// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2020 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
// NOTE: This file is intended to be customised by the end user, and includes only local node policy logic
#include <policy/policy.h>
#include <consensus/validation.h>
#include <coins.h>
#include <span.h>
CAmount GetDustThreshold(const CTxOut& txout, const CFeeRate& dustRelayFeeIn)
{
// "Dust" is defined in terms of dustRelayFee,
// which has units satoshis-per-kilobyte.
// If you'd pay more in fees than the value of the output
// to spend something, then we consider it dust.
// A typical spendable non-segwit txout is 34 bytes big, and will
// need a CTxIn of at least 148 bytes to spend:
// so dust is a spendable txout less than
// 182*dustRelayFee/1000 (in satoshis).
// 546 satoshis at the default rate of 3000 sat/kB.
// A typical spendable segwit txout is 31 bytes big, and will
// need a CTxIn of at least 67 bytes to spend:
// so dust is a spendable txout less than
// 98*dustRelayFee/1000 (in satoshis).
// 294 satoshis at the default rate of 3000 sat/kB.
if (txout.scriptPubKey.IsUnspendable())
return 0;
size_t nSize = GetSerializeSize(txout);
int witnessversion = 0;
std::vector<unsigned char> witnessprogram;
if (txout.scriptPubKey.IsWitnessProgram(witnessversion, witnessprogram)) {
// sum the sizes of the parts of a transaction input
// with 75% segwit discount applied to the script size.
nSize += (32 + 4 + 1 + (107 / WITNESS_SCALE_FACTOR) + 4);
} else {
nSize += (32 + 4 + 1 + 107 + 4); // the 148 mentioned above
}
return dustRelayFeeIn.GetFee(nSize);
}
bool IsDust(const CTxOut& txout, const CFeeRate& dustRelayFeeIn)
{
return (txout.nValue < GetDustThreshold(txout, dustRelayFeeIn));
}
bool IsStandard(const CScript& scriptPubKey, TxoutType& whichType)
{
std::vector<std::vector<unsigned char> > vSolutions;
whichType = Solver(scriptPubKey, vSolutions);
if (whichType == TxoutType::NONSTANDARD) {
return false;
} else if (whichType == TxoutType::MULTISIG) {
unsigned char m = vSolutions.front()[0];
unsigned char n = vSolutions.back()[0];
// Support up to x-of-3 multisig txns as standard
if (n < 1 || n > 3)
return false;
if (m < 1 || m > n)
return false;
} else if (whichType == TxoutType::NULL_DATA &&
(!fAcceptDatacarrier || scriptPubKey.size() > nMaxDatacarrierBytes)) {
return false;
}
return true;
}
bool IsStandardTx(const CTransaction& tx, bool permit_bare_multisig, const CFeeRate& dust_relay_fee, std::string& reason)
{
if (tx.nVersion > TX_MAX_STANDARD_VERSION || tx.nVersion < 1) {
reason = "version";
return false;
}
// Extremely large transactions with lots of inputs can cost the network
// almost as much to process as they cost the sender in fees, because
// computing signature hashes is O(ninputs*txsize). Limiting transactions
// to MAX_STANDARD_TX_WEIGHT mitigates CPU exhaustion attacks.
unsigned int sz = GetTransactionWeight(tx);
if (sz > MAX_STANDARD_TX_WEIGHT) {
reason = "tx-size";
return false;
}
for (const CTxIn& txin : tx.vin)
{
// Biggest 'standard' txin involving only keys is a 15-of-15 P2SH
// multisig with compressed keys (remember the 520 byte limit on
// redeemScript size). That works out to a (15*(33+1))+3=513 byte
// redeemScript, 513+1+15*(73+1)+3=1627 bytes of scriptSig, which
// we round off to 1650(MAX_STANDARD_SCRIPTSIG_SIZE) bytes for
// some minor future-proofing. That's also enough to spend a
// 20-of-20 CHECKMULTISIG scriptPubKey, though such a scriptPubKey
// is not considered standard.
if (txin.scriptSig.size() > MAX_STANDARD_SCRIPTSIG_SIZE) {
reason = "scriptsig-size";
return false;
}
if (!txin.scriptSig.IsPushOnly()) {
reason = "scriptsig-not-pushonly";
return false;
}
}
unsigned int nDataOut = 0;
TxoutType whichType;
for (const CTxOut& txout : tx.vout) {
if (!::IsStandard(txout.scriptPubKey, whichType)) {
reason = "scriptpubkey";
return false;
}
if (whichType == TxoutType::NULL_DATA)
nDataOut++;
else if ((whichType == TxoutType::MULTISIG) && (!permit_bare_multisig)) {
reason = "bare-multisig";
return false;
} else if (IsDust(txout, dust_relay_fee)) {
reason = "dust";
return false;
}
}
// only one OP_RETURN txout is permitted
if (nDataOut > 1) {
reason = "multi-op-return";
return false;
}
return true;
}
/**
* Check transaction inputs to mitigate two
* potential denial-of-service attacks:
*
* 1. scriptSigs with extra data stuffed into them,
* not consumed by scriptPubKey (or P2SH script)
* 2. P2SH scripts with a crazy number of expensive
* CHECKSIG/CHECKMULTISIG operations
*
* Why bother? To avoid denial-of-service attacks; an attacker
* can submit a standard HASH... OP_EQUAL transaction,
* which will get accepted into blocks. The redemption
* script can be anything; an attacker could use a very
* expensive-to-check-upon-redemption script like:
* DUP CHECKSIG DROP ... repeated 100 times... OP_1
*
* Note that only the non-witness portion of the transaction is checked here.
*/
bool AreInputsStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs, bool taproot_active)
{
if (tx.IsCoinBase())
return true; // Coinbases don't use vin normally
for (unsigned int i = 0; i < tx.vin.size(); i++)
{
const CTxOut& prev = mapInputs.AccessCoin(tx.vin[i].prevout).out;
std::vector<std::vector<unsigned char> > vSolutions;
TxoutType whichType = Solver(prev.scriptPubKey, vSolutions);
if (whichType == TxoutType::NONSTANDARD || whichType == TxoutType::WITNESS_UNKNOWN) {
// WITNESS_UNKNOWN failures are typically also caught with a policy
// flag in the script interpreter, but it can be helpful to catch
// this type of NONSTANDARD transaction earlier in transaction
// validation.
return false;
} else if (whichType == TxoutType::SCRIPTHASH) {
std::vector<std::vector<unsigned char> > stack;
// convert the scriptSig into a stack, so we can inspect the redeemScript
if (!EvalScript(stack, tx.vin[i].scriptSig, SCRIPT_VERIFY_NONE, BaseSignatureChecker(), SigVersion::BASE))
return false;
if (stack.empty())
return false;
CScript subscript(stack.back().begin(), stack.back().end());
if (subscript.GetSigOpCount(true) > MAX_P2SH_SIGOPS) {
return false;
}
} else if (whichType == TxoutType::WITNESS_V1_TAPROOT) {
// Don't allow Taproot spends unless Taproot is active.
if (!taproot_active) return false;
}
}
return true;
}
bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
{
if (tx.IsCoinBase())
return true; // Coinbases are skipped
for (unsigned int i = 0; i < tx.vin.size(); i++)
{
// We don't care if witness for this input is empty, since it must not be bloated.
// If the script is invalid without witness, it would be caught sooner or later during validation.
if (tx.vin[i].scriptWitness.IsNull())
continue;
const CTxOut &prev = mapInputs.AccessCoin(tx.vin[i].prevout).out;
// get the scriptPubKey corresponding to this input:
CScript prevScript = prev.scriptPubKey;
bool p2sh = false;
if (prevScript.IsPayToScriptHash()) {
std::vector <std::vector<unsigned char> > stack;
// If the scriptPubKey is P2SH, we try to extract the redeemScript casually by converting the scriptSig
// into a stack. We do not check IsPushOnly nor compare the hash as these will be done later anyway.
// If the check fails at this stage, we know that this txid must be a bad one.
if (!EvalScript(stack, tx.vin[i].scriptSig, SCRIPT_VERIFY_NONE, BaseSignatureChecker(), SigVersion::BASE))
return false;
if (stack.empty())
return false;
prevScript = CScript(stack.back().begin(), stack.back().end());
p2sh = true;
}
int witnessversion = 0;
std::vector<unsigned char> witnessprogram;
// Non-witness program must not be associated with any witness
if (!prevScript.IsWitnessProgram(witnessversion, witnessprogram))
return false;
// Check P2WSH standard limits
if (witnessversion == 0 && witnessprogram.size() == WITNESS_V0_SCRIPTHASH_SIZE) {
if (tx.vin[i].scriptWitness.stack.back().size() > MAX_STANDARD_P2WSH_SCRIPT_SIZE)
return false;
size_t sizeWitnessStack = tx.vin[i].scriptWitness.stack.size() - 1;
if (sizeWitnessStack > MAX_STANDARD_P2WSH_STACK_ITEMS)
return false;
for (unsigned int j = 0; j < sizeWitnessStack; j++) {
if (tx.vin[i].scriptWitness.stack[j].size() > MAX_STANDARD_P2WSH_STACK_ITEM_SIZE)
return false;
}
}
// Check policy limits for Taproot spends:
// - MAX_STANDARD_TAPSCRIPT_STACK_ITEM_SIZE limit for stack item size
// - No annexes
if (witnessversion == 1 && witnessprogram.size() == WITNESS_V1_TAPROOT_SIZE && !p2sh) {
// Taproot spend (non-P2SH-wrapped, version 1, witness program size 32; see BIP 341)
auto stack = MakeSpan(tx.vin[i].scriptWitness.stack);
if (stack.size() >= 2 && !stack.back().empty() && stack.back()[0] == ANNEX_TAG) {
// Annexes are nonstandard as long as no semantics are defined for them.
return false;
}
if (stack.size() >= 2) {
// Script path spend (2 or more stack elements after removing optional annex)
const auto& control_block = SpanPopBack(stack);
SpanPopBack(stack); // Ignore script
if (control_block.empty()) return false; // Empty control block is invalid
if ((control_block[0] & TAPROOT_LEAF_MASK) == TAPROOT_LEAF_TAPSCRIPT) {
// Leaf version 0xc0 (aka Tapscript, see BIP 342)
for (const auto& item : stack) {
if (item.size() > MAX_STANDARD_TAPSCRIPT_STACK_ITEM_SIZE) return false;
}
}
} else if (stack.size() == 1) {
// Key path spend (1 stack element after removing optional annex)
// (no policy rules apply)
} else {
// 0 stack elements; this is already invalid by consensus rules
return false;
}
}
}
return true;
}
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;
}
int64_t GetVirtualTransactionSize(const CTransaction& tx, int64_t nSigOpCost, unsigned int bytes_per_sigop)
{
return GetVirtualTransactionSize(GetTransactionWeight(tx), nSigOpCost, bytes_per_sigop);
}
int64_t GetVirtualTransactionInputSize(const CTxIn& txin, int64_t nSigOpCost, unsigned int bytes_per_sigop)
{
return GetVirtualTransactionSize(GetTransactionInputWeight(txin), nSigOpCost, bytes_per_sigop);
}