quic/core/crypto/p256_key_exchange.cc

// Copyright (c) 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "quic/core/crypto/p256_key_exchange.h"

#include <cstdint>
#include <cstring>
#include <memory>
#include <string>
#include <utility>

#include "absl/memory/memory.h"
#include "absl/strings/string_view.h"
#include "third_party/boringssl/src/include/openssl/ec.h"
#include "third_party/boringssl/src/include/openssl/ecdh.h"
#include "third_party/boringssl/src/include/openssl/err.h"
#include "third_party/boringssl/src/include/openssl/evp.h"
#include "quic/platform/api/quic_logging.h"

namespace quic {

P256KeyExchange::P256KeyExchange(bssl::UniquePtr<EC_KEY> private_key,
                                 const uint8_t* public_key)
    : private_key_(std::move(private_key)) {
  memcpy(public_key_, public_key, sizeof(public_key_));
}

P256KeyExchange::~P256KeyExchange() {}

// static
std::unique_ptr<P256KeyExchange> P256KeyExchange::New() {
  return New(P256KeyExchange::NewPrivateKey());
}

// static
std::unique_ptr<P256KeyExchange> P256KeyExchange::New(absl::string_view key) {
  if (key.empty()) {
    QUIC_DLOG(INFO) << "Private key is empty";
    return nullptr;
  }

  const uint8_t* keyp = reinterpret_cast<const uint8_t*>(key.data());
  bssl::UniquePtr<EC_KEY> private_key(
      d2i_ECPrivateKey(nullptr, &keyp, key.size()));
  if (!private_key.get() || !EC_KEY_check_key(private_key.get())) {
    QUIC_DLOG(INFO) << "Private key is invalid.";
    return nullptr;
  }

  uint8_t public_key[kUncompressedP256PointBytes];
  if (EC_POINT_point2oct(EC_KEY_get0_group(private_key.get()),
                         EC_KEY_get0_public_key(private_key.get()),
                         POINT_CONVERSION_UNCOMPRESSED, public_key,
                         sizeof(public_key), nullptr) != sizeof(public_key)) {
    QUIC_DLOG(INFO) << "Can't get public key.";
    return nullptr;
  }

  return absl::WrapUnique(
      new P256KeyExchange(std::move(private_key), public_key));
}

// static
std::string P256KeyExchange::NewPrivateKey() {
  bssl::UniquePtr<EC_KEY> key(EC_KEY_new_by_curve_name(NID_X9_62_prime256v1));
  if (!key.get() || !EC_KEY_generate_key(key.get())) {
    QUIC_DLOG(INFO) << "Can't generate a new private key.";
    return std::string();
  }

  int key_len = i2d_ECPrivateKey(key.get(), nullptr);
  if (key_len <= 0) {
    QUIC_DLOG(INFO) << "Can't convert private key to string";
    return std::string();
  }
  std::unique_ptr<uint8_t[]> private_key(new uint8_t[key_len]);
  uint8_t* keyp = private_key.get();
  if (!i2d_ECPrivateKey(key.get(), &keyp)) {
    QUIC_DLOG(INFO) << "Can't convert private key to string.";
    return std::string();
  }
  return std::string(reinterpret_cast<char*>(private_key.get()), key_len);
}

bool P256KeyExchange::CalculateSharedKeySync(
    absl::string_view peer_public_value,
    std::string* shared_key) const {
  if (peer_public_value.size() != kUncompressedP256PointBytes) {
    QUIC_DLOG(INFO) << "Peer public value is invalid";
    return false;
  }

  bssl::UniquePtr<EC_POINT> point(
      EC_POINT_new(EC_KEY_get0_group(private_key_.get())));
  if (!point.get() ||
      !EC_POINT_oct2point(/* also test if point is on curve */
                          EC_KEY_get0_group(private_key_.get()), point.get(),
                          reinterpret_cast<const uint8_t*>(
                              peer_public_value.data()),
                          peer_public_value.size(), nullptr)) {
    QUIC_DLOG(INFO) << "Can't convert peer public value to curve point.";
    return false;
  }

  uint8_t result[kP256FieldBytes];
  if (ECDH_compute_key(result, sizeof(result), point.get(), private_key_.get(),
                       nullptr) != sizeof(result)) {
    QUIC_DLOG(INFO) << "Can't compute ECDH shared key.";
    return false;
  }

  shared_key->assign(reinterpret_cast<char*>(result), sizeof(result));
  return true;
}

absl::string_view P256KeyExchange::public_value() const {
  return absl::string_view(reinterpret_cast<const char*>(public_key_),
                           sizeof(public_key_));
}

}  // namespace quic