Precompute sighashes

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

Edited for Zcash by Ariel Gabizon and Jack Grigg

src/gtest/test_validation.cpp

@@ -71,7 +71,8 @@ TEST(Validation, ContextualCheckInputsPassesWithCoinbase) {
     CCoinsViewCache view(&fakeDB);
 
     CValidationState state;
-    EXPECT_TRUE(ContextualCheckInputs(tx, state, view, false, 0, false, Params(CBaseChainParams::MAIN).GetConsensus()));
+    CachedHashes cachedHashes(tx);
+    EXPECT_TRUE(ContextualCheckInputs(tx, state, view, false, 0, false, cachedHashes, Params(CBaseChainParams::MAIN).GetConsensus()));
 }
 
 TEST(Validation, ReceivedBlockTransactions) {

src/main.cpp

@@ -1347,7 +1347,8 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
 
         // Check against previous transactions
         // This is done last to help prevent CPU exhaustion denial-of-service attacks.
-        if (!ContextualCheckInputs(tx, state, view, true, STANDARD_SCRIPT_VERIFY_FLAGS, true, Params().GetConsensus()))
+        CachedHashes cachedHashes(tx);
+        if (!ContextualCheckInputs(tx, state, view, true, STANDARD_SCRIPT_VERIFY_FLAGS, true, cachedHashes, Params().GetConsensus()))
         {
             return error("AcceptToMemoryPool: ConnectInputs failed %s", hash.ToString());
         }
@@ -1361,7 +1362,7 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
         // 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 (!ContextualCheckInputs(tx, state, view, true, MANDATORY_SCRIPT_VERIFY_FLAGS, true, Params().GetConsensus()))
+        if (!ContextualCheckInputs(tx, state, view, true, MANDATORY_SCRIPT_VERIFY_FLAGS, true, cachedHashes, Params().GetConsensus()))
         {
             return error("AcceptToMemoryPool: BUG! PLEASE REPORT THIS! ConnectInputs failed against MANDATORY but not STANDARD flags %s", hash.ToString());
         }
@@ -1726,7 +1727,7 @@ void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, int nHeight)
 
 bool CScriptCheck::operator()() {
     const CScript &scriptSig = ptxTo->vin[nIn].scriptSig;
-    if (!VerifyScript(scriptSig, scriptPubKey, nFlags, CachingTransactionSignatureChecker(ptxTo, nIn, amount, cacheStore), &error)) {
+    if (!VerifyScript(scriptSig, scriptPubKey, nFlags, CachingTransactionSignatureChecker(ptxTo, nIn, amount, cacheStore, *cachedHashes), &error)) {
         return ::error("CScriptCheck(): %s:%d VerifySignature failed: %s", ptxTo->GetHash().ToString(), nIn, ScriptErrorString(error));
     }
     return true;
@@ -1809,7 +1810,7 @@ bool CheckTxInputs(const CTransaction& tx, CValidationState& state, const CCoins
 }
 }// namespace Consensus
 
-bool ContextualCheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheStore, const Consensus::Params& consensusParams, std::vector<CScriptCheck> *pvChecks)
+bool ContextualCheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheStore, CachedHashes& cachedHashes, const Consensus::Params& consensusParams, std::vector<CScriptCheck> *pvChecks)
 {
     if (!tx.IsCoinBase())
     {
@@ -1834,7 +1835,7 @@ bool ContextualCheckInputs(const CTransaction& tx, CValidationState &state, cons
                 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());
@@ -1847,7 +1848,7 @@ bool ContextualCheckInputs(const CTransaction& tx, CValidationState &state, cons
                         // 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())));
                     }
@@ -2237,6 +2238,8 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
         assert(tree.root() == old_tree_root);
     }
 
+    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];
@@ -2265,11 +2268,16 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
             if (nSigOps > MAX_BLOCK_SIGOPS)
                 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;
-            if (!ContextualCheckInputs(tx, state, view, fExpensiveChecks, flags, false, chainparams.GetConsensus(), nScriptCheckThreads ? &vChecks : NULL))
+            if (!ContextualCheckInputs(tx, state, view, fExpensiveChecks, flags, false, cachedHashes[i], chainparams.GetConsensus(), nScriptCheckThreads ? &vChecks : NULL))
                 return false;
             control.Add(vChecks);
         }

src/main.h

@@ -45,6 +45,7 @@ class CInv;
 class CScriptCheck;
 class CValidationInterface;
 class CValidationState;
+class CachedHashes;
 
 struct CNodeStateStats;
 
@@ -330,7 +331,7 @@ unsigned int GetP2SHSigOpCount(const CTransaction& tx, const CCoinsViewCache& ma
  * instead of being performed inline.
  */
 bool ContextualCheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &view, bool fScriptChecks,
-                           unsigned int flags, bool cacheStore, const Consensus::Params& consensusParams,
+                           unsigned int flags, bool cacheStore, CachedHashes& cachedHashes, const Consensus::Params& consensusParams,
                            std::vector<CScriptCheck> *pvChecks = NULL);
 
 /** Check a transaction contextually against a set of consensus rules */
@@ -390,12 +391,13 @@ 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()();
 
@@ -407,6 +409,7 @@ 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/miner.cpp

@@ -293,7 +293,8 @@ CBlockTemplate* CreateNewBlock(const CScript& scriptPubKeyIn)
             // policy here, but we still have to ensure that the block we
             // create only contains transactions that are valid in new blocks.
             CValidationState state;
-            if (!ContextualCheckInputs(tx, state, view, true, MANDATORY_SCRIPT_VERIFY_FLAGS, true, Params().GetConsensus()))
+            CachedHashes cachedHashes(tx);
+            if (!ContextualCheckInputs(tx, state, view, true, MANDATORY_SCRIPT_VERIFY_FLAGS, true, cachedHashes, Params().GetConsensus()))
                 continue;
 
             UpdateCoins(tx, view, nHeight);

src/script/interpreter.cpp

@@ -1050,9 +1050,40 @@ 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 (nIn >= txTo.vin.size() && nIn != NOT_AN_INPUT) {
         //  nIn out of range
@@ -1065,27 +1096,16 @@ uint256 SignatureHash(const CScript& scriptCode, const CTransaction& txTo, unsig
         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];
@@ -1154,7 +1174,7 @@ bool TransactionSignatureChecker::CheckSig(const vector<unsigned char>& vchSigIn
 
     uint256 sighash;
     try {
-        sighash = SignatureHash(scriptCode, *txTo, nIn, nHashType, amount, sigversion);
+        sighash = SignatureHash(scriptCode, *txTo, nIn, nHashType, amount, sigversion, this->cachedHashes);
     } catch (logic_error ex) {
         return false;
     }

src/script/interpreter.h

@@ -88,13 +88,20 @@ enum
     SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY = (1U << 9),
 };
 
+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
 {
@@ -118,12 +125,14 @@ 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;
 };

src/script/sigcache.h

@@ -18,7 +18,7 @@ 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/script/zcashconsensus.cpp

@@ -84,9 +84,9 @@ int zcashconsensus_verify_script(const unsigned char *scriptPubKey, unsigned int
 
          // Regardless of the verification result, the tx did not error.
          set_error(err, zcashconsensus_ERR_OK);
-
+        CachedHashes cachedHashes(tx);
         CAmount am(0);
-        return VerifyScript(tx.vin[nIn].scriptSig, CScript(scriptPubKey, scriptPubKey + scriptPubKeyLen), flags, TransactionSignatureChecker(&tx, nIn, am), NULL);
+        return VerifyScript(tx.vin[nIn].scriptSig, CScript(scriptPubKey, scriptPubKey + scriptPubKeyLen), flags, TransactionSignatureChecker(&tx, nIn, am, cachedHashes), NULL);
     } catch (const std::exception&) {
         return set_error(err, zcashconsensus_ERR_TX_DESERIALIZE); // Error deserializing
     }

src/test/script_P2SH_tests.cpp

@@ -111,18 +111,20 @@ 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

@@ -147,6 +147,7 @@ BOOST_AUTO_TEST_CASE(tx_valid)
             BOOST_CHECK_MESSAGE(CheckTransaction(tx, state, verifier), strTest + comment);
             BOOST_CHECK_MESSAGE(state.IsValid(), comment);
 
+            CachedHashes cachedHashes(tx);
             for (unsigned int i = 0; i < tx.vin.size(); i++)
             {
                 if (!mapprevOutScriptPubKeys.count(tx.vin[i].prevout))
@@ -158,7 +159,7 @@ BOOST_AUTO_TEST_CASE(tx_valid)
                 CAmount amount = 0;
                 unsigned int verify_flags = ParseScriptFlags(test[2].get_str());
                 BOOST_CHECK_MESSAGE(VerifyScript(tx.vin[i].scriptSig, mapprevOutScriptPubKeys[tx.vin[i].prevout],
-                                                 verify_flags, TransactionSignatureChecker(&tx, i, amount), &err),
+                                                 verify_flags, TransactionSignatureChecker(&tx, i, amount, cachedHashes), &err),
                                     strTest + comment);
                 BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_OK, ScriptErrorString(err) + comment);
             }
@@ -231,6 +232,7 @@ BOOST_AUTO_TEST_CASE(tx_invalid)
             CValidationState state;
             fValid = CheckTransaction(tx, state, verifier) && state.IsValid();
 
+            CachedHashes cachedHashes(tx);
             for (unsigned int i = 0; i < tx.vin.size() && fValid; i++)
             {
                 if (!mapprevOutScriptPubKeys.count(tx.vin[i].prevout))
@@ -242,7 +244,7 @@ BOOST_AUTO_TEST_CASE(tx_invalid)
                 unsigned int verify_flags = ParseScriptFlags(test[2].get_str());
                 CAmount amount = 0;
                 fValid = VerifyScript(tx.vin[i].scriptSig, mapprevOutScriptPubKeys[tx.vin[i].prevout],
-                                      verify_flags, TransactionSignatureChecker(&tx, i, amount), &err);
+                                      verify_flags, TransactionSignatureChecker(&tx, i, amount, cachedHashes), &err);
             }
             BOOST_CHECK_MESSAGE(!fValid, strTest + comment);
             BOOST_CHECK_MESSAGE(err != SCRIPT_ERR_OK, ScriptErrorString(err) + comment);