From 2907b58834ab011f7dd0c42d323e440abd227c25 Mon Sep 17 00:00:00 2001 From: Antoine Poinsot Date: Mon, 4 Aug 2025 13:11:33 -0400 Subject: [PATCH] policy: introduce a helper to detect whether a transaction spends Segwit outputs We will use this helper in later commits to detect witness stripping without having to execute every input Script three times in a row. --- src/policy/policy.cpp | 36 ++++++++ src/policy/policy.h | 5 ++ src/test/transaction_tests.cpp | 155 +++++++++++++++++++++++++++++++++ 3 files changed, 196 insertions(+) diff --git a/src/policy/policy.cpp b/src/policy/policy.cpp index 48f2a6a7446..fdb6bc5f341 100644 --- a/src/policy/policy.cpp +++ b/src/policy/policy.cpp @@ -337,6 +337,42 @@ bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs) return true; } +bool SpendsNonAnchorWitnessProg(const CTransaction& tx, const CCoinsViewCache& prevouts) +{ + if (tx.IsCoinBase()) { + return false; + } + + int version; + std::vector program; + for (const auto& txin: tx.vin) { + const auto& prev_spk{prevouts.AccessCoin(txin.prevout).out.scriptPubKey}; + + // Note this includes not-yet-defined witness programs. + if (prev_spk.IsWitnessProgram(version, program) && !prev_spk.IsPayToAnchor(version, program)) { + return true; + } + + // For P2SH extract the redeem script and check if it spends a non-Taproot witness program. Note + // this is fine to call EvalScript (as done in AreInputsStandard/IsWitnessStandard) because this + // function is only ever called after IsStandardTx, which checks the scriptsig is pushonly. + if (prev_spk.IsPayToScriptHash()) { + // If EvalScript fails or results in an empty stack, the transaction is invalid by consensus. + std::vector > stack; + if (!EvalScript(stack, txin.scriptSig, SCRIPT_VERIFY_NONE, BaseSignatureChecker{}, SigVersion::BASE) + || stack.empty()) { + continue; + } + const CScript redeem_script{stack.back().begin(), stack.back().end()}; + if (redeem_script.IsWitnessProgram(version, program)) { + return true; + } + } + } + + return false; +} + int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost, unsigned int bytes_per_sigop) { return (std::max(nWeight, nSigOpCost * bytes_per_sigop) + WITNESS_SCALE_FACTOR - 1) / WITNESS_SCALE_FACTOR; diff --git a/src/policy/policy.h b/src/policy/policy.h index f9a18561bce..ad787630a45 100644 --- a/src/policy/policy.h +++ b/src/policy/policy.h @@ -166,6 +166,11 @@ bool AreInputsStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs) * Also enforce a maximum stack item size limit and no annexes for tapscript spends. */ bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs); +/** + * Check whether this transaction spends any witness program but P2A, including not-yet-defined ones. + * May return `false` early for consensus-invalid transactions. + */ +bool SpendsNonAnchorWitnessProg(const CTransaction& tx, const CCoinsViewCache& prevouts); /** Compute the virtual transaction size (weight reinterpreted as bytes). */ int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost, unsigned int bytes_per_sigop); diff --git a/src/test/transaction_tests.cpp b/src/test/transaction_tests.cpp index 5f03641e99e..137ec7feb50 100644 --- a/src/test/transaction_tests.cpp +++ b/src/test/transaction_tests.cpp @@ -1149,4 +1149,159 @@ BOOST_AUTO_TEST_CASE(max_standard_legacy_sigops) BOOST_CHECK(!::AreInputsStandard(CTransaction(tx_max_sigops), coins)); } +/** Sanity check the return value of SpendsNonAnchorWitnessProg for various output types. */ +BOOST_AUTO_TEST_CASE(spends_witness_prog) +{ + CCoinsView coins_dummy; + CCoinsViewCache coins(&coins_dummy); + CKey key; + key.MakeNewKey(true); + const CPubKey pubkey{key.GetPubKey()}; + CMutableTransaction tx_create{}, tx_spend{}; + tx_create.vout.emplace_back(0, CScript{}); + tx_spend.vin.emplace_back(Txid{}, 0); + std::vector> sol_dummy; + + // CNoDestination, PubKeyDestination, PKHash, ScriptHash, WitnessV0ScriptHash, WitnessV0KeyHash, + // WitnessV1Taproot, PayToAnchor, WitnessUnknown. + static_assert(std::variant_size_v == 9); + + // Go through all defined output types and sanity check SpendsNonAnchorWitnessProg. + + // P2PK + tx_create.vout[0].scriptPubKey = GetScriptForDestination(PubKeyDestination{pubkey}); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::PUBKEY); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(!::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // P2PKH + tx_create.vout[0].scriptPubKey = GetScriptForDestination(PKHash{pubkey}); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::PUBKEYHASH); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(!::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // P2SH + auto redeem_script{CScript{} << OP_1 << OP_CHECKSIG}; + tx_create.vout[0].scriptPubKey = GetScriptForDestination(ScriptHash{redeem_script}); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::SCRIPTHASH); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + tx_spend.vin[0].scriptSig = CScript{} << OP_0 << ToByteVector(redeem_script); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(!::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + tx_spend.vin[0].scriptSig.clear(); + + // native P2WSH + const auto witness_script{CScript{} << OP_12 << OP_HASH160 << OP_DUP << OP_EQUAL}; + tx_create.vout[0].scriptPubKey = GetScriptForDestination(WitnessV0ScriptHash{witness_script}); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::WITNESS_V0_SCRIPTHASH); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // P2SH-wrapped P2WSH + redeem_script = tx_create.vout[0].scriptPubKey; + tx_create.vout[0].scriptPubKey = GetScriptForDestination(ScriptHash(redeem_script)); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::SCRIPTHASH); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + tx_spend.vin[0].scriptSig = CScript{} << ToByteVector(redeem_script); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + tx_spend.vin[0].scriptSig.clear(); + BOOST_CHECK(!::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // native P2WPKH + tx_create.vout[0].scriptPubKey = GetScriptForDestination(WitnessV0KeyHash{pubkey}); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::WITNESS_V0_KEYHASH); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // P2SH-wrapped P2WPKH + redeem_script = tx_create.vout[0].scriptPubKey; + tx_create.vout[0].scriptPubKey = GetScriptForDestination(ScriptHash(redeem_script)); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::SCRIPTHASH); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + tx_spend.vin[0].scriptSig = CScript{} << ToByteVector(redeem_script); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + tx_spend.vin[0].scriptSig.clear(); + BOOST_CHECK(!::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // P2TR + tx_create.vout[0].scriptPubKey = GetScriptForDestination(WitnessV1Taproot{XOnlyPubKey{pubkey}}); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::WITNESS_V1_TAPROOT); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // P2SH-wrapped P2TR (undefined, non-standard) + redeem_script = tx_create.vout[0].scriptPubKey; + tx_create.vout[0].scriptPubKey = GetScriptForDestination(ScriptHash(redeem_script)); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::SCRIPTHASH); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + tx_spend.vin[0].scriptSig = CScript{} << ToByteVector(redeem_script); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + tx_spend.vin[0].scriptSig.clear(); + BOOST_CHECK(!::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // P2A + tx_create.vout[0].scriptPubKey = GetScriptForDestination(PayToAnchor{}); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::ANCHOR); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(!::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // P2SH-wrapped P2A (undefined, non-standard) + redeem_script = tx_create.vout[0].scriptPubKey; + tx_create.vout[0].scriptPubKey = GetScriptForDestination(ScriptHash(redeem_script)); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::SCRIPTHASH); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + tx_spend.vin[0].scriptSig = CScript{} << ToByteVector(redeem_script); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + tx_spend.vin[0].scriptSig.clear(); + + // Undefined version 1 witness program + tx_create.vout[0].scriptPubKey = GetScriptForDestination(WitnessUnknown{1, {0x42, 0x42}}); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::WITNESS_UNKNOWN); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // P2SH-wrapped undefined version 1 witness program + redeem_script = tx_create.vout[0].scriptPubKey; + tx_create.vout[0].scriptPubKey = GetScriptForDestination(ScriptHash(redeem_script)); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::SCRIPTHASH); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + tx_spend.vin[0].scriptSig = CScript{} << ToByteVector(redeem_script); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + tx_spend.vin[0].scriptSig.clear(); + BOOST_CHECK(!::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // Various undefined version >1 32-byte witness programs. + const auto program{ToByteVector(XOnlyPubKey{pubkey})}; + for (int i{2}; i <= 16; ++i) { + tx_create.vout[0].scriptPubKey = GetScriptForDestination(WitnessUnknown{i, program}); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::WITNESS_UNKNOWN); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + + // It's also detected within P2SH. + redeem_script = tx_create.vout[0].scriptPubKey; + tx_create.vout[0].scriptPubKey = GetScriptForDestination(ScriptHash(redeem_script)); + BOOST_CHECK_EQUAL(Solver(tx_create.vout[0].scriptPubKey, sol_dummy), TxoutType::SCRIPTHASH); + tx_spend.vin[0].prevout.hash = tx_create.GetHash(); + tx_spend.vin[0].scriptSig = CScript{} << ToByteVector(redeem_script); + AddCoins(coins, CTransaction{tx_create}, 0, false); + BOOST_CHECK(::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + tx_spend.vin[0].scriptSig.clear(); + BOOST_CHECK(!::SpendsNonAnchorWitnessProg(CTransaction{tx_spend}, coins)); + } +} + BOOST_AUTO_TEST_SUITE_END()