cc/mac/hmac_key_manager.cc

// 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/mac/hmac_key_manager.h"

#include <map>

#include "absl/strings/string_view.h"
#include "tink/mac.h"
#include "tink/key_manager.h"
#include "tink/subtle/hmac_boringssl.h"
#include "tink/subtle/random.h"
#include "tink/util/enums.h"
#include "tink/util/errors.h"
#include "tink/util/protobuf_helper.h"
#include "tink/util/status.h"
#include "tink/util/statusor.h"
#include "tink/util/validation.h"
#include "proto/common.pb.h"
#include "proto/hmac.pb.h"
#include "proto/tink.pb.h"

namespace crypto {
namespace tink {

using google::crypto::tink::HashType;
using google::crypto::tink::HmacKey;
using google::crypto::tink::HmacKeyFormat;
using google::crypto::tink::HmacParams;
using google::crypto::tink::KeyData;
using google::crypto::tink::KeyTemplate;
using portable_proto::MessageLite;
using crypto::tink::util::Enums;
using crypto::tink::util::Status;
using crypto::tink::util::StatusOr;

class HmacKeyFactory : public KeyFactoryBase<HmacKey, HmacKeyFormat> {
 public:
  HmacKeyFactory() {}

  KeyData::KeyMaterialType key_material_type() const override {
    return KeyData::SYMMETRIC;
  }

 protected:
  StatusOr<std::unique_ptr<HmacKey>> NewKeyFromFormat(
      const HmacKeyFormat& hmac_key_format) const override;
};

StatusOr<std::unique_ptr<HmacKey>> HmacKeyFactory::NewKeyFromFormat(
    const HmacKeyFormat& hmac_key_format) const {
  Status status =  HmacKeyManager::Validate(hmac_key_format);
  if (!status.ok()) return status;
  auto hmac_key = absl::make_unique<HmacKey>();
  hmac_key->set_version(HmacKeyManager::kVersion);
  *(hmac_key->mutable_params()) = hmac_key_format.params();
  hmac_key->set_key_value(
      subtle::Random::GetRandomBytes(hmac_key_format.key_size()));
  return absl::implicit_cast<StatusOr<std::unique_ptr<HmacKey>>>(
        std::move(hmac_key));
}

constexpr uint32_t HmacKeyManager::kVersion;

const int kMinKeySizeInBytes = 16;
const int kMinTagSizeInBytes = 10;

HmacKeyManager::HmacKeyManager() : key_factory_(new HmacKeyFactory()) {}

uint32_t HmacKeyManager::get_version() const {
  return kVersion;
}

const KeyFactory& HmacKeyManager::get_key_factory() const {
  return *key_factory_;
}

StatusOr<std::unique_ptr<Mac>> HmacKeyManager::GetPrimitiveFromKey(
    const HmacKey& hmac_key) const {
  Status status = Validate(hmac_key);
  if (!status.ok()) return status;
  auto hmac_result = subtle::HmacBoringSsl::New(
      util::Enums::ProtoToSubtle(hmac_key.params().hash()),
      hmac_key.params().tag_size(),
      hmac_key.key_value());
  if (!hmac_result.ok()) return hmac_result.status();
  return std::move(hmac_result.ValueOrDie());
}

// static
Status HmacKeyManager::Validate(const HmacParams& params) {
  if (params.tag_size() < kMinTagSizeInBytes) {
    return ToStatusF(util::error::INVALID_ARGUMENT,
                     "Invalid HmacParams: tag_size %d is too small.",
                     params.tag_size());
  }
  std::map<HashType, uint32_t> max_tag_size = {{HashType::SHA1, 20},
                                               {HashType::SHA256, 32},
                                               {HashType::SHA512, 64}};
  if (max_tag_size.find(params.hash()) == max_tag_size.end()) {
    return ToStatusF(util::error::INVALID_ARGUMENT,
                     "Invalid HmacParams: HashType '%s' not supported.",
                     Enums::HashName(params.hash()));
  } else {
    if (params.tag_size() > max_tag_size[params.hash()]) {
      return ToStatusF(util::error::INVALID_ARGUMENT,
          "Invalid HmacParams: tag_size %d is too big for HashType '%s'.",
          params.tag_size(), Enums::HashName(params.hash()));
    }
  }
  return Status::OK;
}

// static
Status HmacKeyManager::Validate(const HmacKey& key) {
  Status status = ValidateVersion(key.version(), kVersion);
  if (!status.ok()) return status;
  if (key.key_value().size() < kMinKeySizeInBytes) {
      return ToStatusF(util::error::INVALID_ARGUMENT,
                       "Invalid HmacKey: key_value is too short.");
  }
  return Validate(key.params());
}

// static
Status HmacKeyManager::Validate(const HmacKeyFormat& key_format) {
  if (key_format.key_size() < kMinKeySizeInBytes) {
      return ToStatusF(util::error::INVALID_ARGUMENT,
                       "Invalid HmacKeyFormat: key_size is too small.");
  }
  return Validate(key_format.params());
}

}  // namespace tink
}  // namespace crypto