cc/aead/aes_ctr_hmac_aead_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/aead/aes_ctr_hmac_aead_key_manager.h"

#include <map>

#include "absl/base/casts.h"
#include "tink/aead.h"
#include "tink/key_manager.h"
#include "tink/mac.h"
#include "tink/registry.h"
#include "tink/subtle/aes_ctr_boringssl.h"
#include "tink/subtle/encrypt_then_authenticate.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/aes_ctr_hmac_aead.pb.h"
#include "proto/tink.pb.h"

namespace crypto {
namespace tink {

using crypto::tink::util::Enums;
using crypto::tink::util::Status;
using crypto::tink::util::StatusOr;
using google::crypto::tink::AesCtrHmacAeadKey;
using google::crypto::tink::AesCtrHmacAeadKeyFormat;
using google::crypto::tink::HashType;
using google::crypto::tink::KeyData;

class AesCtrHmacAeadKeyFactory
    : public KeyFactoryBase<AesCtrHmacAeadKey, AesCtrHmacAeadKeyFormat> {
 public:
  AesCtrHmacAeadKeyFactory() = default;

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

 protected:
  StatusOr<std::unique_ptr<AesCtrHmacAeadKey>> NewKeyFromFormat(
      const AesCtrHmacAeadKeyFormat& aes_ctr_hmac_aead_key_format)
      const override {
    Status status =
        AesCtrHmacAeadKeyManager::Validate(aes_ctr_hmac_aead_key_format);
    if (!status.ok()) return status;

    auto aes_ctr_hmac_aead_key = absl::make_unique<AesCtrHmacAeadKey>();
    aes_ctr_hmac_aead_key->set_version(AesCtrHmacAeadKeyManager::kVersion);

    // Generate AesCtrKey.
    auto aes_ctr_key = aes_ctr_hmac_aead_key->mutable_aes_ctr_key();
    aes_ctr_key->set_version(AesCtrHmacAeadKeyManager::kVersion);
    *(aes_ctr_key->mutable_params()) =
        aes_ctr_hmac_aead_key_format.aes_ctr_key_format().params();
    aes_ctr_key->set_key_value(subtle::Random::GetRandomBytes(
        aes_ctr_hmac_aead_key_format.aes_ctr_key_format().key_size()));

    // Generate HmacKey.
    auto hmac_key = aes_ctr_hmac_aead_key->mutable_hmac_key();
    hmac_key->set_version(AesCtrHmacAeadKeyManager::kVersion);
    *(hmac_key->mutable_params()) =
        aes_ctr_hmac_aead_key_format.hmac_key_format().params();
    hmac_key->set_key_value(subtle::Random::GetRandomBytes(
        aes_ctr_hmac_aead_key_format.hmac_key_format().key_size()));

    return absl::implicit_cast<StatusOr<std::unique_ptr<AesCtrHmacAeadKey>>>(
        std::move(aes_ctr_hmac_aead_key));
  }
};

constexpr char AesCtrHmacAeadKeyManager::kHmacKeyType[];
constexpr uint32_t AesCtrHmacAeadKeyManager::kVersion;

const int kMinKeySizeInBytes = 16;
const int kMinIvSizeInBytes = 12;
const int kMinTagSizeInBytes = 10;

AesCtrHmacAeadKeyManager::AesCtrHmacAeadKeyManager()
    : key_factory_(absl::make_unique<AesCtrHmacAeadKeyFactory>()) {}

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

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

StatusOr<std::unique_ptr<Aead>> AesCtrHmacAeadKeyManager::GetPrimitiveFromKey(
    const AesCtrHmacAeadKey& aes_ctr_hmac_aead_key) const {
  Status status = Validate(aes_ctr_hmac_aead_key);
  if (!status.ok()) return status;
  auto aes_ctr_result = subtle::AesCtrBoringSsl::New(
      aes_ctr_hmac_aead_key.aes_ctr_key().key_value(),
      aes_ctr_hmac_aead_key.aes_ctr_key().params().iv_size());
  if (!aes_ctr_result.ok()) return aes_ctr_result.status();

  auto hmac_result = Registry::GetPrimitive<Mac>(
      kHmacKeyType, aes_ctr_hmac_aead_key.hmac_key());
  if (!hmac_result.ok()) return hmac_result.status();

  auto cipher_res = subtle::EncryptThenAuthenticate::New(
      std::move(aes_ctr_result.ValueOrDie()),
      std::move(hmac_result.ValueOrDie()),
      aes_ctr_hmac_aead_key.hmac_key().params().tag_size());
  if (!cipher_res.ok()) {
    return cipher_res.status();
  }
  return std::move(cipher_res.ValueOrDie());
}

// static
Status AesCtrHmacAeadKeyManager::Validate(const AesCtrHmacAeadKey& key) {
  Status status = ValidateVersion(key.version(), kVersion);
  if (!status.ok()) return status;

  // Validate AesCtrKey.
  auto aes_ctr_key = key.aes_ctr_key();
  uint32_t aes_key_size = aes_ctr_key.key_value().size();
  status = ValidateAesKeySize(aes_key_size);
  if (!status.ok()) {
    return status;
  }
  if (aes_ctr_key.params().iv_size() < kMinIvSizeInBytes ||
      aes_ctr_key.params().iv_size() > 16) {
    return ToStatusF(util::error::INVALID_ARGUMENT,
                     "Invalid AesCtrHmacAeadKey: IV size out of range.");
  }
  return Status::OK;
}

// static
Status AesCtrHmacAeadKeyManager::Validate(
    const AesCtrHmacAeadKeyFormat& key_format) {
  // Validate AesCtrKeyFormat.
  auto aes_ctr_key_format = key_format.aes_ctr_key_format();
  auto status = ValidateAesKeySize(aes_ctr_key_format.key_size());
  if (!status.ok()) {
    return status;
  }
  if (aes_ctr_key_format.params().iv_size() < kMinIvSizeInBytes ||
      aes_ctr_key_format.params().iv_size() > 16) {
    return ToStatusF(util::error::INVALID_ARGUMENT,
                     "Invalid AesCtrHmacAeadKeyFormat: IV size out of range.");
  }

  // Validate HmacKeyFormat.
  auto hmac_key_format = key_format.hmac_key_format();
  if (hmac_key_format.key_size() < kMinKeySizeInBytes) {
    return ToStatusF(
        util::error::INVALID_ARGUMENT,
        "Invalid AesCtrHmacAeadKeyFormat: HMAC key_size is too small.");
  }
  auto params = hmac_key_format.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;
}

}  // namespace tink
}  // namespace crypto