Cast: Added support for AES-CTR crypto.

media/cast/cast_defines.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_CAST_CAST_DEFINES_H_
 #define MEDIA_CAST_CAST_DEFINES_H_
 
 #include <map>
 #include <set>
 
@@ skipping 30 matching lines @@
   kDefaultRtpMaxDelayMs = 100,
 };
 
 const uint16 kRtcpCastAllPacketsLost = 0xffff;
 
 const size_t kMinLengthOfRtcp = 8;
 
 // Basic RTP header + cast header.
 const size_t kMinLengthOfRtp = 12 + 6;
 
+const size_t kAesBlockSize = 16;
+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.
 typedef std::map<uint8, PacketIdSet> MissingFramesAndPacketsMap;
 
 // TODO(pwestin): Re-factor the functions bellow into a class with static
 // methods.
 
 // January 1970, in NTP seconds.
 // Network Time Protocol (NTP), which is in seconds relative to 0h UTC on
@@ skipping 99 matching lines @@
     }
     return (frame_id_wrap_count_ << 8) + over_the_wire_frame_id;
   }
 
  private:
   bool first_;
   bool can_we_wrap_;
   uint32 frame_id_wrap_count_;
 };
 
+inline std::string GetAesNonce(uint32 frame_id, const std::string& iv_mask) {
+  std::string aes_nonce(kAesBlockSize, 0);
+
+  // Serializing frame_id in big-endian order (aes_nonce[8] is the most
+  // significant byte of frame_id).
+  aes_nonce[11] = frame_id & 0xff;
+  aes_nonce[10] = (frame_id >> 8) & 0xff;
+  aes_nonce[9] = (frame_id >> 16) & 0xff;
+  aes_nonce[8] = (frame_id >> 24) & 0xff;
+
+  for (size_t i = 0; i < kAesBlockSize; ++i) {
+    aes_nonce[i] ^= iv_mask[i];
+  }
+  return aes_nonce;
+}
+
 }  // namespace cast
 }  // namespace media
 
 #endif  // MEDIA_CAST_CAST_DEFINES_H_