1  // Copyright (c) 2023-present The Bitcoin Core developers
  2  // Distributed under the MIT software license, see the accompanying
  3  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  4  
  5  #include <bip324.h>
  6  #include <chainparams.h>
  7  #include <random.h>
  8  #include <span.h>
  9  #include <test/fuzz/FuzzedDataProvider.h>
 10  #include <test/fuzz/fuzz.h>
 11  #include <test/fuzz/util.h>
 12  
 13  #include <algorithm>
 14  #include <cstdint>
 15  #include <vector>
 16  
 17  namespace {
 18  
 19  void Initialize()
 20  {
 21      static ECC_Context ecc_context{};
 22      SelectParams(ChainType::MAIN);
 23  }
 24  
 25  }  // namespace
 26  
 27  FUZZ_TARGET(bip324_cipher_roundtrip, .init=Initialize)
 28  {
 29      // Test that BIP324Cipher's encryption and decryption agree.
 30  
 31      // Load keys from fuzzer.
 32      FuzzedDataProvider provider(buffer.data(), buffer.size());
 33      // Initiator key
 34      CKey init_key = ConsumePrivateKey(provider, /*compressed=*/true);
 35      if (!init_key.IsValid()) return;
 36      // Initiator entropy
 37      auto init_ent = provider.ConsumeBytes<std::byte>(32);
 38      init_ent.resize(32);
 39      // Responder key
 40      CKey resp_key = ConsumePrivateKey(provider, /*compressed=*/true);
 41      if (!resp_key.IsValid()) return;
 42      // Responder entropy
 43      auto resp_ent = provider.ConsumeBytes<std::byte>(32);
 44      resp_ent.resize(32);
 45  
 46      // Initialize ciphers by exchanging public keys.
 47      BIP324Cipher initiator(init_key, init_ent);
 48      assert(!initiator);
 49      BIP324Cipher responder(resp_key, resp_ent);
 50      assert(!responder);
 51      initiator.Initialize(responder.GetOurPubKey(), true);
 52      assert(initiator);
 53      responder.Initialize(initiator.GetOurPubKey(), false);
 54      assert(responder);
 55  
 56      // Initialize RNG deterministically, to generate contents and AAD. We assume that there are no
 57      // (potentially buggy) edge cases triggered by specific values of contents/AAD, so we can avoid
 58      // reading the actual data for those from the fuzzer input (which would need large amounts of
 59      // data).
 60      InsecureRandomContext rng(provider.ConsumeIntegral<uint64_t>());
 61  
 62      // Compare session IDs and garbage terminators.
 63      assert(std::ranges::equal(initiator.GetSessionID(), responder.GetSessionID()));
 64      assert(std::ranges::equal(initiator.GetSendGarbageTerminator(), responder.GetReceiveGarbageTerminator()));
 65      assert(std::ranges::equal(initiator.GetReceiveGarbageTerminator(), responder.GetSendGarbageTerminator()));
 66  
 67      LIMITED_WHILE(provider.remaining_bytes(), 1000) {
 68          // Mode:
 69          // - Bit 0: whether the ignore bit is set in message
 70          // - Bit 1: whether the responder (0) or initiator (1) sends
 71          // - Bit 2: whether this ciphertext will be corrupted (making it the last sent one)
 72          // - Bit 3-4: controls the maximum aad length (max 4095 bytes)
 73          // - Bit 5-7: controls the maximum content length (max 16383 bytes, for performance reasons)
 74          unsigned mode = provider.ConsumeIntegral<uint8_t>();
 75          bool ignore = mode & 1;
 76          bool from_init = mode & 2;
 77          bool damage = mode & 4;
 78          unsigned aad_length_bits = 4 * ((mode >> 3) & 3);
 79          unsigned aad_length = provider.ConsumeIntegralInRange<unsigned>(0, (1 << aad_length_bits) - 1);
 80          unsigned length_bits = 2 * ((mode >> 5) & 7);
 81          unsigned length = provider.ConsumeIntegralInRange<unsigned>(0, (1 << length_bits) - 1);
 82          // Generate aad and content.
 83          auto aad = rng.randbytes<std::byte>(aad_length);
 84          auto contents = rng.randbytes<std::byte>(length);
 85  
 86          // Pick sides.
 87          auto& sender{from_init ? initiator : responder};
 88          auto& receiver{from_init ? responder : initiator};
 89  
 90          // Encrypt
 91          std::vector<std::byte> ciphertext(length + initiator.EXPANSION);
 92          sender.Encrypt(contents, aad, ignore, ciphertext);
 93  
 94          // Optionally damage 1 bit in either the ciphertext (corresponding to a change in transit)
 95          // or the aad (to make sure that decryption will fail if the AAD mismatches).
 96          if (damage) {
 97              unsigned damage_bit = provider.ConsumeIntegralInRange<unsigned>(0,
 98                  (ciphertext.size() + aad.size()) * 8U - 1U);
 99              unsigned damage_pos = damage_bit >> 3;
100              std::byte damage_val{(uint8_t)(1U << (damage_bit & 7))};
101              if (damage_pos >= ciphertext.size()) {
102                  aad[damage_pos - ciphertext.size()] ^= damage_val;
103              } else {
104                  ciphertext[damage_pos] ^= damage_val;
105              }
106          }
107  
108          // Decrypt length
109          uint32_t dec_length = receiver.DecryptLength(std::span{ciphertext}.first(initiator.LENGTH_LEN));
110          if (!damage) {
111              assert(dec_length == length);
112          } else {
113              // For performance reasons, don't try to decode if length got increased too much.
114              if (dec_length > 16384 + length) break;
115              // Otherwise, just append zeros if dec_length > length.
116              ciphertext.resize(dec_length + initiator.EXPANSION);
117          }
118  
119          // Decrypt
120          std::vector<std::byte> decrypt(dec_length);
121          bool dec_ignore{false};
122          bool ok = receiver.Decrypt(std::span{ciphertext}.subspan(initiator.LENGTH_LEN), aad, dec_ignore, decrypt);
123          // Decryption *must* fail if the packet was damaged, and succeed if it wasn't.
124          assert(!ok == damage);
125          if (!ok) break;
126          assert(ignore == dec_ignore);
127          assert(decrypt == contents);
128      }
129  }