Merge "res_srtp: Move SDP SRTP code from the core to res_srtp."

1 files changed, 31 insertions, 575 deletions

diff --git a/main/sdp_srtp.c b/main/sdp_srtp.c
index a55aedf82..940a6197d 100644
--- a/main/sdp_srtp.c
+++ b/main/sdp_srtp.c
@@ -33,18 +33,12 @@
 
 ASTERISK_REGISTER_FILE()
 
-#include <math.h>                       /* for pow */
-#include <srtp/srtp.h>                  /* for SRTP_MAX_KEY_LEN, etc */
-
 #include "asterisk/linkedlists.h"       /* for AST_LIST_NEXT, etc */
 #include "asterisk/logger.h"            /* for ast_log, LOG_ERROR, etc */
-#include "asterisk/rtp_engine.h"        /* for ast_rtp_engine_dtls, etc */
 #include "asterisk/sdp_srtp.h"          /* for ast_sdp_srtp, etc */
-#include "asterisk/strings.h"           /* for ast_strlen_zero */
-#include "asterisk/utils.h"             /* for ast_set_flag, ast_test_flag, etc */
 
-extern struct ast_srtp_res *res_srtp;
-extern struct ast_srtp_policy_res *res_srtp_policy;
+/*! Registered SDP crypto API */
+static struct ast_sdp_crypto_api *sdp_crypto_api;
 
 struct ast_sdp_srtp *ast_sdp_srtp_alloc(void)
 {
@@ -63,603 +57,49 @@ void ast_sdp_srtp_destroy(struct ast_sdp_srtp *srtp)
 	for (next = AST_LIST_NEXT(srtp, sdp_srtp_list);
 	     srtp;
 	     srtp = next, next = srtp ? AST_LIST_NEXT(srtp, sdp_srtp_list) : NULL) {
-		if (srtp->crypto) {
-			ast_sdp_crypto_destroy(srtp->crypto);
-		}
+		ast_sdp_crypto_destroy(srtp->crypto);
 		srtp->crypto = NULL;
 		ast_free(srtp);
 	}
 }
 
-struct ast_sdp_crypto {
-	char *a_crypto;
-	unsigned char local_key[SRTP_MAX_KEY_LEN];
-	int tag;
-	char local_key64[((SRTP_MAX_KEY_LEN) * 8 + 5) / 6 + 1];
-	unsigned char remote_key[SRTP_MAX_KEY_LEN];
-	int key_len;
-};
-
-static struct ast_sdp_crypto *sdp_crypto_alloc(const int key_len);
-static struct ast_sdp_crypto *crypto_init_keys(struct ast_sdp_crypto *p, const int key_len);
-static int set_crypto_policy(struct ast_srtp_policy *policy, int suite_val, const unsigned char *master_key, int key_len, unsigned long ssrc, int inbound);
-
 void ast_sdp_crypto_destroy(struct ast_sdp_crypto *crypto)
 {
-	ast_free(crypto->a_crypto);
-	crypto->a_crypto = NULL;
-	ast_free(crypto);
-}
-
-static struct ast_sdp_crypto *crypto_init_keys(struct ast_sdp_crypto *p, const int key_len)
-{
-	unsigned char remote_key[key_len];
-
-	if (res_srtp->get_random(p->local_key, key_len) < 0) {
-		return NULL;
-	}
-
-	ast_base64encode(p->local_key64, p->local_key, key_len, sizeof(p->local_key64));
-
-	p->key_len = ast_base64decode(remote_key, p->local_key64, sizeof(remote_key));
-
-	if (p->key_len != key_len) {
-		ast_log(LOG_ERROR, "base64 encode/decode bad len %d != %d\n", p->key_len, key_len);
-		return NULL;
-	}
-
-	if (memcmp(remote_key, p->local_key, p->key_len)) {
-		ast_log(LOG_ERROR, "base64 encode/decode bad key\n");
-		return NULL;
-	}
-
-	ast_debug(1 , "local_key64 %s len %zu\n", p->local_key64, strlen(p->local_key64));
-
-	return p;
-}
-
-static struct ast_sdp_crypto *sdp_crypto_alloc(const int key_len)
-{
-	struct ast_sdp_crypto *p, *result;
-
-	if (!ast_rtp_engine_srtp_is_registered()) {
-		return NULL;
-	}
-
-	if (!(p = ast_calloc(1, sizeof(*p)))) {
-		return NULL;
+	if (sdp_crypto_api) {
+		sdp_crypto_api->dtor(crypto);
 	}
-	p->tag = 1;
-
-	/* default is a key which uses AST_AES_CM_128_HMAC_SHA1_xx */
-	result = crypto_init_keys(p, key_len);
-	if (!result) {
-		ast_sdp_crypto_destroy(p);
-	}
-
-	return result;
 }
 
 struct ast_sdp_crypto *ast_sdp_crypto_alloc(void)
 {
-	return sdp_crypto_alloc(SRTP_MASTER_KEY_LEN);
-}
-
-static int set_crypto_policy(struct ast_srtp_policy *policy, int suite_val, const unsigned char *master_key, int key_len, unsigned long ssrc, int inbound)
-{
-	if (!ast_rtp_engine_srtp_is_registered()) {
-		return -1;
-	}
-
-	if (res_srtp_policy->set_master_key(policy, master_key, key_len, NULL, 0) < 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 crypto_activate(struct ast_sdp_crypto *p, int suite_val, unsigned char *remote_key, int key_len, 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, key_len, stats.local_ssrc, 0) < 0) {
-		goto err;
-	}
-
-	if (set_crypto_policy(remote_policy, suite_val, remote_key, key_len, 0, 1) < 0) {
-		goto err;
-	}
-
-	/* Add the SRTP policies */
-	if (ast_rtp_instance_add_srtp_policy(rtp, remote_policy, local_policy, 0)) {
-		ast_log(LOG_WARNING, "Could not set SRTP policies\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);
+	if (!sdp_crypto_api) {
+		return NULL;
 	}
-
-	return res;
+	return sdp_crypto_api->alloc();
 }
 
 int ast_sdp_crypto_process(struct ast_rtp_instance *rtp, struct ast_sdp_srtp *srtp, const char *attr)
 {
-	char *str = NULL;
-	char *tag = NULL;
-	char *suite = NULL;
-	char *key_params = NULL;
-	char *key_param = NULL;
-	char *session_params = NULL;
-	char *key_salt = NULL;       /* The actual master key and key salt */
-	char *lifetime = NULL;       /* Key lifetime (# of RTP packets) */
-	char *mki = NULL;            /* Master Key Index */
-	int found = 0;
-	int key_len_from_sdp;
-	int key_len_expected;
-	int tag_from_sdp;
-	int suite_val = 0;
-	unsigned char remote_key[SRTP_MAX_KEY_LEN];
-	int taglen;
-	double sdes_lifetime;
-	struct ast_sdp_crypto *crypto;
-	struct ast_sdp_srtp *tmp;
-
-	if (!ast_rtp_engine_srtp_is_registered()) {
+	if (!sdp_crypto_api) {
 		return -1;
 	}
-
-	str = ast_strdupa(attr);
-
-	tag = strsep(&str, " ");
-	suite = strsep(&str, " ");
-	key_params = strsep(&str, " ");
-	session_params = strsep(&str, " ");
-
-	if (!tag || !suite) {
-		ast_log(LOG_WARNING, "Unrecognized crypto attribute a=%s\n", attr);
-		return -1;
-	}
-
-	/* RFC4568 9.1 - tag is 1-9 digits, greater than zero */
-	if (sscanf(tag, "%30d", &tag_from_sdp) != 1 || tag_from_sdp <= 0 || tag_from_sdp > 999999999) {
-		ast_log(LOG_WARNING, "Unacceptable a=crypto tag: %s\n", tag);
-		return -1;
-	}
-
-	if (!ast_strlen_zero(session_params)) {
-		ast_log(LOG_WARNING, "Unsupported crypto parameters: %s\n", session_params);
-		return -1;
-	}
-
-	/* On egress, Asterisk sent several crypto lines in the SIP/SDP offer
-	   The remote party might have choosen another line than the first */
-	for (tmp = srtp; tmp && tmp->crypto && tmp->crypto->tag != tag_from_sdp;) {
-		tmp = AST_LIST_NEXT(tmp, sdp_srtp_list);
-	}
-	if (tmp) { /* tag matched an already created crypto line */
-		unsigned int flags = tmp->flags;
-
-		/* Make that crypto line the head of the list, not by changing the
-		   list structure but by exchanging the content of the list members */
-		crypto = tmp->crypto;
-		tmp->crypto = srtp->crypto;
-		tmp->flags = srtp->flags;
-		srtp->crypto = crypto;
-		srtp->flags = flags;
-	} else {
-		crypto = srtp->crypto;
-		crypto->tag = tag_from_sdp;
-	}
-
-	if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_80")) {
-		suite_val = AST_AES_CM_128_HMAC_SHA1_80;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_80);
-		key_len_expected = 30;
-	} else if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_32")) {
-		suite_val = AST_AES_CM_128_HMAC_SHA1_32;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_32);
-		key_len_expected = 30;
-#ifdef HAVE_SRTP_192
-	} else if (!strcmp(suite, "AES_192_CM_HMAC_SHA1_80")) {
-		suite_val = AST_AES_CM_192_HMAC_SHA1_80;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_80);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_AES_192);
-		key_len_expected = 38;
-	} else if (!strcmp(suite, "AES_192_CM_HMAC_SHA1_32")) {
-		suite_val = AST_AES_CM_192_HMAC_SHA1_32;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_32);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_AES_192);
-		key_len_expected = 38;
-	/* RFC used a different name while in draft, some still use that */
-	} else if (!strcmp(suite, "AES_CM_192_HMAC_SHA1_80")) {
-		suite_val = AST_AES_CM_192_HMAC_SHA1_80;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_80);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_AES_192);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_OLD_NAME);
-		key_len_expected = 38;
-	} else if (!strcmp(suite, "AES_CM_192_HMAC_SHA1_32")) {
-		suite_val = AST_AES_CM_192_HMAC_SHA1_32;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_32);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_AES_192);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_OLD_NAME);
-		key_len_expected = 38;
-#endif
-#ifdef HAVE_SRTP_256
-	} else if (!strcmp(suite, "AES_256_CM_HMAC_SHA1_80")) {
-		suite_val = AST_AES_CM_256_HMAC_SHA1_80;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_80);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_AES_256);
-		key_len_expected = 46;
-	} else if (!strcmp(suite, "AES_256_CM_HMAC_SHA1_32")) {
-		suite_val = AST_AES_CM_256_HMAC_SHA1_32;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_32);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_AES_256);
-		key_len_expected = 46;
-	/* RFC used a different name while in draft, some still use that */
-	} else if (!strcmp(suite, "AES_CM_256_HMAC_SHA1_80")) {
-		suite_val = AST_AES_CM_256_HMAC_SHA1_80;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_80);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_AES_256);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_OLD_NAME);
-		key_len_expected = 46;
-	} else if (!strcmp(suite, "AES_CM_256_HMAC_SHA1_32")) {
-		suite_val = AST_AES_CM_256_HMAC_SHA1_32;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_32);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_AES_256);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_OLD_NAME);
-		key_len_expected = 46;
-#endif
-#ifdef HAVE_SRTP_GCM
-	} else if (!strcmp(suite, "AEAD_AES_128_GCM")) {
-		suite_val = AST_AES_GCM_128;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_16);
-		key_len_expected = AES_128_GCM_KEYSIZE_WSALT;
-	} else if (!strcmp(suite, "AEAD_AES_256_GCM")) {
-		suite_val = AST_AES_GCM_256;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_16);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_AES_256);
-		key_len_expected = AES_256_GCM_KEYSIZE_WSALT;
-	/* RFC contained a (too) short auth tag for RTP media, some still use that */
-	} else if (!strcmp(suite, "AEAD_AES_128_GCM_8")) {
-		suite_val = AST_AES_GCM_128_8;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_8);
-		key_len_expected = AES_128_GCM_KEYSIZE_WSALT;
-	} else if (!strcmp(suite, "AEAD_AES_256_GCM_8")) {
-		suite_val = AST_AES_GCM_256_8;
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_TAG_8);
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_AES_256);
-		key_len_expected = AES_256_GCM_KEYSIZE_WSALT;
-#endif
-	} else {
-		ast_verb(1, "Unsupported crypto suite: %s\n", suite);
-		return -1;
-	}
-
-	while ((key_param = strsep(&key_params, ";"))) {
-		unsigned int n_lifetime;
-		char *method = NULL;
-		char *info = NULL;
-
-		method = strsep(&key_param, ":");
-		info = strsep(&key_param, ";");
-		sdes_lifetime = 0;
-
-		if (strcmp(method, "inline")) {
-			continue;
-		}
-
-		key_salt = strsep(&info, "|");
-
-		/* The next parameter can be either lifetime or MKI */
-		lifetime = strsep(&info, "|");
-		if (!lifetime) {
-			found = 1;
-			break;
-		}
-
-		mki = strchr(lifetime, ':');
-		if (mki) {
-			mki = lifetime;
-			lifetime = NULL;
-		} else {
-			mki = strsep(&info, "|");
-		}
-
-		if (mki && *mki != '1') {
-			ast_log(LOG_NOTICE, "Crypto MKI handling is not supported: ignoring attribute %s\n", attr);
-			continue;
-		}
-
-		if (lifetime) {
-			if (!strncmp(lifetime, "2^", 2)) {
-				char *lifetime_val = lifetime + 2;
-
-				/* Exponential lifetime */
-				if (sscanf(lifetime_val, "%30u", &n_lifetime) != 1) {
-					ast_log(LOG_NOTICE, "Failed to parse lifetime value in crypto attribute: %s\n", attr);
-					continue;
-				}
-
-				if (n_lifetime > 48) {
-					/* Yeah... that's a bit big. */
-					ast_log(LOG_NOTICE, "Crypto lifetime exponent of '%u' is a bit large; using 48\n", n_lifetime);
-					n_lifetime = 48;
-				}
-				sdes_lifetime = pow(2, n_lifetime);
-			} else {
-				/* Decimal lifetime */
-				if (sscanf(lifetime, "%30u", &n_lifetime) != 1) {
-					ast_log(LOG_NOTICE, "Failed to parse lifetime value in crypto attribute: %s\n", attr);
-					continue;
-				}
-				sdes_lifetime = n_lifetime;
-			}
-
-			/* Accept anything above 10 hours. Less than 10; reject. */
-			if (sdes_lifetime < 1800000) {
-				ast_log(LOG_NOTICE, "Rejecting crypto attribute '%s': lifetime '%f' too short\n", attr, sdes_lifetime);
-				continue;
-			}
-		}
-
-		ast_debug(2, "Crypto attribute '%s' accepted with lifetime '%f', MKI '%s'\n",
-			attr, sdes_lifetime, mki ? mki : "-");
-
-		found = 1;
-		break;
-	}
-
-	if (!found) {
-		ast_log(LOG_NOTICE, "SRTP crypto offer not acceptable: '%s'\n", attr);
-		return -1;
-	}
-
-	key_len_from_sdp = ast_base64decode(remote_key, key_salt, sizeof(remote_key));
-	if (key_len_from_sdp != key_len_expected) {
-		ast_log(LOG_WARNING, "SRTP descriptions key length is '%d', not '%d'\n",
-			key_len_from_sdp, key_len_expected);
-		return -1;
-	}
-
-	/* on default, the key is 30 (AES-128); throw that away (only) when the suite changed actually */
-	/* ingress: optional, but saves one expensive call to get_random(.) */
-	/*  egress: required, because the local key was communicated before the remote key is processed */
-	if (crypto->key_len != key_len_from_sdp) {
-		if (!crypto_init_keys(crypto, key_len_from_sdp)) {
-			return -1;
-		}
-	} else if (!memcmp(crypto->remote_key, remote_key, key_len_from_sdp)) {
-		ast_debug(1, "SRTP remote key unchanged; maintaining current policy\n");
-		ast_set_flag(srtp, AST_SRTP_CRYPTO_OFFER_OK);
-		return 0;
-	}
-
-	if (key_len_from_sdp > sizeof(crypto->remote_key)) {
-		ast_log(LOG_ERROR,
-			"SRTP key buffer is %zu although it must be at least %d bytes\n",
-			sizeof(crypto->remote_key), key_len_from_sdp);
-		return -1;
-	}
-	memcpy(crypto->remote_key, remote_key, key_len_from_sdp);
-
-	if (crypto_activate(crypto, suite_val, remote_key, key_len_from_sdp, rtp) < 0) {
-		return -1;
-	}
-
-	if (ast_test_flag(srtp, AST_SRTP_CRYPTO_TAG_32)) {
-		taglen = 32;
-	} else if (ast_test_flag(srtp, AST_SRTP_CRYPTO_TAG_16)) {
-		taglen = 16;
-	} else if (ast_test_flag(srtp, AST_SRTP_CRYPTO_TAG_8)) {
-		taglen = 8;
-	} else {
-		taglen = 80;
-	}
-	if (ast_test_flag(srtp, AST_SRTP_CRYPTO_AES_256)) {
-		taglen |= 0x0200;
-	} else if (ast_test_flag(srtp, AST_SRTP_CRYPTO_AES_192)) {
-		taglen |= 0x0100;
-	}
-	if (ast_test_flag(srtp, AST_SRTP_CRYPTO_OLD_NAME)) {
-		taglen |= 0x0080;
-	}
-
-	/* Finally, rebuild the crypto line */
-	if (ast_sdp_crypto_build_offer(crypto, taglen)) {
-		return -1;
-	}
-
-	ast_set_flag(srtp, AST_SRTP_CRYPTO_OFFER_OK);
-	return 0;
+	return sdp_crypto_api->parse_offer(rtp, srtp, attr);
 }
 
 int ast_sdp_crypto_build_offer(struct ast_sdp_crypto *p, int taglen)
 {
-	/* Rebuild the crypto line */
-	if (p->a_crypto) {
-		ast_free(p->a_crypto);
-	}
-
-	if ((taglen & 0x007f) == 8) {
-		if (ast_asprintf(&p->a_crypto, "%d AEAD_AES_%d_GCM_%d inline:%s",
-				 p->tag, 128 + ((taglen & 0x0300) >> 2), taglen & 0x007f, p->local_key64) == -1) {
-				 ast_log(LOG_ERROR, "Could not allocate memory for crypto line\n");
-			return -1;
-		}
-	} else if ((taglen & 0x007f) == 16) {
-		if (ast_asprintf(&p->a_crypto, "%d AEAD_AES_%d_GCM inline:%s",
-				 p->tag, 128 + ((taglen & 0x0300) >> 2), p->local_key64) == -1) {
-				 ast_log(LOG_ERROR, "Could not allocate memory for crypto line\n");
-			return -1;
-		}
-	} else if ((taglen & 0x0300) && !(taglen & 0x0080)) {
-		if (ast_asprintf(&p->a_crypto, "%d AES_%d_CM_HMAC_SHA1_%d inline:%s",
-				 p->tag, 128 + ((taglen & 0x0300) >> 2), taglen & 0x007f, p->local_key64) == -1) {
-				 ast_log(LOG_ERROR, "Could not allocate memory for crypto line\n");
-			return -1;
-		}
-	} else {
-		if (ast_asprintf(&p->a_crypto, "%d AES_CM_%d_HMAC_SHA1_%d inline:%s",
-				 p->tag, 128 + ((taglen & 0x0300) >> 2), taglen & 0x007f, p->local_key64) == -1) {
-				 ast_log(LOG_ERROR, "Could not allocate memory for crypto line\n");
-			return -1;
-		}
+	if (!sdp_crypto_api) {
+		return -1;
 	}
-
-	ast_debug(1, "Crypto line: a=crypto:%s\n", p->a_crypto);
-
-	return 0;
+	return sdp_crypto_api->build_offer(p, taglen);
 }
 
 const char *ast_sdp_srtp_get_attrib(struct ast_sdp_srtp *srtp, int dtls_enabled, int default_taglen_32)
 {
-	int taglen;
-
-	if (!srtp) {
+	if (!sdp_crypto_api) {
 		return NULL;
 	}
-
-	/* Set encryption properties */
-	if (!srtp->crypto) {
-
-		if (AST_LIST_NEXT(srtp, sdp_srtp_list)) {
-			srtp->crypto = ast_sdp_crypto_alloc();
-			ast_log(LOG_ERROR, "SRTP SDP list was not empty\n");
-		} else {
-			const int len = default_taglen_32 ? AST_SRTP_CRYPTO_TAG_32 : AST_SRTP_CRYPTO_TAG_80;
-			const int attr[][3] = {
-			/* This array creates the following list:
-			 * a=crypto:1 AES_CM_128_HMAC_SHA1_ ...
-			 * a=crypto:2 AEAD_AES_128_GCM ...
-			 * a=crypto:3 AES_256_CM_HMAC_SHA1_ ...
-			 * a=crypto:4 AEAD_AES_256_GCM ...
-			 * a=crypto:5 AES_192_CM_HMAC_SHA1_ ...
-			 * something like 'AEAD_AES_192_GCM' is not specified by the RFCs
-			 *
-			 * If you want to prefer another crypto suite or you want to
-			 * exclude a suite, change this array and recompile Asterisk.
-			 * This list cannot be changed from rtp.conf because you should
-			 * know what you are doing. Especially AES-192 and AES-GCM are
-			 * broken in many VoIP clients, see
-			 * https://github.com/cisco/libsrtp/pull/170
-			 * https://github.com/cisco/libsrtp/pull/184
-			 * Furthermore, AES-GCM uses a shorter crypto-suite string which
-			 * causes Nokia phones based on Symbian/S60 to reject the whole
-			 * INVITE with status 500, even if a matching suite was offered.
-			 * AES-256 might just waste your processor cycles, especially if
-			 * your TLS transport is not secured with equivalent grade, see
-			 * https://security.stackexchange.com/q/61361
-			 * Therefore, AES-128 was preferred here.
-			 *
-			 * If you want to enable one of those defines, please, go for
-			 * CFLAGS='-DENABLE_SRTP_AES_GCM' ./configure && sudo make install
-			 */
-				{ len, 0, 30 },
-#if defined(HAVE_SRTP_GCM) && defined(ENABLE_SRTP_AES_GCM)
-				{ AST_SRTP_CRYPTO_TAG_16, 0, AES_128_GCM_KEYSIZE_WSALT },
-#endif
-#if defined(HAVE_SRTP_256) && defined(ENABLE_SRTP_AES_256)
-				{ len, AST_SRTP_CRYPTO_AES_256, 46 },
-#endif
-#if defined(HAVE_SRTP_GCM) && defined(ENABLE_SRTP_AES_GCM) && defined(ENABLE_SRTP_AES_256)
-				{ AST_SRTP_CRYPTO_TAG_16, AST_SRTP_CRYPTO_AES_256, AES_256_GCM_KEYSIZE_WSALT },
-#endif
-#if defined(HAVE_SRTP_192) && defined(ENABLE_SRTP_AES_192)
-				{ len, AST_SRTP_CRYPTO_AES_192, 38 },
-#endif
-			};
-			struct ast_sdp_srtp *tmp = srtp;
-			int i;
-
-			for (i = 0; i < ARRAY_LEN(attr); i++) {
-				if (attr[i][0]) {
-					ast_set_flag(tmp, attr[i][0]);
-				}
-				if (attr[i][1]) {
-					ast_set_flag(tmp, attr[i][1]);
-				}
-				tmp->crypto = sdp_crypto_alloc(attr[i][2]); /* key_len */
-				tmp->crypto->tag = (i + 1); /* tag starts at 1 */
-
-				if (i < ARRAY_LEN(attr) - 1) {
-					AST_LIST_NEXT(tmp, sdp_srtp_list) = ast_sdp_srtp_alloc();
-					tmp = AST_LIST_NEXT(tmp, sdp_srtp_list);
-				}
-			}
-		}
-	}
-
-	if (dtls_enabled) {
-		/* If DTLS-SRTP is enabled the key details will be pulled from TLS */
-		return NULL;
-	}
-
-	/* set the key length based on INVITE or settings */
-	if (ast_test_flag(srtp, AST_SRTP_CRYPTO_TAG_80)) {
-		taglen = 80;
-	} else if (ast_test_flag(srtp, AST_SRTP_CRYPTO_TAG_32)) {
-		taglen = 32;
-	} else if (ast_test_flag(srtp, AST_SRTP_CRYPTO_TAG_16)) {
-		taglen = 16;
-	} else if (ast_test_flag(srtp, AST_SRTP_CRYPTO_TAG_8)) {
-		taglen = 8;
-	} else {
-		taglen = default_taglen_32 ? 32 : 80;
-	}
-	if (ast_test_flag(srtp, AST_SRTP_CRYPTO_AES_256)) {
-		taglen |= 0x0200;
-	} else if (ast_test_flag(srtp, AST_SRTP_CRYPTO_AES_192)) {
-		taglen |= 0x0100;
-	}
-	if (ast_test_flag(srtp, AST_SRTP_CRYPTO_OLD_NAME)) {
-		taglen |= 0x0080;
-	}
-
-	if (srtp->crypto && (ast_sdp_crypto_build_offer(srtp->crypto, taglen) >= 0)) {
-		return srtp->crypto->a_crypto;
-	}
-
-	ast_log(LOG_WARNING, "No SRTP key management enabled\n");
-	return NULL;
+	return sdp_crypto_api->get_attr(srtp, dtls_enabled, default_taglen_32);
 }
 
 char *ast_sdp_get_rtp_profile(unsigned int sdes_active, struct ast_rtp_instance *instance, unsigned int using_avpf,
@@ -682,3 +122,19 @@ char *ast_sdp_get_rtp_profile(unsigned int sdes_active, struct ast_rtp_instance
 	}
 }
 
+int ast_sdp_crypto_register(struct ast_sdp_crypto_api *api)
+{
+	if (sdp_crypto_api) {
+		return -1;
+	}
+	sdp_crypto_api = api;
+	return 0;
+}
+
+void ast_sdp_crypto_unregister(struct ast_sdp_crypto_api *api)
+{
+	if (sdp_crypto_api == api) {
+		sdp_crypto_api = NULL;
+	}
+}
+