Add support for encrypted WebM files as defined in the RFC.

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 be5e724c14af8d4f0dc23c4f1d98b7e401a031be..35fba2e1a0bef772f6f3687cf340228d632ee433 100644
--- a/media/webm/webm_cluster_parser.cc
+++ b/media/webm/webm_cluster_parser.cc
@@ -5,6 +5,7 @@
 #include "media/webm/webm_cluster_parser.h"
 
 #include "base/logging.h"
+#include "base/sys_byteorder.h"
 #include "media/base/data_buffer.h"
 #include "media/base/decrypt_config.h"
 #include "media/webm/webm_constants.h"
@@ -193,15 +194,33 @@ bool WebMClusterParser::OnBlock(int track_num, int timecode,
   base::TimeDelta timestamp = base::TimeDelta::FromMicroseconds(
       (cluster_timecode_ + timecode) * timecode_multiplier_);
 
+  // Every encrypted Block has an HMAC and IV prepended to it. Current WebM

[ddorwin, 2012/07/11 01:00:27]

"encrypted WebM" or "WebM encryption"? Same in next file and other references to
the RFC.

[fgalligan1, 2012/07/11 22:06:33]

Done.

+  // encrypted request for comments specification is here

[ddorwin, 2012/07/11 01:00:27]

I suggest reiterating here that for encrypted blocks:
 * the decoder buffer includes the IV and encrypted frame but not the HMAC
 * the HMAC and IV are in the DecryptConfig

[fgalligan1, 2012/07/11 22:06:33]

Done.

+  // http://wiki.webmproject.org/encryption/webm-encryption-rfc
+  bool encrypted = track_num == video_.track_num() &&
+                         video_encryption_key_id_.get();

[xhwang, 2012/07/10 06:31:25]

indentation: should align with "track_num".

[fgalligan1, 2012/07/11 22:06:33]

Done.

+  // If encrypted skip past the HMAC.
+  int data_offset = (encrypted) ? kWebMIntegrityCheckSize : 0;
+
   // The first bit of the flags is set when the block contains only keyframes.
   // http://www.matroska.org/technical/specs/index.html
   bool is_keyframe = (flags & 0x80) != 0;
   scoped_refptr<StreamParserBuffer> buffer =
-      StreamParserBuffer::CopyFrom(data, size, is_keyframe);
-
-  if (track_num == video_.track_num() && video_encryption_key_id_.get()) {
+      StreamParserBuffer::CopyFrom(data + data_offset,
+                                   size - data_offset,
+                                   is_keyframe);
+
+  if (encrypted) {
+    uint64 network_iv;
+    memcpy(&network_iv,
+           data + kWebMIntegrityCheckSize,

[ddorwin, 2012/07/11 01:00:27]

local var iv_offset might help readability (and fit on one line)

[fgalligan1, 2012/07/11 22:06:33]

It fits on one line (must have had a refactor). If you still want me to add a
local var for readability let me know.

+           sizeof(network_iv));
+    const uint64 iv = base::NetToHost64(network_iv);
     buffer->SetDecryptConfig(scoped_ptr<DecryptConfig>(new DecryptConfig(
-        video_encryption_key_id_.get(), video_encryption_key_id_size_)));
+        data, kWebMIntegrityCheckSize,
+        reinterpret_cast<const uint8*>(&iv), sizeof(iv),
+        video_encryption_key_id_.get(), video_encryption_key_id_size_,
+        sizeof(iv))));
   }
 
   buffer->SetTimestamp(timestamp);