116 lines
4.2 KiB
C++
116 lines
4.2 KiB
C++
// Copyright 2014 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 <packager/media/formats/webm/webm_crypto_helpers.h>
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#include <absl/base/internal/endian.h>
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#include <glog/logging.h>
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#include <packager/media/base/buffer_reader.h>
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#include <packager/media/formats/webm/webm_constants.h>
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namespace shaka {
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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::vector<uint8_t> GenerateWebMCounterBlock(const uint8_t* iv, int iv_size) {
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std::vector<uint8_t> counter_block(iv, iv + iv_size);
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counter_block.insert(counter_block.end(),
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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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// TODO(tinskip): Add unit test for this function.
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bool WebMCreateDecryptConfig(const uint8_t* data,
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int data_size,
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const uint8_t* key_id,
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size_t key_id_size,
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std::unique_ptr<DecryptConfig>* decrypt_config,
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int* data_offset) {
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int header_size = kWebMSignalByteSize;
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if (data_size < header_size) {
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DVLOG(1) << "Empty WebM sample.";
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return false;
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}
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uint8_t signal_byte = data[0];
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if (signal_byte & kWebMEncryptedSignal) {
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// Encrypted sample.
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header_size += kWebMIvSize;
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if (data_size < header_size) {
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DVLOG(1) << "Encrypted WebM sample too small to hold IV: " << data_size;
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return false;
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}
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std::vector<SubsampleEntry> subsamples;
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if (signal_byte & kWebMPartitionedSignal) {
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// Encrypted sample with subsamples / partitioning.
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header_size += kWebMNumPartitionsSize;
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if (data_size < header_size) {
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DVLOG(1)
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<< "Encrypted WebM sample too small to hold number of partitions: "
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<< data_size;
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return false;
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}
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uint8_t num_partitions = data[kWebMSignalByteSize + kWebMIvSize];
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BufferReader offsets_buffer(data + header_size, data_size - header_size);
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header_size += num_partitions * kWebMPartitionOffsetSize;
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uint32_t subsample_offset = 0;
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bool encrypted_subsample = false;
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uint16_t clear_size = 0;
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uint32_t encrypted_size = 0;
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for (uint8_t partition_idx = 0; partition_idx < num_partitions;
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++partition_idx) {
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uint32_t partition_offset;
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if (!offsets_buffer.Read4(&partition_offset)) {
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DVLOG(1)
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<< "Encrypted WebM sample too small to hold partition offsets: "
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<< data_size;
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return false;
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}
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if (partition_offset < subsample_offset) {
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DVLOG(1) << "Partition offsets out of order.";
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return false;
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}
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if (encrypted_subsample) {
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encrypted_size = partition_offset - subsample_offset;
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subsamples.push_back(SubsampleEntry(clear_size, encrypted_size));
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} else {
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clear_size = partition_offset - subsample_offset;
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if (partition_idx == (num_partitions - 1)) {
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encrypted_size = data_size - header_size - subsample_offset - clear_size;
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subsamples.push_back(SubsampleEntry(clear_size, encrypted_size));
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}
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}
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subsample_offset = partition_offset;
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encrypted_subsample = !encrypted_subsample;
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}
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if (!(num_partitions % 2)) {
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// Even number of partitions. Add one last all-clear subsample.
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clear_size = data_size - header_size - subsample_offset;
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encrypted_size = 0;
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subsamples.push_back(SubsampleEntry(clear_size, encrypted_size));
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}
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}
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decrypt_config->reset(new DecryptConfig(
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std::vector<uint8_t>(key_id, key_id + key_id_size),
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GenerateWebMCounterBlock(data + kWebMSignalByteSize, kWebMIvSize),
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subsamples));
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} else {
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// Clear sample.
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decrypt_config->reset();
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}
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*data_offset = header_size;
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return true;
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}
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} // namespace media
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} // namespace shaka
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