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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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1
nts_ke.h
View file

@ -40,6 +40,7 @@
#define NKE_RECORD_COOKIE 5
#define NKE_RECORD_NTPV4_SERVER_NEGOTIATION 6
#define NKE_RECORD_NTPV4_PORT_NEGOTIATION 7
#define NKE_RECORD_COMPLIANT_128GCM_EXPORT 1024
#define NKE_NEXT_PROTOCOL_NTPV4 0

26
nts_ke_client.c
View file

@ -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,

23
nts_ke_server.c
View file

@ -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;

5
test/unit/nts_ke_client.c
View file

@ -88,9 +88,12 @@ prepare_response(NKSN_Instance session, int valid)
if (random() % 2) {
length = random() % (sizeof (data) + 1);
TEST_CHECK(NKSN_AddRecord(session, 0, 1000 + random() % 1000, data, length));
TEST_CHECK(NKSN_AddRecord(session, 0, 2000 + random() % 1000, data, length));
}
if (random() % 2)
TEST_CHECK(NKSN_AddRecord(session, 0, NKE_RECORD_COMPLIANT_128GCM_EXPORT, NULL, 0));
if (index != 8) {
for (i = 0; i < NKE_MAX_COOKIES; i++) {
length = (random() % sizeof (data) + 1) / 4 * 4;

7
test/unit/nts_ke_server.c
View file

@ -92,7 +92,7 @@ prepare_request(NKSN_Instance session, int valid)
if (index == 8) {
length = random() % (sizeof (data) + 1);
TEST_CHECK(NKSN_AddRecord(session, 1, 1000 + random() % 1000, data, length));
TEST_CHECK(NKSN_AddRecord(session, 1, 2000 + random() % 1000, data, length));
}
if (random() % 2) {
@ -106,9 +106,12 @@ prepare_request(NKSN_Instance session, int valid)
TEST_CHECK(NKSN_AddRecord(session, 0, NKE_RECORD_NTPV4_PORT_NEGOTIATION, data, length));
}
if (random() % 2)
TEST_CHECK(NKSN_AddRecord(session, 0, NKE_RECORD_COMPLIANT_128GCM_EXPORT, NULL, 0));
if (random() % 2) {
length = random() % (sizeof (data) + 1);
TEST_CHECK(NKSN_AddRecord(session, 0, 1000 + random() % 1000, data, length));
TEST_CHECK(NKSN_AddRecord(session, 0, 2000 + random() % 1000, data, length));
}
TEST_CHECK(NKSN_EndMessage(session));