test_network_crypto.cpp

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/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <https://www.gnu.org/licenses/old-licenses/gpl-2.0>.
 */

 
#include "../stdafx.h"
 
#include "../3rdparty/catch2/catch.hpp"
 
#include "../core/format.hpp"
#include "../network/network_crypto_internal.h"
#include "../network/core/packet.h"
#include "../string_func.h"
 
#include "../safeguards.h"
 
/* The length of the hexadecimal representation of a X25519 key must fit in the key length. */
static_assert(NETWORK_SECRET_KEY_LENGTH >= X25519_KEY_SIZE * 2 + 1);
static_assert(NETWORK_PUBLIC_KEY_LENGTH >= X25519_KEY_SIZE * 2 + 1);
 
class MockNetworkSocketHandler : public NetworkSocketHandler {
public:
  MockNetworkSocketHandler(std::unique_ptr<NetworkEncryptionHandler> &&receive = {}, std::unique_ptr<NetworkEncryptionHandler> &&send = {})
  {
    this->receive_encryption_handler = std::move(receive);
    this->send_encryption_handler = std::move(send);
  }
};
 
static MockNetworkSocketHandler mock_socket_handler;
 
static std::tuple<Packet, bool> CreatePacketForReading(Packet &source, MockNetworkSocketHandler *socket_handler)
{
  source.PrepareToSend();
 
  Packet dest(socket_handler, COMPAT_MTU, source.Size());
 
  auto transfer_in = [&source](std::span<uint8_t> dest_data) {
    auto transfer_out = [&dest_data](std::span<const uint8_t> source_data) {
      std::ranges::copy(source_data, dest_data.begin());
      return source_data.size();
    };
    return source.TransferOutWithLimit(transfer_out, dest_data.size());
  };
  dest.TransferIn(transfer_in);
 
  bool valid = dest.PrepareToRead();
  dest.Recv_uint8(); // Ignore the type
  return { dest, valid };
}
 
class TestPasswordRequestHandler : public NetworkAuthenticationPasswordRequestHandler {
private:
  std::string password;
public:
  TestPasswordRequestHandler(std::string &password) : password(password) {}
  void SendResponse() override {}
  void AskUserForPassword(std::shared_ptr<NetworkAuthenticationPasswordRequest> request) override { request->Reply(this->password); }
};
 
static void TestAuthentication(NetworkAuthenticationServerHandler &server, NetworkAuthenticationClientHandler &client,
    NetworkAuthenticationServerHandler::ResponseResult expected_response_result,
    NetworkAuthenticationClientHandler::RequestResult expected_request_result)
{
  Packet request(&mock_socket_handler, PacketType{});
  server.SendRequest(request);
 
  bool valid;
  std::tie(request, valid) = CreatePacketForReading(request, &mock_socket_handler);
  CHECK(valid);
  CHECK(client.ReceiveRequest(request) == expected_request_result);
 
  Packet response(&mock_socket_handler, PacketType{});
  client.SendResponse(response);
 
  std::tie(response, valid) = CreatePacketForReading(response, &mock_socket_handler);
  CHECK(valid);
  CHECK(server.ReceiveResponse(response) == expected_response_result);
}
 
 
TEST_CASE("Authentication_KeyExchangeOnly")
{
  X25519KeyExchangeOnlyServerHandler server(X25519SecretKey::CreateRandom());
  X25519KeyExchangeOnlyClientHandler client(X25519SecretKey::CreateRandom());
 
  TestAuthentication(server, client, NetworkAuthenticationServerHandler::ResponseResult::Authenticated, NetworkAuthenticationClientHandler::RequestResult::ReadyForResponse);
}
 
 
static void TestAuthenticationPAKE(std::string server_password, std::string client_password,
    NetworkAuthenticationServerHandler::ResponseResult expected_response_result)
{
  NetworkAuthenticationDefaultPasswordProvider server_password_provider(server_password);
  X25519PAKEServerHandler server(X25519SecretKey::CreateRandom(), &server_password_provider);
  X25519PAKEClientHandler client(X25519SecretKey::CreateRandom(), std::make_shared<TestPasswordRequestHandler>(client_password));
 
  TestAuthentication(server, client, expected_response_result, NetworkAuthenticationClientHandler::RequestResult::AwaitUserInput);
}
 
TEST_CASE("Authentication_PAKE")
{
  SECTION("Correct password") {
    TestAuthenticationPAKE("sikrit", "sikrit", NetworkAuthenticationServerHandler::ResponseResult::Authenticated);
  }
 
  SECTION("Empty password") {
    TestAuthenticationPAKE("", "", NetworkAuthenticationServerHandler::ResponseResult::Authenticated);
  }
 
  SECTION("Wrong password") {
    TestAuthenticationPAKE("sikrit", "secret", NetworkAuthenticationServerHandler::ResponseResult::NotAuthenticated);
  }
}
 
 
static void TestAuthenticationAuthorizedKey(const X25519SecretKey &client_secret_key, const X25519PublicKey &server_expected_public_key,
    NetworkAuthenticationServerHandler::ResponseResult expected_response_result)
{
  NetworkAuthorizedKeys authorized_keys;
  authorized_keys.Add(FormatArrayAsHex(server_expected_public_key));
 
  NetworkAuthenticationDefaultAuthorizedKeyHandler authorized_key_handler(authorized_keys);
  X25519AuthorizedKeyServerHandler server(X25519SecretKey::CreateRandom(), &authorized_key_handler);
  X25519AuthorizedKeyClientHandler client(client_secret_key);
 
  TestAuthentication(server, client, expected_response_result, NetworkAuthenticationClientHandler::RequestResult::ReadyForResponse);
}
 
TEST_CASE("Authentication_AuthorizedKey")
{
  auto client_secret_key = X25519SecretKey::CreateRandom();
  auto valid_client_public_key = client_secret_key.CreatePublicKey();
  auto invalid_client_public_key = X25519SecretKey::CreateRandom().CreatePublicKey();
 
  SECTION("Correct public key") {
    TestAuthenticationAuthorizedKey(client_secret_key, valid_client_public_key, NetworkAuthenticationServerHandler::ResponseResult::Authenticated);
  }
 
  SECTION("Incorrect public key") {
    TestAuthenticationAuthorizedKey(client_secret_key, invalid_client_public_key, NetworkAuthenticationServerHandler::ResponseResult::NotAuthenticated);
  }
}
 
 
TEST_CASE("Authentication_Combined")
{
  auto client_secret_key = X25519SecretKey::CreateRandom();
  std::string client_secret_key_str = FormatArrayAsHex(client_secret_key);
  auto client_public_key = client_secret_key.CreatePublicKey();
  std::string client_public_key_str = FormatArrayAsHex(client_public_key);
 
  NetworkAuthorizedKeys valid_authorized_keys;
  valid_authorized_keys.Add(client_public_key_str);
  NetworkAuthenticationDefaultAuthorizedKeyHandler valid_authorized_key_handler(valid_authorized_keys);
 
  NetworkAuthorizedKeys invalid_authorized_keys;
  invalid_authorized_keys.Add("not-a-valid-authorized-key");
  NetworkAuthenticationDefaultAuthorizedKeyHandler invalid_authorized_key_handler(invalid_authorized_keys);
 
  NetworkAuthorizedKeys no_authorized_keys;
  NetworkAuthenticationDefaultAuthorizedKeyHandler no_authorized_key_handler(no_authorized_keys);
 
  std::string no_password = "";
  NetworkAuthenticationDefaultPasswordProvider no_password_provider(no_password);
  std::string valid_password = "sikrit";
  NetworkAuthenticationDefaultPasswordProvider valid_password_provider(valid_password);
  std::string invalid_password = "secret";
  NetworkAuthenticationDefaultPasswordProvider invalid_password_provider(invalid_password);
 
  auto client = NetworkAuthenticationClientHandler::Create(std::make_shared<TestPasswordRequestHandler>(valid_password), client_secret_key_str, client_public_key_str);
 
  SECTION("Invalid authorized keys, invalid password") {
    auto server = NetworkAuthenticationServerHandler::Create(&invalid_password_provider, &invalid_authorized_key_handler);
 
    TestAuthentication(*server, *client, NetworkAuthenticationServerHandler::ResponseResult::RetryNextMethod, NetworkAuthenticationClientHandler::RequestResult::ReadyForResponse);
    TestAuthentication(*server, *client, NetworkAuthenticationServerHandler::ResponseResult::NotAuthenticated, NetworkAuthenticationClientHandler::RequestResult::AwaitUserInput);
  }
 
  SECTION("Invalid authorized keys, valid password") {
    auto server = NetworkAuthenticationServerHandler::Create(&valid_password_provider, &invalid_authorized_key_handler);
 
    TestAuthentication(*server, *client, NetworkAuthenticationServerHandler::ResponseResult::RetryNextMethod, NetworkAuthenticationClientHandler::RequestResult::ReadyForResponse);
    TestAuthentication(*server, *client, NetworkAuthenticationServerHandler::ResponseResult::Authenticated, NetworkAuthenticationClientHandler::RequestResult::AwaitUserInput);
  }
 
  SECTION("Valid authorized keys, valid password") {
    auto server = NetworkAuthenticationServerHandler::Create(&valid_password_provider, &valid_authorized_key_handler);
 
    TestAuthentication(*server, *client, NetworkAuthenticationServerHandler::ResponseResult::Authenticated, NetworkAuthenticationClientHandler::RequestResult::ReadyForResponse);
  }
 
  SECTION("No authorized keys, invalid password") {
    auto server = NetworkAuthenticationServerHandler::Create(&invalid_password_provider, &no_authorized_key_handler);
 
    TestAuthentication(*server, *client, NetworkAuthenticationServerHandler::ResponseResult::NotAuthenticated, NetworkAuthenticationClientHandler::RequestResult::AwaitUserInput);
  }
 
  SECTION("No authorized keys, valid password") {
    auto server = NetworkAuthenticationServerHandler::Create(&valid_password_provider, &no_authorized_key_handler);
 
    TestAuthentication(*server, *client, NetworkAuthenticationServerHandler::ResponseResult::Authenticated, NetworkAuthenticationClientHandler::RequestResult::AwaitUserInput);
  }
 
  SECTION("No authorized keys, no password") {
    auto server = NetworkAuthenticationServerHandler::Create(&no_password_provider, &no_authorized_key_handler);
 
    TestAuthentication(*server, *client, NetworkAuthenticationServerHandler::ResponseResult::Authenticated, NetworkAuthenticationClientHandler::RequestResult::ReadyForResponse);
  }
}
 
 
static void CheckEncryption(MockNetworkSocketHandler *sending_socket_handler, MockNetworkSocketHandler *receiving_socket_handler)
{
  PacketType sent_packet_type{ 1 };
  uint64_t sent_value = 0x1234567890ABCDEF;
  std::set<PacketType> encrypted_packet_types;
 
  for (int i = 0; i < 10; i++) {
    Packet request(sending_socket_handler, sent_packet_type);
    request.Send_uint64(sent_value);
 
    auto [response, valid] = CreatePacketForReading(request, receiving_socket_handler);
    CHECK(valid);
    CHECK(response.Recv_uint64() == sent_value);
 
    encrypted_packet_types.insert(request.GetPacketType());
  }
  /*
   * Check whether it looks like encryption has happened. This is done by checking the value
   * of the packet type after encryption. If after a few iterations more than one encrypted
   * value has been seen, then we know that some type of encryption/scrambling is happening.
   *
   * Technically this check could fail erroneously when 16 subsequent encryptions yield the
   * same encrypted packet type. However, with encryption that byte should have random value
   * value, so the chance of this happening are tiny given enough iterations.
   * Roughly in the order of 2**((iterations - 1) * 8), which with 10 iterations is in the
   * one-in-sextillion (10**21) order of magnitude.
   */
  CHECK(encrypted_packet_types.size() != 1);
 
}
 
TEST_CASE("Encryption handling")
{
  X25519KeyExchangeOnlyServerHandler server(X25519SecretKey::CreateRandom());
  X25519KeyExchangeOnlyClientHandler client(X25519SecretKey::CreateRandom());
 
  TestAuthentication(server, client, NetworkAuthenticationServerHandler::ResponseResult::Authenticated, NetworkAuthenticationClientHandler::RequestResult::ReadyForResponse);
 
  Packet packet(&mock_socket_handler, PacketType{});
  server.SendEnableEncryption(packet);
 
  bool valid;
  std::tie(packet, valid) = CreatePacketForReading(packet, &mock_socket_handler);
  CHECK(valid);
  CHECK(client.ReceiveEnableEncryption(packet));
 
  MockNetworkSocketHandler server_socket_handler(server.CreateClientToServerEncryptionHandler(), server.CreateServerToClientEncryptionHandler());
  MockNetworkSocketHandler client_socket_handler(client.CreateServerToClientEncryptionHandler(), client.CreateClientToServerEncryptionHandler());
 
  SECTION("Encryption happening client -> server") {
    CheckEncryption(&client_socket_handler, &server_socket_handler);
  }
 
  SECTION("Encryption happening server -> client") {
    CheckEncryption(&server_socket_handler, &client_socket_handler);
  }
 
  SECTION("Unencrypted packet sent causes invalid read packet") {
    Packet request(&mock_socket_handler, PacketType{});
    request.Send_uint64(0);
 
    auto [response, valid] = CreatePacketForReading(request, &client_socket_handler);
    CHECK(!valid);
  }
}