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// Copyright 2019 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.
#ifndef STREAMING_CAST_FRAME_CRYPTO_H_
#define STREAMING_CAST_FRAME_CRYPTO_H_
#include <stddef.h>
#include <stdint.h>
#include <array>
#include <vector>
#include "openssl/aes.h"
#include "platform/base/macros.h"
#include "streaming/cast/encoded_frame.h"
namespace openscreen {
namespace cast_streaming {
// A subclass of EncodedFrame that represents an EncodedFrame with encrypted
// payload data. It can only be value-constructed by FrameCrypto, but can be
// moved freely thereafter. Use FrameCrypto (below) to explicitly convert
// between EncryptedFrames and EncodedFrames.
struct EncryptedFrame : public EncodedFrame {
~EncryptedFrame();
EncryptedFrame(EncryptedFrame&&) MAYBE_NOEXCEPT;
EncryptedFrame& operator=(EncryptedFrame&&) MAYBE_NOEXCEPT;
private:
friend class FrameCrypto;
EncryptedFrame();
OSP_DISALLOW_COPY_AND_ASSIGN(EncryptedFrame);
};
// Encrypts EncodedFrames before sending, or decrypts EncryptedFrames that have
// been received.
class FrameCrypto {
public:
// Construct with the given 16-bytes AES key and IV mask. Both arguments
// should be randomly-generated for each new streaming session.
// GenerateRandomBytes() can be used to create them.
FrameCrypto(const std::array<uint8_t, 16>& aes_key,
const std::array<uint8_t, 16>& cast_iv_mask);
~FrameCrypto();
EncryptedFrame Encrypt(const EncodedFrame& encoded_frame) const;
EncodedFrame Decrypt(const EncryptedFrame& encrypted_frame) const;
// Returns random bytes from a cryptographically-secure RNG source.
static std::array<uint8_t, 16> GenerateRandomBytes();
private:
// The 244-byte AES_KEY struct, derived from the |aes_key| passed to the ctor,
// and initialized by boringssl's AES_set_encrypt_key() function.
const AES_KEY aes_key_;
// Random bytes used in the custom heuristic to generate a different
// initialization vector for each frame.
const std::array<uint8_t, 16> cast_iv_mask_;
// AES-CTR is symmetric. Thus, the "meat" of both Encrypt() and Decrypt() is
// the same.
std::vector<uint8_t> EncryptCommon(FrameId frame_id,
const std::vector<uint8_t>& in) const;
};
} // namespace cast_streaming
} // namespace openscreen
#endif // STREAMING_CAST_FRAME_CRYPTO_H_
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