shaka-packager/packager/media/base/fixed_key_source.cc

// Copyright 2016 Google Inc. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd

#include "packager/media/base/fixed_key_source.h"

#include <algorithm>
#include "packager/base/logging.h"
#include "packager/base/strings/string_number_conversions.h"

namespace {
const char kEmptyDrmLabel[] = "";
}  // namespace

namespace shaka {
namespace media {

FixedKeySource::~FixedKeySource() {}

Status FixedKeySource::FetchKeys(EmeInitDataType init_data_type,
                                 const std::vector<uint8_t>& init_data) {
  // Do nothing for fixed key encryption/decryption.
  return Status::OK;
}

Status FixedKeySource::GetKey(const std::string& stream_label,
                              EncryptionKey* key) {
  DCHECK(key);
  // Try to find the key with label |stream_label|. If it is not available,
  // fall back to the default empty label if it is available.
  auto iter = encryption_key_map_.find(stream_label);
  if (iter == encryption_key_map_.end()) {
    iter = encryption_key_map_.find(kEmptyDrmLabel);
    if (iter == encryption_key_map_.end()) {
      return Status(error::NOT_FOUND,
                    "Key for '" + stream_label + "' was not found.");
    }
  }
  *key = *iter->second;
  return Status::OK;
}

Status FixedKeySource::GetKey(const std::vector<uint8_t>& key_id,
                              EncryptionKey* key) {
  DCHECK(key);
  for (const auto& pair : encryption_key_map_) {
    if (pair.second->key_id == key_id) {
      *key = *pair.second;
      return Status::OK;
    }
  }
  return Status(error::INTERNAL_ERROR,
                "Key for key_id=" + base::HexEncode(&key_id[0], key_id.size()) +
                    " was not found.");
}

Status FixedKeySource::GetCryptoPeriodKey(uint32_t crypto_period_index,
                                          const std::string& stream_label,
                                          EncryptionKey* key) {
  Status status = GetKey(stream_label, key);
  if (!status.ok())
    return status;

  // A naive key rotation algorithm is implemented here by left rotating the
  // key, key_id and pssh. Note that this implementation is only intended for
  // testing purpose. The actual key rotation algorithm can be much more
  // complicated.
  LOG(WARNING)
      << "This naive key rotation algorithm should not be used in production.";
  std::rotate(key->key_id.begin(),
              key->key_id.begin() + (crypto_period_index % key->key_id.size()),
              key->key_id.end());
  std::rotate(key->key.begin(),
              key->key.begin() + (crypto_period_index % key->key.size()),
              key->key.end());

  for (auto& key_system : key->key_system_info) {
    std::vector<uint8_t> pssh_data = key_system.pssh_data();
    if (!pssh_data.empty()) {
      std::rotate(pssh_data.begin(),
                  pssh_data.begin() + (crypto_period_index % pssh_data.size()),
                  pssh_data.end());
      key_system.set_pssh_data(pssh_data);
    }

    // Rotate the key_ids in pssh as well if exists.
    // Save a local copy of the key ids before clearing the key ids in
    // |key_system|. The key ids will be updated and added back later.
    std::vector<std::vector<uint8_t>> key_ids_copy = key_system.key_ids();
    key_system.clear_key_ids();
    for (std::vector<uint8_t>& key_id : key_ids_copy) {
      std::rotate(key_id.begin(),
                  key_id.begin() + (crypto_period_index % key_id.size()),
                  key_id.end());
      key_system.add_key_id(key_id);
    }
  }

  return Status::OK;
}

std::unique_ptr<FixedKeySource> FixedKeySource::Create(
    const RawKeyParams& raw_key) {
  std::vector<ProtectionSystemSpecificInfo> key_system_info;
  if (!raw_key.pssh.empty()) {
    if (!ProtectionSystemSpecificInfo::ParseBoxes(
            raw_key.pssh.data(), raw_key.pssh.size(), &key_system_info)) {
      LOG(ERROR) << "--pssh argument should be full PSSH boxes.";
      return std::unique_ptr<FixedKeySource>();
    }
  } else {
    // If there aren't any PSSH boxes given, create one with the common system
    // ID.
    key_system_info.resize(1);
    for (const auto& entry : raw_key.key_map) {
      const RawKeyParams::KeyInfo& key_pair = entry.second;
      key_system_info.back().add_key_id(key_pair.key_id);
    }
    key_system_info.back().set_system_id(kCommonSystemId,
                                         arraysize(kCommonSystemId));
    key_system_info.back().set_pssh_box_version(1);
  }

  EncryptionKeyMap encryption_key_map;
  for (const auto& entry : raw_key.key_map) {
    const std::string& drm_label = entry.first;
    const RawKeyParams::KeyInfo& key_pair = entry.second;

    if (key_pair.key_id.size() != 16) {
      LOG(ERROR) << "Invalid key ID size '" << key_pair.key_id.size()
                 << "', must be 16 bytes.";
      return std::unique_ptr<FixedKeySource>();
    }
    if (key_pair.key.size() != 16) {
      // CENC only supports AES-128, i.e. 16 bytes.
      LOG(ERROR) << "Invalid key size '" << key_pair.key.size()
                 << "', must be 16 bytes.";
      return std::unique_ptr<FixedKeySource>();
    }

    std::unique_ptr<EncryptionKey> encryption_key(new EncryptionKey);
    encryption_key->key_id = key_pair.key_id;
    encryption_key->key = key_pair.key;
    encryption_key->iv = raw_key.iv;
    encryption_key->key_system_info = key_system_info;
    encryption_key_map[drm_label] = std::move(encryption_key);
  }

  return std::unique_ptr<FixedKeySource>(
      new FixedKeySource(std::move(encryption_key_map)));
}

FixedKeySource::FixedKeySource() {}
FixedKeySource::FixedKeySource(EncryptionKeyMap&& encryption_key_map)
    : encryption_key_map_(std::move(encryption_key_map)) {}

}  // namespace media
}  // namespace shaka