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1 : : // Copyright (c) 2023 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 : 1 : void Initialize()
20 : : {
21 [ + - + - : 1 : static ECC_Context ecc_context{};
+ - ]
22 : 1 : SelectParams(ChainType::MAIN);
23 : 1 : }
24 : :
25 : : } // namespace
26 : :
27 [ + - ]: 972 : FUZZ_TARGET(bip324_cipher_roundtrip, .init=Initialize)
28 : : {
29 : : // Test that BIP324Cipher's encryption and decryption agree.
30 : :
31 : : // Load keys from fuzzer.
32 : 560 : FuzzedDataProvider provider(buffer.data(), buffer.size());
33 : : // Initiator key
34 : 560 : CKey init_key = ConsumePrivateKey(provider, /*compressed=*/true);
35 [ + + ]: 560 : if (!init_key.IsValid()) return;
36 : : // Initiator entropy
37 [ + - ]: 557 : auto init_ent = provider.ConsumeBytes<std::byte>(32);
38 [ + - ]: 557 : init_ent.resize(32);
39 : : // Responder key
40 : 557 : CKey resp_key = ConsumePrivateKey(provider, /*compressed=*/true);
41 [ + + ]: 557 : if (!resp_key.IsValid()) return;
42 : : // Responder entropy
43 [ + - ]: 553 : auto resp_ent = provider.ConsumeBytes<std::byte>(32);
44 [ + - ]: 553 : resp_ent.resize(32);
45 : :
46 : : // Initialize ciphers by exchanging public keys.
47 : 553 : BIP324Cipher initiator(init_key, init_ent);
48 [ - + ]: 553 : assert(!initiator);
49 : 553 : BIP324Cipher responder(resp_key, resp_ent);
50 [ - + ]: 553 : assert(!responder);
51 : 553 : initiator.Initialize(responder.GetOurPubKey(), true);
52 [ - + ]: 553 : assert(initiator);
53 : 553 : responder.Initialize(initiator.GetOurPubKey(), false);
54 [ - + ]: 553 : 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 : 553 : InsecureRandomContext rng(provider.ConsumeIntegral<uint64_t>());
61 : :
62 : : // Compare session IDs and garbage terminators.
63 [ - + ]: 1106 : assert(std::ranges::equal(initiator.GetSessionID(), responder.GetSessionID()));
64 [ - + ]: 1106 : assert(std::ranges::equal(initiator.GetSendGarbageTerminator(), responder.GetReceiveGarbageTerminator()));
65 [ - + ]: 1106 : assert(std::ranges::equal(initiator.GetReceiveGarbageTerminator(), responder.GetSendGarbageTerminator()));
66 : :
67 [ + + + + ]: 45584 : 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 : 45344 : unsigned mode = provider.ConsumeIntegral<uint8_t>();
75 : 45344 : bool ignore = mode & 1;
76 : 45344 : bool from_init = mode & 2;
77 : 45344 : bool damage = mode & 4;
78 : 45344 : unsigned aad_length_bits = 4 * ((mode >> 3) & 3);
79 : 45344 : unsigned aad_length = provider.ConsumeIntegralInRange<unsigned>(0, (1 << aad_length_bits) - 1);
80 : 45344 : unsigned length_bits = 2 * ((mode >> 5) & 7);
81 : 45344 : unsigned length = provider.ConsumeIntegralInRange<unsigned>(0, (1 << length_bits) - 1);
82 : : // Generate aad and content.
83 : 45344 : auto aad = rng.randbytes<std::byte>(aad_length);
84 : 45344 : auto contents = rng.randbytes<std::byte>(length);
85 : :
86 : : // Pick sides.
87 [ + + ]: 45344 : auto& sender{from_init ? initiator : responder};
88 : 37704 : auto& receiver{from_init ? responder : initiator};
89 : :
90 : : // Encrypt
91 [ + - ]: 45344 : std::vector<std::byte> ciphertext(length + initiator.EXPANSION);
92 : 45344 : 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 [ + + ]: 45344 : if (damage) {
97 : 313 : unsigned damage_bit = provider.ConsumeIntegralInRange<unsigned>(0,
98 : 313 : (ciphertext.size() + aad.size()) * 8U - 1U);
99 : 313 : unsigned damage_pos = damage_bit >> 3;
100 : 313 : std::byte damage_val{(uint8_t)(1U << (damage_bit & 7))};
101 [ + + ]: 313 : if (damage_pos >= ciphertext.size()) {
102 : 35 : aad[damage_pos - ciphertext.size()] ^= damage_val;
103 : : } else {
104 : 278 : ciphertext[damage_pos] ^= damage_val;
105 : : }
106 : : }
107 : :
108 : : // Decrypt length
109 : 45344 : uint32_t dec_length = receiver.DecryptLength(Span{ciphertext}.first(initiator.LENGTH_LEN));
110 [ + + ]: 45344 : if (!damage) {
111 [ - + ]: 45031 : assert(dec_length == length);
112 : : } else {
113 : : // For performance reasons, don't try to decode if length got increased too much.
114 [ + + ]: 313 : if (dec_length > 16384 + length) break;
115 : : // Otherwise, just append zeros if dec_length > length.
116 [ + - ]: 269 : ciphertext.resize(dec_length + initiator.EXPANSION);
117 : : }
118 : :
119 : : // Decrypt
120 [ + - ]: 45300 : std::vector<std::byte> decrypt(dec_length);
121 : 45300 : bool dec_ignore{false};
122 : 45300 : bool ok = receiver.Decrypt(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 [ - + ]: 45300 : assert(!ok == damage);
125 [ + + ]: 45300 : if (!ok) break;
126 [ - + ]: 45031 : assert(ignore == dec_ignore);
127 [ - + ]: 45031 : assert(decrypt == contents);
128 : 45613 : }
129 : 564 : }
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