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

media/base/decrypt_config.h

Index: media/base/decrypt_config.h
diff --git a/media/base/decrypt_config.h b/media/base/decrypt_config.h
index 5fca7876d330c78c76ade6c624ba00b85b49c70c..fae988f240487c1a46c5ae6c16a60cef420eb8ae 100644
--- a/media/base/decrypt_config.h
+++ b/media/base/decrypt_config.h
@@ -14,13 +14,32 @@ namespace media {
 // Contains all information that a decryptor needs to decrypt.
 class MEDIA_EXPORT DecryptConfig {
  public:
-  explicit DecryptConfig(const uint8* key_id, int key_id_size);
+  // The sizes are from the WebM encrypted specification. Current WebM
+  // encrypted request for comments specification is here
+  // http://wiki.webmproject.org/encryption/webm-encryption-rfc.

[xhwang, 2012/06/14 19:42:27]

Remove the trailing "." as people may also copy that as part of the URL.

[fgalligan1, 2012/07/03 22:00:15]

Done.

+  static const int kIvSize = 8;
+  static const int kKeySize = 16;
+  static const int kWebMIntegrityCheckSize = 12;

[xhwang, 2012/06/14 19:42:27]

If we pass the whole encrypted frame (with prepending hmac and iv) to the
decryptor, we don't need to expose these here: we can hide them in the
HmacAesDecryptor. The DecryptConfig should contain data that is needed for
decryption but not readily available in the encrypted frame.

Also, we try to limit WebM specific stuff in the media/webm/ folder. 

[ddorwin, 2012/06/14 21:41:24]

This class should be container-independent. We want all the container stuff in
the demuxer because we want the decryptors to be container-independent (even if
they have decoders). All of these values are WebM-specific (though CENC uses
128-bit keys too).

+
+  DecryptConfig(const uint8* hmac, int hmac_size,

[ddorwin, 2012/06/14 21:41:24]

CENC (and other containers) do not support HMAC, so we probably need something
closer to the current AesDecryptor. Preferably, we can do this with just if
statements (and method extraction, if necessary). We can specify that
hmac_size==0 means the container does not support it (or one was not present in
the stream?)

+                uint64 iv,

[ddorwin, 2012/06/14 21:41:24]

In CENC, the IV_size can vary and be as large as 16 bytes. I suggest we just
support longer IVs (and specifying size) now. Unless there is a 128 type, switch
to pointer and size now; that also has the advantage of all parameters being
consistent.

[fgalligan1, 2012/07/03 22:00:15]

Done.

+                const uint8* key_id, int key_id_size);
   ~DecryptConfig();
 
+  const uint8* hmac() const { return hmac_.get(); }
+  int hmac_size() const { return hmac_size_; }
+  uint64 iv() const { return iv_; }
   const uint8* key_id() const { return key_id_.get(); }
   int key_id_size() const { return key_id_size_; }
 
  private:
+  // HMAC defined from the WebM specification.
+  scoped_array<uint8> hmac_;
+  int hmac_size_;
+
+  // Initialization vector defined from the WebM specification.
+  uint64 iv_;
+
   scoped_array<uint8> key_id_;
   int key_id_size_;