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Precompute sighashes
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Original version by Nicolas Dorier. Precomputing version by Pieter Wuille.
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@sipa
sipa committed Aug 16, 2016
1 parent 2c2d471 commit d2c5d04
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Showing 8 changed files with 78 additions and 38 deletions.
22 changes: 13 additions & 9 deletions src/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1492,12 +1492,13 @@ bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState& state, const C

// Check against previous transactions
// This is done last to help prevent CPU exhaustion denial-of-service attacks.
if (!CheckInputs(tx, state, view, true, scriptVerifyFlags, true)) {
CachedHashes cachedHashes(tx);
if (!CheckInputs(tx, state, view, true, scriptVerifyFlags, true, cachedHashes)) {
// SCRIPT_VERIFY_CLEANSTACK requires SCRIPT_VERIFY_WITNESS, so we
// need to turn both off, and compare against just turning off CLEANSTACK
// to see if the failure is specifically due to witness validation.
if (CheckInputs(tx, state, view, true, scriptVerifyFlags & ~(SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_CLEANSTACK), true) &&
!CheckInputs(tx, state, view, true, scriptVerifyFlags & ~SCRIPT_VERIFY_CLEANSTACK, true)) {
if (CheckInputs(tx, state, view, true, scriptVerifyFlags & ~(SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_CLEANSTACK), true, cachedHashes) &&
!CheckInputs(tx, state, view, true, scriptVerifyFlags & ~SCRIPT_VERIFY_CLEANSTACK, true, cachedHashes)) {
// Only the witness is wrong, so the transaction itself may be fine.
state.SetCorruptionPossible();
}
Expand All @@ -1513,7 +1514,7 @@ bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState& state, const C
// There is a similar check in CreateNewBlock() to prevent creating
// invalid blocks, however allowing such transactions into the mempool
// can be exploited as a DoS attack.
if (!CheckInputs(tx, state, view, true, MANDATORY_SCRIPT_VERIFY_FLAGS, true))
if (!CheckInputs(tx, state, view, true, MANDATORY_SCRIPT_VERIFY_FLAGS, true, cachedHashes))
{
return error("%s: BUG! PLEASE REPORT THIS! ConnectInputs failed against MANDATORY but not STANDARD flags %s, %s",
__func__, hash.ToString(), FormatStateMessage(state));
Expand Down Expand Up @@ -1910,7 +1911,7 @@ void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, int nHeight)
bool CScriptCheck::operator()() {
const CScript &scriptSig = ptxTo->vin[nIn].scriptSig;
const CScriptWitness *witness = (nIn < ptxTo->wit.vtxinwit.size()) ? &ptxTo->wit.vtxinwit[nIn].scriptWitness : NULL;
if (!VerifyScript(scriptSig, scriptPubKey, witness, nFlags, CachingTransactionSignatureChecker(ptxTo, nIn, amount, cacheStore), &error)) {
if (!VerifyScript(scriptSig, scriptPubKey, witness, nFlags, CachingTransactionSignatureChecker(ptxTo, nIn, amount, cacheStore, *cachedHashes), &error)) {
return false;
}
return true;
Expand Down Expand Up @@ -1969,7 +1970,7 @@ bool CheckTxInputs(const CTransaction& tx, CValidationState& state, const CCoins
}
}// namespace Consensus

bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheStore, std::vector<CScriptCheck> *pvChecks)
bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheStore, CachedHashes& cachedHashes, std::vector<CScriptCheck> *pvChecks)
{
if (!tx.IsCoinBase())
{
Expand All @@ -1996,7 +1997,7 @@ bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsVi
assert(coins);

// Verify signature
CScriptCheck check(*coins, tx, i, flags, cacheStore);
CScriptCheck check(*coins, tx, i, flags, cacheStore, &cachedHashes);
if (pvChecks) {
pvChecks->push_back(CScriptCheck());
check.swap(pvChecks->back());
Expand All @@ -2009,7 +2010,7 @@ bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsVi
// avoid splitting the network between upgraded and
// non-upgraded nodes.
CScriptCheck check2(*coins, tx, i,
flags & ~STANDARD_NOT_MANDATORY_VERIFY_FLAGS, cacheStore);
flags & ~STANDARD_NOT_MANDATORY_VERIFY_FLAGS, cacheStore, &cachedHashes);
if (check2())
return state.Invalid(false, REJECT_NONSTANDARD, strprintf("non-mandatory-script-verify-flag (%s)", ScriptErrorString(check.GetScriptError())));
}
Expand Down Expand Up @@ -2405,6 +2406,8 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
std::vector<std::pair<uint256, CDiskTxPos> > vPos;
vPos.reserve(block.vtx.size());
blockundo.vtxundo.reserve(block.vtx.size() - 1);
std::vector<CachedHashes> cachedHashes;
cachedHashes.reserve(block.vtx.size()); // Required so that pointers to individual CachedHashes don't get invalidated
for (unsigned int i = 0; i < block.vtx.size(); i++)
{
const CTransaction &tx = block.vtx[i];
Expand Down Expand Up @@ -2451,13 +2454,14 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
return state.DoS(100, error("ConnectBlock(): too many sigops"),
REJECT_INVALID, "bad-blk-sigops");

cachedHashes.emplace_back(tx);
if (!tx.IsCoinBase())
{
nFees += view.GetValueIn(tx)-tx.GetValueOut();

std::vector<CScriptCheck> vChecks;
bool fCacheResults = fJustCheck; /* Don't cache results if we're actually connecting blocks (still consult the cache, though) */
if (!CheckInputs(tx, state, view, fScriptChecks, flags, fCacheResults, nScriptCheckThreads ? &vChecks : NULL))
if (!CheckInputs(tx, state, view, fScriptChecks, flags, fCacheResults, cachedHashes[i], nScriptCheckThreads ? &vChecks : NULL))
return error("ConnectBlock(): CheckInputs on %s failed with %s",
tx.GetHash().ToString(), FormatStateMessage(state));
control.Add(vChecks);
Expand Down
9 changes: 6 additions & 3 deletions src/main.h
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,7 @@ class CScriptCheck;
class CTxMemPool;
class CValidationInterface;
class CValidationState;
class CachedHashes;

struct CNodeStateStats;
struct LockPoints;
Expand Down Expand Up @@ -347,7 +348,7 @@ int64_t GetTransactionSigOpCost(const CTransaction& tx, const CCoinsViewCache& i
* instead of being performed inline.
*/
bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &view, bool fScriptChecks,
unsigned int flags, bool cacheStore, std::vector<CScriptCheck> *pvChecks = NULL);
unsigned int flags, bool cacheStore, CachedHashes& cachedHashes, std::vector<CScriptCheck> *pvChecks = NULL);

/** Apply the effects of this transaction on the UTXO set represented by view */
void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, int nHeight);
Expand Down Expand Up @@ -421,12 +422,13 @@ class CScriptCheck
unsigned int nFlags;
bool cacheStore;
ScriptError error;
CachedHashes *cachedHashes;

public:
CScriptCheck(): amount(0), ptxTo(0), nIn(0), nFlags(0), cacheStore(false), error(SCRIPT_ERR_UNKNOWN_ERROR) {}
CScriptCheck(const CCoins& txFromIn, const CTransaction& txToIn, unsigned int nInIn, unsigned int nFlagsIn, bool cacheIn) :
CScriptCheck(const CCoins& txFromIn, const CTransaction& txToIn, unsigned int nInIn, unsigned int nFlagsIn, bool cacheIn, CachedHashes* cachedHashesIn) :
scriptPubKey(txFromIn.vout[txToIn.vin[nInIn].prevout.n].scriptPubKey), amount(txFromIn.vout[txToIn.vin[nInIn].prevout.n].nValue),
ptxTo(&txToIn), nIn(nInIn), nFlags(nFlagsIn), cacheStore(cacheIn), error(SCRIPT_ERR_UNKNOWN_ERROR) { }
ptxTo(&txToIn), nIn(nInIn), nFlags(nFlagsIn), cacheStore(cacheIn), error(SCRIPT_ERR_UNKNOWN_ERROR), cachedHashes(cachedHashesIn) { }

bool operator()();

Expand All @@ -438,6 +440,7 @@ class CScriptCheck
std::swap(nFlags, check.nFlags);
std::swap(cacheStore, check.cacheStore);
std::swap(error, check.error);
std::swap(cachedHashes, check.cachedHashes);
}

ScriptError GetScriptError() const { return error; }
Expand Down
4 changes: 2 additions & 2 deletions src/script/bitcoinconsensus.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -84,8 +84,8 @@ static int verify_script(const unsigned char *scriptPubKey, unsigned int scriptP

// Regardless of the verification result, the tx did not error.
set_error(err, bitcoinconsensus_ERR_OK);

return VerifyScript(tx.vin[nIn].scriptSig, CScript(scriptPubKey, scriptPubKey + scriptPubKeyLen), nIn < tx.wit.vtxinwit.size() ? &tx.wit.vtxinwit[nIn].scriptWitness : NULL, flags, TransactionSignatureChecker(&tx, nIn, amount), NULL);
CachedHashes cachedHashes(tx);
return VerifyScript(tx.vin[nIn].scriptSig, CScript(scriptPubKey, scriptPubKey + scriptPubKeyLen), nIn < tx.wit.vtxinwit.size() ? &tx.wit.vtxinwit[nIn].scriptWitness : NULL, flags, TransactionSignatureChecker(&tx, nIn, amount, cachedHashes), NULL);
} catch (const std::exception&) {
return set_error(err, bitcoinconsensus_ERR_TX_DESERIALIZE); // Error deserializing
}
Expand Down
54 changes: 37 additions & 17 deletions src/script/interpreter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1108,37 +1108,57 @@ class CTransactionSignatureSerializer {
}
};

uint256 GetPrevoutHash(const CTransaction& txTo) {
CHashWriter ss(SER_GETHASH, 0);
for (unsigned int n = 0; n < txTo.vin.size(); n++) {
ss << txTo.vin[n].prevout;
}
return ss.GetHash();
}

uint256 GetSequenceHash(const CTransaction& txTo) {
CHashWriter ss(SER_GETHASH, 0);
for (unsigned int n = 0; n < txTo.vin.size(); n++) {
ss << txTo.vin[n].nSequence;
}
return ss.GetHash();
}

uint256 GetOutputsHash(const CTransaction& txTo) {
CHashWriter ss(SER_GETHASH, 0);
for (unsigned int n = 0; n < txTo.vout.size(); n++) {
ss << txTo.vout[n];
}
return ss.GetHash();
}

} // anon namespace

uint256 SignatureHash(const CScript& scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType, const CAmount& amount, SigVersion sigversion)
CachedHashes::CachedHashes(const CTransaction& txTo)
{
hashPrevouts = GetPrevoutHash(txTo);
hashSequence = GetSequenceHash(txTo);
hashOutputs = GetOutputsHash(txTo);
}

uint256 SignatureHash(const CScript& scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType, const CAmount& amount, SigVersion sigversion, const CachedHashes* cache)
{
if (sigversion == SIGVERSION_WITNESS_V0) {
uint256 hashPrevouts;
uint256 hashSequence;
uint256 hashOutputs;

if (!(nHashType & SIGHASH_ANYONECANPAY)) {
CHashWriter ss(SER_GETHASH, 0);
for (unsigned int n = 0; n < txTo.vin.size(); n++) {
ss << txTo.vin[n].prevout;
}
hashPrevouts = ss.GetHash(); // TODO: cache this value for all signatures in a transaction
hashPrevouts = cache ? cache->hashPrevouts : GetPrevoutHash(txTo);
}

if (!(nHashType & SIGHASH_ANYONECANPAY) && (nHashType & 0x1f) != SIGHASH_SINGLE && (nHashType & 0x1f) != SIGHASH_NONE) {
CHashWriter ss(SER_GETHASH, 0);
for (unsigned int n = 0; n < txTo.vin.size(); n++) {
ss << txTo.vin[n].nSequence;
}
hashSequence = ss.GetHash(); // TODO: cache this value for all signatures in a transaction
hashSequence = cache ? cache->hashSequence : GetSequenceHash(txTo);
}


if ((nHashType & 0x1f) != SIGHASH_SINGLE && (nHashType & 0x1f) != SIGHASH_NONE) {
CHashWriter ss(SER_GETHASH, 0);
for (unsigned int n = 0; n < txTo.vout.size(); n++) {
ss << txTo.vout[n];
}
hashOutputs = ss.GetHash(); // TODO: cache this value for all signatures in a transaction
hashOutputs = cache ? cache->hashOutputs : GetOutputsHash(txTo);
} else if ((nHashType & 0x1f) == SIGHASH_SINGLE && nIn < txTo.vout.size()) {
CHashWriter ss(SER_GETHASH, 0);
ss << txTo.vout[nIn];
Expand Down Expand Up @@ -1209,7 +1229,7 @@ bool TransactionSignatureChecker::CheckSig(const vector<unsigned char>& vchSigIn
int nHashType = vchSig.back();
vchSig.pop_back();

uint256 sighash = SignatureHash(scriptCode, *txTo, nIn, nHashType, amount, sigversion);
uint256 sighash = SignatureHash(scriptCode, *txTo, nIn, nHashType, amount, sigversion, this->cachedHashes);

if (!VerifySignature(vchSig, pubkey, sighash))
return false;
Expand Down
13 changes: 11 additions & 2 deletions src/script/interpreter.h
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Original file line number Diff line number Diff line change
Expand Up @@ -98,13 +98,20 @@ enum

bool CheckSignatureEncoding(const std::vector<unsigned char> &vchSig, unsigned int flags, ScriptError* serror);

struct CachedHashes
{
uint256 hashPrevouts, hashSequence, hashOutputs;

CachedHashes(const CTransaction& tx);
};

enum SigVersion
{
SIGVERSION_BASE = 0,
SIGVERSION_WITNESS_V0 = 1,
};

uint256 SignatureHash(const CScript &scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType, const CAmount& amount, SigVersion sigversion);
uint256 SignatureHash(const CScript &scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType, const CAmount& amount, SigVersion sigversion, const CachedHashes* cache = NULL);

class BaseSignatureChecker
{
Expand Down Expand Up @@ -133,12 +140,14 @@ class TransactionSignatureChecker : public BaseSignatureChecker
const CTransaction* txTo;
unsigned int nIn;
const CAmount amount;
const CachedHashes* cachedHashes;

protected:
virtual bool VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& vchPubKey, const uint256& sighash) const;

public:
TransactionSignatureChecker(const CTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn) : txTo(txToIn), nIn(nInIn), amount(amountIn) {}
TransactionSignatureChecker(const CTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn) : txTo(txToIn), nIn(nInIn), amount(amountIn), cachedHashes(NULL) {}
TransactionSignatureChecker(const CTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn, const CachedHashes& cachedHashesIn) : txTo(txToIn), nIn(nInIn), amount(amountIn), cachedHashes(&cachedHashesIn) {}
bool CheckSig(const std::vector<unsigned char>& scriptSig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const;
bool CheckLockTime(const CScriptNum& nLockTime) const;
bool CheckSequence(const CScriptNum& nSequence) const;
Expand Down
2 changes: 1 addition & 1 deletion src/script/sigcache.h
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,7 @@ class CachingTransactionSignatureChecker : public TransactionSignatureChecker
bool store;

public:
CachingTransactionSignatureChecker(const CTransaction* txToIn, unsigned int nInIn, const CAmount& amount, bool storeIn) : TransactionSignatureChecker(txToIn, nInIn, amount), store(storeIn) {}
CachingTransactionSignatureChecker(const CTransaction* txToIn, unsigned int nInIn, const CAmount& amount, bool storeIn, CachedHashes& cachedHashesIn) : TransactionSignatureChecker(txToIn, nInIn, amount, cachedHashesIn), store(storeIn) {}

bool VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& vchPubKey, const uint256& sighash) const;
};
Expand Down
6 changes: 4 additions & 2 deletions src/test/script_P2SH_tests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -107,18 +107,20 @@ BOOST_AUTO_TEST_CASE(sign)
}
// All of the above should be OK, and the txTos have valid signatures
// Check to make sure signature verification fails if we use the wrong ScriptSig:
for (int i = 0; i < 8; i++)
for (int i = 0; i < 8; i++) {
CachedHashes cachedHashes(txTo[i]);
for (int j = 0; j < 8; j++)
{
CScript sigSave = txTo[i].vin[0].scriptSig;
txTo[i].vin[0].scriptSig = txTo[j].vin[0].scriptSig;
bool sigOK = CScriptCheck(CCoins(txFrom, 0), txTo[i], 0, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_STRICTENC, false)();
bool sigOK = CScriptCheck(CCoins(txFrom, 0), txTo[i], 0, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_STRICTENC, false, &cachedHashes)();
if (i == j)
BOOST_CHECK_MESSAGE(sigOK, strprintf("VerifySignature %d %d", i, j));
else
BOOST_CHECK_MESSAGE(!sigOK, strprintf("VerifySignature %d %d", i, j));
txTo[i].vin[0].scriptSig = sigSave;
}
}
}

BOOST_AUTO_TEST_CASE(norecurse)
Expand Down
6 changes: 4 additions & 2 deletions src/test/transaction_tests.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -153,6 +153,7 @@ BOOST_AUTO_TEST_CASE(tx_valid)
BOOST_CHECK_MESSAGE(CheckTransaction(tx, state), strTest);
BOOST_CHECK(state.IsValid());

CachedHashes cachedHashes(tx);
for (unsigned int i = 0; i < tx.vin.size(); i++)
{
if (!mapprevOutScriptPubKeys.count(tx.vin[i].prevout))
Expand All @@ -168,7 +169,7 @@ BOOST_AUTO_TEST_CASE(tx_valid)
unsigned int verify_flags = ParseScriptFlags(test[2].get_str());
const CScriptWitness *witness = (i < tx.wit.vtxinwit.size()) ? &tx.wit.vtxinwit[i].scriptWitness : NULL;
BOOST_CHECK_MESSAGE(VerifyScript(tx.vin[i].scriptSig, mapprevOutScriptPubKeys[tx.vin[i].prevout],
witness, verify_flags, TransactionSignatureChecker(&tx, i, amount), &err),
witness, verify_flags, TransactionSignatureChecker(&tx, i, amount, cachedHashes), &err),
strTest);
BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_OK, ScriptErrorString(err));
}
Expand Down Expand Up @@ -237,6 +238,7 @@ BOOST_AUTO_TEST_CASE(tx_invalid)
CValidationState state;
fValid = CheckTransaction(tx, state) && state.IsValid();

CachedHashes cachedHashes(tx);
for (unsigned int i = 0; i < tx.vin.size() && fValid; i++)
{
if (!mapprevOutScriptPubKeys.count(tx.vin[i].prevout))
Expand All @@ -252,7 +254,7 @@ BOOST_AUTO_TEST_CASE(tx_invalid)
}
const CScriptWitness *witness = (i < tx.wit.vtxinwit.size()) ? &tx.wit.vtxinwit[i].scriptWitness : NULL;
fValid = VerifyScript(tx.vin[i].scriptSig, mapprevOutScriptPubKeys[tx.vin[i].prevout],
witness, verify_flags, TransactionSignatureChecker(&tx, i, amount), &err);
witness, verify_flags, TransactionSignatureChecker(&tx, i, amount, cachedHashes), &err);
}
BOOST_CHECK_MESSAGE(!fValid, strTest);
BOOST_CHECK_MESSAGE(err != SCRIPT_ERR_OK, ScriptErrorString(err));
Expand Down

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