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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.
#include "cast/streaming/frame_crypto.h"
#include <random>
#include <utility>
#include "openssl/crypto.h"
#include "openssl/err.h"
#include "openssl/rand.h"
#include "util/big_endian.h"
#include "util/crypto/openssl_util.h"
#include "util/crypto/random_bytes.h"
namespace openscreen {
namespace cast {
EncryptedFrame::EncryptedFrame() {
data = absl::Span<uint8_t>(owned_data_);
}
EncryptedFrame::~EncryptedFrame() = default;
EncryptedFrame::EncryptedFrame(EncryptedFrame&& other) noexcept
: EncodedFrame(static_cast<EncodedFrame&&>(other)),
owned_data_(std::move(other.owned_data_)) {
data = absl::Span<uint8_t>(owned_data_);
other.data = absl::Span<uint8_t>{};
}
EncryptedFrame& EncryptedFrame::operator=(EncryptedFrame&& other) {
this->EncodedFrame::operator=(static_cast<EncodedFrame&&>(other));
owned_data_ = std::move(other.owned_data_);
data = absl::Span<uint8_t>(owned_data_);
other.data = absl::Span<uint8_t>{};
return *this;
}
FrameCrypto::FrameCrypto(const std::array<uint8_t, 16>& aes_key,
const std::array<uint8_t, 16>& cast_iv_mask)
: aes_key_{}, cast_iv_mask_(cast_iv_mask) {
// Ensure that the library has been initialized. CRYPTO_library_init() may be
// safely called multiple times during the life of a process.
CRYPTO_library_init();
// Initialize the 244-byte AES_KEY struct once, here at construction time. The
// const_cast<> is reasonable as this is a one-time-ctor-initialized value
// that will remain constant from here onward.
const int return_code = AES_set_encrypt_key(
aes_key.data(), aes_key.size() * 8, const_cast<AES_KEY*>(&aes_key_));
if (return_code != 0) {
ClearOpenSSLERRStack(CURRENT_LOCATION);
OSP_LOG_FATAL << "Failure when setting encryption key; unsafe to continue.";
OSP_NOTREACHED();
}
}
FrameCrypto::~FrameCrypto() = default;
EncryptedFrame FrameCrypto::Encrypt(const EncodedFrame& encoded_frame) const {
EncryptedFrame result;
encoded_frame.CopyMetadataTo(&result);
result.owned_data_.resize(encoded_frame.data.size());
result.data = absl::Span<uint8_t>(result.owned_data_);
EncryptCommon(encoded_frame.frame_id, encoded_frame.data, result.data);
return result;
}
void FrameCrypto::Decrypt(const EncryptedFrame& encrypted_frame,
EncodedFrame* encoded_frame) const {
encrypted_frame.CopyMetadataTo(encoded_frame);
// AES-CTC is symmetric. Thus, decryption back to the plaintext is the same as
// encrypting the ciphertext; and both are the same size.
if (encrypted_frame.data.size() < encoded_frame->data.size()) {
encoded_frame->data = absl::Span<uint8_t>(encoded_frame->data.data(),
encrypted_frame.data.size());
}
EncryptCommon(encrypted_frame.frame_id, encrypted_frame.data,
encoded_frame->data);
}
void FrameCrypto::EncryptCommon(FrameId frame_id,
absl::Span<const uint8_t> in,
absl::Span<uint8_t> out) const {
OSP_DCHECK(!frame_id.is_null());
OSP_DCHECK_EQ(in.size(), out.size());
// Compute the AES nonce for Cast Streaming payload encryption, which is based
// on the |frame_id|.
std::array<uint8_t, 16> aes_nonce{/* zero initialized */};
static_assert(AES_BLOCK_SIZE == sizeof(aes_nonce),
"AES_BLOCK_SIZE is not 16 bytes.");
WriteBigEndian<uint32_t>(frame_id.lower_32_bits(), aes_nonce.data() + 8);
for (size_t i = 0; i < aes_nonce.size(); ++i) {
aes_nonce[i] ^= cast_iv_mask_[i];
}
std::array<uint8_t, 16> ecount_buf{/* zero initialized */};
unsigned int block_offset = 0;
AES_ctr128_encrypt(in.data(), out.data(), in.size(), &aes_key_,
aes_nonce.data(), ecount_buf.data(), &block_offset);
}
} // namespace cast
} // namespace openscreen
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