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.
GenerateWebMCounterBlock(const uint8 * iv,int iv_size)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
WebMCreateDecryptConfig(const uint8 * data,int data_size,const uint8 * key_id,int key_id_size)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>();
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>();
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
61