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// 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"
#include "base/hash_tables.h"
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_ptr.h"
#include "base/string_piece.h"
#include "base/synchronization/lock.h"
#include "media/base/decryptor.h"
#include "media/base/media_export.h"
namespace crypto {
class SymmetricKey;
}
namespace media {
class DecryptorClient;
// Decrypts an AES encrypted buffer into an unencrypted buffer. The AES
// encryption must be CTR with a key size of 128bits. Optionally checks the
// integrity of the encrypted data.
class MEDIA_EXPORT AesDecryptor : public Decryptor {
public:
// The AesDecryptor does not take ownership of the |client|. The |client|
// must be valid throughout the lifetime of the AesDecryptor.
explicit AesDecryptor(DecryptorClient* client);
virtual ~AesDecryptor();
// Decryptor implementation.
virtual void GenerateKeyRequest(const std::string& key_system,
const uint8* init_data,
int init_data_length) OVERRIDE;
virtual void AddKey(const std::string& key_system,
const uint8* key,
int key_length,
const uint8* init_data,
int init_data_length,
const std::string& session_id) OVERRIDE;
virtual void CancelKeyRequest(const std::string& key_system,
const std::string& session_id) OVERRIDE;
// Decrypts |encrypted| buffer. |encrypted| should not be NULL. |encrypted|
// will signal if an integrity check must be performed before decryption.
// Returns a DecoderBuffer with the decrypted data if the decryption
// succeeded through |decrypt_cb|.
virtual void Decrypt(const scoped_refptr<DecoderBuffer>& encrypted,
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 derives the WebM decryption key and HMAC.
bool Init();
crypto::SymmetricKey* decryption_key() { return decryption_key_.get(); }
crypto::SymmetricKey* webm_decryption_key()
{ 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);
};
// Sets |key| for |key_id|. The AesDecryptor takes the ownership of the |key|.
void SetKey(const std::string& key_id, scoped_ptr<DecryptionKey> key);
// Gets a DecryptionKey associated with |key_id|. The AesDecryptor still owns
// the key. Returns NULL if no key is associated with |key_id|.
DecryptionKey* GetKey(const std::string& key_id) const;
// KeyMap owns the DecryptionKey* and must delete them when they are
// not needed any more.
typedef base::hash_map<std::string, DecryptionKey*> KeyMap;
// Since only Decrypt() is called off the renderer thread, we only need to
// protect |key_map_|, the only member variable that is shared between
// Decrypt() and other methods.
KeyMap key_map_; // Protected by the |key_map_lock_|.
mutable base::Lock key_map_lock_; // Protects the |key_map_|.
// Make session ID unique per renderer by making it static.
// TODO(xhwang): Make session ID more strictly defined if needed:
// https://www.w3.org/Bugs/Public/show_bug.cgi?id=16739#c0
static uint32 next_session_id_;
DecryptorClient* const client_;
DISALLOW_COPY_AND_ASSIGN(AesDecryptor);
};
} // namespace media
#endif // MEDIA_CRYPTO_AES_DECRYPTOR_H_
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