Precompute sighashes

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

4 files changed, 51 insertions, 22 deletions

diff --git a/src/script/bitcoinconsensus.cpp b/src/script/bitcoinconsensus.cpp
index 62fd9031f8..01a8babb67 100644
--- a/src/script/bitcoinconsensus.cpp
+++ b/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);
-
-        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
     }
diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
index bc027e9f0c..459feaa0f4 100644
--- a/src/script/interpreter.cpp
+++ b/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);
-            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];
@@ -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;
diff --git a/src/script/interpreter.h b/src/script/interpreter.h
index bd2f211663..b4da113eec 100644
--- a/src/script/interpreter.h
+++ b/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;
diff --git a/src/script/sigcache.h b/src/script/sigcache.h
index 050bf8cc42..551f8b2253 100644
--- a/src/script/sigcache.h
+++ b/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;
 };