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..9bb8977905ef3685f61d943c1b18a213feb20b38 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 kAesBlockSize = 16;
+
 // Each uint16 represents one packet id within a cast frame.
 typedef std::set<uint16> PacketIdSet;
 // Each uint8 represents one cast frame.
@@ -130,6 +132,47 @@ inline base::TimeTicks ConvertNtpToTimeTicks(uint32 ntp_seconds,
   return base::TimeTicks::UnixEpoch() + elapsed_since_unix_epoch;
 }
 
+inline char ConvertFromBase16Char(char base_16) {

[Alpha Left Google, 2013/11/07 01:10:11]

Don't do this. You should assume the key and IV are already binary strings. It
is really the application (test app / chrome) to convert from base64 to binary.
Also there's already base/base64.h that does the conversion.

[pwestin, 2013/11/07 17:16:04]

Moved to test app. I did find the base 64 but not the base 16 in chromium 

+  DCHECK((base_16 >= '0' && base_16 <= '9') ||
+         (base_16 >= 'a' && base_16 <= 'f') ||
+         (base_16 >= 'A' && base_16 <= 'F'));
+
+  if (base_16 >= '0' && base_16 <= '9') {
+    return base_16 - '0';
+  }
+  if (base_16 >= 'a' && base_16 <= 'f') {
+    return base_16 - 'a' + 10;
+  }
+  return base_16 - 'A' + 10;
+}
+
+inline std::string ConvertFromBase16String(std::string base_16) {
+  std::string compressed;
+  DCHECK(base_16.size() % 2 == 0) << "Must be a multiple of 2";
+  compressed.reserve(base_16.size() / 2);
+
+  for (std::string::iterator it = base_16.begin(); it != base_16.end(); ++it) {
+    char first_part = ConvertFromBase16Char(*it++);
+    char second_part = ConvertFromBase16Char(*it);
+    compressed.push_back((first_part << 4) + second_part);
+  }
+  return compressed;
+}
+
+inline std::string GetAesNounce(uint32 frame_id, const std::string& iv_mask) {
+  std::string aes_ivec(kAesBlockSize, 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 < kAesBlockSize; ++i) {
+    aes_ivec[i] ^= iv_mask[i];
+  }
+  return aes_ivec;
+}
+
 }  // namespace cast
 }  // namespace media