_address.ip_addr;
+  if (new_address.port == 0)
+    new_address.port = inst->default_ntp_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;
+  }
+
+  inst->ntp_address = new_address;
+
+  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;
+    }
+
+    inst->nke = NKC_CreateInstance(&inst->nts_address, inst->name, inst->cert_set);
+
+    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));
+
+  /* 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;
+  inst->ntp_address.ip_addr = *address;
+
+  reset_instance(inst);
+
+  DEBUG_LOG("NTS reset");
+
+  load_cookies(inst);
+}
+
+/* ================================================== */
+
+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 || !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 ||
+        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,
+                                       uint32_t cert_set, uint16_t ntp_port);
+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 +1,283 @@
+/*
+  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)
+{
+  const char **certs, **keys;
+
+  /* Create an NTS-NTP server instance only if NTS-KE server is enabled */
+  if (CNF_GetNtsServerCertAndKeyFiles(&certs, &keys) <= 0) {
+    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
@@ -87,7 +87,7 @@ static const struct request_length request_lengths[] = {
  REQ_LENGTH_ENTRY(del_source, null),           /* DEL_SOURCE */
  REQ_LENGTH_ENTRY(null, null),                 /* WRITERTC */
  REQ_LENGTH_ENTRY(dfreq, null),                /* DFREQ */
-  REQ_LENGTH_ENTRY(doffset, null),              /* DOFFSET */
+  { 0, 0 },                                     /* DOFFSET - not supported */
  REQ_LENGTH_ENTRY(null, tracking),             /* TRACKING */
  REQ_LENGTH_ENTRY(sourcestats, sourcestats),   /* SOURCESTATS */
  REQ_LENGTH_ENTRY(null, rtc),                  /* RTCREPORT */
@@ -110,14 +110,25 @@ 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 */
+  REQ_LENGTH_ENTRY(doffset, null),              /* DOFFSET2 */
 };

 static const uint16_t reply_lengths[] = {
@@ -132,13 +143,19 @@ static const uint16_t reply_lengths[] = {
  0,                                            /* SUBNETS_ACCESSED - not supported */
  0,                                            /* CLIENT_ACCESSES - not supported */
  0,                                            /* CLIENT_ACCESSES_BY_INDEX - not supported */
-  0,                                            /* MANUAL_LIST - variable length */
+  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 */
 };

 /* ================================================== */
@@ -195,21 +212,6 @@ PKL_ReplyLength(CMD_Reply *r)
  if (type < 1 || type >= N_REPLY_TYPES)
    return 0;

-  /* Length of MANUAL_LIST depends on number of samples stored in it */
-  if (type == RPY_MANUAL_LIST) {
-    uint32_t ns;
-
-    if (r->status != htons(STT_SUCCESS))
-      return offsetof(CMD_Reply, data);
-
-    ns = ntohl(r->data.manual_list.n_samples);
-    if (ns > MAX_MANUAL_LIST_SAMPLES)
-      return 0;
-
-    return offsetof(CMD_Reply, data.manual_list.samples) +
-           ns * sizeof (RPY_ManualListSample);
-  }
-
  return reply_lengths[type];
 }

--- 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()) {
-    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 +541,14 @@ 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);
-  assert(!port || port == CNF_GetNTPPort());
+  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())
    return bind(sock, address, address_len);
@@ -588,6 +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);
@@ -615,7 +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;
  }

@@ -669,20 +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)
@@ -690,23 +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);
+    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
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2009-2011, 2013-2014, 2016-2017
+ * Copyright (C) Miroslav Lichvar  2009-2011, 2013-2014, 2016-2019
 * 
 * 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
@@ -37,8 +37,12 @@
 #include "sources.h"
 #include "logging.h"
 #include "regress.h"
+#include "samplefilt.h"
 #include "sched.h"

+/* Maximum offset of locked reference as a fraction of the PPS interval */
+#define PPS_LOCK_LIMIT 0.4
+
 /* list of refclock drivers */
 extern RefclockDriver RCL_SHM_driver;
 extern RefclockDriver RCL_SOCK_driver;
@@ -79,13 +83,15 @@ struct RCL_Instance_Record {
  int pps_rate;
  int pps_active;
  int max_lock_age;
-  struct MedianFilter filter;
+  int stratum;
+  int tai;
  uint32_t ref_id;
  uint32_t lock_ref;
  double offset;
  double delay;
  double precision;
  double pulse_width;
+  SPF_Instance filter;
  SCH_TimeoutID timeout_id;
  SRC_Instance source;
 };
@@ -103,18 +109,6 @@ static void slew_samples(struct timespec *raw, struct timespec *cooked, double d
 static void add_dispersion(double dispersion, void *anything);
 static void log_sample(RCL_Instance instance, struct timespec *sample_time, int filtered, int pulse, double raw_offset, double cooked_offset, double dispersion);

-static void filter_init(struct MedianFilter *filter, int length, double max_dispersion);
-static void filter_fini(struct MedianFilter *filter);
-static void filter_reset(struct MedianFilter *filter);
-static double filter_get_avg_sample_dispersion(struct MedianFilter *filter);
-static void filter_add_sample(struct MedianFilter *filter, struct timespec *sample_time, double offset, double dispersion);
-static int filter_get_last_sample(struct MedianFilter *filter, struct timespec *sample_time, double *offset, double *dispersion);
-static int filter_get_samples(struct MedianFilter *filter);
-static int filter_select_samples(struct MedianFilter *filter);
-static int filter_get_sample(struct MedianFilter *filter, struct timespec *sample_time, double *offset, double *dispersion);
-static void filter_slew_samples(struct MedianFilter *filter, struct timespec *when, double dfreq, double doffset);
-static void filter_add_dispersion(struct MedianFilter *filter, double dispersion);
-
 static RCL_Instance
 get_refclock(unsigned int index)
 {
@@ -149,7 +143,7 @@ RCL_Finalise(void)
    if (inst->driver->fini)
      inst->driver->fini(inst);

-    filter_fini(&inst->filter);
+    SPF_DestroyInstance(inst->filter);
    Free(inst->driver_parameter);
    SRC_DestroyInstance(inst->source);
    Free(inst);
@@ -181,16 +175,16 @@ RCL_AddRefclock(RefclockParameters *params)
    inst->driver = &RCL_PHC_driver;
  } else {
    LOG_FATAL("unknown refclock driver %s", params->driver_name);
-    return 0;
  }

-  if (!inst->driver->init && !inst->driver->poll) {
+  if (!inst->driver->init && !inst->driver->poll)
    LOG_FATAL("refclock driver %s is not compiled in", params->driver_name);
-    return 0;
-  }
+
+  if (params->tai && !CNF_GetLeapSecTimezone())
+    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;
@@ -200,6 +194,8 @@ RCL_AddRefclock(RefclockParameters *params)
  inst->pps_rate = params->pps_rate;
  inst->pps_active = 0;
  inst->max_lock_age = params->max_lock_age;
+  inst->stratum = params->stratum;
+  inst->tai = params->tai;
  inst->lock_ref = params->lock_ref_id;
  inst->offset = params->offset;
  inst->delay = params->delay;
@@ -251,30 +247,30 @@ RCL_AddRefclock(RefclockParameters *params)
    }
  }

-  if (inst->driver->init)
-    if (!inst->driver->init(inst)) {
-      LOG_FATAL("refclock %s initialisation failed", params->driver_name);
-      return 0;
-    }
+  if (inst->driver->init && !inst->driver->init(inst))
+    LOG_FATAL("refclock %s initialisation failed", params->driver_name);

-  filter_init(&inst->filter, params->filter_length, params->max_dispersion);
+  /* Require the filter to have at least 4 samples to produce a filtered
+     sample, or be full for shorter lengths, and combine 60% of samples
+     closest to the median */
+  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;
 }

 void
 RCL_StartRefclocks(void)
 {
-  unsigned int i, j, n;
+  unsigned int i, j, n, lock_index;

  n = ARR_GetSize(refclocks);

@@ -284,13 +280,31 @@ RCL_StartRefclocks(void)
    SRC_SetActive(inst->source);
    inst->timeout_id = SCH_AddTimeoutByDelay(0.0, poll_timeout, (void *)inst);

-    if (inst->lock_ref) {
-      /* Replace lock refid with index to refclocks */
-      for (j = 0; j < n && get_refclock(j)->ref_id != inst->lock_ref; j++)
-        ;
-      inst->lock_ref = j < n ? j : -1;
-    } else
-      inst->lock_ref = -1;
+    /* Replace lock refid with the refclock's index, or -1 if not valid */
+
+    lock_index = -1;
+
+    if (inst->lock_ref != 0) {
+      for (j = 0; j < n; j++) {
+        RCL_Instance inst2 = get_refclock(j);
+
+        if (inst->lock_ref != inst2->ref_id)
+          continue;
+
+        if (inst->driver->poll && inst2->driver->poll &&
+            (double)inst->max_lock_age / inst->pps_rate < UTI_Log2ToDouble(inst2->driver_poll))
+          LOG(LOGS_WARN, "%s maxlockage too small for %s",
+              UTI_RefidToString(inst->ref_id), UTI_RefidToString(inst2->ref_id));
+
+        lock_index = j;
+        break;
+      }
+
+      if (lock_index == -1 || lock_index == i)
+        LOG(LOGS_WARN, "Invalid lock refid %s", UTI_RefidToString(inst->lock_ref));
+    }
+
+    inst->lock_ref = lock_index;
  }
 }

@@ -331,31 +345,100 @@ RCL_GetDriverParameter(RCL_Instance instance)
  return instance->driver_parameter;
 }

+static char *
+get_next_driver_option(RCL_Instance instance, char *option)
+{
+  if (option == NULL)
+    option = instance->driver_parameter;
+
+  option += strlen(option) + 1;
+
+  if (option >= instance->driver_parameter + instance->driver_parameter_length)
+    return NULL;
+
+  return option;
+}
+
+void
+RCL_CheckDriverOptions(RCL_Instance instance, const char **options)
+{
+  char *option;
+  int i, len;
+
+  for (option = get_next_driver_option(instance, NULL);
+       option;
+       option = get_next_driver_option(instance, option)) {
+    for (i = 0; options && options[i]; i++) {
+      len = strlen(options[i]);
+      if (!strncmp(options[i], option, len) &&
+          (option[len] == '=' || option[len] == '\0'))
+        break;
+    }
+
+    if (!options || !options[i])
+      LOG_FATAL("Invalid refclock driver option %s", option);
+  }
+}
+
 char *
 RCL_GetDriverOption(RCL_Instance instance, char *name)
 {
-  char *s, *e;
-  int n;
+  char *option;
+  int len;

-  s = instance->driver_parameter;
-  e = s + instance->driver_parameter_length;
-  n = strlen(name);
+  len = strlen(name);

-  while (1) {
-    s += strlen(s) + 1;
-    if (s >= e)
-      break;
-    if (!strncmp(name, s, n)) {
-      if (s[n] == '=')
-        return s + n + 1;
-      if (s[n] == '\0')
-        return s + n;
+  for (option = get_next_driver_option(instance, NULL);
+       option;
+       option = get_next_driver_option(instance, option)) {
+    if (!strncmp(name, option, len)) {
+      if (option[len] == '=')
+        return option + len + 1;
+      if (option[len] == '\0')
+        return option + len;
    }
  }

  return NULL;
 }

+static int
+convert_tai_offset(struct timespec *sample_time, double *offset)
+{
+  struct timespec tai_ts, utc_ts;
+  int tai_offset;
+
+  /* Get approximate TAI-UTC offset for the reference time in TAI */
+  UTI_AddDoubleToTimespec(sample_time, *offset, &tai_ts);
+  tai_offset = REF_GetTaiOffset(&tai_ts);
+
+  /* Get TAI-UTC offset for the reference time in UTC +/- 1 second */
+  UTI_AddDoubleToTimespec(&tai_ts, -tai_offset, &utc_ts);
+  tai_offset = REF_GetTaiOffset(&utc_ts);
+
+  if (!tai_offset)
+    return 0;
+
+  *offset -= tai_offset;
+
+  return 1;
+}
+
+static int
+accumulate_sample(RCL_Instance instance, struct timespec *sample_time, double offset, double dispersion)
+{
+  NTP_Sample sample;
+
+  sample.time = *sample_time;
+  sample.offset = offset;
+  sample.peer_delay = instance->delay;
+  sample.root_delay = instance->delay;
+  sample.peer_dispersion = dispersion;
+  sample.root_dispersion = dispersion;
+
+  return SPF_AccumulateSample(instance->filter, &sample);
+}
+
 int
 RCL_AddSample(RCL_Instance instance, struct timespec *sample_time, double offset, int leap)
 {
@@ -385,7 +468,15 @@ RCL_AddSample(RCL_Instance instance, struct timespec *sample_time, double offset
      return 0;
  }

-  filter_add_sample(&instance->filter, &cooked_time, offset - correction + instance->offset, dispersion);
+  if (instance->tai && !convert_tai_offset(sample_time, &offset)) {
+    DEBUG_LOG("refclock sample ignored unknown TAI offset");
+    return 0;
+  }
+
+  if (!accumulate_sample(instance, &cooked_time,
+                         offset - correction + instance->offset, dispersion))
+    return 0;
+
  instance->pps_active = 0;

  log_sample(instance, &cooked_time, 0, 0, offset, offset - correction + instance->offset, dispersion);
@@ -461,20 +552,19 @@ RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,

  if (instance->lock_ref != -1) {
    RCL_Instance lock_refclock;
-    struct timespec ref_sample_time;
-    double sample_diff, ref_offset, ref_dispersion, shift;
+    NTP_Sample ref_sample;
+    double sample_diff, shift;

    lock_refclock = get_refclock(instance->lock_ref);

-    if (!filter_get_last_sample(&lock_refclock->filter,
-          &ref_sample_time, &ref_offset, &ref_dispersion)) {
+    if (!SPF_GetLastSample(lock_refclock->filter, &ref_sample)) {
      DEBUG_LOG("refclock pulse ignored no ref sample");
      return 0;
    }

-    ref_dispersion += filter_get_avg_sample_dispersion(&lock_refclock->filter);
+    ref_sample.root_dispersion += SPF_GetAvgSampleDispersion(lock_refclock->filter);

-    sample_diff = UTI_DiffTimespecsToDouble(cooked_time, &ref_sample_time);
+    sample_diff = UTI_DiffTimespecsToDouble(cooked_time, &ref_sample.time);
    if (fabs(sample_diff) >= (double)instance->max_lock_age / rate) {
      DEBUG_LOG("refclock pulse ignored samplediff=%.9f",
          sample_diff);
@@ -482,26 +572,27 @@ RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
    }

    /* Align the offset to the reference sample */
-    if ((ref_offset - offset) >= 0.0)
-      shift = (long)((ref_offset - offset) * rate + 0.5) / (double)rate;
+    if ((ref_sample.offset - offset) >= 0.0)
+      shift = (long)((ref_sample.offset - offset) * rate + 0.5) / (double)rate;
    else
-      shift = (long)((ref_offset - offset) * rate - 0.5) / (double)rate;
+      shift = (long)((ref_sample.offset - offset) * rate - 0.5) / (double)rate;

    offset += shift;

-    if (fabs(ref_offset - offset) + ref_dispersion + dispersion >= 0.2 / rate) {
+    if (fabs(ref_sample.offset - offset) +
+        ref_sample.root_dispersion + dispersion > PPS_LOCK_LIMIT / rate) {
      DEBUG_LOG("refclock pulse ignored offdiff=%.9f refdisp=%.9f disp=%.9f",
-          ref_offset - offset, ref_dispersion, dispersion);
+                ref_sample.offset - offset, ref_sample.root_dispersion, dispersion);
      return 0;
    }

-    if (!check_pulse_edge(instance, ref_offset - offset, 0.0))
+    if (!check_pulse_edge(instance, ref_sample.offset - offset, 0.0))
      return 0;

    leap = lock_refclock->leap_status;

    DEBUG_LOG("refclock pulse offset=%.9f offdiff=%.9f samplediff=%.9f",
-              offset, ref_offset - offset, sample_diff);
+              offset, ref_sample.offset - offset, sample_diff);
  } else {
    struct timespec ref_time;
    int is_synchronised, stratum;
@@ -519,7 +610,7 @@ RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
      DEBUG_LOG("refclock pulse ignored offset=%.9f sync=%d dist=%.9f",
                offset, leap != LEAP_Unsynchronised, distance);
      /* Drop also all stored samples */
-      filter_reset(&instance->filter);
+      SPF_DropSamples(instance->filter);
      return 0;
    }

@@ -527,7 +618,9 @@ RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
      return 0;
  }

-  filter_add_sample(&instance->filter, cooked_time, offset, dispersion);
+  if (!accumulate_sample(instance, cooked_time, offset, dispersion))
+    return 0;
+
  instance->leap_status = leap;
  instance->pps_active = 1;

@@ -556,17 +649,13 @@ RCL_GetDriverPoll(RCL_Instance instance)
 static int
 valid_sample_time(RCL_Instance instance, struct timespec *sample_time)
 {
-  struct timespec now, last_sample_time;
-  double diff, last_offset, last_dispersion;
+  struct timespec now;
+  double diff;

  LCL_ReadCookedTime(&now, NULL);
  diff = UTI_DiffTimespecsToDouble(&now, sample_time);

-  if (diff < 0.0 || diff > UTI_Log2ToDouble(instance->poll + 1) ||
-      (filter_get_samples(&instance->filter) > 0 &&
-       filter_get_last_sample(&instance->filter, &last_sample_time,
-                              &last_offset, &last_dispersion) &&
-       UTI_CompareTimespecs(&last_sample_time, sample_time) >= 0)) {
+  if (diff < 0.0 || diff > UTI_Log2ToDouble(instance->poll + 1)) {
    DEBUG_LOG("%s refclock sample time %s not valid age=%.6f",
              UTI_RefidToString(instance->ref_id),
              UTI_TimespecToString(sample_time), diff);
@@ -610,7 +699,8 @@ pps_stratum(RCL_Instance instance, struct timespec *ts)
 static void
 poll_timeout(void *arg)
 {
-  int poll;
+  NTP_Sample sample;
+  int poll, stratum;

  RCL_Instance inst = (RCL_Instance)arg;

@@ -623,26 +713,21 @@ poll_timeout(void *arg)
  }
  
  if (!(inst->driver->poll && inst->driver_polled < (1 << (inst->poll - inst->driver_poll)))) {
-    double offset, dispersion;
-    struct timespec sample_time;
-    int sample_ok, stratum;
-
-    sample_ok = filter_get_sample(&inst->filter, &sample_time, &offset, &dispersion);
    inst->driver_polled = 0;

-    if (sample_ok) {
+    if (SPF_GetFilteredSample(inst->filter, &sample)) {
+      /* Handle special case when PPS is used with the local reference */
      if (inst->pps_active && inst->lock_ref == -1)
-        /* Handle special case when PPS is used with local stratum */
-        stratum = pps_stratum(inst, &sample_time);
+        stratum = pps_stratum(inst, &sample.time);
      else
-        stratum = 0;
+        stratum = inst->stratum;

      SRC_UpdateReachability(inst->source, 1);
-      SRC_AccumulateSample(inst->source, &sample_time, offset,
-          inst->delay, dispersion, inst->delay, dispersion, stratum, inst->leap_status);
+      SRC_UpdateStatus(inst->source, stratum, inst->leap_status);
+      SRC_AccumulateSample(inst->source, &sample);
      SRC_SelectSource(inst->source);

-      log_sample(inst, &sample_time, 1, 0, 0.0, offset, dispersion);
+      log_sample(inst, &sample.time, 1, 0, 0.0, sample.offset, sample.peer_dispersion);
    } else {
      SRC_UpdateReachability(inst->source, 0);
    }
@@ -659,9 +744,9 @@ slew_samples(struct timespec *raw, struct timespec *cooked, double dfreq,

  for (i = 0; i < ARR_GetSize(refclocks); i++) {
    if (change_type == LCL_ChangeUnknownStep)
-      filter_reset(&get_refclock(i)->filter);
+      SPF_DropSamples(get_refclock(i)->filter);
    else
-      filter_slew_samples(&get_refclock(i)->filter, cooked, dfreq, doffset);
+      SPF_SlewSamples(get_refclock(i)->filter, cooked, dfreq, doffset);
  }
 }

@@ -671,7 +756,7 @@ add_dispersion(double dispersion, void *anything)
  unsigned int i;

  for (i = 0; i < ARR_GetSize(refclocks); i++)
-    filter_add_dispersion(&get_refclock(i)->filter, dispersion);
+    SPF_AddDispersion(get_refclock(i)->filter, dispersion);
 }

 static void
@@ -703,320 +788,3 @@ log_sample(RCL_Instance instance, struct timespec *sample_time, int filtered, in
      dispersion);
  }
 }
-
-static void
-filter_init(struct MedianFilter *filter, int length, double max_dispersion)
-{
-  if (length < 1)
-    length = 1;
-
-  filter->length = length;
-  filter->index = -1;
-  filter->used = 0;
-  filter->last = -1;
-  /* set first estimate to system precision */
-  filter->avg_var_n = 0;
-  filter->avg_var = LCL_GetSysPrecisionAsQuantum() * LCL_GetSysPrecisionAsQuantum();
-  filter->max_var = max_dispersion * max_dispersion;
-  filter->samples = MallocArray(struct FilterSample, filter->length);
-  filter->selected = MallocArray(int, filter->length);
-  filter->x_data = MallocArray(double, filter->length);
-  filter->y_data = MallocArray(double, filter->length);
-  filter->w_data = MallocArray(double, filter->length);
-}
-
-static void
-filter_fini(struct MedianFilter *filter)
-{
-  Free(filter->samples);
-  Free(filter->selected);
-  Free(filter->x_data);
-  Free(filter->y_data);
-  Free(filter->w_data);
-}
-
-static void
-filter_reset(struct MedianFilter *filter)
-{
-  filter->index = -1;
-  filter->used = 0;
-}
-
-static double
-filter_get_avg_sample_dispersion(struct MedianFilter *filter)
-{
-  return sqrt(filter->avg_var);
-}
-
-static void
-filter_add_sample(struct MedianFilter *filter, struct timespec *sample_time, double offset, double dispersion)
-{
-  filter->index++;
-  filter->index %= filter->length;
-  filter->last = filter->index;
-  if (filter->used < filter->length)
-    filter->used++;
-
-  filter->samples[filter->index].sample_time = *sample_time;
-  filter->samples[filter->index].offset = offset;
-  filter->samples[filter->index].dispersion = dispersion;
-
-  DEBUG_LOG("filter sample %d t=%s offset=%.9f dispersion=%.9f",
-      filter->index, UTI_TimespecToString(sample_time), offset, dispersion);
-}
-
-static int
-filter_get_last_sample(struct MedianFilter *filter, struct timespec *sample_time, double *offset, double *dispersion)
-{
-  if (filter->last < 0)
-    return 0;
-
-  *sample_time = filter->samples[filter->last].sample_time;
-  *offset = filter->samples[filter->last].offset;
-  *dispersion = filter->samples[filter->last].dispersion;
-  return 1;
-}
-
-static int
-filter_get_samples(struct MedianFilter *filter)
-{
-  return filter->used;
-}
-
-static const struct FilterSample *tmp_sorted_array;
-
-static int
-sample_compare(const void *a, const void *b)
-{
-  const struct FilterSample *s1, *s2;
-
-  s1 = &tmp_sorted_array[*(int *)a];
-  s2 = &tmp_sorted_array[*(int *)b];
-
-  if (s1->offset < s2->offset)
-    return -1;
-  else if (s1->offset > s2->offset)
-    return 1;
-  return 0;
-}
-
-int
-filter_select_samples(struct MedianFilter *filter)
-{
-  int i, j, k, o, from, to, *selected;
-  double min_dispersion;
-
-  if (filter->used < 1)
-    return 0;
-
-  /* for lengths below 4 require full filter,
-     for 4 and above require at least 4 samples */
-  if ((filter->length < 4 && filter->used != filter->length) ||
-      (filter->length >= 4 && filter->used < 4))
-    return 0;
-
-  selected = filter->selected;
-
-  if (filter->used > 4) {
-    /* select samples with dispersion better than 1.5 * minimum */
-
-    for (i = 1, min_dispersion = filter->samples[0].dispersion; i < filter->used; i++) {
-      if (min_dispersion > filter->samples[i].dispersion)
-        min_dispersion = filter->samples[i].dispersion;
-    }
-
-    for (i = j = 0; i < filter->used; i++) {
-      if (filter->samples[i].dispersion <= 1.5 * min_dispersion)
-        selected[j++] = i;
-    }
-  } else {
-    j = 0;
-  }
-
-  if (j < 4) {
-    /* select all samples */
-
-    for (j = 0; j < filter->used; j++)
-      selected[j] = j;
-  }
-
-  /* and sort their indices by offset */
-  tmp_sorted_array = filter->samples;
-  qsort(selected, j, sizeof (int), sample_compare);
-
-  /* select 60 percent of the samples closest to the median */ 
-  if (j > 2) {
-    from = j / 5;
-    if (from < 1)
-      from = 1;
-    to = j - from;
-  } else {
-    from = 0;
-    to = j;
-  }
-
-  /* mark unused samples and sort the rest from oldest to newest */
-
-  o = filter->used - filter->index - 1;
-
-  for (i = 0; i < from; i++)
-    selected[i] = -1;
-  for (; i < to; i++)
-    selected[i] = (selected[i] + o) % filter->used;
-  for (; i < filter->used; i++)
-    selected[i] = -1;
-
-  for (i = from; i < to; i++) {
-    j = selected[i];
-    selected[i] = -1;
-    while (j != -1 && selected[j] != j) {
-      k = selected[j];
-      selected[j] = j;
-      j = k;
-    }
-  }
-
-  for (i = j = 0, k = -1; i < filter->used; i++) {
-    if (selected[i] != -1)
-      selected[j++] = (selected[i] + filter->used - o) % filter->used;
-  }
-
-  return j;
-}
-
-static int
-filter_get_sample(struct MedianFilter *filter, struct timespec *sample_time, double *offset, double *dispersion)
-{
-  struct FilterSample *s, *ls;
-  int i, n, dof;
-  double x, y, d, e, var, prev_avg_var;
-
-  n = filter_select_samples(filter);
-
-  if (n < 1)
-    return 0;
-
-  ls = &filter->samples[filter->selected[n - 1]];
-
-  /* prepare data */
-  for (i = 0; i < n; i++) {
-    s = &filter->samples[filter->selected[i]];
-
-    filter->x_data[i] = UTI_DiffTimespecsToDouble(&s->sample_time, &ls->sample_time);
-    filter->y_data[i] = s->offset;
-    filter->w_data[i] = s->dispersion;
-  }
-
-  /* mean offset, sample time and sample dispersion */ 
-  for (i = 0, x = y = e = 0.0; i < n; i++) {
-    x += filter->x_data[i];
-    y += filter->y_data[i];
-    e += filter->w_data[i];
-  }
-  x /= n;
-  y /= n;
-  e /= n;
-
-  if (n >= 4) {
-    double b0, b1, s2, sb0, sb1;
-
-    /* set y axis to the mean sample time */
-    for (i = 0; i < n; i++)
-      filter->x_data[i] -= x;
-
-    /* make a linear fit and use the estimated standard deviation of intercept
-       as dispersion */
-    RGR_WeightedRegression(filter->x_data, filter->y_data, filter->w_data, n,
-        &b0, &b1, &s2, &sb0, &sb1);
-    var = s2;
-    d = sb0;
-    dof = n - 2;
-  } else if (n >= 2) {
-    for (i = 0, d = 0.0; i < n; i++)
-      d += (filter->y_data[i] - y) * (filter->y_data[i] - y);
-    var = d / (n - 1);
-    d = sqrt(var);
-    dof = n - 1;
-  } else {
-    var = filter->avg_var;
-    d = sqrt(var);
-    dof = 1;
-  }
-
-  /* avoid having zero dispersion */
-  if (var < 1e-20) {
-    var = 1e-20;
-    d = sqrt(var);
-  }
-
-  /* drop the sample if variance is larger than allowed maximum */
-  if (filter->max_var > 0.0 && var > filter->max_var) {
-    DEBUG_LOG("filter dispersion too large disp=%.9f max=%.9f",
-        sqrt(var), sqrt(filter->max_var));
-    return 0;
-  }
-
-  prev_avg_var = filter->avg_var;
-
-  /* update exponential moving average of the variance */
-  if (filter->avg_var_n > 50) {
-    filter->avg_var += dof / (dof + 50.0) * (var - filter->avg_var);
-  } else {
-    filter->avg_var = (filter->avg_var * filter->avg_var_n + var * dof) /
-      (dof + filter->avg_var_n);
-    if (filter->avg_var_n == 0)
-      prev_avg_var = filter->avg_var;
-    filter->avg_var_n += dof;
-  }
-
-  /* reduce noise in sourcestats weights by using the long-term average
-     instead of the estimated variance if it's not significantly lower */
-  if (var * dof / RGR_GetChi2Coef(dof) < prev_avg_var)
-    d = sqrt(filter->avg_var) * d / sqrt(var);
-
-  if (d < e)
-    d = e;
-
-  UTI_AddDoubleToTimespec(&ls->sample_time, x, sample_time);
-  *offset = y;
-  *dispersion = d;
-
-  filter_reset(filter);
-
-  return 1;
-}
-
-static void
-filter_slew_samples(struct MedianFilter *filter, struct timespec *when, double dfreq, double doffset)
-{
-  int i, first, last;
-  double delta_time;
-  struct timespec *sample;
-
-  if (filter->last < 0)
-    return;
-
-  /* always slew the last sample as it may be needed by PPS refclocks */
-  if (filter->used > 0) {
-    first = 0;
-    last = filter->used - 1;
-  } else {
-    first = last = filter->last;
-  }
-
-  for (i = first; i <= last; i++) {
-    sample = &filter->samples[i].sample_time;
-    UTI_AdjustTimespec(sample, when, sample, &delta_time, dfreq, doffset);
-    filter->samples[i].offset -= delta_time;
-  }
-}
-
-static void
-filter_add_dispersion(struct MedianFilter *filter, double dispersion)
-{
-  int i;
-
-  for (i = 0; i < filter->used; i++) {
-    filter->samples[i].dispersion += dispersion;
-  }
-}
--- a/refclock.h
+++ b/refclock.h
@@ -43,6 +43,8 @@ typedef struct {
  int max_samples;
  int sel_options;
  int max_lock_age;
+  int stratum;
+  int tai;
  uint32_t ref_id;
  uint32_t lock_ref_id;
  double offset;
@@ -70,6 +72,7 @@ extern void RCL_ReportSource(RPT_SourceReport *report, struct timespec *now);
 extern void RCL_SetDriverData(RCL_Instance instance, void *data);
 extern void *RCL_GetDriverData(RCL_Instance instance);
 extern char *RCL_GetDriverParameter(RCL_Instance instance);
+extern void RCL_CheckDriverOptions(RCL_Instance instance, const char **options);
 extern char *RCL_GetDriverOption(RCL_Instance instance, char *name);
 extern int RCL_AddSample(RCL_Instance instance, struct timespec *sample_time, double offset, int leap);
 extern int RCL_AddPulse(RCL_Instance instance, struct timespec *pulse_time, double second);
--- a/refclock_phc.c
+++ b/refclock_phc.c
@@ -56,17 +56,18 @@ static void read_ext_pulse(int sockfd, int event, void *anything);

 static int phc_initialise(RCL_Instance instance)
 {
+  const char *options[] = {"nocrossts", "extpps", "pin", "channel", "clear", NULL};
  struct phc_instance *phc;
  int phc_fd, rising_edge;
  char *path, *s;

+  RCL_CheckDriverOptions(instance, options);
+
  path = RCL_GetDriverParameter(instance);
 
  phc_fd = SYS_Linux_OpenPHC(path, 0);
-  if (phc_fd < 0) {
+  if (phc_fd < 0)
    LOG_FATAL("Could not open PHC");
-    return 0;
-  }

  phc = MallocNew(struct phc_instance);
  phc->fd = phc_fd;
@@ -80,7 +81,7 @@ static int phc_initialise(RCL_Instance instance)
    s = RCL_GetDriverOption(instance, "channel");
    phc->channel = s ? atoi(s) : 0;
    rising_edge = RCL_GetDriverOption(instance, "clear") ? 0 : 1;
-    phc->clock = HCL_CreateInstance(UTI_Log2ToDouble(RCL_GetDriverPoll(instance)));
+    phc->clock = HCL_CreateInstance(0, 16, UTI_Log2ToDouble(RCL_GetDriverPoll(instance)));

    if (!SYS_Linux_SetPHCExtTimestamping(phc->fd, phc->pin, phc->channel,
                                         rising_edge, !rising_edge, 1))
--- a/refclock_pps.c
+++ b/refclock_pps.c
@@ -48,59 +48,49 @@ struct pps_instance {
 };

 static int pps_initialise(RCL_Instance instance) {
+  const char *options[] = {"clear", NULL};
  pps_handle_t handle;
  pps_params_t params;
  struct pps_instance *pps;
  int fd, edge_clear, mode;
  char *path;

+  RCL_CheckDriverOptions(instance, options);
+
  path = RCL_GetDriverParameter(instance);
  edge_clear = RCL_GetDriverOption(instance, "clear") ? 1 : 0;

  fd = open(path, O_RDWR);
-  if (fd < 0) {
-    LOG_FATAL("open() failed on %s", path);
-    return 0;
-  }
+  if (fd < 0)
+    LOG_FATAL("Could not open %s : %s", path, strerror(errno));

  UTI_FdSetCloexec(fd);

-  if (time_pps_create(fd, &handle) < 0) {
-    LOG_FATAL("time_pps_create() failed on %s", path);
-    return 0;
-  }
+  if (time_pps_create(fd, &handle) < 0)
+    LOG_FATAL("time_pps_create() failed on %s : %s", path, strerror(errno));

-  if (time_pps_getcap(handle, &mode) < 0) {
-    LOG_FATAL("time_pps_getcap() failed on %s", path);
-    return 0;
-  }
+  if (time_pps_getcap(handle, &mode) < 0)
+    LOG_FATAL("time_pps_getcap() failed on %s : %s", path, strerror(errno));

-  if (time_pps_getparams(handle, &params) < 0) {
-    LOG_FATAL("time_pps_getparams() failed on %s", path);
-    return 0;
-  }
+  if (time_pps_getparams(handle, &params) < 0)
+    LOG_FATAL("time_pps_getparams() failed on %s : %s", path, strerror(errno));

  if (!edge_clear) {
-    if (!(mode & PPS_CAPTUREASSERT)) {
+    if (!(mode & PPS_CAPTUREASSERT))
      LOG_FATAL("CAPTUREASSERT not supported on %s", path);
-      return 0;
-    }
+
    params.mode |= PPS_CAPTUREASSERT;
    params.mode &= ~PPS_CAPTURECLEAR;
  } else {
-    if (!(mode & PPS_CAPTURECLEAR)) {
+    if (!(mode & PPS_CAPTURECLEAR))
      LOG_FATAL("CAPTURECLEAR not supported on %s", path);
-      return 0;
-    }
+
    params.mode |= PPS_CAPTURECLEAR;
    params.mode &= ~PPS_CAPTUREASSERT;
  }

-  if (time_pps_setparams(handle, &params) < 0) {
-    LOG_FATAL("time_pps_setparams() failed on %s", path);
-    return 0;
-  }
-
+  if (time_pps_setparams(handle, &params) < 0)
+    LOG_FATAL("time_pps_setparams() failed on %s : %s", path, strerror(errno));

  pps = MallocNew(struct pps_instance);
  pps->handle = handle;
@@ -147,7 +137,7 @@ static int pps_poll(RCL_Instance instance)

  if (seq == pps->last_seq || UTI_IsZeroTimespec(&ts)) {
    DEBUG_LOG("PPS sample ignored seq=%lu ts=%s",
-              seq, UTI_TimespecToString(&ts));
+              (unsigned long)seq, UTI_TimespecToString(&ts));
    return 0;
  }

--- a/refclock_shm.c
+++ b/refclock_shm.c
@@ -59,23 +59,26 @@ struct shmTime {
 };

 static int shm_initialise(RCL_Instance instance) {
+  const char *options[] = {"perm", NULL};
  int id, param, perm;
  char *s;
  struct shmTime *shm;

+  RCL_CheckDriverOptions(instance, options);
+
  param = atoi(RCL_GetDriverParameter(instance));
  s = RCL_GetDriverOption(instance, "perm");
  perm = s ? strtol(s, NULL, 8) & 0777 : 0600;

  id = shmget(SHMKEY + param, sizeof (struct shmTime), IPC_CREAT | perm);
  if (id == -1) {
-    LOG_FATAL("shmget() failed");
+    LOG_FATAL("shmget() failed : %s", strerror(errno));
    return 0;
  }
   
  shm = (struct shmTime *)shmat(id, 0, 0);
  if ((long)shm == -1) {
-    LOG_FATAL("shmat() failed");
+    LOG_FATAL("shmat() failed : %s", strerror(errno));
    return 0;
  }

--- 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

@@ -69,20 +70,19 @@ static void read_sample(int sockfd, int event, void *anything)
  s = recv(sockfd, &sample, sizeof (sample), 0);

  if (s < 0) {
-    LOG(LOGS_ERR, "Could not read SOCK sample : %s",
-        strerror(errno));
+    DEBUG_LOG("Could not read SOCK sample : %s", strerror(errno));
    return;
  }

  if (s != sizeof (sample)) {
-    LOG(LOGS_WARN, "Unexpected length of SOCK sample : %d != %ld",
-        s, (long)sizeof (sample));
+    DEBUG_LOG("Unexpected length of SOCK sample : %d != %ld",
+              s, (long)sizeof (sample));
    return;
  }

  if (sample.magic != SOCK_MAGIC) {
-    LOG(LOGS_WARN, "Unexpected magic number in SOCK sample : %x != %x",
-        sample.magic, SOCK_MAGIC);
+    DEBUG_LOG("Unexpected magic number in SOCK sample : %x != %x",
+              (unsigned int)sample.magic, (unsigned int)SOCK_MAGIC);
    return;
  }

@@ -98,31 +98,16 @@ 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;

+  RCL_CheckDriverOptions(instance, NULL);
+
  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 is 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() failed");
-    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);
@@ -135,7 +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  2009-2017
+ * 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;
@@ -325,84 +342,26 @@ REF_GetLeapMode(void)
  return leap_mode;
 }

-/* ================================================== */
-
-static double
-Sqr(double x)
-{
-  return x*x;
-}
-
-/* ================================================== */
-#if 0
-static double
-Cube(double x)
-{
-  return x*x*x;
-}
-#endif
-
 /* ================================================== */
 /* Update the drift coefficients to the file. */

 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))
+    ;
 }

 /* ================================================== */
@@ -468,16 +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;
@@ -499,8 +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);
  }
 }
@@ -528,28 +486,35 @@ maybe_log_offset(double offset, time_t now)
  double abs_offset;
  FILE *p;
  char buffer[BUFLEN], host[BUFLEN];
-  struct tm stm;
+  struct tm *tm;

  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 &&
      (abs_offset > mail_change_threshold)) {
-    snprintf(buffer, sizeof(buffer), "%s %." S_MAX_USER_LEN "s", MAIL_PROGRAM, mail_change_user);
+    snprintf(buffer, sizeof (buffer), "%s -t", MAIL_PROGRAM);
    p = popen(buffer, "w");
    if (p) {
      if (gethostname(host, sizeof(host)) < 0) {
        strcpy(host, "<UNKNOWN>");
      }
+      host[sizeof (host) - 1] = '\0';
+
+      fprintf(p, "To: %s\n", mail_change_user);
      fprintf(p, "Subject: chronyd reports change to system clock on node [%s]\n", host);
      fputs("\n", p);
-      stm = *localtime(&now);
-      strftime(buffer, sizeof(buffer), "On %A, %d %B %Y\n  with the system clock reading %H:%M:%S (%Z)", &stm);
-      fputs(buffer, p);
+
+      tm = localtime(&now);
+      if (tm) {
+        strftime(buffer, sizeof (buffer),
+                 "On %A, %d %B %Y\n  with the system clock reading %H:%M:%S (%Z)", tm);
+        fputs(buffer, p);
+      }
+
      /* If offset < 0 the local clock is slow, so we are applying a
         positive change to it to bring it into line, hence the
         negation of 'offset' in the next statement (and earlier) */
@@ -592,8 +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");
@@ -760,10 +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--;
@@ -807,7 +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;

@@ -846,6 +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,
@@ -929,34 +909,69 @@ special_mode_sync(int valid, double offset)

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

-void
-REF_SetReference(int stratum,
-                 NTP_Leap leap,
-                 int combined_sources,
-                 uint32_t ref_id,
-                 IPAddr *ref_ip,
-                 struct timespec *ref_time,
-                 double offset,
-                 double offset_sd,
-                 double frequency,
-                 double skew,
-                 double root_delay,
-                 double root_dispersion
-                 )
+static void
+get_clock_estimates(int manual,
+                    double measured_freq, double measured_skew,
+                    double *estimated_freq, double *estimated_skew,
+                    double *residual_freq)
+{
+  double gain, expected_freq, expected_skew, extra_skew;
+
+  /* We assume that the local clock is running according to our previously
+     determined value */
+  expected_freq = 0.0;
+  expected_skew = our_skew;
+
+  /* Set new frequency based on weighted average of the expected and measured
+     skew.  Disable updates that are based on totally unreliable frequency
+     information unless it is a manual reference. */
+  if (manual) {
+    gain = 1.0;
+  } else if (fabs(measured_skew) > max_update_skew) {
+    DEBUG_LOG("Skew %f too large to track", measured_skew);
+    gain = 0.0;
+  } else {
+    gain = 3.0 * SQUARE(expected_skew) /
+           (3.0 * SQUARE(expected_skew) + SQUARE(measured_skew));
+  }
+
+  gain = CLAMP(0.0, gain, 1.0);
+
+  *estimated_freq = expected_freq + gain * (measured_freq - expected_freq);
+  *residual_freq = measured_freq - *estimated_freq;
+
+  extra_skew = sqrt(SQUARE(expected_freq - *estimated_freq) * (1.0 - gain) +
+                    SQUARE(measured_freq - *estimated_freq) * gain);
+
+  *estimated_skew = expected_skew + gain * (measured_skew - expected_skew) + extra_skew;
+}
+
+/* ================================================== */
+
+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,
+                 double offset, double offset_sd,
+                 double frequency, double frequency_sd, double skew,
+                 double root_delay, double root_dispersion)
 {
-  double previous_skew, new_skew;
-  double previous_freq, new_freq;
-  double old_weight, new_weight, sum_weight;
-  double delta_freq1, delta_freq2;
-  double skew1, skew2;
-  double our_offset;
-  double our_frequency;
-  double abs_freq_ppm;
-  double update_interval;
-  double elapsed, correction_rate, orig_root_distance;
  double uncorrected_offset, accumulate_offset, step_offset;
+  double residual_frequency, local_abs_frequency;
+  double elapsed, mono_now, update_interval, correction_rate, orig_root_distance;
  struct timespec now, raw_now;
-  NTP_int64 ref_fuzz;
+  int manual;

  assert(initialised);

@@ -966,23 +981,32 @@ REF_SetReference(int stratum,
    return;
  }

-  /* Guard against dividing by zero and NaN */
-  if (!(skew > MIN_SKEW))
-    skew = MIN_SKEW;
+  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);
-  our_offset = offset + elapsed * frequency;
+  offset += elapsed * frequency;

-  if (!is_offset_ok(our_offset))
+  if (last_ref_update != 0.0) {
+    update_interval = mono_now - last_ref_update;
+  } else {
+    update_interval = 0.0;
+  }
+
+  /* Get new estimates of the frequency and skew including the new data */
+  get_clock_estimates(manual, frequency, skew,
+                      &frequency, &skew, &residual_frequency);
+
+  if (!is_offset_ok(offset))
    return;

  orig_root_distance = our_root_delay / 2.0 + get_root_dispersion(&now);

-  are_we_synchronised = leap != LEAP_Unsynchronised ? 1 : 0;
+  are_we_synchronised = leap != LEAP_Unsynchronised;
  our_stratum = stratum + 1;
  our_ref_id = ref_id;
  if (ref_ip)
@@ -990,17 +1014,15 @@ REF_SetReference(int stratum,
  else
    our_ref_ip.family = IPADDR_UNSPEC;
  our_ref_time = *ref_time;
+  our_skew = skew;
+  our_residual_freq = residual_frequency;
  our_root_delay = root_delay;
  our_root_dispersion = root_dispersion;
-
-  if (last_ref_update.tv_sec) {
-    update_interval = UTI_DiffTimespecsToDouble(&now, &last_ref_update);
-    if (update_interval < 0.0)
-      update_interval = 0.0;
-  } else {
-    update_interval = 0.0;
-  }
-  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;

  /* We want to correct the offset quickly, but we also want to keep the
     frequency error caused by the correction itself low.
@@ -1018,108 +1040,60 @@ REF_SetReference(int stratum,
  correction_rate = correction_time_ratio * 0.5 * offset_sd * update_interval;

  /* Check if the clock should be stepped */
-  if (is_step_limit_reached(our_offset, uncorrected_offset)) {
+  if (is_step_limit_reached(offset, uncorrected_offset)) {
    /* Cancel the uncorrected offset and correct the total offset by step */
    accumulate_offset = uncorrected_offset;
-    step_offset = our_offset - uncorrected_offset;
+    step_offset = offset - uncorrected_offset;
  } else {
-    accumulate_offset = our_offset;
+    accumulate_offset = offset;
    step_offset = 0.0;
  }

-  /* Eliminate updates that are based on totally unreliable frequency
-     information. Ignore this limit with manual reference. */
-
-  if (fabs(skew) < max_update_skew || leap == LEAP_Unsynchronised) {
-
-    previous_skew = our_skew;
-    new_skew = skew;
-
-    previous_freq = 0.0; /* We assume that the local clock is running
-                          according to our previously determined
-                          value; note that this is a delta frequency
-                          --- absolute frequencies are only known in
-                          the local module. */
-    new_freq = frequency;
-
-    /* Set new frequency based on weighted average of old and new skew. With
-       manual reference the old frequency has no weight. */
-
-    old_weight = leap != LEAP_Unsynchronised ? 1.0 / Sqr(previous_skew) : 0.0;
-    new_weight = 3.0 / Sqr(new_skew);
-
-    sum_weight = old_weight + new_weight;
-
-    our_frequency = (previous_freq * old_weight + new_freq * new_weight) / sum_weight;
-
-    delta_freq1 = previous_freq - our_frequency;
-    delta_freq2 = new_freq - our_frequency;
-
-    skew1 = sqrt((Sqr(delta_freq1) * old_weight + Sqr(delta_freq2) * new_weight) / sum_weight);
-    skew2 = (previous_skew * old_weight + new_skew * new_weight) / sum_weight;
-    our_skew = skew1 + skew2;
-
-    our_residual_freq = new_freq - our_frequency;
-
-    LCL_AccumulateFrequencyAndOffset(our_frequency, accumulate_offset, correction_rate);
+  /* Adjust the clock */
+  LCL_AccumulateFrequencyAndOffset(frequency, accumulate_offset, correction_rate);
    
-  } else {
-    DEBUG_LOG("Skew %f too large to track, offset=%f", skew, accumulate_offset);
-
-    LCL_AccumulateOffset(accumulate_offset, correction_rate);
-
-    our_residual_freq = frequency;
-  }
-
-  update_leap_status(leap, raw_now.tv_sec, 0);
-  maybe_log_offset(our_offset, raw_now.tv_sec);
+  maybe_log_offset(offset, raw_now.tv_sec);

  if (step_offset != 0.0) {
    if (LCL_ApplyStepOffset(step_offset))
      LOG(LOGS_WARN, "System clock was stepped by %.6f seconds", -step_offset);
  }

-  LCL_SetSyncStatus(are_we_synchronised, offset_sd, offset_sd + root_delay / 2.0 + root_dispersion);
+  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);

-  abs_freq_ppm = LCL_ReadAbsoluteFrequency();
+  local_abs_frequency = LCL_ReadAbsoluteFrequency();

-  write_log(&now, combined_sources, abs_freq_ppm, our_offset, offset_sd,
-            uncorrected_offset, orig_root_distance);
+  write_log(&now, combined_sources, local_abs_frequency,
+            offset, offset_sd, uncorrected_offset, orig_root_distance);

  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) {
-      update_drift_file(abs_freq_ppm, our_skew);
+    if (drift_file_age >= MAX_DRIFTFILE_AGE) {
+      update_drift_file(local_abs_frequency, our_skew);
      drift_file_age = 0.0;
    }
  }

  /* Update fallback drifts */
  if (fb_drifts && are_we_synchronised) {
-    update_fb_drifts(abs_freq_ppm, update_interval);
-    schedule_fb_drift(&now);
+    update_fb_drifts(local_abs_frequency, update_interval);
+    schedule_fb_drift();
  }

-  last_ref_update_interval = update_interval;
-  last_offset = our_offset;
-
  /* Update the moving average of squares of offset, quickly on start */
  if (avg2_moving) {
-    avg2_offset += 0.1 * (our_offset * our_offset - avg2_offset);
+    avg2_offset += 0.1 * (SQUARE(offset) - avg2_offset);
  } else {
-    if (avg2_offset > 0.0 && avg2_offset < our_offset * our_offset)
+    if (avg2_offset > 0.0 && avg2_offset < SQUARE(offset))
      avg2_moving = 1;
-    avg2_offset = our_offset * our_offset;
+    avg2_offset = SQUARE(offset);
  }
 }

@@ -1138,7 +1112,7 @@ REF_SetManualReference
     only supposed to be used with the local source option, really.
     Log as MANU in the tracking log, packets will have NTP_REFID_LOCAL. */
  REF_SetReference(0, LEAP_Unsynchronised, 1, 0x4D414E55UL, NULL,
-                   ref_time, offset, 0.0, frequency, skew, 0.0, 0.0);
+                   ref_time, offset, 0.0, frequency, skew, skew, 0.0, 0.0);
 }

 /* ================================================== */
@@ -1163,7 +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);
@@ -1180,6 +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
 (
@@ -1193,7 +1186,7 @@ REF_GetReferenceParams
 double *root_dispersion
 )
 {
-  double dispersion;
+  double dispersion, delta;

  assert(initialised);

@@ -1225,13 +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 */
@@ -1333,22 +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;
@@ -1356,6 +1355,18 @@ int REF_IsLeapSecondClose(void)

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

+int
+REF_GetTaiOffset(struct timespec *ts)
+{
+  int tai_offset;
+
+  get_tz_leap(ts->tv_sec, &tai_offset);
+
+  return tai_offset;
+}
+
+/* ================================================== */
+
 void
 REF_GetTrackingReport(RPT_TrackingReport *rep)
 {
--- a/reference.h
+++ b/reference.h
@@ -144,6 +144,7 @@ extern void REF_SetReference
 double offset,
 double offset_sd,
 double frequency,
+ double frequency_sd,
 double skew,
 double root_delay,
 double root_dispersion
@@ -161,6 +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);
@@ -180,9 +184,12 @@ 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);

 extern void REF_GetTrackingReport(RPT_TrackingReport *rep);

--- 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
@@ -148,6 +148,8 @@ RTC_Initialise(int initial_set)
    if (driver.init) {
      if ((driver.init)()) {
        driver_initialised = 1;
+      } else {
+        LOG(LOGS_ERR, "RTC driver could not be initialised");
      }
    } else {
      LOG(LOGS_ERR, "RTC not supported on this operating system");
@@ -160,7 +162,7 @@ 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
@@ -352,7 +352,7 @@ rtc_from_t(const time_t *t)

 static time_t
 t_from_rtc(struct tm *stm) {
-  struct tm temp1, temp2;
+  struct tm temp1, temp2, *tm;
  long diff;
  time_t t1, t2;

@@ -360,12 +360,14 @@ t_from_rtc(struct tm *stm) {
  temp1.tm_isdst = 0;
  
  t1 = mktime(&temp1);
-  if (rtc_on_utc) {
-    temp2 = *gmtime(&t1);
-  } else {
-    temp2 = *localtime(&t1);
+
+  tm = rtc_on_utc ? gmtime(&t1) : localtime(&t1);
+  if (!tm) {
+    DEBUG_LOG("gmtime()/localtime() failed");
+    return -1;
  }
-  
+
+  temp2 = *tm;
  temp2.tm_isdst = 0;
  t2 = mktime(&temp2);
  diff = t2 - t1;
@@ -388,12 +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++) {
@@ -443,7 +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,
@@ -464,67 +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
@@ -534,6 +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);
@@ -544,18 +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;
@@ -588,12 +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);
@@ -601,29 +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
@@ -0,0 +1,451 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2009-2011, 2014, 2016, 2018
+ * 
+ * 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.
+ * 
+ **********************************************************************
+
+  =======================================================================
+
+  Routines implementing a median sample filter.
+
+  */
+
+#include "config.h"
+
+#include "local.h"
+#include "logging.h"
+#include "memory.h"
+#include "regress.h"
+#include "samplefilt.h"
+#include "util.h"
+
+#define MIN_SAMPLES 1
+#define MAX_SAMPLES 256
+
+struct SPF_Instance_Record {
+  int min_samples;
+  int max_samples;
+  int index;
+  int used;
+  int last;
+  int avg_var_n;
+  double avg_var;
+  double max_var;
+  double combine_ratio;
+  NTP_Sample *samples;
+  int *selected;
+  double *x_data;
+  double *y_data;
+  double *w_data;
+};
+
+/* ================================================== */
+
+SPF_Instance
+SPF_CreateInstance(int min_samples, int max_samples, double max_dispersion, double combine_ratio)
+{
+  SPF_Instance filter;
+
+  filter = MallocNew(struct SPF_Instance_Record);
+
+  min_samples = CLAMP(MIN_SAMPLES, min_samples, MAX_SAMPLES);
+  max_samples = CLAMP(MIN_SAMPLES, max_samples, MAX_SAMPLES);
+  max_samples = MAX(min_samples, max_samples);
+  combine_ratio = CLAMP(0.0, combine_ratio, 1.0);
+
+  filter->min_samples = min_samples;
+  filter->max_samples = max_samples;
+  filter->index = -1;
+  filter->used = 0;
+  filter->last = -1;
+  /* Set the first estimate to the system precision */
+  filter->avg_var_n = 0;
+  filter->avg_var = SQUARE(LCL_GetSysPrecisionAsQuantum());
+  filter->max_var = SQUARE(max_dispersion);
+  filter->combine_ratio = combine_ratio;
+  filter->samples = MallocArray(NTP_Sample, filter->max_samples);
+  filter->selected = MallocArray(int, filter->max_samples);
+  filter->x_data = MallocArray(double, filter->max_samples);
+  filter->y_data = MallocArray(double, filter->max_samples);
+  filter->w_data = MallocArray(double, filter->max_samples);
+
+  return filter;
+}
+
+/* ================================================== */
+
+void
+SPF_DestroyInstance(SPF_Instance filter)
+{
+  Free(filter->samples);
+  Free(filter->selected);
+  Free(filter->x_data);
+  Free(filter->y_data);
+  Free(filter->w_data);
+  Free(filter);
+}
+
+/* ================================================== */
+
+/* Check that samples times are strictly increasing */
+
+static int
+check_sample(SPF_Instance filter, NTP_Sample *sample)
+{
+  if (filter->used <= 0)
+    return 1;
+
+  if (UTI_CompareTimespecs(&filter->samples[filter->last].time, &sample->time) >= 0) {
+    DEBUG_LOG("filter non-increasing sample time %s", UTI_TimespecToString(&sample->time));
+    return 0;
+  }
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+SPF_AccumulateSample(SPF_Instance filter, NTP_Sample *sample)
+{
+  if (!check_sample(filter, sample))
+      return 0;
+
+  filter->index++;
+  filter->index %= filter->max_samples;
+  filter->last = filter->index;
+  if (filter->used < filter->max_samples)
+    filter->used++;
+
+  filter->samples[filter->index] = *sample;
+
+  DEBUG_LOG("filter sample %d t=%s offset=%.9f peer_disp=%.9f",
+            filter->index, UTI_TimespecToString(&sample->time),
+            sample->offset, sample->peer_dispersion);
+  return 1;
+}
+
+/* ================================================== */
+
+int
+SPF_GetLastSample(SPF_Instance filter, NTP_Sample *sample)
+{
+  if (filter->last < 0)
+    return 0;
+
+  *sample = filter->samples[filter->last];
+  return 1;
+}
+
+/* ================================================== */
+
+int
+SPF_GetNumberOfSamples(SPF_Instance filter)
+{
+  return filter->used;
+}
+
+/* ================================================== */
+
+double
+SPF_GetAvgSampleDispersion(SPF_Instance filter)
+{
+  return sqrt(filter->avg_var);
+}
+
+/* ================================================== */
+
+void
+SPF_DropSamples(SPF_Instance filter)
+{
+  filter->index = -1;
+  filter->used = 0;
+}
+
+/* ================================================== */
+
+static const NTP_Sample *tmp_sort_samples;
+
+static int
+compare_samples(const void *a, const void *b)
+{
+  const NTP_Sample *s1, *s2;
+
+  s1 = &tmp_sort_samples[*(int *)a];
+  s2 = &tmp_sort_samples[*(int *)b];
+
+  if (s1->offset < s2->offset)
+    return -1;
+  else if (s1->offset > s2->offset)
+    return 1;
+  return 0;
+}
+
+/* ================================================== */
+
+static int
+select_samples(SPF_Instance filter)
+{
+  int i, j, k, o, from, to, *selected;
+  double min_dispersion;
+
+  if (filter->used < filter->min_samples)
+    return 0;
+
+  selected = filter->selected;
+
+  /* With 4 or more samples, select those that have peer dispersion smaller
+     than 1.5x of the minimum dispersion */
+  if (filter->used > 4) {
+    for (i = 1, min_dispersion = filter->samples[0].peer_dispersion; i < filter->used; i++) {
+      if (min_dispersion > filter->samples[i].peer_dispersion)
+        min_dispersion = filter->samples[i].peer_dispersion;
+    }
+
+    for (i = j = 0; i < filter->used; i++) {
+      if (filter->samples[i].peer_dispersion <= 1.5 * min_dispersion)
+        selected[j++] = i;
+    }
+  } else {
+    j = 0;
+  }
+
+  if (j < 4) {
+    /* Select all samples */
+
+    for (j = 0; j < filter->used; j++)
+      selected[j] = j;
+  }
+
+  /* And sort their indices by offset */
+  tmp_sort_samples = filter->samples;
+  qsort(selected, j, sizeof (int), compare_samples);
+
+  /* Select samples closest to the median */
+  if (j > 2) {
+    from = j * (1.0 - filter->combine_ratio) / 2.0;
+    from = CLAMP(1, from, (j - 1) / 2);
+  } else {
+    from = 0;
+  }
+
+  to = j - from;
+
+  /* Mark unused samples and sort the rest by their time */
+
+  o = filter->used - filter->index - 1;
+
+  for (i = 0; i < from; i++)
+    selected[i] = -1;
+  for (; i < to; i++)
+    selected[i] = (selected[i] + o) % filter->used;
+  for (; i < filter->used; i++)
+    selected[i] = -1;
+
+  for (i = from; i < to; i++) {
+    j = selected[i];
+    selected[i] = -1;
+    while (j != -1 && selected[j] != j) {
+      k = selected[j];
+      selected[j] = j;
+      j = k;
+    }
+  }
+
+  for (i = j = 0; i < filter->used; i++) {
+    if (selected[i] != -1)
+      selected[j++] = (selected[i] + filter->used - o) % filter->used;
+  }
+
+  assert(j > 0 && j <= filter->max_samples);
+
+  return j;
+}
+
+/* ================================================== */
+
+static int
+combine_selected_samples(SPF_Instance filter, int n, NTP_Sample *result)
+{
+  double mean_peer_dispersion, mean_root_dispersion, mean_peer_delay, mean_root_delay;
+  double mean_x, mean_y, disp, var, prev_avg_var;
+  NTP_Sample *sample, *last_sample;
+  int i, dof;
+
+  last_sample = &filter->samples[filter->selected[n - 1]];
+
+  /* Prepare data */
+  for (i = 0; i < n; i++) {
+    sample = &filter->samples[filter->selected[i]];
+
+    filter->x_data[i] = UTI_DiffTimespecsToDouble(&sample->time, &last_sample->time);
+    filter->y_data[i] = sample->offset;
+    filter->w_data[i] = sample->peer_dispersion;
+  }
+
+  /* Calculate mean offset and interval since the last sample */
+  for (i = 0, mean_x = mean_y = 0.0; i < n; i++) {
+    mean_x += filter->x_data[i];
+    mean_y += filter->y_data[i];
+  }
+  mean_x /= n;
+  mean_y /= n;
+
+  if (n >= 4) {
+    double b0, b1, s2, sb0, sb1;
+
+    /* Set y axis to the mean sample time */
+    for (i = 0; i < n; i++)
+      filter->x_data[i] -= mean_x;
+
+    /* Make a linear fit and use the estimated standard deviation of the
+       intercept as dispersion */
+    RGR_WeightedRegression(filter->x_data, filter->y_data, filter->w_data, n,
+                           &b0, &b1, &s2, &sb0, &sb1);
+    var = s2;
+    disp = sb0;
+    dof = n - 2;
+  } else if (n >= 2) {
+    for (i = 0, disp = 0.0; i < n; i++)
+      disp += (filter->y_data[i] - mean_y) * (filter->y_data[i] - mean_y);
+    var = disp / (n - 1);
+    disp = sqrt(var);
+    dof = n - 1;
+  } else {
+    var = filter->avg_var;
+    disp = sqrt(var);
+    dof = 1;
+  }
+
+  /* Avoid working with zero dispersion */
+  if (var < 1e-20) {
+    var = 1e-20;
+    disp = sqrt(var);
+  }
+
+  /* Drop the sample if the variance is larger than the maximum */
+  if (filter->max_var > 0.0 && var > filter->max_var) {
+    DEBUG_LOG("filter dispersion too large disp=%.9f max=%.9f",
+              sqrt(var), sqrt(filter->max_var));
+    return 0;
+  }
+
+  prev_avg_var = filter->avg_var;
+
+  /* Update the exponential moving average of the variance */
+  if (filter->avg_var_n > 50) {
+    filter->avg_var += dof / (dof + 50.0) * (var - filter->avg_var);
+  } else {
+    filter->avg_var = (filter->avg_var * filter->avg_var_n + var * dof) /
+      (dof + filter->avg_var_n);
+    if (filter->avg_var_n == 0)
+      prev_avg_var = filter->avg_var;
+    filter->avg_var_n += dof;
+  }
+
+  /* Use the long-term average of variance instead of the estimated value
+     unless it is significantly smaller in order to reduce the noise in
+     sourcestats weights */
+  if (var * dof / RGR_GetChi2Coef(dof) < prev_avg_var)
+    disp = sqrt(filter->avg_var) * disp / sqrt(var);
+
+  mean_peer_dispersion = mean_root_dispersion = mean_peer_delay = mean_root_delay = 0.0;
+
+  for (i = 0; i < n; i++) {
+    sample = &filter->samples[filter->selected[i]];
+
+    mean_peer_dispersion += sample->peer_dispersion;
+    mean_root_dispersion += sample->root_dispersion;
+    mean_peer_delay += sample->peer_delay;
+    mean_root_delay += sample->root_delay;
+  }
+
+  mean_peer_dispersion /= n;
+  mean_root_dispersion /= n;
+  mean_peer_delay /= n;
+  mean_root_delay /= n;
+
+  UTI_AddDoubleToTimespec(&last_sample->time, mean_x, &result->time);
+  result->offset = mean_y;
+  result->peer_dispersion = MAX(disp, mean_peer_dispersion);
+  result->root_dispersion = MAX(disp, mean_root_dispersion);
+  result->peer_delay = mean_peer_delay;
+  result->root_delay = mean_root_delay;
+
+  return 1;
+}
+
+/* ================================================== */
+
+int
+SPF_GetFilteredSample(SPF_Instance filter, NTP_Sample *sample)
+{
+  int n;
+
+  n = select_samples(filter);
+
+  if (n < 1)
+    return 0;
+
+  if (!combine_selected_samples(filter, n, sample))
+    return 0;
+
+  SPF_DropSamples(filter);
+
+  return 1;
+}
+
+/* ================================================== */
+
+void
+SPF_SlewSamples(SPF_Instance filter, struct timespec *when, double dfreq, double doffset)
+{
+  int i, first, last;
+  double delta_time;
+
+  if (filter->last < 0)
+    return;
+
+  /* Always slew the last sample as it may be returned even if no new
+     samples were accumulated */
+  if (filter->used > 0) {
+    first = 0;
+    last = filter->used - 1;
+  } else {
+    first = last = filter->last;
+  }
+
+  for (i = first; i <= last; i++) {
+    UTI_AdjustTimespec(&filter->samples[i].time, when, &filter->samples[i].time,
+                       &delta_time, dfreq, doffset);
+    filter->samples[i].offset -= delta_time;
+  }
+}
+
+/* ================================================== */
+
+void
+SPF_AddDispersion(SPF_Instance filter, double dispersion)
+{
+  int i;
+
+  for (i = 0; i < filter->used; i++) {
+    filter->samples[i].peer_dispersion += dispersion;
+    filter->samples[i].root_dispersion += dispersion;
+  }
+}
--- a/samplefilt.h
+++ b/samplefilt.h
@@ -0,0 +1,49 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2018
+ * 
+ * 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 sample filter.
+
+  */
+
+#ifndef GOT_SAMPLEFILT_H
+#define GOT_SAMPLEFILT_H
+
+#include "ntp.h"
+
+typedef struct SPF_Instance_Record *SPF_Instance;
+
+extern SPF_Instance SPF_CreateInstance(int min_samples, int max_samples,
+                                       double max_dispersion, double combine_ratio);
+extern void SPF_DestroyInstance(SPF_Instance filter);
+
+extern int SPF_AccumulateSample(SPF_Instance filter, NTP_Sample *sample);
+extern int SPF_GetLastSample(SPF_Instance filter, NTP_Sample *sample);
+extern int SPF_GetNumberOfSamples(SPF_Instance filter);
+extern double SPF_GetAvgSampleDispersion(SPF_Instance filter);
+extern void SPF_DropSamples(SPF_Instance filter);
+extern int SPF_GetFilteredSample(SPF_Instance filter, NTP_Sample *sample);
+extern void SPF_SlewSamples(SPF_Instance filter, struct timespec *when,
+                            double dfreq, double doffset);
+extern void SPF_AddDispersion(SPF_Instance filter, double dispersion);
+
+#endif
--- 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 */
@@ -105,7 +111,8 @@ static struct timespec last_class_dispatch[SCH_NumberOfClasses];

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

-static int need_to_exit;
+/* Flag terminating the main loop, which can be set from a signal handler */
+static volatile int need_to_exit;

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

@@ -136,6 +143,8 @@ 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 +156,8 @@ void
 SCH_Finalise(void) {
  ARR_DestroyInstance(file_handlers);

+  LCL_RemoveParameterChangeHandler(handle_slew, NULL);
+
  initialised = 0;
 }

@@ -219,13 +230,16 @@ SCH_RemoveFileHandler(int fd)
 /* ================================================== */

 void
-SCH_SetFileHandlerEvents(int fd, int events)
+SCH_SetFileHandlerEvent(int fd, int event, int enable)
 {
  FileHandlerEntry *ptr;

-  assert(events);
  ptr = ARR_GetElement(file_handlers, fd);
-  ptr->events = events;
+
+  if (enable)
+    ptr->events |= event;
+  else
+    ptr->events &= ~event;
 }

 /* ================================================== */
@@ -244,6 +258,14 @@ 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 *
@@ -477,12 +499,15 @@ SCH_RemoveTimeout(SCH_TimeoutID id)

 static void
 dispatch_timeouts(struct timespec *now) {
+  unsigned long n_done, n_entries_on_start;
  TimerQueueEntry *ptr;
  SCH_TimeoutHandler handler;
  SCH_ArbitraryArgument arg;
-  int n_done = 0, n_entries_on_start = n_timer_queue_entries;

-  while (1) {
+  n_entries_on_start = n_timer_queue_entries;
+  n_done = 0;
+
+  do {
    LCL_ReadRawTime(now);

    if (!(n_timer_queue_entries > 0 &&
@@ -505,16 +530,21 @@ dispatch_timeouts(struct timespec *now) {
    /* Increment count of timeouts handled */
    ++n_done;

-    /* If more timeouts were handled than there were in the timer queue on
-       start and there are now, assume some code is scheduling timeouts with
-       negative delays and abort.  Make the actual limit higher in case the
-       machine is temporarily overloaded and dispatching the handlers takes
-       more time than was delay of a scheduled timeout. */
-    if (n_done > n_timer_queue_entries * 4 &&
-        n_done > n_entries_on_start * 4) {
+    /* If the number of dispatched timeouts is significantly larger than the
+       length of the queue on start and now, assume there is a bug causing
+       an infinite loop by constantly adding a timeout with a zero or negative
+       delay.  Check the actual rate of timeouts to avoid false positives in
+       case the execution slowed down so much (e.g. due to memory thrashing)
+       that it repeatedly takes more time to handle the timeout than is its
+       delay.  This is a safety mechanism intended to stop a full-speed flood
+       of NTP requests due to a bug in the NTP polling. */
+
+    if (n_done > 20 &&
+        n_done > 4 * MAX(n_timer_queue_entries, n_entries_on_start) &&
+        fabs(UTI_DiffTimespecsToDouble(now, &last_select_ts_raw)) / n_done < 0.01)
      LOG_FATAL("Possible infinite loop in scheduling");
-    }
-  }
+
+  } while (!need_to_exit);
 }

 /* ================================================== */
@@ -531,7 +561,8 @@ dispatch_filehandlers(int nfd, fd_set *read_fds, fd_set *write_fds, fd_set *exce
    if (except_fds && FD_ISSET(fd, except_fds)) {
      /* This descriptor has an exception, dispatch its handler */
      ptr = (FileHandlerEntry *)ARR_GetElement(file_handlers, fd);
-      (ptr->handler)(fd, SCH_FILE_EXCEPTION, ptr->arg);
+      if (ptr->handler)
+        (ptr->handler)(fd, SCH_FILE_EXCEPTION, ptr->arg);
      nfd--;

      /* Don't try to read from it now */
@@ -544,14 +575,16 @@ dispatch_filehandlers(int nfd, fd_set *read_fds, fd_set *write_fds, fd_set *exce
    if (read_fds && FD_ISSET(fd, read_fds)) {
      /* This descriptor can be read from, dispatch its handler */
      ptr = (FileHandlerEntry *)ARR_GetElement(file_handlers, fd);
-      (ptr->handler)(fd, SCH_FILE_INPUT, ptr->arg);
+      if (ptr->handler)
+        (ptr->handler)(fd, SCH_FILE_INPUT, ptr->arg);
      nfd--;
    }

    if (write_fds && FD_ISSET(fd, write_fds)) {
      /* This descriptor can be written to, dispatch its handler */
      ptr = (FileHandlerEntry *)ARR_GetElement(file_handlers, fd);
-      (ptr->handler)(fd, SCH_FILE_OUTPUT, ptr->arg);
+      if (ptr->handler)
+        (ptr->handler)(fd, SCH_FILE_OUTPUT, ptr->arg);
      nfd--;
    }
  }
@@ -700,6 +733,31 @@ 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)
 {
@@ -750,6 +808,8 @@ 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
@@ -60,11 +60,14 @@ extern void SCH_Finalise(void);
 /* Register a handler for when select goes true on a file descriptor */
 extern void SCH_AddFileHandler(int fd, int events, SCH_FileHandler handler, SCH_ArbitraryArgument arg);
 extern void SCH_RemoveFileHandler(int fd);
-extern void SCH_SetFileHandlerEvents(int fd, int events);
+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/Show More
+++ b/Show More