Add support for v0.3 of the encrypted WebM specification.

media/webm/webm_cluster_parser.cc

Index: media/webm/webm_cluster_parser.cc
diff --git a/media/webm/webm_cluster_parser.cc b/media/webm/webm_cluster_parser.cc
index e9ef93e3fb14c8bd29197f0e826dcff6c9bf25a1..e7d8cfd00ea2895b2d4c29830de0a6f59b9355d2 100644
--- a/media/webm/webm_cluster_parser.cc
+++ b/media/webm/webm_cluster_parser.cc
@@ -220,12 +220,14 @@ bool WebMClusterParser::OnBlock(int track_num, int timecode,
   // Every encrypted Block has an HMAC and IV prepended to it. Current encrypted
   // WebM request for comments specification is here
   // http://wiki.webmproject.org/encryption/webm-encryption-rfc
-  bool encrypted = track_num == video_.track_num() &&
-                   video_encryption_key_id_.get();
-  // If encrypted skip past the HMAC. Encrypted buffers must include the IV and
-  // the encrypted frame because the decryptor will verify this data before
-  // decryption. The HMAC and IV will be copied into DecryptConfig.
-  int offset = (encrypted) ? kWebMHmacSize : 0;
+  bool encrypted_stream = track_num == video_.track_num() &&

[xhwang, 2012/08/01 00:45:41]

"encrypted_stream" is a noun. How about something like "is_stream_encrypted".

Also, in WebM, we use "track" instead of "stream", correct? If so,
"is_track_encrypted"?

[fgalligan1, 2012/08/01 01:36:10]

Done.

+                          video_encryption_key_id_.get();
+
+  // If stream is encrypted skip past the HMAC. Encrypted buffers must include
+  // the signal byte, the IV (if frame is encrypted) and
+  // the frame because the decryptor will verify this data before decryption.
+  // The HMAC and IV will be copied into DecryptConfig.
+  int offset = (encrypted_stream) ? kWebMHmacSize : 0;
 
   // The first bit of the flags is set when the block contains only keyframes.
   // http://www.matroska.org/technical/specs/index.html
@@ -233,21 +235,34 @@ bool WebMClusterParser::OnBlock(int track_num, int timecode,
   scoped_refptr<StreamParserBuffer> buffer =
       StreamParserBuffer::CopyFrom(data + offset, size - offset, is_keyframe);
 
-  if (encrypted) {
-    uint64 network_iv;
-    memcpy(&network_iv, data + kWebMHmacSize, sizeof(network_iv));
-    const uint64 iv = base::NetToHost64(network_iv);
+  if (encrypted_stream) {
+    int data_offset = 1;
+    uint8 signal_byte = data[kWebMHmacSize];

[xhwang, 2012/08/01 00:45:41]

How about moving "int data_offset = 1" after this line and change it to:
int data_offset = sizeof(signal_byte);

[fgalligan1, 2012/08/01 01:36:10]

Done.

+
+    // Setting the DecryptConfig object of the buffer while leaving the
+    // initialization vector empty will tell the decryptor that the frame is
+    // unencrypted but integrity should still be checked.
+    std::string counter_block_str;
+
+    if (signal_byte & kWebMEncryptedFrame) {
+      uint64 network_iv;
+      memcpy(&network_iv, data + kWebMHmacSize + 1, sizeof(network_iv));

[xhwang, 2012/08/01 00:45:41]

s/1/data_offset/

[fgalligan1, 2012/08/01 01:36:10]

Done.

+      const uint64 iv = base::NetToHost64(network_iv);
+
+      scoped_array<uint8> counter_block(GenerateCounterBlock(iv));
+      counter_block_str.assign(
+          reinterpret_cast<const char*>(counter_block.get()),
+          DecryptConfig::kDecryptionKeySize);

[xhwang, 2012/08/01 00:45:41]

This code will be much easier if GenerateCounterBlock() returns std::string. See
comment above.

[fgalligan1, 2012/08/01 01:36:10]

Done.

+      data_offset += sizeof(iv);
+    }
 
-    scoped_array<uint8> counter_block(GenerateCounterBlock(iv));
     buffer->SetDecryptConfig(scoped_ptr<DecryptConfig>(new DecryptConfig(
         std::string(
             reinterpret_cast<const char*>(video_encryption_key_id_.get()),
             video_encryption_key_id_size_),
-        std::string(
-            reinterpret_cast<const char*>(counter_block.get()),
-            DecryptConfig::kDecryptionKeySize),
+        counter_block_str,
         std::string(reinterpret_cast<const char*>(data), kWebMHmacSize),
-        sizeof(iv),
+        data_offset,
         std::vector<SubsampleEntry>())));
   }