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// Copyright 2017 Google Inc.
//
// 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
//
// http://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 "tink/subtle/aes_cmac_boringssl.h"
#include <cstdint>
#include <memory>
#include <string>
#include <utility>
#include "absl/memory/memory.h"
#include "absl/status/status.h"
#include "openssl/cmac.h"
#include "openssl/evp.h"
#include "tink/internal/aes_util.h"
#include "tink/internal/ssl_unique_ptr.h"
#include "tink/internal/util.h"
#include "tink/subtle/subtle_util.h"
#include "tink/util/errors.h"
#include "tink/util/status.h"
#include "tink/util/statusor.h"
namespace crypto {
namespace tink {
namespace subtle {
// CMAC key sizes in bytes.
// The small key size is used only to check RFC 4493's test vectors due to
// the attack described in
// https://www.math.uwaterloo.ca/~ajmeneze/publications/tightness.pdf. We
// check this restriction in AesCmacManager.
static constexpr size_t kSmallKeySize = 16;
static constexpr size_t kBigKeySize = 32;
static constexpr size_t kMaxTagSize = 16;
// static
util::StatusOr<std::unique_ptr<Mac>> AesCmacBoringSsl::New(util::SecretData key,
uint32_t tag_size) {
auto status = internal::CheckFipsCompatibility<AesCmacBoringSsl>();
if (!status.ok()) return status;
if (key.size() != kSmallKeySize && key.size() != kBigKeySize) {
return ToStatusF(absl::StatusCode::kInvalidArgument,
"Invalid key size: expected %d or %d, found %d",
kSmallKeySize, kBigKeySize, key.size());
}
if (tag_size > kMaxTagSize) {
return ToStatusF(absl::StatusCode::kInvalidArgument,
"Invalid tag size: expected lower than %d, found %d",
kMaxTagSize, tag_size);
}
return {absl::WrapUnique(new AesCmacBoringSsl(std::move(key), tag_size))};
}
util::StatusOr<std::string> AesCmacBoringSsl::ComputeMac(
absl::string_view data) const {
// BoringSSL expects a non-null pointer for data,
// regardless of whether the size is 0.
data = internal::EnsureStringNonNull(data);
std::string result;
ResizeStringUninitialized(&result, kMaxTagSize);
internal::SslUniquePtr<CMAC_CTX> context(CMAC_CTX_new());
util::StatusOr<const EVP_CIPHER*> cipher =
internal::GetAesCbcCipherForKeySize(key_.size());
if (!cipher.ok()) {
return cipher.status();
}
size_t len = 0;
const uint8_t* key_ptr = reinterpret_cast<const uint8_t*>(&key_[0]);
const uint8_t* data_ptr = reinterpret_cast<const uint8_t*>(data.data());
uint8_t* result_ptr = reinterpret_cast<uint8_t*>(&result[0]);
if (CMAC_Init(context.get(), key_ptr, key_.size(), *cipher, nullptr) <= 0 ||
CMAC_Update(context.get(), data_ptr, data.size()) <= 0 ||
CMAC_Final(context.get(), result_ptr, &len) == 0) {
return util::Status(absl::StatusCode::kInternal, "Failed to compute CMAC");
}
result.resize(tag_size_);
return result;
}
util::Status AesCmacBoringSsl::VerifyMac(absl::string_view mac,
absl::string_view data) const {
if (mac.size() != tag_size_) {
return ToStatusF(absl::StatusCode::kInvalidArgument,
"Incorrect tag size: expected %d, found %d", tag_size_,
mac.size());
}
util::StatusOr<std::string> computed_mac = ComputeMac(data);
if (!computed_mac.ok()) return computed_mac.status();
if (CRYPTO_memcmp(computed_mac->data(), mac.data(), tag_size_) != 0) {
return util::Status(absl::StatusCode::kInvalidArgument,
"CMAC verification failed");
}
return util::OkStatus();
}
} // namespace subtle
} // namespace tink
} // namespace crypto
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