signet.cpp raw
1 // Copyright (c) 2019-2021 The Limenka 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 <signet.h>
6
7 #include <common/system.h>
8 #include <consensus/merkle.h>
9 #include <consensus/params.h>
10 #include <consensus/validation.h>
11 #include <core_io.h>
12 #include <hash.h>
13 #include <logging.h>
14 #include <primitives/block.h>
15 #include <primitives/transaction.h>
16 #include <script/interpreter.h>
17 #include <span.h>
18 #include <streams.h>
19 #include <uint256.h>
20 #include <util/strencodings.h>
21
22 #include <algorithm>
23 #include <array>
24 #include <cstdint>
25 #include <vector>
26
27 static constexpr uint8_t SIGNET_HEADER[4] = {0xec, 0xc7, 0xda, 0xa2};
28
29 static constexpr unsigned int BLOCK_SCRIPT_VERIFY_FLAGS = SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_DERSIG | SCRIPT_VERIFY_NULLDUMMY | SCRIPT_VERIFY_TAPROOT | SCRIPT_VERIFY_NULLFAIL;
30
31 static bool FetchAndClearCommitmentSection(const Span<const uint8_t> header, CScript& witness_commitment, std::vector<uint8_t>& result)
32 {
33 CScript replacement;
34 bool found_header = false;
35 result.clear();
36
37 opcodetype opcode;
38 CScript::const_iterator pc = witness_commitment.begin();
39 std::vector<uint8_t> pushdata;
40 while (witness_commitment.GetOp(pc, opcode, pushdata)) {
41 if (pushdata.size() > 0) {
42 if (!found_header && pushdata.size() > header.size() && std::ranges::equal(Span{pushdata}.first(header.size()), header)) {
43 // pushdata only counts if it has the header _and_ some data
44 result.insert(result.end(), pushdata.begin() + header.size(), pushdata.end());
45 pushdata.erase(pushdata.begin() + header.size(), pushdata.end());
46 found_header = true;
47 }
48 replacement << pushdata;
49 } else {
50 replacement << opcode;
51 }
52 }
53
54 if (found_header) witness_commitment = replacement;
55 return found_header;
56 }
57
58 static uint256 ComputeModifiedMerkleRoot(const CMutableTransaction& cb, const CBlock& block)
59 {
60 std::vector<uint256> leaves;
61 leaves.resize(block.vtx.size());
62 leaves[0] = cb.GetHash();
63 for (size_t s = 1; s < block.vtx.size(); ++s) {
64 leaves[s] = block.vtx[s]->GetHash();
65 }
66 return ComputeMerkleRoot(std::move(leaves));
67 }
68
69 std::optional<SignetTxs> SignetTxs::Create(const CBlock& block, const CScript& challenge)
70 {
71 CMutableTransaction tx_to_spend;
72 tx_to_spend.version = 0;
73 tx_to_spend.nLockTime = 0;
74 tx_to_spend.vin.emplace_back(COutPoint(), CScript(OP_0), 0);
75 tx_to_spend.vout.emplace_back(0, challenge);
76
77 CMutableTransaction tx_spending;
78 tx_spending.version = 0;
79 tx_spending.nLockTime = 0;
80 tx_spending.vin.emplace_back(COutPoint(), CScript(), 0);
81 tx_spending.vout.emplace_back(0, CScript(OP_RETURN));
82
83 // can't fill any other fields before extracting signet
84 // responses from block coinbase tx
85
86 // find and delete signet signature
87 if (block.vtx.empty()) return std::nullopt; // no coinbase tx in block; invalid
88 CMutableTransaction modified_cb(*block.vtx.at(0));
89
90 const int cidx = GetWitnessCommitmentIndex(block);
91 if (cidx == NO_WITNESS_COMMITMENT) {
92 return std::nullopt; // require a witness commitment
93 }
94
95 CScript& witness_commitment = modified_cb.vout.at(cidx).scriptPubKey;
96
97 std::vector<uint8_t> signet_solution;
98 if (!FetchAndClearCommitmentSection(SIGNET_HEADER, witness_commitment, signet_solution)) {
99 // no signet solution -- allow this to support OP_TRUE as trivial block challenge
100 } else {
101 try {
102 SpanReader v{signet_solution};
103 v >> tx_spending.vin[0].scriptSig;
104 v >> tx_spending.vin[0].scriptWitness.stack;
105 if (!v.empty()) return std::nullopt; // extraneous data encountered
106 } catch (const std::exception&) {
107 return std::nullopt; // parsing error
108 }
109 }
110 uint256 signet_merkle = ComputeModifiedMerkleRoot(modified_cb, block);
111
112 std::vector<uint8_t> block_data;
113 VectorWriter writer{block_data, 0};
114 writer << block.nVersion;
115 writer << block.hashPrevBlock;
116 writer << signet_merkle;
117 writer << block.nTime;
118 tx_to_spend.vin[0].scriptSig << block_data;
119 tx_spending.vin[0].prevout = COutPoint(tx_to_spend.GetHash(), 0);
120
121 return SignetTxs{tx_to_spend, tx_spending};
122 }
123
124 // Signet block solution checker
125 bool CheckSignetBlockSolution(const CBlock& block, const Consensus::Params& consensusParams)
126 {
127 if (block.GetHash() == consensusParams.hashGenesisBlock) {
128 // genesis block solution is always valid
129 return true;
130 }
131
132 const CScript challenge(consensusParams.signet_challenge.begin(), consensusParams.signet_challenge.end());
133 const std::optional<SignetTxs> signet_txs = SignetTxs::Create(block, challenge);
134
135 if (!signet_txs) {
136 LogDebug(BCLog::VALIDATION, "CheckSignetBlockSolution: Errors in block (block solution parse failure)\n");
137 return false;
138 }
139
140 const CScript& scriptSig = signet_txs->m_to_sign.vin[0].scriptSig;
141 const CScriptWitness& witness = signet_txs->m_to_sign.vin[0].scriptWitness;
142
143 PrecomputedTransactionData txdata;
144 txdata.Init(signet_txs->m_to_sign, {signet_txs->m_to_spend.vout[0]});
145 TransactionSignatureChecker sigcheck(&signet_txs->m_to_sign, /* nInIn= */ 0, /* amountIn= */ signet_txs->m_to_spend.vout[0].nValue, txdata, MissingDataBehavior::ASSERT_FAIL);
146
147 if (!VerifyScript(scriptSig, signet_txs->m_to_spend.vout[0].scriptPubKey, &witness, BLOCK_SCRIPT_VERIFY_FLAGS, sigcheck)) {
148 LogDebug(BCLog::VALIDATION, "CheckSignetBlockSolution: Errors in block (block solution invalid)\n");
149 return false;
150 }
151 return true;
152 }
153