| // Copyright (c) 2013 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. |
| |
| #include "media/webm/webm_crypto_helpers.h" |
| |
| #include "base/logging.h" |
| #include "base/sys_byteorder.h" |
| #include "media/base/decrypt_config.h" |
| #include "media/webm/webm_constants.h" |
| |
| namespace media { |
| namespace { |
| |
| // 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. |
| // |iv_size| is the size of |iv| in btyes. Returns a string of |
| // kDecryptionKeySize bytes. |
| std::string GenerateWebMCounterBlock(const uint8* iv, int iv_size) { |
| std::string counter_block(reinterpret_cast<const char*>(iv), iv_size); |
| counter_block.append(DecryptConfig::kDecryptionKeySize - iv_size, 0); |
| return counter_block; |
| } |
| |
| } // namespace anonymous |
| |
| scoped_ptr<DecryptConfig> WebMCreateDecryptConfig( |
| const uint8* data, int data_size, |
| const uint8* key_id, int key_id_size) { |
| if (data_size < kWebMSignalByteSize) { |
| DVLOG(1) << "Got a block from an encrypted stream with no data."; |
| return scoped_ptr<DecryptConfig>(NULL); |
| } |
| |
| uint8 signal_byte = data[0]; |
| int frame_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. |
| std::string counter_block; |
| |
| if (signal_byte & kWebMFlagEncryptedFrame) { |
| if (data_size < kWebMSignalByteSize + kWebMIvSize) { |
| DVLOG(1) << "Got an encrypted block with not enough data " << data_size; |
| return scoped_ptr<DecryptConfig>(NULL); |
| } |
| counter_block = GenerateWebMCounterBlock(data + frame_offset, kWebMIvSize); |
| frame_offset += kWebMIvSize; |
| } |
| |
| scoped_ptr<DecryptConfig> config(new DecryptConfig( |
| std::string(reinterpret_cast<const char*>(key_id), key_id_size), |
| counter_block, |
| frame_offset, |
| std::vector<SubsampleEntry>())); |
| return config.Pass(); |
| } |
| |
| } // namespace media |