media/cast/common/transport_encryption_handler.cc

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "media/cast/common/transport_encryption_handler.h"

#include <stddef.h>

#include <memory>

#include "base/logging.h"
#include "base/notreached.h"
#include "crypto/encryptor.h"
#include "crypto/symmetric_key.h"

namespace media {
namespace cast {

namespace {

// Crypto.
const size_t kAesBlockSize = 16;
const size_t kAesKeySize = 16;

std::string GetAesNonce(FrameId frame_id, const std::string& iv_mask) {
  DCHECK(!frame_id.is_null());

  std::string aes_nonce(kAesBlockSize, 0);

  // Serializing frame_id in big-endian order (aes_nonce[8] is the most
  // significant byte of frame_id).
  const uint32_t truncated_id = frame_id.lower_32_bits();
  aes_nonce[11] = truncated_id & 0xff;
  aes_nonce[10] = (truncated_id >> 8) & 0xff;
  aes_nonce[9] = (truncated_id >> 16) & 0xff;
  aes_nonce[8] = (truncated_id >> 24) & 0xff;

  for (size_t i = 0; i < kAesBlockSize; ++i) {
    aes_nonce[i] ^= iv_mask[i];
  }
  return aes_nonce;
}

}  // namespace

TransportEncryptionHandler::TransportEncryptionHandler()
    : key_(), encryptor_(), iv_mask_(), is_activated_(false) {}

TransportEncryptionHandler::~TransportEncryptionHandler() = default;

bool TransportEncryptionHandler::Initialize(const std::string& aes_key,
                                            const std::string& aes_iv_mask) {
  is_activated_ = false;
  if (aes_iv_mask.size() == kAesKeySize && aes_key.size() == kAesKeySize) {
    iv_mask_ = aes_iv_mask;
    key_ = crypto::SymmetricKey::Import(crypto::SymmetricKey::AES, aes_key);
    encryptor_ = std::make_unique<crypto::Encryptor>();
    encryptor_->Init(key_.get(), crypto::Encryptor::CTR, std::string());
    is_activated_ = true;
  } else if (aes_iv_mask.size() != 0 || aes_key.size() != 0) {
    DCHECK_EQ(aes_iv_mask.size(), 0u)
        << "Invalid Crypto configuration: aes_iv_mask.size";
    DCHECK_EQ(aes_key.size(), 0u)
        << "Invalid Crypto configuration: aes_key.size";
    return false;
  }
  return true;
}

bool TransportEncryptionHandler::Encrypt(FrameId frame_id,
                                         const base::StringPiece& data,
                                         std::string* encrypted_data) {
  if (!is_activated_)
    return false;
  if (!encryptor_->SetCounter(GetAesNonce(frame_id, iv_mask_))) {
    NOTREACHED() << "Failed to set counter";
    return false;
  }
  if (!encryptor_->Encrypt(data, encrypted_data)) {
    NOTREACHED() << "Encrypt error";
    return false;
  }
  return true;
}

bool TransportEncryptionHandler::Decrypt(FrameId frame_id,
                                         const base::StringPiece& ciphertext,
                                         std::string* plaintext) {
  if (!is_activated_) {
    return false;
  }
  if (!encryptor_->SetCounter(GetAesNonce(frame_id, iv_mask_))) {
    NOTREACHED() << "Failed to set counter";
    return false;
  }
  if (!encryptor_->Decrypt(ciphertext, plaintext)) {
    VLOG(1) << "Decryption error";
    return false;
  }
  return true;
}

}  // namespace cast
}  // namespace media