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/*
* Copyright 2018 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "fcp/secagg/shared/aes_gcm_encryption.h"
#include <cstdint>
#include <string>
#include "fcp/base/monitoring.h"
#include "fcp/secagg/shared/aes_key.h"
#include "fcp/secagg/shared/prng.h"
#include "openssl/cipher.h"
#include "openssl/evp.h"
#include "openssl/rand.h"
namespace fcp {
namespace secagg {
constexpr int kIvSize = 12;
constexpr int kTagSize = 16;
AesGcmEncryption::AesGcmEncryption() {}
std::string AesGcmEncryption::Encrypt(const AesKey& key,
const std::string& plaintext) {
FCP_CHECK(key.size() != 0) << "Encrypt called with blank key.";
FCP_CHECK(key.size() == AesKey::kSize)
<< "Encrypt called with key of " << key.size()
<< " bytes, but 32 bytes are required.";
std::vector<uint8_t> ciphertext_buffer;
ciphertext_buffer.resize(kIvSize + plaintext.length() + kTagSize);
FCP_CHECK(RAND_bytes(ciphertext_buffer.data(), kIvSize));
// ScopedEVP_AEAD_CTX will automatically call EVP_AEAD_CTX_cleanup when going
// out of scope.
bssl::ScopedEVP_AEAD_CTX ctx;
FCP_CHECK(EVP_AEAD_CTX_init(ctx.get(), EVP_aead_aes_256_gcm(),
const_cast<uint8_t*>(key.data()), key.size(),
EVP_AEAD_DEFAULT_TAG_LENGTH, nullptr) == 1);
size_t len;
FCP_CHECK(EVP_AEAD_CTX_seal(
ctx.get(), ciphertext_buffer.data() + kIvSize, &len,
plaintext.size() + kTagSize, ciphertext_buffer.data(), kIvSize,
reinterpret_cast<const uint8_t*>(plaintext.c_str()),
plaintext.size(), nullptr, 0) == 1);
return std::string(ciphertext_buffer.begin(), ciphertext_buffer.end());
}
StatusOr<std::string> AesGcmEncryption::Decrypt(const AesKey& key,
const std::string& ciphertext) {
FCP_CHECK(key.size() != 0) << "Decrypt called with blank key.";
FCP_CHECK(key.size() == AesKey::kSize)
<< "Decrypt called with key of " << key.size()
<< " bytes, but 32 bytes are required.";
if (ciphertext.size() < kIvSize + kTagSize) {
return FCP_STATUS(DATA_LOSS) << "Ciphertext is too short.";
}
size_t len;
std::vector<uint8_t> plaintext_buffer;
plaintext_buffer.resize(ciphertext.size() - kIvSize - kTagSize);
// ScopedEVP_AEAD_CTX will automatically call EVP_AEAD_CTX_cleanup when going
// out of scope.
bssl::ScopedEVP_AEAD_CTX ctx;
FCP_CHECK(EVP_AEAD_CTX_init(ctx.get(), EVP_aead_aes_256_gcm(),
const_cast<uint8_t*>(key.data()), key.size(),
EVP_AEAD_DEFAULT_TAG_LENGTH, nullptr) == 1);
if (EVP_AEAD_CTX_open(
ctx.get(), plaintext_buffer.data(), &len, plaintext_buffer.size(),
reinterpret_cast<const uint8_t*>(ciphertext.data()), kIvSize,
reinterpret_cast<const uint8_t*>(ciphertext.data() + kIvSize),
ciphertext.size() - kIvSize, nullptr, 0) != 1) {
return FCP_STATUS(DATA_LOSS) << "Verification of ciphertext failed.";
}
return std::string(plaintext_buffer.begin(), plaintext_buffer.end());
}
} // namespace secagg
} // namespace fcp
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