Merge pull request #733 from vopatek/fix-rtcp-mki-when-rtp-short-auth

Fix srtp_unprotect_rtcp_mki when RTP auth != RTCP

Author: pabuhler

srtp/srtp.c

@@ -1638,24 +1638,16 @@ static void srtp_calc_aead_iv(srtp_session_keys_t *session_keys,
     v128_xor(iv, &in, &salt);
 }
 
-srtp_session_keys_t *srtp_get_session_keys(srtp_stream_ctx_t *stream,
-                                           const uint8_t *hdr,
-                                           unsigned int pkt_octet_len,
-                                           unsigned int *mki_size)
+static srtp_session_keys_t *srtp_get_session_keys(srtp_stream_ctx_t *stream,
+                                                  const uint8_t *hdr,
+                                                  unsigned int pkt_octet_len,
+                                                  unsigned int *mki_size,
+                                                  unsigned int tag_len)
 {
     unsigned int base_mki_start_location = pkt_octet_len;
     unsigned int mki_start_location = 0;
-    unsigned int tag_len = 0;
     unsigned int i = 0;
 
-    // Determine the authentication tag size
-    if (stream->session_keys[0].rtp_cipher->algorithm == SRTP_AES_GCM_128 ||
-        stream->session_keys[0].rtp_cipher->algorithm == SRTP_AES_GCM_256) {
-        tag_len = 0;
-    } else {
-        tag_len = srtp_auth_get_tag_length(stream->session_keys[0].rtp_auth);
-    }
-
     if (tag_len > base_mki_start_location) {
         *mki_size = 0;
         return NULL;
@@ -1680,6 +1672,44 @@ srtp_session_keys_t *srtp_get_session_keys(srtp_stream_ctx_t *stream,
     return NULL;
 }
 
+static srtp_session_keys_t *srtp_get_session_keys_rtp(
+    srtp_stream_ctx_t *stream,
+    const uint8_t *hdr,
+    unsigned int pkt_octet_len,
+    unsigned int *mki_size)
+{
+    unsigned int tag_len = 0;
+
+    // Determine the authentication tag size
+    if (stream->session_keys[0].rtp_cipher->algorithm == SRTP_AES_GCM_128 ||
+        stream->session_keys[0].rtp_cipher->algorithm == SRTP_AES_GCM_256) {
+        tag_len = 0;
+    } else {
+        tag_len = srtp_auth_get_tag_length(stream->session_keys[0].rtp_auth);
+    }
+
+    return srtp_get_session_keys(stream, hdr, pkt_octet_len, mki_size, tag_len);
+}
+
+static srtp_session_keys_t *srtp_get_session_keys_rtcp(
+    srtp_stream_ctx_t *stream,
+    const uint8_t *hdr,
+    unsigned int pkt_octet_len,
+    unsigned int *mki_size)
+{
+    unsigned int tag_len = 0;
+
+    // Determine the authentication tag size
+    if (stream->session_keys[0].rtcp_cipher->algorithm == SRTP_AES_GCM_128 ||
+        stream->session_keys[0].rtcp_cipher->algorithm == SRTP_AES_GCM_256) {
+        tag_len = 0;
+    } else {
+        tag_len = srtp_auth_get_tag_length(stream->session_keys[0].rtcp_auth);
+    }
+
+    return srtp_get_session_keys(stream, hdr, pkt_octet_len, mki_size, tag_len);
+}
+
 static srtp_err_status_t srtp_estimate_index(srtp_rdbx_t *rdbx,
                                              uint32_t roc,
                                              srtp_xtd_seq_num_t *est,
@@ -2583,8 +2613,8 @@ srtp_err_status_t srtp_unprotect_mki(srtp_ctx_t *ctx,
     /* Determine if MKI is being used and what session keys should be used */
     if (use_mki) {
         session_keys =
-            srtp_get_session_keys(stream, (const uint8_t *)hdr,
-                                  (unsigned int)*pkt_octet_len, &mki_size);
+            srtp_get_session_keys_rtp(stream, (const uint8_t *)hdr,
+                                      (unsigned int)*pkt_octet_len, &mki_size);
 
         if (session_keys == NULL)
             return srtp_err_status_bad_mki;
@@ -4293,7 +4323,7 @@ srtp_err_status_t srtp_unprotect_rtcp_mki(srtp_t ctx,
      * Determine if MKI is being used and what session keys should be used
      */
     if (use_mki) {
-        session_keys = srtp_get_session_keys(
+        session_keys = srtp_get_session_keys_rtcp(
             stream, (uint8_t *)hdr, (unsigned int)*pkt_octet_len, &mki_size);
 
         if (session_keys == NULL)

test/srtp_driver.c

@@ -4279,6 +4279,38 @@ const srtp_policy_t aes_256_hmac_policy = {
     NULL
 };
 
+const srtp_policy_t aes_256_hmac_32_policy = {
+    { ssrc_any_outbound, 0 }, /* SSRC */
+    {
+        /* SRTP policy */
+        SRTP_AES_ICM_256,               /* cipher type                 */
+        SRTP_AES_ICM_256_KEY_LEN_WSALT, /* cipher key length in octets */
+        SRTP_HMAC_SHA1,                 /* authentication func type    */
+        20,                             /* auth key length in octets   */
+        4,                              /* auth tag length in octets   */
+        sec_serv_conf_and_auth          /* security services flag      */
+    },
+    {
+        /* SRTCP policy */
+        SRTP_AES_ICM_256,               /* cipher type                 */
+        SRTP_AES_ICM_256_KEY_LEN_WSALT, /* cipher key length in octets */
+        SRTP_HMAC_SHA1,                 /* authentication func type    */
+        20,                             /* auth key length in octets   */
+        10,                             /* auth tag length in octets.
+                                           80 bits per RFC 3711. */
+        sec_serv_conf_and_auth          /* security services flag      */
+    },
+    NULL,
+    (srtp_master_key_t **)test_256_keys,
+    2,    /* indicates the number of Master keys          */
+    NULL, /* indicates that EKT is not in use             */
+    128,  /* replay window size                           */
+    0,    /* retransmission not allowed                   */
+    NULL, /* no encrypted extension headers               */
+    0,    /* list of encrypted extension headers is empty */
+    NULL
+};
+
 char ekt_test_policy = 'x';
 
 const srtp_policy_t hmac_only_with_ekt_policy = {
@@ -4333,6 +4365,7 @@ const srtp_policy_t *policy_array[] = {
 #endif
     &null_policy,
     &aes_256_hmac_policy,
+    &aes_256_hmac_32_policy,
     NULL
 };
 // clang-format on