Add SRTP support for Asterisk

After 5 years in mantis and over a year on reviewboard, SRTP support is finally
being comitted. This includes generic CHANNEL dialplan functions that work for
getting the status of whether a call has secure media or signaling as defined
by the underlying channel technology and for setting whether or not a new
channel being bridged to a calling channel should have secure signaling or
media. See doc/tex/secure-calls.tex for examples.

Original patch by mikma, updated for trunk and revised by me.

(closes issue #5413)
Reported by: mikma
Tested by: twilson, notthematrix, hemanshurpatel

Review: https://reviewboard.asterisk.org/r/191/


git-svn-id: http://svn.digium.com/svn/asterisk/trunk@268894 f38db490-d61c-443f-a65b-d21fe96a405b

1 files changed, 310 insertions, 0 deletions

diff --git a/channels/sip/sdp_crypto.c b/channels/sip/sdp_crypto.c
new file mode 100644
index 000000000..94bf85619
--- /dev/null
+++ b/channels/sip/sdp_crypto.c
@@ -0,0 +1,310 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2006 - 2007, Mikael Magnusson
+ *
+ * Mikael Magnusson <mikma@users.sourceforge.net>
+ *
+ * See http://www.asterisk.org for more information about
+ * the Asterisk project. Please do not directly contact
+ * any of the maintainers of this project for assistance;
+ * the project provides a web site, mailing lists and IRC
+ * channels for your use.
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License Version 2. See the LICENSE file
+ * at the top of the source tree.
+ */
+
+/*! \file sdp_crypto.c
+ *
+ * \brief SDP Security descriptions
+ *
+ * Specified in RFC 4568
+ *
+ * \author Mikael Magnusson <mikma@users.sourceforge.net>
+ */
+
+#include "asterisk.h"
+
+ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
+
+#include "asterisk/options.h"
+#include "asterisk/utils.h"
+#include "include/sdp_crypto.h"
+
+#define SRTP_MASTER_LEN 30
+#define SRTP_MASTERKEY_LEN 16
+#define SRTP_MASTERSALT_LEN ((SRTP_MASTER_LEN) - (SRTP_MASTERKEY_LEN))
+#define SRTP_MASTER_LEN64 (((SRTP_MASTER_LEN) * 8 + 5) / 6 + 1)
+
+extern struct ast_srtp_res *res_srtp;
+extern struct ast_srtp_policy_res *res_srtp_policy;
+
+struct sdp_crypto {
+	char *a_crypto;
+	unsigned char local_key[SRTP_MASTER_LEN];
+	char local_key64[SRTP_MASTER_LEN64];
+};
+
+static int set_crypto_policy(struct ast_srtp_policy *policy, int suite_val, const unsigned char *master_key, unsigned long ssrc, int inbound);
+
+static struct sdp_crypto *sdp_crypto_alloc(void)
+{
+	struct sdp_crypto *crypto;
+
+	return crypto = ast_calloc(1, sizeof(*crypto));
+}
+
+void sdp_crypto_destroy(struct sdp_crypto *crypto)
+{
+	ast_free(crypto->a_crypto);
+	crypto->a_crypto = NULL;
+	ast_free(crypto);
+}
+
+struct sdp_crypto *sdp_crypto_setup(void)
+{
+	struct sdp_crypto *p;
+	int key_len;
+	unsigned char remote_key[SRTP_MASTER_LEN];
+
+	if (!ast_rtp_engine_srtp_is_registered()) {
+		return NULL;
+	}
+
+	if (!(p = sdp_crypto_alloc())) {
+		return NULL;
+	}
+
+	if (res_srtp->get_random(p->local_key, sizeof(p->local_key)) < 0) {
+		sdp_crypto_destroy(p);
+		return NULL;
+	}
+
+	ast_base64encode(p->local_key64, p->local_key, SRTP_MASTER_LEN, sizeof(p->local_key64));
+
+	key_len = ast_base64decode(remote_key, p->local_key64, sizeof(remote_key));
+
+	if (key_len != SRTP_MASTER_LEN) {
+		ast_log(LOG_ERROR, "base64 encode/decode bad len %d != %d\n", key_len, SRTP_MASTER_LEN);
+		ast_free(p);
+		return NULL;
+	}
+
+	if (memcmp(remote_key, p->local_key, SRTP_MASTER_LEN)) {
+		ast_log(LOG_ERROR, "base64 encode/decode bad key\n");
+		ast_free(p);
+		return NULL;
+	}
+
+	ast_debug(1 , "local_key64 %s len %zu\n", p->local_key64, strlen(p->local_key64));
+
+	return p;
+}
+
+static int set_crypto_policy(struct ast_srtp_policy *policy, int suite_val, const unsigned char *master_key, unsigned long ssrc, int inbound)
+{
+	const unsigned char *master_salt = NULL;
+
+	if (!ast_rtp_engine_srtp_is_registered()) {
+		return -1;
+	}
+
+	master_salt = master_key + SRTP_MASTERKEY_LEN;
+	if (res_srtp_policy->set_master_key(policy, master_key, SRTP_MASTERKEY_LEN, master_salt, SRTP_MASTERSALT_LEN) < 0) {
+		return -1;
+	}
+
+	if (res_srtp_policy->set_suite(policy, suite_val)) {
+		ast_log(LOG_WARNING, "Could not set remote SRTP suite\n");
+		return -1;
+	}
+
+	res_srtp_policy->set_ssrc(policy, ssrc, inbound);
+
+	return 0;
+}
+
+static int sdp_crypto_activate(struct sdp_crypto *p, int suite_val, unsigned char *remote_key, struct ast_rtp_instance *rtp)
+{
+	struct ast_srtp_policy *local_policy = NULL;
+	struct ast_srtp_policy *remote_policy = NULL;
+	struct ast_rtp_instance_stats stats = {0,};
+	int res = -1;
+
+	if (!ast_rtp_engine_srtp_is_registered()) {
+		return -1;
+	}
+
+	if (!p) {
+		return -1;
+	}
+
+	if (!(local_policy = res_srtp_policy->alloc())) {
+		return -1;
+	}
+
+	if (!(remote_policy = res_srtp_policy->alloc())) {
+		goto err;
+	}
+
+	if (ast_rtp_instance_get_stats(rtp, &stats, AST_RTP_INSTANCE_STAT_LOCAL_SSRC)) {
+		goto err;
+	}
+
+	if (set_crypto_policy(local_policy, suite_val, p->local_key, stats.local_ssrc, 0) < 0) {
+		goto err;
+	}
+
+	if (set_crypto_policy(remote_policy, suite_val, remote_key, 0, 1) < 0) {
+		goto err;
+	}
+
+	/* FIXME MIKMA */
+	/* ^^^ I wish I knew what needed fixing... */
+	if (ast_rtp_instance_add_srtp_policy(rtp, local_policy)) {
+		ast_log(LOG_WARNING, "Could not set local SRTP policy\n");
+		goto err;
+	}
+
+	if (ast_rtp_instance_add_srtp_policy(rtp, remote_policy)) {
+		ast_log(LOG_WARNING, "Could not set remote SRTP policy\n");
+		goto err;
+	}
+
+	ast_debug(1 , "SRTP policy activated\n");
+	res = 0;
+
+err:
+	if (local_policy) {
+		res_srtp_policy->destroy(local_policy);
+	}
+
+	if (remote_policy) {
+		res_srtp_policy->destroy(remote_policy);
+	}
+
+	return res;
+}
+
+int sdp_crypto_process(struct sdp_crypto *p, const char *attr, struct ast_rtp_instance *rtp)
+{
+	char *str = NULL;
+	char *name = NULL;
+	char *tag = NULL;
+	char *suite = NULL;
+	char *key_params = NULL;
+	char *key_param = NULL;
+	char *session_params = NULL;
+	char *key_salt = NULL;
+	char *lifetime = NULL;
+	int found = 0;
+	int attr_len = strlen(attr);
+	int key_len = 0;
+	int suite_val = 0;
+	unsigned char remote_key[SRTP_MASTER_LEN];
+
+	if (!ast_rtp_engine_srtp_is_registered()) {
+		return -1;
+	}
+
+	str = ast_strdupa(attr);
+
+	name = strsep(&str, ":");
+	tag = strsep(&str, " ");
+	suite = strsep(&str, " ");
+	key_params = strsep(&str, " ");
+	session_params = strsep(&str, " ");
+
+	if (!tag || !suite) {
+		ast_log(LOG_WARNING, "Unrecognized a=%s", attr);
+		return -1;
+	}
+
+	if (session_params) {
+		ast_log(LOG_WARNING, "Unsupported crypto parameters: %s", session_params);
+		return -1;
+	}
+
+	if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_80")) {
+		suite_val = AST_AES_CM_128_HMAC_SHA1_80;
+	} else if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_32")) {
+		suite_val = AST_AES_CM_128_HMAC_SHA1_32;
+	} else {
+		ast_log(LOG_WARNING, "Unsupported crypto suite: %s\n", suite);
+		return -1;
+	}
+
+	while ((key_param = strsep(&key_params, ";"))) {
+		char *method = NULL;
+		char *info = NULL;
+
+		method = strsep(&key_param, ":");
+		info = strsep(&key_param, ";");
+
+		if (!strcmp(method, "inline")) {
+			key_salt = strsep(&info, "|");
+			lifetime = strsep(&info, "|");
+
+			if (lifetime) {
+				ast_log(LOG_NOTICE, "Crypto life time unsupported: %s\n", attr);
+				continue;
+			}
+
+			found = 1;
+			break;
+		}
+	}
+
+	if (!found) {
+		ast_log(LOG_NOTICE, "SRTP crypto offer not acceptable\n");
+		return -1;
+	}
+
+
+	if ((key_len = ast_base64decode(remote_key, key_salt, sizeof(remote_key))) != SRTP_MASTER_LEN) {
+		ast_log(LOG_WARNING, "SRTP sdescriptions key %d != %d\n", key_len, SRTP_MASTER_LEN);
+		return -1;
+	}
+
+	if (sdp_crypto_activate(p, suite_val, remote_key, rtp) < 0) {
+		return -1;
+	}
+
+	if (!p->a_crypto) {
+		if (!(p->a_crypto = ast_calloc(1, attr_len + 11))) {
+			ast_log(LOG_ERROR, "Could not allocate memory for a_crypto\n");
+			return -1;
+		}
+
+		snprintf(p->a_crypto, attr_len + 10, "a=crypto:%s %s inline:%s\r\n", tag, suite, p->local_key64);
+	}
+
+	return 0;
+}
+
+int sdp_crypto_offer(struct sdp_crypto *p)
+{
+	char crypto_buf[128];
+	const char *crypto_suite = "AES_CM_128_HMAC_SHA1_80"; /* Crypto offer */
+
+	if (p->a_crypto) {
+		ast_free(p->a_crypto);
+	}
+
+	if (snprintf(crypto_buf, sizeof(crypto_buf), "a=crypto:1 %s inline:%s\r\n",  crypto_suite, p->local_key64) < 1) {
+		return -1;
+	}
+
+	if (!(p->a_crypto = ast_strdup(crypto_buf))) {
+		return -1;
+	}
+
+	return 0;
+}
+
+const char *sdp_crypto_attrib(struct sdp_crypto *p)
+{
+	return p->a_crypto;
+}