1  // Copyright (c) 2019-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 <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 script_verify_flags BLOCK_SCRIPT_VERIFY_FLAGS = SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_DERSIG | SCRIPT_VERIFY_NULLDUMMY;
 30  
 31  static bool FetchAndClearCommitmentSection(const std::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(std::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().ToUint256();
 63      for (size_t s = 1; s < block.vtx.size(); ++s) {
 64          leaves[s] = block.vtx[s]->GetHash().ToUint256();
 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  }