cc/subtle/encrypt_then_authenticate_test.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/subtle/encrypt_then_authenticate.h"

#include <memory>
#include <string>
#include <utility>
#include <vector>

#include "gtest/gtest.h"
#include "absl/strings/string_view.h"
#include "tink/subtle/aes_ctr_boringssl.h"
#include "tink/subtle/common_enums.h"
#include "tink/subtle/hmac_boringssl.h"
#include "tink/subtle/random.h"
#include "tink/util/secret_data.h"
#include "tink/util/statusor.h"
#include "tink/util/test_util.h"

namespace crypto {
namespace tink {
namespace subtle {
namespace {

// Copied from
// https://tools.ietf.org/html/draft-mcgrew-aead-aes-cbc-hmac-sha2-05.
// We use CTR but the RFC uses CBC mode, so it's not possible to compare
// plaintexts. However, the tests are still valueable to ensure that we correcly
// compute HMAC over ciphertext and associated_data.
struct TestVector {
  absl::string_view mac_key;
  absl::string_view enc_key;
  absl::string_view ciphertext;
  absl::string_view associated_data;
  HashType hash_type;
  int iv_size;
  int tag_size;
};

constexpr TestVector test_vectors[] = {
    {"000102030405060708090a0b0c0d0e0f", "101112131415161718191a1b1c1d1e1f",
     "1af38c2dc2b96ffdd86694092341bc04"
     "c80edfa32ddf39d5ef00c0b468834279"
     "a2e46a1b8049f792f76bfe54b903a9c9"
     "a94ac9b47ad2655c5f10f9aef71427e2"
     "fc6f9b3f399a221489f16362c7032336"
     "09d45ac69864e3321cf82935ac4096c8"
     "6e133314c54019e8ca7980dfa4b9cf1b"
     "384c486f3a54c51078158ee5d79de59f"
     "bd34d848b3d69550a67646344427ade5"
     "4b8851ffb598f7f80074b9473c82e2db"
     "652c3fa36b0a7c5b3219fab3a30bc1c4",
     "546865207365636f6e64207072696e63"
     "69706c65206f66204175677573746520"
     "4b6572636b686f666673",
     HashType::SHA256, 16, 16},
    {"000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f",
     "202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f",
     "1af38c2dc2b96ffdd86694092341bc04"
     "4affaaadb78c31c5da4b1b590d10ffbd"
     "3dd8d5d302423526912da037ecbcc7bd"
     "822c301dd67c373bccb584ad3e9279c2"
     "e6d12a1374b77f077553df829410446b"
     "36ebd97066296ae6427ea75c2e0846a1"
     "1a09ccf5370dc80bfecbad28c73f09b3"
     "a3b75e662a2594410ae496b2e2e6609e"
     "31e6e02cc837f053d21f37ff4f51950b"
     "be2638d09dd7a4930930806d0703b1f6"
     "4dd3b4c088a7f45c216839645b2012bf"
     "2e6269a8c56a816dbc1b267761955bc5",
     "546865207365636f6e64207072696e63"
     "69706c65206f66204175677573746520"
     "4b6572636b686f666673",
     HashType::SHA512, 16, 32},
};

util::StatusOr<std::unique_ptr<Aead>> createAead2(
    util::SecretData encryption_key, int iv_size, util::SecretData mac_key,
    uint8_t tag_size, HashType hash_type) {
  auto ind_cipher_res =
      AesCtrBoringSsl::New(std::move(encryption_key), iv_size);
  if (!ind_cipher_res.ok()) {
    return ind_cipher_res.status();
  }

  auto mac_res = HmacBoringSsl::New(hash_type, tag_size, std::move(mac_key));
  if (!mac_res.ok()) {
    return mac_res.status();
  }
  auto cipher_res = EncryptThenAuthenticate::New(
      std::move(ind_cipher_res.value()), std::move(mac_res.value()), tag_size);
  if (!cipher_res.ok()) {
    return cipher_res.status();
  }
  return std::move(cipher_res.value());
}

util::StatusOr<std::unique_ptr<Aead>> createAead(int encryption_key_size,
                                                 int iv_size, int mac_key_size,
                                                 int tag_size,
                                                 HashType hash_type) {
  util::SecretData encryption_key =
      Random::GetRandomKeyBytes(encryption_key_size);
  util::SecretData mac_key = Random::GetRandomKeyBytes(mac_key_size);
  return createAead2(std::move(encryption_key), iv_size, std::move(mac_key),
                     tag_size, hash_type);
}

TEST(AesGcmBoringSslTest, testRfcVectors) {
  for (const TestVector& test : test_vectors) {
    util::SecretData mac_key =
        util::SecretDataFromStringView(test::HexDecodeOrDie(test.mac_key));
    util::SecretData enc_key =
        util::SecretDataFromStringView(test::HexDecodeOrDie(test.enc_key));
    std::string ct = test::HexDecodeOrDie(test.ciphertext);
    std::string associated_data = test::HexDecodeOrDie(test.associated_data);
    auto res = createAead2(std::move(enc_key), test.iv_size, std::move(mac_key),
                           test.tag_size, test.hash_type);
    EXPECT_TRUE(res.ok()) << res.status();
    auto cipher = std::move(res.value());
    auto pt = cipher->Decrypt(ct, associated_data);
    EXPECT_TRUE(pt.ok()) << pt.status();
  }
}

TEST(EncryptThenAuthenticateTest, testEncryptDecrypt) {
  int encryption_key_size = 16;
  int iv_size = 12;
  int mac_key_size = 16;
  int tag_size = 16;
  auto res = createAead(encryption_key_size, iv_size, mac_key_size, tag_size,
                        HashType::SHA1);
  EXPECT_TRUE(res.ok()) << res.status();
  auto cipher = std::move(res.value());

  std::string message = "Some data to encrypt.";
  std::string associated_data = "Some associated data.";
  auto ct = cipher->Encrypt(message, associated_data);
  EXPECT_TRUE(ct.ok()) << ct.status();
  EXPECT_EQ(ct.value().size(), message.size() + iv_size + tag_size);
  auto pt = cipher->Decrypt(ct.value(), associated_data);
  EXPECT_TRUE(pt.ok()) << pt.status();
  EXPECT_EQ(pt.value(), message);
}

TEST(EncryptThenAuthenticateTest, testEncryptDecrypt_randomMessage) {
  int encryption_key_size = 16;
  int iv_size = 12;
  int mac_key_size = 16;
  int tag_size = 16;
  auto res = createAead(encryption_key_size, iv_size, mac_key_size, tag_size,
                        HashType::SHA1);
  EXPECT_TRUE(res.ok()) << res.status();
  auto cipher = std::move(res.value());

  for (int i = 0; i < 256; i++) {
    std::string message = Random::GetRandomBytes(i);
    std::string associated_data = Random::GetRandomBytes(i);
    auto ct = cipher->Encrypt(message, associated_data);
    EXPECT_TRUE(ct.ok()) << ct.status();
    EXPECT_EQ(ct.value().size(), message.size() + iv_size + tag_size);
    auto pt = cipher->Decrypt(ct.value(), associated_data);
    EXPECT_TRUE(pt.ok()) << pt.status();
    EXPECT_EQ(pt.value(), message);
  }
}

TEST(AesCtrBoringSslTest, testMultipleEncrypt) {
  int encryption_key_size = 16;
  int iv_size = 12;
  int mac_key_size = 16;
  int tag_size = 16;
  auto res = createAead(encryption_key_size, iv_size, mac_key_size, tag_size,
                        HashType::SHA1);
  EXPECT_TRUE(res.ok()) << res.status();
  auto cipher = std::move(res.value());

  std::string message = Random::GetRandomBytes(20);
  std::string associated_data = Random::GetRandomBytes(20);
  auto ct1 = cipher->Encrypt(message, associated_data);
  auto ct2 = cipher->Encrypt(message, associated_data);
  EXPECT_NE(ct1.value(), ct2.value());
}

TEST(EncryptThenAuthenticateTest, testEncryptDecrypt_invalidTagSize) {
  int encryption_key_size = 16;
  int iv_size = 12;
  int mac_key_size = 16;
  int tag_size = 9;
  auto res = createAead(encryption_key_size, iv_size, mac_key_size, tag_size,
                        HashType::SHA1);
  EXPECT_FALSE(res.ok()) << res.status();
}

TEST(EncryptThenAuthenticateTest, testDecrypt_modifiedCiphertext) {
  int encryption_key_size = 16;
  int iv_size = 12;
  int mac_key_size = 16;
  int tag_size = 16;
  auto res = createAead(encryption_key_size, iv_size, mac_key_size, tag_size,
                        HashType::SHA1);
  EXPECT_TRUE(res.ok()) << res.status();
  auto cipher = std::move(res.value());

  std::string message = "Some data to encrypt.";
  std::string associated_data = "Some data to authenticate.";
  std::string ct = cipher->Encrypt(message, associated_data).value();
  EXPECT_TRUE(cipher->Decrypt(ct, associated_data).ok());
  // Modify the ciphertext
  for (size_t i = 0; i < ct.size() * 8; i++) {
    std::string modified_ct = ct;
    modified_ct[i / 8] ^= 1 << (i % 8);
    EXPECT_FALSE(cipher->Decrypt(modified_ct, associated_data).ok()) << i;
  }

  // Modify the associated data
  for (size_t i = 0; i < associated_data.size() * 8; i++) {
    std::string modified_associated_data = associated_data;
    modified_associated_data[i / 8] ^= 1 << (i % 8);
    auto decrypted = cipher->Decrypt(ct, modified_associated_data);
    EXPECT_FALSE(decrypted.ok()) << i << " pt:" << decrypted.value();
  }

  // Truncate the ciphertext
  for (size_t i = 0; i < ct.size(); i++) {
    std::string truncated_ct(ct, 0, i);
    EXPECT_FALSE(cipher->Decrypt(truncated_ct, associated_data).ok()) << i;
  }
}

TEST(EncryptThenAuthenticateTest, testParamsEmptyVersusNullStringView) {
  int encryption_key_size = 16;
  int iv_size = 12;
  int mac_key_size = 16;
  int tag_size = 16;
  auto cipher = std::move(createAead(encryption_key_size, iv_size, mac_key_size,
                                     tag_size, HashType::SHA1)
                              .value());

  {  // associated_data null string_view.
    const std::string message = "Some data to encrypt.";
    const absl::string_view associated_data;
    const std::string ct = cipher->Encrypt(message, "").value();
    EXPECT_TRUE(cipher->Decrypt(ct, associated_data).ok());
  }
  {  // Both message and associated_data null string_view.
    const absl::string_view message;
    const absl::string_view associated_data;
    const std::string ct = cipher->Encrypt(message, "").value();
    EXPECT_TRUE(cipher->Decrypt(ct, associated_data).ok());
  }
}

// EncryptThenAuthenticate computes the MAC over associated_data || ciphertext
// || associated_data_size_in_bits, where associated_data_size_in_bits =
// associated_data.size() * 8 [1]. associated_data.size() returns a size_t which
// is usually unsigned long or unsigned long long. On 32-bit machines (and maybe
// others), long is 32-bit int. If associated_data.size() returns a number equal
// to or larger than 2^29, an overflow will occur when multiplying with 8 to get
// the size in bits. This leads to an authentication bypass vulnerability. This
// test ensures that the overflow issue and the auth bypass vulnerability are
// fixed.
TEST(EncryptThenAuthenticateTest, testAuthBypassShouldNotWork) {
  int encryption_key_size = 16;
  int iv_size = 12;
  int mac_key_size = 16;
  int tag_size = 16;
  auto cipher = std::move(createAead(encryption_key_size, iv_size, mac_key_size,
                                     tag_size, HashType::SHA1)
                              .value());

  // Encrypt a message...
  const std::string message = "Some data to encrypt.";
  // ...with a long associated_data whose size in bits converted to an unsigned
  // 32-bit integer is 0.
  std::string associated_data;
  constexpr size_t kAssociatedDataSize = 1 << 29;
  constexpr size_t kCiphertextSpace = 1000;
  associated_data.reserve(kAssociatedDataSize + kCiphertextSpace);
  associated_data.resize(kAssociatedDataSize, 'a');
  auto encrypted = cipher->Encrypt(message, associated_data);
  EXPECT_TRUE(encrypted.ok()) << encrypted.status();
  auto ct = encrypted.value();
  auto decrypted = cipher->Decrypt(ct, associated_data);
  EXPECT_TRUE(decrypted.ok()) << decrypted.status();

  // Test that the 2^29-byte associated_data is NOT considered equal to an empty
  // associated_data. That is, test that a valid tag for (ciphertext,
  // associated_data) is INVALID for (associated_data + ciphertext, "").
  ct = std::move(associated_data) + ct;
  decrypted = cipher->Decrypt(ct, "");
  EXPECT_FALSE(decrypted.ok());
}

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