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policy: introduce a helper to detect whether a transaction spends Segwit outputs

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We will use this helper in later commits to detect witness stripping without having
to execute every input Script three times in a row.
This commit is contained in:
Antoine Poinsot
2025-08-04 13:11:33 -04:00
parent eb073209db
commit 2907b58834
3 changed files with 196 additions and 0 deletions
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36
src/policy/policy.cpp
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@@ -337,6 +337,42 @@ bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
return true; return true;
} }
bool SpendsNonAnchorWitnessProg(const CTransaction& tx, const CCoinsViewCache& prevouts)
{
if (tx.IsCoinBase()) {
return false;
}
int version;
std::vector<uint8_t> 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 <std::vector<uint8_t>> 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) 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; return (std::max(nWeight, nSigOpCost * bytes_per_sigop) + WITNESS_SCALE_FACTOR - 1) / WITNESS_SCALE_FACTOR;

5
src/policy/policy.h
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@@ -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. * Also enforce a maximum stack item size limit and no annexes for tapscript spends.
*/ */
bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs); 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). */ /** Compute the virtual transaction size (weight reinterpreted as bytes). */
int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost, unsigned int bytes_per_sigop); int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost, unsigned int bytes_per_sigop);

155
src/test/transaction_tests.cpp
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@@ -1149,4 +1149,159 @@ BOOST_AUTO_TEST_CASE(max_standard_legacy_sigops)
BOOST_CHECK(!::AreInputsStandard(CTransaction(tx_max_sigops), coins)); 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<std::vector<uint8_t>> sol_dummy;
// CNoDestination, PubKeyDestination, PKHash, ScriptHash, WitnessV0ScriptHash, WitnessV0KeyHash,
// WitnessV1Taproot, PayToAnchor, WitnessUnknown.
static_assert(std::variant_size_v<CTxDestination> == 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() BOOST_AUTO_TEST_SUITE_END()