Cast: Added support for AES-CTR crypto.

media/cast/cast_defines.h

Index: media/cast/cast_defines.h
diff --git a/media/cast/cast_defines.h b/media/cast/cast_defines.h
index f44e5fb82614a3ab20bea4e195952594ac571aeb..32810229e4e05514dd4ddacaae96aa3b8a64e5d3 100644
--- a/media/cast/cast_defines.h
+++ b/media/cast/cast_defines.h
@@ -46,6 +46,8 @@ const size_t kMinLengthOfRtcp = 8;
 // Basic RTP header + cast header.
 const size_t kMinLengthOfRtp = 12 + 6;
 
+const size_t kAesKeySize = 16;
+
 // Each uint16 represents one packet id within a cast frame.
 typedef std::set<uint16> PacketIdSet;
 // Each uint8 represents one cast frame.
@@ -130,6 +132,20 @@ inline base::TimeTicks ConvertNtpToTimeTicks(uint32 ntp_seconds,
   return base::TimeTicks::UnixEpoch() + elapsed_since_unix_epoch;
 }
 
+inline std::string GetAesNounce(uint32 frame_id, const std::string& iv_mask) {
+  std::string aes_ivec(kAesKeySize, 0);
+
+  aes_ivec[11] = frame_id & 0xff;
+  aes_ivec[10] = (frame_id >> 8) & 0xff;
+  aes_ivec[9] = (frame_id >> 16) & 0xff;
+  aes_ivec[8] = (frame_id >> 24) & 0xff;
+
+  for (size_t i = 0; i < kAesKeySize; ++i) {
+    aes_ivec[i] ^= iv_mask[i];
+  }
+  return aes_ivec;
+}
+
 }  // namespace cast
 }  // namespace media