text: // 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 <string>
  
  #include "openssl/cmac.h"
  #include "openssl/err.h"
  #include "tink/mac.h"
  #include "tink/subtle/common_enums.h"
  #include "tink/subtle/subtle_util_boringssl.h"
  #include "tink/util/errors.h"
  #include "tink/util/status.h"
  #include "tink/util/statusor.h"
  
  namespace crypto {
  namespace tink {
  namespace subtle {
  
  // static
  util::StatusOr<std::unique_ptr<Mac>> AesCmacBoringSsl::New(
      const std::string& key_value, uint32_t tag_size) {
    if (key_value.size() != kSmallKeySize && key_value.size() != kBigKeySize) {
      return util::Status(util::error::INTERNAL, "invalid key size");
    }
    if (tag_size > kMaxTagSize) {
      return util::Status(util::error::INTERNAL, "invalid tag size");
    }
    std::unique_ptr<Mac> cmac(new AesCmacBoringSsl(key_value, tag_size));
    return std::move(cmac);
  }
  
  AesCmacBoringSsl::AesCmacBoringSsl(const std::string& key_value,
                                     uint32_t tag_size)
      : key_value_(key_value), tag_size_(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 = SubtleUtilBoringSSL::EnsureNonNull(data);
  
    uint8_t buf[kMaxTagSize];
    const int res =
        AES_CMAC(buf, reinterpret_cast<const uint8_t*>(key_value_.data()),
                 key_value_.size(), reinterpret_cast<const uint8_t*>(data.data()),
                 data.size());
    if (res == 0) {
      return util::Status(util::error::INTERNAL,
                          "BoringSSL failed to compute CMAC");
    }
    return std::string(reinterpret_cast<char*>(buf), tag_size_);
  }
  
  util::Status AesCmacBoringSsl::VerifyMac(absl::string_view mac,
                                           absl::string_view data) const {
    // BoringSSL expects a non-null pointer for data,
    // regardless of whether the size is 0.
    data = SubtleUtilBoringSSL::EnsureNonNull(data);
  
    if (mac.size() != tag_size_) {
      return util::Status(util::error::INVALID_ARGUMENT, "incorrect tag size");
    }
    uint8_t buf[kMaxTagSize];
    const int res =
        AES_CMAC(buf, reinterpret_cast<const uint8_t*>(key_value_.data()),
                 key_value_.size(), reinterpret_cast<const uint8_t*>(data.data()),
                 data.size());
    if (res == 0) {
      return util::Status(util::error::INTERNAL,
                          "BoringSSL failed to compute CMAC");
    }
    uint8_t diff = 0;
    for (uint32_t i = 0; i < tag_size_; i++) {
      diff |= buf[i] ^ static_cast<uint8_t>(mac[i]);
    }
    if (diff == 0) {
      return util::Status::OK;
    } else {
      return util::Status(util::error::INVALID_ARGUMENT, "verification failed");
    }
  }
  
  }  // namespace subtle
  }  // namespace tink
  }  // namespace crypto
  