diff options
| -rw-r--r-- | include/asterisk/sdp_srtp.h | 95 | ||||
| -rw-r--r-- | main/sdp_srtp.c | 606 | ||||
| -rw-r--r-- | res/res_srtp.c | 587 |
3 files changed, 711 insertions, 577 deletions
diff --git a/include/asterisk/sdp_srtp.h b/include/asterisk/sdp_srtp.h index 5d8f0e7d1..cf89fa9e0 100644 --- a/include/asterisk/sdp_srtp.h +++ b/include/asterisk/sdp_srtp.h @@ -63,6 +63,100 @@ struct ast_sdp_srtp *ast_sdp_srtp_alloc(void); */ void ast_sdp_srtp_destroy(struct ast_sdp_srtp *srtp); +/*! \brief Destroy a previously allocated ast_sdp_crypto struct */ +typedef void (*sdp_crypto_destroy_cb)(struct ast_sdp_crypto *crypto); + +/*! + * \brief Initialize and return an ast_sdp_crypto struct + * + * \details + * This function allocates a new ast_sdp_crypto struct and initializes its values + * + * \retval NULL on failure + * \retval a pointer to a new ast_sdp_crypto structure + */ +typedef struct ast_sdp_crypto *(*sdp_crypto_alloc_cb)(void); + +/*! + * \brief Generate an SRTP a=crypto offer + * + * \details + * The offer is stored on the ast_sdp_crypto struct in a_crypto + * + * \param crypto A valid ast_sdp_crypto struct + * \param taglen Length + * + * \retval 0 success + * \retval nonzero failure + */ +typedef int (*sdp_crypto_build_offer_cb)(struct ast_sdp_crypto *crypto, int taglen); + +/*! + * \brief Parse the a=crypto line from SDP and set appropriate values on the + * ast_sdp_crypto struct. + * + * The attribute line should already have "a=crypto:" removed. + * + * \param p A valid ast_sdp_crypto struct + * \param attr the a:crypto line from SDP + * \param rtp The rtp instance associated with the SDP being parsed + * \param srtp SRTP structure + * + * \retval 0 success + * \retval nonzero failure + */ +typedef int (*sdp_crypto_parse_offer_cb)(struct ast_rtp_instance *rtp, struct ast_sdp_srtp *srtp, const char *attr); + +/*! + * \brief Get the crypto attribute line for the srtp structure + * + * \details + * The attribute line does not contain the initial "a=crypto:" and does + * not terminate with "\r\n". + * + * \param srtp The ast_sdp_srtp structure for which to get an attribute line + * \param dtls_enabled Whether this connection is encrypted with datagram TLS + * \param default_taglen_32 Whether to default to a tag length of 32 instead of 80 + * + * \retval An attribute line containing cryptographic information + * \retval NULL if the srtp structure does not require an attribute line containing crypto information + */ +typedef const char *(*sdp_srtp_get_attr_cb)(struct ast_sdp_srtp *srtp, int dtls_enabled, int default_taglen_32); + +struct ast_sdp_crypto_api { + /*! Destroy a crypto struct */ + sdp_crypto_destroy_cb dtor; + /*! Allocate a crypto struct */ + sdp_crypto_alloc_cb alloc; + /*! Build a SDP a=crypto offer line parameter string */ + sdp_crypto_build_offer_cb build_offer; + /*! Parse a SDP a=crypto offer line parameter string */ + sdp_crypto_parse_offer_cb parse_offer; + /*! Get the SDP a=crypto offer line parameter string */ + sdp_srtp_get_attr_cb get_attr; +}; + +/*! + * \brief Register SDP SRTP crypto processing routines. + * \since 14.0.0 + * + * \param api Callbacks to register. + * + * \retval 0 on success. + * \retval -1 on error. + */ +int ast_sdp_crypto_register(struct ast_sdp_crypto_api *api); + +/*! + * \brief Unregister SDP SRTP crypto processing routines. + * \since 14.0.0 + * + * \param api Callbacks to unregister. + * + * \return Nothing + */ +void ast_sdp_crypto_unregister(struct ast_sdp_crypto_api *api); + /*! \brief Initialize an return an ast_sdp_crypto struct * * \details @@ -104,7 +198,6 @@ int ast_sdp_crypto_process(struct ast_rtp_instance *rtp, struct ast_sdp_srtp *sr */ int ast_sdp_crypto_build_offer(struct ast_sdp_crypto *p, int taglen); - /*! \brief Get the crypto attribute line for the srtp structure * * The attribute line does not contain the initial "a=crypto:" and does 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; + } +} + diff --git a/res/res_srtp.c b/res/res_srtp.c index 59fda76dd..1fb16ce6b 100644 --- a/res/res_srtp.c +++ b/res/res_srtp.c @@ -39,6 +39,7 @@ ASTERISK_REGISTER_FILE() +#include <math.h> /* for pow */ #include <srtp/srtp.h> #ifdef HAVE_OPENSSL #include <openssl/rand.h> @@ -50,6 +51,7 @@ ASTERISK_REGISTER_FILE() #include "asterisk/frame.h" /* for AST_FRIENDLY_OFFSET */ #include "asterisk/logger.h" /* for ast_log, ast_debug, etc */ #include "asterisk/module.h" /* for ast_module_info, etc */ +#include "asterisk/sdp_srtp.h" #include "asterisk/res_srtp.h" /* for ast_srtp_cb, ast_srtp_suite, etc */ #include "asterisk/rtp_engine.h" /* for ast_rtp_engine_register_srtp, etc */ #include "asterisk/utils.h" /* for ast_free, ast_calloc */ @@ -578,10 +580,587 @@ static int ast_srtp_change_source(struct ast_srtp *srtp, unsigned int from_ssrc, return 0; } +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 void res_sdp_crypto_dtor(struct ast_sdp_crypto *crypto) +{ + if (crypto) { + ast_free(crypto->a_crypto); + crypto->a_crypto = NULL; + ast_free(crypto); + + ast_module_unref(ast_module_info->self); + } +} + +static struct ast_sdp_crypto *crypto_init_keys(struct ast_sdp_crypto *p, const int key_len) +{ + unsigned char remote_key[key_len]; + + if (srtp_res.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 (!(p = ast_calloc(1, sizeof(*p)))) { + return NULL; + } + p->tag = 1; + ast_module_ref(ast_module_info->self); + + /* default is a key which uses AST_AES_CM_128_HMAC_SHA1_xx */ + result = crypto_init_keys(p, key_len); + if (!result) { + res_sdp_crypto_dtor(p); + } + + return result; +} + +static struct ast_sdp_crypto *res_sdp_crypto_alloc(void) +{ + return sdp_crypto_alloc(SRTP_MASTER_KEY_LEN); +} + +static int res_sdp_crypto_build_offer(struct ast_sdp_crypto *p, int taglen) +{ + int res; + + /* Rebuild the crypto line */ + ast_free(p->a_crypto); + p->a_crypto = NULL; + + if ((taglen & 0x007f) == 8) { + res = ast_asprintf(&p->a_crypto, "%d AEAD_AES_%d_GCM_%d inline:%s", + p->tag, 128 + ((taglen & 0x0300) >> 2), taglen & 0x007f, p->local_key64); + } else if ((taglen & 0x007f) == 16) { + res = ast_asprintf(&p->a_crypto, "%d AEAD_AES_%d_GCM inline:%s", + p->tag, 128 + ((taglen & 0x0300) >> 2), p->local_key64); + } else if ((taglen & 0x0300) && !(taglen & 0x0080)) { + res = 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); + } else { + res = 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); + } + if (res == -1 || !p->a_crypto) { + ast_log(LOG_ERROR, "Could not allocate memory for crypto line\n"); + return -1; + } + + ast_debug(1, "Crypto line: a=crypto:%s\n", p->a_crypto); + + return 0; +} + +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 (policy_res.set_master_key(policy, master_key, key_len, NULL, 0) < 0) { + return -1; + } + + if (policy_res.set_suite(policy, suite_val)) { + ast_log(LOG_WARNING, "Could not set remote SRTP suite\n"); + return -1; + } + + policy_res.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 (!p) { + return -1; + } + + if (!(local_policy = policy_res.alloc())) { + return -1; + } + + if (!(remote_policy = policy_res.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) { + policy_res.destroy(local_policy); + } + + if (remote_policy) { + policy_res.destroy(remote_policy); + } + + return res; +} + +static int res_sdp_crypto_parse_offer(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; + + 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 (res_sdp_crypto_build_offer(crypto, taglen)) { + return -1; + } + + ast_set_flag(srtp, AST_SRTP_CRYPTO_OFFER_OK); + return 0; +} + +static const char *res_sdp_srtp_get_attr(struct ast_sdp_srtp *srtp, int dtls_enabled, int default_taglen_32) +{ + int taglen; + + if (!srtp) { + return NULL; + } + + /* Set encryption properties */ + if (!srtp->crypto) { + if (AST_LIST_NEXT(srtp, sdp_srtp_list)) { + srtp->crypto = res_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 && (res_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; +} + +static struct ast_sdp_crypto_api res_sdp_crypto_api = { + .dtor = res_sdp_crypto_dtor, + .alloc = res_sdp_crypto_alloc, + .build_offer = res_sdp_crypto_build_offer, + .parse_offer = res_sdp_crypto_parse_offer, + .get_attr = res_sdp_srtp_get_attr, +}; + static void res_srtp_shutdown(void) { - srtp_install_event_handler(NULL); + ast_sdp_crypto_unregister(&res_sdp_crypto_api); ast_rtp_engine_unregister_srtp(); + srtp_install_event_handler(NULL); #ifdef HAVE_SRTP_SHUTDOWN srtp_shutdown(); #endif @@ -607,6 +1186,12 @@ static int res_srtp_init(void) return -1; } + if (ast_sdp_crypto_register(&res_sdp_crypto_api)) { + ast_log(AST_LOG_WARNING, "Failed to register SDP SRTP crypto API\n"); + res_srtp_shutdown(); + return -1; + } + g_initialized = 1; return 0; } |