61 lines
2.0 KiB
C++
61 lines
2.0 KiB
C++
// Copyright (c) 2013 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "media/webm/webm_crypto_helpers.h"
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#include "base/logging.h"
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#include "base/sys_byteorder.h"
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#include "media/base/decrypt_config.h"
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#include "media/webm/webm_constants.h"
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namespace media {
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namespace {
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// Generates a 16 byte CTR counter block. The CTR counter block format is a
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// CTR IV appended with a CTR block counter. |iv| is an 8 byte CTR IV.
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// |iv_size| is the size of |iv| in btyes. Returns a string of
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// kDecryptionKeySize bytes.
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std::string GenerateWebMCounterBlock(const uint8* iv, int iv_size) {
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std::string counter_block(reinterpret_cast<const char*>(iv), iv_size);
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counter_block.append(DecryptConfig::kDecryptionKeySize - iv_size, 0);
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return counter_block;
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}
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} // namespace anonymous
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scoped_ptr<DecryptConfig> WebMCreateDecryptConfig(
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const uint8* data, int data_size,
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const uint8* key_id, int key_id_size) {
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if (data_size < kWebMSignalByteSize) {
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DVLOG(1) << "Got a block from an encrypted stream with no data.";
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return scoped_ptr<DecryptConfig>();
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}
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uint8 signal_byte = data[0];
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int frame_offset = sizeof(signal_byte);
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// Setting the DecryptConfig object of the buffer while leaving the
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// initialization vector empty will tell the decryptor that the frame is
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// unencrypted.
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std::string counter_block;
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if (signal_byte & kWebMFlagEncryptedFrame) {
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if (data_size < kWebMSignalByteSize + kWebMIvSize) {
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DVLOG(1) << "Got an encrypted block with not enough data " << data_size;
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return scoped_ptr<DecryptConfig>();
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}
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counter_block = GenerateWebMCounterBlock(data + frame_offset, kWebMIvSize);
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frame_offset += kWebMIvSize;
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}
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scoped_ptr<DecryptConfig> config(new DecryptConfig(
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std::string(reinterpret_cast<const char*>(key_id), key_id_size),
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counter_block,
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frame_offset,
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std::vector<SubsampleEntry>()));
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return config.Pass();
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}
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} // namespace media
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