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| 1 // Copyright (c) 2013 The Chromium Authors. All rights reserved. |
| 2 // Use of this source code is governed by a BSD-style license that can be |
| 3 // found in the LICENSE file. |
| 4 |
| 5 #include "media/webm/webm_crypto_helpers.h" |
| 6 |
| 7 #include "base/logging.h" |
| 8 #include "base/sys_byteorder.h" |
| 9 #include "media/base/decrypt_config.h" |
| 10 #include "media/webm/webm_constants.h" |
| 11 |
| 12 namespace media { |
| 13 namespace { |
| 14 |
| 15 // Generates a 16 byte CTR counter block. The CTR counter block format is a |
| 16 // CTR IV appended with a CTR block counter. |iv| is an 8 byte CTR IV. |
| 17 // |iv_size| is the size of |iv| in btyes. Returns a string of |
| 18 // kDecryptionKeySize bytes. |
| 19 std::string GenerateWebMCounterBlock(const uint8* iv, int iv_size) { |
| 20 std::string counter_block(reinterpret_cast<const char*>(iv), iv_size); |
| 21 counter_block.append(DecryptConfig::kDecryptionKeySize - iv_size, 0); |
| 22 return counter_block; |
| 23 } |
| 24 |
| 25 } // namespace anonymous |
| 26 |
| 27 scoped_ptr<DecryptConfig> WebMCreateDecryptConfig( |
| 28 const uint8* data, int data_size, |
| 29 const uint8* key_id, int key_id_size) { |
| 30 if (data_size < kWebMSignalByteSize) { |
| 31 DVLOG(1) << "Got a block from an encrypted stream with no data."; |
| 32 return scoped_ptr<DecryptConfig>(NULL); |
| 33 } |
| 34 |
| 35 uint8 signal_byte = data[0]; |
| 36 int frame_offset = sizeof(signal_byte); |
| 37 |
| 38 // Setting the DecryptConfig object of the buffer while leaving the |
| 39 // initialization vector empty will tell the decryptor that the frame is |
| 40 // unencrypted. |
| 41 std::string counter_block; |
| 42 |
| 43 if (signal_byte & kWebMFlagEncryptedFrame) { |
| 44 if (data_size < kWebMSignalByteSize + kWebMIvSize) { |
| 45 DVLOG(1) << "Got an encrypted block with not enough data " << data_size; |
| 46 return scoped_ptr<DecryptConfig>(NULL); |
| 47 } |
| 48 counter_block = GenerateWebMCounterBlock(data + frame_offset, kWebMIvSize); |
| 49 frame_offset += kWebMIvSize; |
| 50 } |
| 51 |
| 52 scoped_ptr<DecryptConfig> config(new DecryptConfig( |
| 53 std::string(reinterpret_cast<const char*>(key_id), key_id_size), |
| 54 counter_block, |
| 55 frame_offset, |
| 56 std::vector<SubsampleEntry>())); |
| 57 return config.Pass(); |
| 58 } |
| 59 |
| 60 } // namespace media |
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