cc/hybrid/ecies_aead_hkdf_dem_helper.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/hybrid/ecies_aead_hkdf_dem_helper.h"

#include <utility>

#include "absl/memory/memory.h"
#include "tink/aead.h"
#include "tink/key_manager.h"
#include "tink/registry.h"
#include "tink/util/errors.h"
#include "tink/util/protobuf_helper.h"
#include "tink/util/statusor.h"
#include "proto/aes_ctr_hmac_aead.pb.h"
#include "proto/aes_gcm.pb.h"
#include "proto/tink.pb.h"
#include "proto/xchacha20_poly1305.pb.h"

namespace crypto {
namespace tink {

using ::google::crypto::tink::AesCtrHmacAeadKey;
using ::google::crypto::tink::AesCtrHmacAeadKeyFormat;
using ::google::crypto::tink::AesGcmKey;
using ::google::crypto::tink::AesGcmKeyFormat;
using ::google::crypto::tink::KeyTemplate;
using ::google::crypto::tink::XChaCha20Poly1305Key;
using ::google::crypto::tink::XChaCha20Poly1305KeyFormat;

util::StatusOr<EciesAeadHkdfDemHelper::DemKeyParams>
EciesAeadHkdfDemHelper::GetKeyParams(const KeyTemplate& key_template) {
  const std::string& type_url = key_template.type_url();
  if (type_url == "type.googleapis.com/google.crypto.tink.AesGcmKey") {
    AesGcmKeyFormat key_format;
    if (!key_format.ParseFromString(key_template.value())) {
      return util::Status(util::error::INVALID_ARGUMENT,
                          "Invalid AesGcmKeyFormat in DEM key template");
    }
    return {{AES_GCM_KEY, key_format.key_size()}};
  }
  if (type_url == "type.googleapis.com/google.crypto.tink.AesCtrHmacAeadKey") {
    AesCtrHmacAeadKeyFormat key_format;
    if (!key_format.ParseFromString(key_template.value())) {
      return util::Status(util::error::INVALID_ARGUMENT,
                          "Invalid AesCtrHmacKeyFormat in DEM key template");
    }
    uint32_t dem_key_size = key_format.aes_ctr_key_format().key_size() +
                            key_format.hmac_key_format().key_size();
    return {{AES_CTR_HMAC_AEAD_KEY, dem_key_size,
             key_format.aes_ctr_key_format().key_size()}};
  }
  if (type_url ==
      "type.googleapis.com/google.crypto.tink.XChaCha20Poly1305Key") {
    if (!XChaCha20Poly1305KeyFormat().ParseFromString(key_template.value())) {
      return util::Status(util::error::INVALID_ARGUMENT,
                          "Invalid XChaCha20KeyFormat in DEM key template");
    }
    return {{XCHACHA20_POLY1305_KEY, 32}};
  }
  return ToStatusF(util::error::INVALID_ARGUMENT,
                     "Unsupported DEM key type '%s'.", type_url);
}

// static
util::StatusOr<std::unique_ptr<const EciesAeadHkdfDemHelper>>
EciesAeadHkdfDemHelper::New(const KeyTemplate& dem_key_template) {
  auto key_params_or = GetKeyParams(dem_key_template);
  if (!key_params_or.ok()) return key_params_or.status();
  DemKeyParams key_params = key_params_or.ValueOrDie();
  const std::string& dem_type_url = dem_key_template.type_url();
  auto key_manager_or = Registry::get_key_manager<Aead>(dem_type_url);
  if (!key_manager_or.ok()) {
    return ToStatusF(util::error::FAILED_PRECONDITION,
                     "No manager for DEM key type '%s' found in the registry.",
                     dem_type_url);
  }
  const KeyManager<Aead>* key_manager = key_manager_or.ValueOrDie();
  return {absl::WrapUnique(
      new EciesAeadHkdfDemHelper(key_manager, dem_key_template, key_params))};
}

util::StatusOr<std::unique_ptr<Aead>> EciesAeadHkdfDemHelper::GetAead(
    const util::SecretData& symmetric_key_value) const {
  if (symmetric_key_value.size() != key_params_.key_size_in_bytes) {
    return util::Status(util::error::INTERNAL,
                        "Wrong length of symmetric key.");
  }
  auto key_or = key_manager_->get_key_factory().NewKey(key_template_.value());
  if (!key_or.ok()) return key_or.status();
  auto key = std::move(key_or).ValueOrDie();
  if (!ReplaceKeyBytes(symmetric_key_value, key.get())) {
    return util::Status(util::error::INTERNAL, "Generation of DEM-key failed.");
  }
  auto aead_or = key_manager_->GetPrimitive(*key);
  ZeroKeyBytes(key.get());
  return aead_or;
}

bool EciesAeadHkdfDemHelper::ReplaceKeyBytes(
    const util::SecretData& key_bytes,
    portable_proto::MessageLite* proto) const {
  switch (key_params_.key_type) {
    case AES_GCM_KEY: {
      AesGcmKey* key = static_cast<AesGcmKey*>(proto);
      key->set_key_value(std::string(util::SecretDataAsStringView(key_bytes)));
      return true;
    }
    case AES_CTR_HMAC_AEAD_KEY: {
      AesCtrHmacAeadKey* key = static_cast<AesCtrHmacAeadKey*>(proto);
      auto aes_ctr_key = key->mutable_aes_ctr_key();
      aes_ctr_key->set_key_value(
          std::string(util::SecretDataAsStringView(key_bytes).substr(
              0, key_params_.aes_ctr_key_size_in_bytes)));
      auto hmac_key = key->mutable_hmac_key();
      hmac_key->set_key_value(
          std::string(util::SecretDataAsStringView(key_bytes).substr(
              key_params_.aes_ctr_key_size_in_bytes)));
      return true;
    }
    case XCHACHA20_POLY1305_KEY: {
      XChaCha20Poly1305Key* key = static_cast<XChaCha20Poly1305Key*>(proto);
      key->set_key_value(std::string(util::SecretDataAsStringView(key_bytes)));
      return true;
    }
  }
  return false;
}

void EciesAeadHkdfDemHelper::ZeroKeyBytes(
    portable_proto::MessageLite* proto) const {
  switch (key_params_.key_type) {
    case AES_GCM_KEY: {
      AesGcmKey* key = static_cast<AesGcmKey*>(proto);
      std::unique_ptr<std::string> key_value =
          absl::WrapUnique(key->release_key_value());
      util::SafeZeroString(key_value.get());
      break;
    }
    case AES_CTR_HMAC_AEAD_KEY: {
      AesCtrHmacAeadKey* key = static_cast<AesCtrHmacAeadKey*>(proto);
      std::unique_ptr<std::string> aes_ctr_key_value =
          absl::WrapUnique(key->mutable_aes_ctr_key()->release_key_value());
      util::SafeZeroString(aes_ctr_key_value.get());
      std::unique_ptr<std::string> hmac_key_value =
          absl::WrapUnique(key->mutable_hmac_key()->release_key_value());
      util::SafeZeroString(hmac_key_value.get());
      break;
    }
    case XCHACHA20_POLY1305_KEY: {
      XChaCha20Poly1305Key* key = static_cast<XChaCha20Poly1305Key*>(proto);
      std::unique_ptr<std::string> key_value =
          absl::WrapUnique(key->release_key_value());
      util::SafeZeroString(key_value.get());
      break;
    }
  }
}

}  // namespace tink
}  // namespace crypto