1 files changed, 29 insertions, 32 deletions

diff --git a/media/webm/webm_cluster_parser.cc b/media/webm/webm_cluster_parser.cc
index 7878fa8..e9ef93e 100644
--- a/media/webm/webm_cluster_parser.cc
+++ b/media/webm/webm_cluster_parser.cc
@@ -14,11 +14,20 @@ namespace media {
 
 // Generates a 16 byte CTR counter block. The CTR counter block format is a
 // CTR IV appended with a CTR block counter. |iv| is an 8 byte CTR IV.
-// Returns a string of kDecryptionKeySize bytes.
-static std::string GenerateCounterBlock(uint64 iv) {
-  std::string counter_block(reinterpret_cast<char*>(&iv), sizeof(iv));
-  counter_block.append(DecryptConfig::kDecryptionKeySize - sizeof(iv), 0);
-  return counter_block;
+// Always returns a valid pointer to a buffer of kDecryptionKeySize bytes.
+static scoped_array<uint8> GenerateCounterBlock(uint64 iv) {
+  scoped_array<uint8> counter_block_data(
+      new uint8[DecryptConfig::kDecryptionKeySize]);
+
+  // Set the IV.
+  memcpy(counter_block_data.get(), &iv, sizeof(iv));
+
+  // Set block counter to all 0's.
+  memset(counter_block_data.get() + sizeof(iv),
+         0,
+         DecryptConfig::kDecryptionKeySize - sizeof(iv));
+
+  return counter_block_data.Pass();
 }
 
 WebMClusterParser::WebMClusterParser(int64 timecode_scale,
@@ -211,14 +220,12 @@ 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 is_track_encrypted = track_num == video_.track_num() &&
-                            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 = (is_track_encrypted) ? kWebMHmacSize : 0;
+  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;
 
   // The first bit of the flags is set when the block contains only keyframes.
   // http://www.matroska.org/technical/specs/index.html
@@ -226,31 +233,21 @@ bool WebMClusterParser::OnBlock(int track_num, int timecode,
   scoped_refptr<StreamParserBuffer> buffer =
       StreamParserBuffer::CopyFrom(data + offset, size - offset, is_keyframe);
 
-  if (is_track_encrypted) {
-    uint8 signal_byte = data[kWebMHmacSize];
-    int data_offset = sizeof(signal_byte);
-
-    // 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;
-
-    if (signal_byte & kWebMFlagEncryptedFrame) {
-      uint64 network_iv;
-      memcpy(&network_iv, data + kWebMHmacSize + data_offset,
-             sizeof(network_iv));
-      const uint64 iv = base::NetToHost64(network_iv);
-      counter_block = GenerateCounterBlock(iv);
-      data_offset += sizeof(iv);
-    }
+  if (encrypted) {
+    uint64 network_iv;
+    memcpy(&network_iv, data + kWebMHmacSize, sizeof(network_iv));
+    const uint64 iv = base::NetToHost64(network_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_),
-        counter_block,
+        std::string(
+            reinterpret_cast<const char*>(counter_block.get()),
+            DecryptConfig::kDecryptionKeySize),
         std::string(reinterpret_cast<const char*>(data), kWebMHmacSize),
-        data_offset,
+        sizeof(iv),
         std::vector<SubsampleEntry>())));
   }