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nts: negotiate compliant export of AES-128-GCM-SIV keys

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Add client and server support for a new NTS-KE record to negotiate use
of the compliant key exporter context with the AES-128-GCM-SIV AEAD as
specified here:

https://chrony-project.org/doc/spec/nts-compliant-128gcm.html
This commit is contained in:
Miroslav Lichvar
2024-09-19 12:08:36 +02:00
parent 2adda9c12c
commit 0707865413
5 changed files with 52 additions and 10 deletions
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23
nts_ke_server.c
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@@ -337,7 +337,8 @@ helper_signal(int x)
/* ================================================== */
static int
prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_algorithm)
prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_algorithm,
int compliant_128gcm)
{
SIV_Algorithm exporter_algorithm;
NKE_Context context;
@@ -372,6 +373,11 @@ prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_a
if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, &datum, sizeof (datum)))
return 0;
if (compliant_128gcm) {
if (!NKSN_AddRecord(session, 0, NKE_RECORD_COMPLIANT_128GCM_EXPORT, NULL, 0))
return 0;
}
if (CNF_GetNTPPort() != NTP_PORT) {
datum = htons(CNF_GetNTPPort());
if (!NKSN_AddRecord(session, 1, NKE_RECORD_NTPV4_PORT_NEGOTIATION, &datum, sizeof (datum)))
@@ -389,8 +395,9 @@ prepare_response(NKSN_Instance session, int error, int next_protocol, int aead_a
exporter_algorithm = aead_algorithm;
/* With AES-128-GCM-SIV, set the algorithm ID in the RFC5705 key exporter
context incorrectly for compatibility with older chrony clients */
if (exporter_algorithm == AEAD_AES_128_GCM_SIV)
context incorrectly for compatibility with older chrony clients unless
the client requested the compliant context */
if (exporter_algorithm == AEAD_AES_128_GCM_SIV && !compliant_128gcm)
exporter_algorithm = AEAD_AES_SIV_CMAC_256;
if (!NKSN_GetKeys(session, aead_algorithm, exporter_algorithm,
@@ -419,6 +426,7 @@ 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 compliant_128gcm = 0;
int i, critical, type, length;
uint16_t data[NKE_MAX_RECORD_BODY_LENGTH / sizeof (uint16_t)];
@@ -459,6 +467,13 @@ process_request(NKSN_Instance session)
aead_algorithm = ntohs(data[i]);
}
break;
case NKE_RECORD_COMPLIANT_128GCM_EXPORT:
if (length != 0) {
error = NKE_ERROR_BAD_REQUEST;
break;
}
compliant_128gcm = 1;
break;
case NKE_RECORD_ERROR:
case NKE_RECORD_WARNING:
case NKE_RECORD_COOKIE:
@@ -477,7 +492,7 @@ process_request(NKSN_Instance session)
error = NKE_ERROR_BAD_REQUEST;
}
if (!prepare_response(session, error, next_protocol, aead_algorithm))
if (!prepare_response(session, error, next_protocol, aead_algorithm, compliant_128gcm))
return 0;
return 1;