Add Common Encryption support to BMFF, including subsample decryption.

media/crypto/aes_decryptor.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_CRYPTO_AES_DECRYPTOR_H_
 #define MEDIA_CRYPTO_AES_DECRYPTOR_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 43 matching lines @@
                        const DecryptCB& decrypt_cb) OVERRIDE;
 
  private:
   // Helper class that manages the decryption key and HMAC key. The HMAC key
   // may be NULL.
   class DecryptionKey {
    public:
     explicit DecryptionKey(const std::string& secret);
     ~DecryptionKey();
 
-    // Creates the encryption key and HMAC. If |derive_webm_keys| is true then
-    // the object will derive the decryption key and the HMAC key from
-    // |secret_|.
-    bool Init(bool derive_webm_keys);
+    // Creates the encryption key, and derives the WebM decryption key and HMAC.
+    bool Init();
 
     crypto::SymmetricKey* decryption_key() { return decryption_key_.get(); }
+    crypto::SymmetricKey* webm_decryption_key()

[ddorwin, 2012/07/24 01:00:10]

This should be the same as the above value. IOW, not a separate member. I see
your TODO in the .cc. We can cover this comment there.

[strobe_, 2012/07/25 01:05:13]

OK, anything needed here?

+      { return webm_decryption_key_.get(); }
     base::StringPiece hmac_key() { return base::StringPiece(hmac_key_); }
 
    private:
     // The base secret that is used to derive the decryption key and optionally
     // the HMAC key.
     const std::string secret_;
 
     // The key used to decrypt the data.
     scoped_ptr<crypto::SymmetricKey> decryption_key_;
 
+    // The key used for decryption of WebM media, derived from the secret.
+    scoped_ptr<crypto::SymmetricKey> webm_decryption_key_;
+
     // The key used to perform the integrity check.  Currently the HMAC key is
     // defined by the WebM encrypted specification. Current encrypted WebM
     // request for comments specification is here
     // http://wiki.webmproject.org/encryption/webm-encryption-rfc
     std::string hmac_key_;
 
     DISALLOW_COPY_AND_ASSIGN(DecryptionKey);
   };
 
   // KeyMap owns the DecryptionKey* and must delete them when they are
@@ skipping 12 matching lines @@
   static uint32 next_session_id_;
 
   DecryptorClient* const client_;
 
   DISALLOW_COPY_AND_ASSIGN(AesDecryptor);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_CRYPTO_AES_DECRYPTOR_H_