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-rw-r--r--nts_ntp_server.c283
1 files changed, 283 insertions, 0 deletions
diff --git a/nts_ntp_server.c b/nts_ntp_server.c
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--- /dev/null
+++ 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 parsing */
+ 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;
+}
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