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// Copyright (c) 2019-2021 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <signet.h>
#include <array>
#include <cstdint>
#include <vector>
#include <consensus/merkle.h>
#include <consensus/params.h>
#include <consensus/validation.h>
#include <core_io.h>
#include <hash.h>
#include <primitives/block.h>
#include <primitives/transaction.h>
#include <span.h>
#include <script/interpreter.h>
#include <script/standard.h>
#include <streams.h>
#include <util/strencodings.h>
#include <util/system.h>
#include <uint256.h>
static constexpr uint8_t SIGNET_HEADER[4] = {0xec, 0xc7, 0xda, 0xa2};
static constexpr unsigned int BLOCK_SCRIPT_VERIFY_FLAGS = SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_DERSIG | SCRIPT_VERIFY_NULLDUMMY;
static bool FetchAndClearCommitmentSection(const Span<const uint8_t> header, CScript& witness_commitment, std::vector<uint8_t>& result)
{
CScript replacement;
bool found_header = false;
result.clear();
opcodetype opcode;
CScript::const_iterator pc = witness_commitment.begin();
std::vector<uint8_t> pushdata;
while (witness_commitment.GetOp(pc, opcode, pushdata)) {
if (pushdata.size() > 0) {
if (!found_header && pushdata.size() > (size_t)header.size() && Span{pushdata}.first(header.size()) == header) {
// pushdata only counts if it has the header _and_ some data
result.insert(result.end(), pushdata.begin() + header.size(), pushdata.end());
pushdata.erase(pushdata.begin() + header.size(), pushdata.end());
found_header = true;
}
replacement << pushdata;
} else {
replacement << opcode;
}
}
if (found_header) witness_commitment = replacement;
return found_header;
}
static uint256 ComputeModifiedMerkleRoot(const CMutableTransaction& cb, const CBlock& block)
{
std::vector<uint256> leaves;
leaves.resize(block.vtx.size());
leaves[0] = cb.GetHash();
for (size_t s = 1; s < block.vtx.size(); ++s) {
leaves[s] = block.vtx[s]->GetHash();
}
return ComputeMerkleRoot(std::move(leaves));
}
std::optional<SignetTxs> SignetTxs::Create(const CBlock& block, const CScript& challenge)
{
CMutableTransaction tx_to_spend;
tx_to_spend.nVersion = 0;
tx_to_spend.nLockTime = 0;
tx_to_spend.vin.emplace_back(COutPoint(), CScript(OP_0), 0);
tx_to_spend.vout.emplace_back(0, challenge);
CMutableTransaction tx_spending;
tx_spending.nVersion = 0;
tx_spending.nLockTime = 0;
tx_spending.vin.emplace_back(COutPoint(), CScript(), 0);
tx_spending.vout.emplace_back(0, CScript(OP_RETURN));
// can't fill any other fields before extracting signet
// responses from block coinbase tx
// find and delete signet signature
if (block.vtx.empty()) return std::nullopt; // no coinbase tx in block; invalid
CMutableTransaction modified_cb(*block.vtx.at(0));
const int cidx = GetWitnessCommitmentIndex(block);
if (cidx == NO_WITNESS_COMMITMENT) {
return std::nullopt; // require a witness commitment
}
CScript& witness_commitment = modified_cb.vout.at(cidx).scriptPubKey;
std::vector<uint8_t> signet_solution;
if (!FetchAndClearCommitmentSection(SIGNET_HEADER, witness_commitment, signet_solution)) {
// no signet solution -- allow this to support OP_TRUE as trivial block challenge
} else {
try {
SpanReader v{SER_NETWORK, INIT_PROTO_VERSION, signet_solution};
v >> tx_spending.vin[0].scriptSig;
v >> tx_spending.vin[0].scriptWitness.stack;
if (!v.empty()) return std::nullopt; // extraneous data encountered
} catch (const std::exception&) {
return std::nullopt; // parsing error
}
}
uint256 signet_merkle = ComputeModifiedMerkleRoot(modified_cb, block);
std::vector<uint8_t> block_data;
CVectorWriter writer(SER_NETWORK, INIT_PROTO_VERSION, block_data, 0);
writer << block.nVersion;
writer << block.hashPrevBlock;
writer << signet_merkle;
writer << block.nTime;
tx_to_spend.vin[0].scriptSig << block_data;
tx_spending.vin[0].prevout = COutPoint(tx_to_spend.GetHash(), 0);
return SignetTxs{tx_to_spend, tx_spending};
}
// Signet block solution checker
bool CheckSignetBlockSolution(const CBlock& block, const Consensus::Params& consensusParams)
{
if (block.GetHash() == consensusParams.hashGenesisBlock) {
// genesis block solution is always valid
return true;
}
const CScript challenge(consensusParams.signet_challenge.begin(), consensusParams.signet_challenge.end());
const std::optional<SignetTxs> signet_txs = SignetTxs::Create(block, challenge);
if (!signet_txs) {
LogPrint(BCLog::VALIDATION, "CheckSignetBlockSolution: Errors in block (block solution parse failure)\n");
return false;
}
const CScript& scriptSig = signet_txs->m_to_sign.vin[0].scriptSig;
const CScriptWitness& witness = signet_txs->m_to_sign.vin[0].scriptWitness;
PrecomputedTransactionData txdata;
txdata.Init(signet_txs->m_to_sign, {signet_txs->m_to_spend.vout[0]});
TransactionSignatureChecker sigcheck(&signet_txs->m_to_sign, /* nInIn= */ 0, /* amountIn= */ signet_txs->m_to_spend.vout[0].nValue, txdata, MissingDataBehavior::ASSERT_FAIL);
if (!VerifyScript(scriptSig, signet_txs->m_to_spend.vout[0].scriptPubKey, &witness, BLOCK_SCRIPT_VERIFY_FLAGS, sigcheck)) {
LogPrint(BCLog::VALIDATION, "CheckSignetBlockSolution: Errors in block (block solution invalid)\n");
return false;
}
return true;
}
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