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Relax IsStandard rules for pay-to-script-hash transactions
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Relax the AreInputsStandard() tests for P2SH transactions --
allow any Script in a P2SH transaction to be relayed/mined,
as long as it has 15 or fewer signature operations.

Rationale: https://gist.github.com/gavinandresen/88be40c141bc67acb247

I don't have an easy way to test this, but the code changes are
straightforward and I've updated the AreInputsStandard unit tests.
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@gavinandresen
gavinandresen committed Jun 23, 2014
1 parent 36db663 commit 7f3b4e9
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Showing 3 changed files with 97 additions and 66 deletions.
43 changes: 23 additions & 20 deletions src/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -582,15 +582,13 @@ bool IsFinalTx(const CTransaction &tx, int nBlockHeight, int64_t nBlockTime)
}

//
// Check transaction inputs, and make sure any
// pay-to-script-hash transactions are evaluating IsStandard scripts
// Check transaction inputs to mitigate two
// potential denial-of-service attacks:
//
// 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
// 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
//
bool AreInputsStandard(const CTransaction& tx, CCoinsViewCache& mapInputs)
{
Expand All @@ -614,8 +612,9 @@ bool AreInputsStandard(const CTransaction& tx, CCoinsViewCache& mapInputs)
// 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 the
// IsStandard() call returns false
// beside "push data" in the scriptSig
// IsStandard() will have already returned false
// and this method isn't called.
vector<vector<unsigned char> > stack;
if (!EvalScript(stack, tx.vin[i].scriptSig, tx, i, false, 0))
return false;
Expand All @@ -627,16 +626,20 @@ bool AreInputsStandard(const CTransaction& tx, CCoinsViewCache& mapInputs)
CScript subscript(stack.back().begin(), stack.back().end());
vector<vector<unsigned char> > vSolutions2;
txnouttype whichType2;
if (!Solver(subscript, whichType2, vSolutions2))
return false;
if (whichType2 == TX_SCRIPTHASH)
return false;

int tmpExpected;
tmpExpected = ScriptSigArgsExpected(whichType2, vSolutions2);
if (tmpExpected < 0)
return false;
nArgsExpected += tmpExpected;
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)
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2 changes: 2 additions & 0 deletions src/main.h
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,8 @@ static const unsigned int DEFAULT_BLOCK_PRIORITY_SIZE = 50000;
static const unsigned int MAX_STANDARD_TX_SIZE = 100000;
/** The maximum allowed number of signature check operations in a block (network rule) */
static const unsigned int MAX_BLOCK_SIGOPS = MAX_BLOCK_SIZE/50;
/** Maxiumum number of signature check operations in an IsStandard() P2SH script */
static const unsigned int MAX_P2SH_SIGOPS = 15;
/** The maximum number of orphan transactions kept in memory */
static const unsigned int MAX_ORPHAN_TRANSACTIONS = MAX_BLOCK_SIZE/100;
/** Default for -maxorphanblocks, maximum number of orphan blocks kept in memory */
Expand Down
118 changes: 72 additions & 46 deletions src/test/script_P2SH_tests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -256,66 +256,86 @@ BOOST_AUTO_TEST_CASE(AreInputsStandard)
CCoinsView coinsDummy;
CCoinsViewCache coins(coinsDummy);
CBasicKeyStore keystore;
CKey key[3];
CKey key[6];
vector<CPubKey> keys;
for (int i = 0; i < 3; i++)
for (int i = 0; i < 6; i++)
{
key[i].MakeNewKey(true);
keystore.AddKey(key[i]);
keys.push_back(key[i].GetPubKey());
}
for (int i = 0; i < 3; i++)
keys.push_back(key[i].GetPubKey());

CMutableTransaction txFrom;
txFrom.vout.resize(6);
txFrom.vout.resize(7);

// First three are standard:
CScript pay1; pay1.SetDestination(key[0].GetPubKey().GetID());
keystore.AddCScript(pay1);
CScript payScriptHash1; payScriptHash1.SetDestination(pay1.GetID());
CScript pay1of3; pay1of3.SetMultisig(1, keys);

txFrom.vout[0].scriptPubKey = payScriptHash1;
txFrom.vout[0].scriptPubKey.SetDestination(pay1.GetID()); // P2SH (OP_CHECKSIG)
txFrom.vout[0].nValue = 1000;
txFrom.vout[1].scriptPubKey = pay1;
txFrom.vout[1].scriptPubKey = pay1; // ordinary OP_CHECKSIG
txFrom.vout[1].nValue = 2000;
txFrom.vout[2].scriptPubKey = pay1of3;
txFrom.vout[2].scriptPubKey = pay1of3; // ordinary OP_CHECKMULTISIG
txFrom.vout[2].nValue = 3000;

// Last three non-standard:
CScript empty;
keystore.AddCScript(empty);
txFrom.vout[3].scriptPubKey = empty;
// vout[3] is complicated 1-of-3 AND 2-of-3
// ... that is OK if wrapped in P2SH:
CScript oneAndTwo;
oneAndTwo << OP_1 << key[0].GetPubKey() << key[1].GetPubKey() << key[2].GetPubKey();
oneAndTwo << OP_3 << OP_CHECKMULTISIGVERIFY;
oneAndTwo << OP_2 << key[3].GetPubKey() << key[4].GetPubKey() << key[5].GetPubKey();
oneAndTwo << OP_3 << OP_CHECKMULTISIG;
keystore.AddCScript(oneAndTwo);
txFrom.vout[3].scriptPubKey.SetDestination(oneAndTwo.GetID());
txFrom.vout[3].nValue = 4000;
// Can't use SetPayToScriptHash, it checks for the empty Script. So:
txFrom.vout[4].scriptPubKey << OP_HASH160 << Hash160(empty) << OP_EQUAL;

// vout[4] is max sigops:
CScript fifteenSigops; fifteenSigops << OP_1;
for (int i = 0; i < MAX_P2SH_SIGOPS; i++)
fifteenSigops << key[i%3].GetPubKey();
fifteenSigops << OP_15 << OP_CHECKMULTISIG;
keystore.AddCScript(fifteenSigops);
txFrom.vout[4].scriptPubKey.SetDestination(fifteenSigops.GetID());
txFrom.vout[4].nValue = 5000;
CScript oneOfEleven;
oneOfEleven << OP_1;
for (int i = 0; i < 11; i++)
oneOfEleven << key[0].GetPubKey();
oneOfEleven << OP_11 << OP_CHECKMULTISIG;
txFrom.vout[5].scriptPubKey.SetDestination(oneOfEleven.GetID());
txFrom.vout[5].nValue = 6000;

// vout[5/6] are non-standard because they exceed MAX_P2SH_SIGOPS
CScript sixteenSigops; sixteenSigops << OP_16 << OP_CHECKMULTISIG;
keystore.AddCScript(sixteenSigops);
txFrom.vout[5].scriptPubKey.SetDestination(fifteenSigops.GetID());
txFrom.vout[5].nValue = 5000;
CScript twentySigops; twentySigops << OP_CHECKMULTISIG;
keystore.AddCScript(twentySigops);
txFrom.vout[6].scriptPubKey.SetDestination(twentySigops.GetID());
txFrom.vout[6].nValue = 6000;


coins.SetCoins(txFrom.GetHash(), CCoins(txFrom, 0));

CMutableTransaction txTo;
txTo.vout.resize(1);
txTo.vout[0].scriptPubKey.SetDestination(key[1].GetPubKey().GetID());

txTo.vin.resize(3);
txTo.vin[0].prevout.n = 0;
txTo.vin[0].prevout.hash = txFrom.GetHash();
txTo.vin.resize(5);
for (int i = 0; i < 5; i++)
{
txTo.vin[i].prevout.n = i;
txTo.vin[i].prevout.hash = txFrom.GetHash();
}
BOOST_CHECK(SignSignature(keystore, txFrom, txTo, 0));
txTo.vin[1].prevout.n = 1;
txTo.vin[1].prevout.hash = txFrom.GetHash();
BOOST_CHECK(SignSignature(keystore, txFrom, txTo, 1));
txTo.vin[2].prevout.n = 2;
txTo.vin[2].prevout.hash = txFrom.GetHash();
BOOST_CHECK(SignSignature(keystore, txFrom, txTo, 2));
// SignSignature doesn't know how to sign these. We're
// not testing validating signatures, so just create
// dummy signatures that DO include the correct P2SH scripts:
txTo.vin[3].scriptSig << OP_11 << OP_11 << static_cast<vector<unsigned char> >(oneAndTwo);
txTo.vin[4].scriptSig << static_cast<vector<unsigned char> >(fifteenSigops);

BOOST_CHECK(::AreInputsStandard(txTo, coins));
BOOST_CHECK_EQUAL(GetP2SHSigOpCount(txTo, coins), 1U);
// 22 P2SH sigops for all inputs (1 for vin[0], 6 for vin[3], 15 for vin[4]
BOOST_CHECK_EQUAL(GetP2SHSigOpCount(txTo, coins), 22U);

// Make sure adding crap to the scriptSigs makes them non-standard:
for (int i = 0; i < 3; i++)
Expand All @@ -326,23 +346,29 @@ BOOST_AUTO_TEST_CASE(AreInputsStandard)
txTo.vin[i].scriptSig = t;
}

CMutableTransaction txToNonStd;
txToNonStd.vout.resize(1);
txToNonStd.vout[0].scriptPubKey.SetDestination(key[1].GetPubKey().GetID());
txToNonStd.vout[0].nValue = 1000;
txToNonStd.vin.resize(2);
txToNonStd.vin[0].prevout.n = 4;
txToNonStd.vin[0].prevout.hash = txFrom.GetHash();
txToNonStd.vin[0].scriptSig << Serialize(empty);
txToNonStd.vin[1].prevout.n = 5;
txToNonStd.vin[1].prevout.hash = txFrom.GetHash();
txToNonStd.vin[1].scriptSig << OP_0 << Serialize(oneOfEleven);

BOOST_CHECK(!::AreInputsStandard(txToNonStd, coins));
BOOST_CHECK_EQUAL(GetP2SHSigOpCount(txToNonStd, coins), 11U);

txToNonStd.vin[0].scriptSig.clear();
BOOST_CHECK(!::AreInputsStandard(txToNonStd, coins));
CMutableTransaction txToNonStd1;
txToNonStd1.vout.resize(1);
txToNonStd1.vout[0].scriptPubKey.SetDestination(key[1].GetPubKey().GetID());
txToNonStd1.vout[0].nValue = 1000;
txToNonStd1.vin.resize(1);
txToNonStd1.vin[0].prevout.n = 5;
txToNonStd1.vin[0].prevout.hash = txFrom.GetHash();
txToNonStd1.vin[0].scriptSig << static_cast<vector<unsigned char> >(sixteenSigops);

BOOST_CHECK(!::AreInputsStandard(txToNonStd1, coins));
BOOST_CHECK_EQUAL(GetP2SHSigOpCount(txToNonStd1, coins), 16U);

CMutableTransaction txToNonStd2;
txToNonStd2.vout.resize(1);
txToNonStd2.vout[0].scriptPubKey.SetDestination(key[1].GetPubKey().GetID());
txToNonStd2.vout[0].nValue = 1000;
txToNonStd2.vin.resize(1);
txToNonStd2.vin[0].prevout.n = 6;
txToNonStd2.vin[0].prevout.hash = txFrom.GetHash();
txToNonStd2.vin[0].scriptSig << static_cast<vector<unsigned char> >(twentySigops);

BOOST_CHECK(!::AreInputsStandard(txToNonStd2, coins));
BOOST_CHECK_EQUAL(GetP2SHSigOpCount(txToNonStd2, coins), 20U);
}

BOOST_AUTO_TEST_SUITE_END()

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