Precompute sighashes

Original version by Nicolas Dorier. Precomputing version by Pieter Wuille.

src/main.cpp

@@ -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) &&
+            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)) {
+                !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();
             }
@@ -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));
@@ -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;
@@ -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())
     {
@@ -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());
@@ -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())));
                     }
@@ -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];
@@ -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);

src/main.h

@@ -38,6 +38,7 @@ class CScriptCheck;
 class CTxMemPool;
 class CValidationInterface;
 class CValidationState;
+class CachedHashes;
 
 struct CNodeStateStats;
 struct LockPoints;
@@ -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);
@@ -421,12 +422,13 @@ private:
     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()();
 
@@ -438,6 +440,7 @@ public:
         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; }

src/script/bitcoinconsensus.cpp

@@ -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);
-
+        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), NULL);
+        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
     }

src/script/interpreter.cpp

@@ -1108,9 +1108,40 @@ public:
     }
 };
 
+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;
@@ -1118,27 +1149,16 @@ uint256 SignatureHash(const CScript& scriptCode, const CTransaction& txTo, unsig
         uint256 hashOutputs;
 
         if (!(nHashType & SIGHASH_ANYONECANPAY)) {
-            CHashWriter ss(SER_GETHASH, 0);
+            hashPrevouts = cache ? cache->hashPrevouts : GetPrevoutHash(txTo);
-            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
         }
 
         if (!(nHashType & SIGHASH_ANYONECANPAY) && (nHashType & 0x1f) != SIGHASH_SINGLE && (nHashType & 0x1f) != SIGHASH_NONE) {
-            CHashWriter ss(SER_GETHASH, 0);
+            hashSequence = cache ? cache->hashSequence : GetSequenceHash(txTo);
-            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
         }
 
+
         if ((nHashType & 0x1f) != SIGHASH_SINGLE && (nHashType & 0x1f) != SIGHASH_NONE) {
-            CHashWriter ss(SER_GETHASH, 0);
+            hashOutputs = cache ? cache->hashOutputs : GetOutputsHash(txTo);
-            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
         } else if ((nHashType & 0x1f) == SIGHASH_SINGLE && nIn < txTo.vout.size()) {
             CHashWriter ss(SER_GETHASH, 0);
             ss << txTo.vout[nIn];
@@ -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;

src/script/interpreter.h

@@ -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
 {
@@ -133,12 +140,14 @@ private:
     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;

src/script/sigcache.h

@@ -22,7 +22,7 @@ private:
     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;
 };

src/test/script_P2SH_tests.cpp

@@ -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)

src/test/transaction_tests.cpp

@@ -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))
@@ -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));
             }
@@ -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))
@@ -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));