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 28 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 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 64 matching lines @@
   int64 ntp_time_us = static_cast<int64>(ntp_seconds) *
       base::Time::kMicrosecondsPerSecond +
           static_cast<int64>(ntp_fractions) / kMagicFractionalUnit;
 
   base::TimeDelta elapsed_since_unix_epoch =
       base::TimeDelta::FromMicroseconds(ntp_time_us -
           (kUnixEpochInNtpSeconds * base::Time::kMicrosecondsPerSecond));
   return base::TimeTicks::UnixEpoch() + elapsed_since_unix_epoch;
 }
 
+inline std::string GetAesNounce(uint32 frame_id, const std::string& iv_mask) {

[wtc, 2013/11/13 20:57:17]

Nit: this function should be documented.

Nounce => Nonce?

[pwestin, 2013/11/15 19:38:17]

Done.

+  std::string aes_ivec(kAesKeySize, 0);

[wtc, 2013/11/13 20:57:17]

What does "ivec" stands for?

[pwestin, 2013/11/15 19:38:17]

Done.

+
+  aes_ivec[11] = frame_id & 0xff;

[wtc, 2013/11/13 20:57:17]

Nit: it may be useful to add a comment to point out you are serializing frame_id
in big-endian order (aes_ivec[8] is the most significant byte of frame_id).

[pwestin, 2013/11/15 19:38:17]

Done.

+  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) {

[wtc, 2013/11/13 20:57:17]

OK, after reading this function, I am now sure we should add a new constant,
kAesBlockSize, to be used with iv_mask. kAesBlockSize is also 16, but
conceptually it is not the size of the AES key (which can be 16, 24, or 32
bytes).

[pwestin, 2013/11/15 19:38:17]

Done.

+    aes_ivec[i] ^= iv_mask[i];
+  }
+  return aes_ivec;
+}
+
 }  // namespace cast
 }  // namespace media
 
 #endif  // MEDIA_CAST_CAST_DEFINES_H_