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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2014 The Bitcoin 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 "main.h"
#include "tinyformat.h"
#include "util.h"
#include "utilstrencodings.h"
#include <boost/foreach.hpp>
/**
* 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
*
* Check transaction inputs, and make sure any
* pay-to-script-hash transactions are evaluating IsStandard scripts
*
* 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
*/
bool IsStandard(const CScript& scriptPubKey, txnouttype& whichType)
{
std::vector<std::vector<unsigned char> > vSolutions;
if (!Solver(scriptPubKey, whichType, vSolutions))
return false;
if (whichType == TX_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;
}
return whichType != TX_NONSTANDARD;
}
bool IsStandardTx(const CTransaction& tx, std::string& reason)
{
if (tx.nVersion > CTransaction::CURRENT_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_SIZE mitigates CPU exhaustion attacks.
unsigned int sz = tx.GetSerializeSize(SER_NETWORK, CTransaction::CURRENT_VERSION);
if (sz >= MAX_STANDARD_TX_SIZE) {
reason = "tx-size";
return false;
}
BOOST_FOREACH(const CTxIn& txin, tx.vin)
{
// Biggest 'standard' txin 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 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() > 1650) {
reason = "scriptsig-size";
return false;
}
if (!txin.scriptSig.IsPushOnly()) {
reason = "scriptsig-not-pushonly";
return false;
}
}
unsigned int nDataOut = 0;
txnouttype whichType;
BOOST_FOREACH(const CTxOut& txout, tx.vout) {
if (!::IsStandard(txout.scriptPubKey, whichType)) {
reason = "scriptpubkey";
return false;
}
if (whichType == TX_NULL_DATA)
nDataOut++;
else if ((whichType == TX_MULTISIG) && (!fIsBareMultisigStd)) {
reason = "bare-multisig";
return false;
} else if (txout.IsDust(::minRelayTxFee)) {
reason = "dust";
return false;
}
}
// only one OP_RETURN txout is permitted
if (nDataOut > 1) {
reason = "multi-op-return";
return false;
}
return true;
}
bool AreInputsStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
{
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.GetOutputFor(tx.vin[i]);
std::vector<std::vector<unsigned char> > vSolutions;
txnouttype whichType;
// get the scriptPubKey corresponding to this input:
const CScript& prevScript = prev.scriptPubKey;
if (!Solver(prevScript, whichType, vSolutions))
return false;
int nArgsExpected = ScriptSigArgsExpected(whichType, vSolutions);
if (nArgsExpected < 0)
return false;
// Transactions with extra stuff in their scriptSigs are
// non-standard. Note that this EvalScript() call will
// be quick, because if there are any operations
// beside "push data" in the scriptSig
// IsStandardTx() will have already returned false
// and this method isn't called.
std::vector<std::vector<unsigned char> > stack;
if (!EvalScript(stack, tx.vin[i].scriptSig, SCRIPT_VERIFY_NONE, BaseSignatureChecker()))
return false;
if (whichType == TX_SCRIPTHASH)
{
if (stack.empty())
return false;
CScript subscript(stack.back().begin(), stack.back().end());
std::vector<std::vector<unsigned char> > vSolutions2;
txnouttype whichType2;
if (Solver(subscript, whichType2, vSolutions2))
{
int tmpExpected = ScriptSigArgsExpected(whichType2, vSolutions2);
if (tmpExpected < 0)
return false;
nArgsExpected += tmpExpected;
}
else
{
// Any other Script with less than 15 sigops OK:
unsigned int sigops = subscript.GetSigOpCount(true);
// ... extra data left on the stack after execution is OK, too:
return (sigops <= MAX_P2SH_SIGOPS);
}
}
if (stack.size() != (unsigned int)nArgsExpected)
return false;
}
return true;
}
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