Fix RTP/RTCP authentication tag length

The tag is truncated from 20 bytes to 4 bytes

include/crypto.hh

@@ -25,6 +25,9 @@ namespace uvg_rtp {
                     void update(uint8_t *data, size_t len);
                     void final(uint8_t *digest);
 
+                    /* truncate digest to "size" bytes */
+                    void final(uint8_t *digest, size_t size);
+
                 private:
                     CryptoPP::HMAC<CryptoPP::SHA1> hmac_;
             };

include/queue.hh

@@ -67,7 +67,7 @@ namespace uvg_rtp {
         void *media_headers;
 
         /* Pointer to RTP authentication (if enabled) */
-        uint64_t *rtp_auth_tags;
+        uint32_t *rtp_auth_tags;
 
         size_t chunk_ptr;
         size_t hdr_ptr;

include/srtp/base.hh

@@ -24,8 +24,8 @@
 #define AES_KEY_LENGTH     16 /* 128 bits */
 #define HMAC_KEY_LENGTH    32 /* 256 bits */
 #define SALT_LENGTH        14 /* 112 bits */
-#define AUTH_TAG_LENGTH     8
-#define SRTCP_INDEX_LENGTH  8
+#define AUTH_TAG_LENGTH     4
+#define SRTCP_INDEX_LENGTH  4
 
 namespace uvg_rtp {
 

src/crypto.cc

@@ -24,6 +24,14 @@ void uvg_rtp::crypto::hmac::sha1::final(uint8_t *digest)
     hmac_.Final(digest);
 }
 
+void uvg_rtp::crypto::hmac::sha1::final(uint8_t *digest, size_t size)
+{
+    uint8_t d[20] = { 0 };
+
+    hmac_.Final(d);
+    memcpy(digest, d, size);
+}
+
 /* ***************** hmac-sha256 ***************** */
 
 uvg_rtp::crypto::hmac::sha256::sha256(uint8_t *key, size_t key_size):

src/queue.cc

@@ -80,7 +80,7 @@ rtp_error_t uvg_rtp::frame_queue::init_transaction()
     active_->dealloc_hook = dealloc_hook_;
 
     if (flags_ & RCE_SRTP_AUTHENTICATE_RTP)
-        active_->rtp_auth_tags = new uint64_t[max_mcount_];
+        active_->rtp_auth_tags = new uint32_t[max_mcount_];
     else
         active_->rtp_auth_tags = nullptr;
 
@@ -251,7 +251,7 @@ rtp_error_t uvg_rtp::frame_queue::enqueue_message(uint8_t *message, size_t messa
 
     if (flags_ & RCE_SRTP_AUTHENTICATE_RTP) {
         tmp.push_back({
-            sizeof(uint64_t),
+            sizeof(uint32_t),
             (uint8_t *)&active_->rtp_auth_tags[active_->rtpauth_ptr++]
         });
     }
@@ -292,7 +292,7 @@ rtp_error_t uvg_rtp::frame_queue::enqueue_message(std::vector<std::pair<size_t,
 
     if (flags_ & RCE_SRTP_AUTHENTICATE_RTP) {
         tmp.push_back({
-            sizeof(uint64_t),
+            sizeof(uint32_t),
             (uint8_t *)&active_->rtp_auth_tags[active_->rtpauth_ptr++]
         });
     }

src/srtp/srtp.cc

@@ -51,12 +51,12 @@ rtp_error_t uvg_rtp::srtp::recv_packet_handler(void *arg, int flags, frame::rtp_
 
     /* Calculate authentication tag for the packet and compare it against the one we received */
     if (srtp->authenticate_rtp()) {
-        uint64_t digest = 0;
+        uint32_t digest = 0;
         auto hmac_sha1  = uvg_rtp::crypto::hmac::sha1(ctx->key_ctx.remote.auth_key, AES_KEY_LENGTH);
 
         hmac_sha1.update(frame->dgram, frame->dgram_size - AUTH_TAG_LENGTH);
         hmac_sha1.update((uint8_t *)&ctx->roc, sizeof(ctx->roc));
-        hmac_sha1.final((uint8_t *)&digest);
+        hmac_sha1.final((uint8_t *)&digest, sizeof(uint32_t));
 
         if (memcmp(&digest, &frame->dgram[frame->dgram_size - AUTH_TAG_LENGTH], AUTH_TAG_LENGTH)) {
             LOG_ERROR("Authentication tag mismatch!");
@@ -122,7 +122,7 @@ authenticate:
         hmac_sha1.update((uint8_t *)buffers[i].second, buffers[i].first);
 
     hmac_sha1.update((uint8_t *)&ctx->roc, sizeof(ctx->roc));
-    hmac_sha1.final((uint8_t *)buffers[buffers.size() - 1].second);
+    hmac_sha1.final((uint8_t *)buffers[buffers.size() - 1].second, sizeof(uint32_t));
 
     return ret;
 }