Add support for GCM cipher suites from RFC 7714.

talk/session/media/srtpfilter.cc

Index: talk/session/media/srtpfilter.cc
diff --git a/talk/session/media/srtpfilter.cc b/talk/session/media/srtpfilter.cc
index 4a54740cef2be0433e8f0fda07344f7a49667409..382c644ede2f460ced2966f0508b881f15654548 100644
--- a/talk/session/media/srtpfilter.cc
+++ b/talk/session/media/srtpfilter.cc
@@ -73,10 +73,6 @@ extern "C" debug_module_t mod_aes_hmac;
 
 namespace cricket {
 
-const int SRTP_MASTER_KEY_BASE64_LEN = SRTP_MASTER_KEY_LEN * 4 / 3;
-const int SRTP_MASTER_KEY_KEY_LEN = 16;
-const int SRTP_MASTER_KEY_SALT_LEN = 14;
-
 #ifndef HAVE_SRTP
 
 // This helper function is used on systems that don't (yet) have SRTP,
@@ -674,19 +670,34 @@ bool SrtpSession::SetKey(int type, int cs, const uint8_t* key, int len) {
   srtp_policy_t policy;
   memset(&policy, 0, sizeof(policy));
 
+  int expected_key_len;
   if (cs == rtc::SRTP_AES128_CM_SHA1_80) {
     crypto_policy_set_aes_cm_128_hmac_sha1_80(&policy.rtp);
     crypto_policy_set_aes_cm_128_hmac_sha1_80(&policy.rtcp);
+    // Master key is 128 bits key + 112 bits salt.
+    expected_key_len = 16 + 14;
   } else if (cs == rtc::SRTP_AES128_CM_SHA1_32) {
     crypto_policy_set_aes_cm_128_hmac_sha1_32(&policy.rtp);   // rtp is 32,
     crypto_policy_set_aes_cm_128_hmac_sha1_80(&policy.rtcp);  // rtcp still 80
+    // Master key is 128 bits key + 112 bits salt.
+    expected_key_len = 16 + 14;
+  } else if (cs == rtc::SRTP_AEAD_AES_128_GCM) {
+    crypto_policy_set_aes_gcm_128_16_auth(&policy.rtp);
+    crypto_policy_set_aes_gcm_128_16_auth(&policy.rtcp);
+    // Master key is 128 bits key + 96 bits salt.
+    expected_key_len = 16 + 12;
+  } else if (cs == rtc::SRTP_AEAD_AES_256_GCM) {
+    crypto_policy_set_aes_gcm_256_16_auth(&policy.rtp);
+    crypto_policy_set_aes_gcm_256_16_auth(&policy.rtcp);
+    // Master key is 256 bits key + 96 bits salt.
+    expected_key_len = 32 + 12;

[pthatcher1, 2015/12/18 20:31:32]

This seems duplicative with the new SrtpCryptoSuiteParams function you added. 
Can you use that here to avoid duplicating information in the code base?

[joachim, 2015/12/19 15:26:23]

Right, I wrote that code before adding the new function. Changed.

   } else {
     LOG(LS_WARNING) << "Failed to create SRTP session: unsupported"
                     << " cipher_suite " << cs;
     return false;
   }
 
-  if (!key || len != SRTP_MASTER_KEY_LEN) {
+  if (!key || len != expected_key_len) {
     LOG(LS_WARNING) << "Failed to create SRTP session: invalid key";
     return false;
   }
@@ -716,7 +727,6 @@ bool SrtpSession::SetKey(int type, int cs, const uint8_t* key, int len) {
     return false;
   }
 
-
   rtp_auth_tag_len_ = policy.rtp.auth_tag_len;
   rtcp_auth_tag_len_ = policy.rtcp.auth_tag_len;
   return true;