cc/subtle/xchacha20_poly1305_boringssl.cc

// Copyright 2018 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/xchacha20_poly1305_boringssl.h"

#include <string>
#include <vector>

#include "openssl/err.h"
#include "openssl/evp.h"
#include "tink/aead.h"
#include "tink/subtle/random.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 const bool IsValidKeySize(uint32_t size_in_bytes) {
  return size_in_bytes == 32;
}

XChacha20Poly1305BoringSsl::XChacha20Poly1305BoringSsl(
    absl::string_view key_value, const EVP_AEAD* aead)
    : key_(key_value), aead_(aead) {}

util::StatusOr<std::unique_ptr<Aead>> XChacha20Poly1305BoringSsl::New(
    absl::string_view key_value) {
  if (!IsValidKeySize(key_value.size())) {
    return util::Status(util::error::INTERNAL, "Invalid key size");
  }

  const EVP_AEAD* cipher = EVP_aead_xchacha20_poly1305();
  if (cipher == nullptr) {
    return util::Status(util::error::INTERNAL, "Failed to get EVP_AEAD");
  }

  std::unique_ptr<Aead> aead(new XChacha20Poly1305BoringSsl(key_value, cipher));
  return std::move(aead);
}

util::StatusOr<std::string> XChacha20Poly1305BoringSsl::Encrypt(
    absl::string_view plaintext, absl::string_view additional_data) const {
  bssl::UniquePtr<EVP_AEAD_CTX> ctx(
      EVP_AEAD_CTX_new(aead_, reinterpret_cast<const uint8_t*>(key_.data()),
                       key_.size(), TAG_SIZE));
  if (ctx.get() == nullptr) {
    return util::Status(util::error::INTERNAL,
                        "could not initialize EVP_AEAD_CTX");
  }

  // BoringSSL expects a non-null pointer for plaintext and additional_data,
  // regardless of whether the size is 0.
  plaintext = SubtleUtilBoringSSL::EnsureNonNull(plaintext);
  additional_data = SubtleUtilBoringSSL::EnsureNonNull(additional_data);

  const std::string nonce = Random::GetRandomBytes(NONCE_SIZE);
  if (nonce.size() != NONCE_SIZE) {
    return util::Status(util::error::INTERNAL,
                        "Failed to get enough random bytes for nonce");
  }

  size_t ciphertext_size = nonce.size() + plaintext.size() + TAG_SIZE;

  // Write the nonce in the output buffer.
  std::vector<uint8_t> ct(ciphertext_size + 1);
  memcpy(&ct[0], reinterpret_cast<const uint8_t*>(nonce.data()), nonce.size());
  size_t written = nonce.size();

  // Encrypt the plaintext and store it after the nonce.
  size_t out_len = 0;
  int ret = EVP_AEAD_CTX_seal(
      ctx.get(), &ct[written], &out_len, ciphertext_size - written,
      reinterpret_cast<const uint8_t*>(nonce.data()), nonce.size(),
      reinterpret_cast<const uint8_t*>(plaintext.data()), plaintext.size(),
      reinterpret_cast<const uint8_t*>(additional_data.data()),
      additional_data.size());
  if (ret != 1) {
    return util::Status(util::error::INTERNAL, "EVP_AEAD_CTX_seal failed");
  }
  written += out_len;

  // Verify that all the expected data has been written.
  if (written != ciphertext_size) {
    return util::Status(util::error::INTERNAL, "Incorrect ciphertext size");
  }
  return std::string(reinterpret_cast<const char*>(&ct[0]), written);
}

util::StatusOr<std::string> XChacha20Poly1305BoringSsl::Decrypt(
    absl::string_view ciphertext, absl::string_view additional_data) const {
  // BoringSSL expects a non-null pointer for additional_data,
  // regardless of whether the size is 0.
  additional_data = SubtleUtilBoringSSL::EnsureNonNull(additional_data);

  if (ciphertext.size() < NONCE_SIZE + TAG_SIZE) {
    return util::Status(util::error::INTERNAL, "Ciphertext too short");
  }

  bssl::UniquePtr<EVP_AEAD_CTX> ctx(
      EVP_AEAD_CTX_new(aead_, reinterpret_cast<const uint8_t*>(key_.data()),
                       key_.size(), TAG_SIZE));
  if (ctx.get() == nullptr) {
    return util::Status(util::error::INTERNAL,
                        "could not initialize EVP_AEAD_CTX");
  }

  size_t out_size = ciphertext.size() - NONCE_SIZE - TAG_SIZE;
  std::vector<uint8_t> out(out_size + 1);

  absl::string_view nonce = ciphertext.substr(0, NONCE_SIZE);
  absl::string_view encrypted =
      ciphertext.substr(NONCE_SIZE, out_size + TAG_SIZE);

  size_t len = 0;
  int ret = EVP_AEAD_CTX_open(
      ctx.get(), &out[0], &len, out_size,
      reinterpret_cast<const uint8_t*>(nonce.data()), nonce.size(),
      reinterpret_cast<const uint8_t*>(encrypted.data()), encrypted.size(),
      reinterpret_cast<const uint8_t*>(additional_data.data()),
      additional_data.size());
  if (ret != 1) {
    return util::Status(util::error::INTERNAL, "EVP_AEAD_CTX_open failed");
  }

  if (len != out_size) {
    return util::Status(util::error::INTERNAL, "Incorrect output size");
  }

  return std::string(reinterpret_cast<const char*>(&out[0]), out_size);
}

}  // namespace subtle
}  // namespace tink
}  // namespace crypto