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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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26
nts_ke_client.c
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@@ -50,6 +50,7 @@ struct NKC_Instance_Record {
int got_response;
int resolving_name;
int compliant_128gcm;
NKE_Context context;
NKE_Cookie cookies[NKE_MAX_COOKIES];
int num_cookies;
@@ -103,7 +104,7 @@ prepare_request(NKC_Instance inst)
{
NKSN_Instance session = inst->session;
uint16_t data[2];
int length;
int i, length;
NKSN_BeginMessage(session);
@@ -120,6 +121,14 @@ prepare_request(NKC_Instance inst)
length * sizeof (data[0])))
return 0;
for (i = 0; i < length; i++) {
if (data[i] == htons(AEAD_AES_128_GCM_SIV)) {
if (!NKSN_AddRecord(session, 0, NKE_RECORD_COMPLIANT_128GCM_EXPORT, NULL, 0))
return 0;
break;
}
}
if (!NKSN_EndMessage(session))
return 0;
@@ -139,6 +148,7 @@ process_response(NKC_Instance inst)
assert(sizeof (data) % sizeof (uint16_t) == 0);
assert(sizeof (uint16_t) == 2);
inst->compliant_128gcm = 0;
inst->num_cookies = 0;
inst->ntp_address.ip_addr.family = IPADDR_UNSPEC;
inst->ntp_address.port = 0;
@@ -175,6 +185,15 @@ process_response(NKC_Instance inst)
aead_algorithm = ntohs(data[0]);
inst->context.algorithm = aead_algorithm;
break;
case NKE_RECORD_COMPLIANT_128GCM_EXPORT:
if (length != 0) {
DEBUG_LOG("Non-empty compliant-128gcm record");
error = 1;
break;
}
DEBUG_LOG("Compliant AES-128-GCM-SIV export");
inst->compliant_128gcm = 1;
break;
case NKE_RECORD_ERROR:
if (length == 2)
DEBUG_LOG("NTS-KE error %d", ntohs(data[0]));
@@ -266,8 +285,9 @@ handle_message(void *arg)
exporter_algorithm = inst->context.algorithm;
/* With AES-128-GCM-SIV, set the algorithm ID in the RFC5705 key exporter
context incorrectly for compatibility with older chrony servers */
if (exporter_algorithm == AEAD_AES_128_GCM_SIV)
context incorrectly for compatibility with older chrony servers unless
the server confirmed support for the compliant context */
if (exporter_algorithm == AEAD_AES_128_GCM_SIV && !inst->compliant_128gcm)
exporter_algorithm = AEAD_AES_SIV_CMAC_256;
if (!NKSN_GetKeys(inst->session, inst->context.algorithm, exporter_algorithm,