Optimize CHECKSIGADD Script Validation

Author: JeremyRubin

src/script/interpreter.cpp

@@ -1500,7 +1500,7 @@ static bool HandleMissingData(MissingDataBehavior mdb)
 }
 
 template<typename T>
-bool SignatureHashSchnorr(uint256& hash_out, const ScriptExecutionData& execdata, const T& tx_to, uint32_t in_pos, uint8_t hash_type, SigVersion sigversion, const PrecomputedTransactionData& cache, MissingDataBehavior mdb)
+bool SignatureHashSchnorr(uint256& hash_out, ScriptExecutionData& execdata, const T& tx_to, uint32_t in_pos, uint8_t hash_type, SigVersion sigversion, const PrecomputedTransactionData& cache, MissingDataBehavior mdb)
 {
     uint8_t ext_flag, key_version;
     switch (sigversion) {
@@ -1568,9 +1568,12 @@ bool SignatureHashSchnorr(uint256& hash_out, const ScriptExecutionData& execdata
     // Data about the output (if only one).
     if (output_type == SIGHASH_SINGLE) {
         if (in_pos >= tx_to.vout.size()) return false;
-        CHashWriter sha_single_output(SER_GETHASH, 0);
-        sha_single_output << tx_to.vout[in_pos];
-        ss << sha_single_output.GetSHA256();
+        if (!execdata.m_output_hash) {
+            CHashWriter sha_single_output(SER_GETHASH, 0);
+            sha_single_output << tx_to.vout[in_pos];
+            execdata.m_output_hash = sha_single_output.GetSHA256();
+        }
+        ss << execdata.m_output_hash.value();
     }
 
     // Additional data for BIP 342 signatures
@@ -1692,7 +1695,7 @@ bool GenericTransactionSignatureChecker<T>::CheckECDSASignature(const std::vecto
 }
 
 template <class T>
-bool GenericTransactionSignatureChecker<T>::CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey_in, SigVersion sigversion, const ScriptExecutionData& execdata, ScriptError* serror) const
+bool GenericTransactionSignatureChecker<T>::CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey_in, SigVersion sigversion, ScriptExecutionData& execdata, ScriptError* serror) const
 {
     assert(sigversion == SigVersion::TAPROOT || sigversion == SigVersion::TAPSCRIPT);
     // Schnorr signatures have 32-byte public keys. The caller is responsible for enforcing this.

src/script/interpreter.h

@@ -11,6 +11,7 @@
 #include <span.h>
 #include <primitives/transaction.h>
 
+#include <optional>
 #include <vector>
 #include <stdint.h>
 
@@ -215,6 +216,9 @@ struct ScriptExecutionData
     bool m_validation_weight_left_init = false;
     //! How much validation weight is left (decremented for every successful non-empty signature check).
     int64_t m_validation_weight_left;
+
+    //! The hash of the corresponding output
+    std::optional<uint256> m_output_hash;
 };
 
 /** Signature hash sizes */
@@ -244,7 +248,7 @@ class BaseSignatureChecker
         return false;
     }
 
-    virtual bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, const ScriptExecutionData& execdata, ScriptError* serror = nullptr) const
+    virtual bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, ScriptExecutionData& execdata, ScriptError* serror = nullptr) const
     {
         return false;
     }
@@ -272,7 +276,7 @@ enum class MissingDataBehavior
 };
 
 template<typename T>
-bool SignatureHashSchnorr(uint256& hash_out, const ScriptExecutionData& execdata, const T& tx_to, uint32_t in_pos, uint8_t hash_type, SigVersion sigversion, const PrecomputedTransactionData& cache, MissingDataBehavior mdb);
+bool SignatureHashSchnorr(uint256& hash_out, ScriptExecutionData& execdata, const T& tx_to, uint32_t in_pos, uint8_t hash_type, SigVersion sigversion, const PrecomputedTransactionData& cache, MissingDataBehavior mdb);
 
 template <class T>
 class GenericTransactionSignatureChecker : public BaseSignatureChecker
@@ -292,7 +296,7 @@ class GenericTransactionSignatureChecker : public BaseSignatureChecker
     GenericTransactionSignatureChecker(const T* txToIn, unsigned int nInIn, const CAmount& amountIn, MissingDataBehavior mdb) : txTo(txToIn), m_mdb(mdb), nIn(nInIn), amount(amountIn), txdata(nullptr) {}
     GenericTransactionSignatureChecker(const T* txToIn, unsigned int nInIn, const CAmount& amountIn, const PrecomputedTransactionData& txdataIn, MissingDataBehavior mdb) : txTo(txToIn), m_mdb(mdb), nIn(nInIn), amount(amountIn), txdata(&txdataIn) {}
     bool CheckECDSASignature(const std::vector<unsigned char>& scriptSig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const override;
-    bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, const ScriptExecutionData& execdata, ScriptError* serror = nullptr) const override;
+    bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, ScriptExecutionData& execdata, ScriptError* serror = nullptr) const override;
     bool CheckLockTime(const CScriptNum& nLockTime) const override;
     bool CheckSequence(const CScriptNum& nSequence) const override;
 };
@@ -313,7 +317,7 @@ class DeferringSignatureChecker : public BaseSignatureChecker
         return m_checker.CheckECDSASignature(scriptSig, vchPubKey, scriptCode, sigversion);
     }
 
-    bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, const ScriptExecutionData& execdata, ScriptError* serror = nullptr) const override
+    bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, ScriptExecutionData& execdata, ScriptError* serror = nullptr) const override
     {
         return m_checker.CheckSchnorrSignature(sig, pubkey, sigversion, execdata, serror);
     }

src/script/sign.cpp

@@ -542,7 +542,7 @@ class DummySignatureChecker final : public BaseSignatureChecker
 public:
     DummySignatureChecker() {}
     bool CheckECDSASignature(const std::vector<unsigned char>& scriptSig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const override { return true; }
-    bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, const ScriptExecutionData& execdata, ScriptError* serror) const override { return true; }
+    bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, ScriptExecutionData& execdata, ScriptError* serror) const override { return true; }
 };
 const DummySignatureChecker DUMMY_CHECKER;
 

src/test/fuzz/signature_checker.cpp

@@ -34,7 +34,7 @@ class FuzzedSignatureChecker : public BaseSignatureChecker
         return m_fuzzed_data_provider.ConsumeBool();
     }
 
-    bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, const ScriptExecutionData& execdata, ScriptError* serror = nullptr) const override
+    bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, ScriptExecutionData& execdata, ScriptError* serror = nullptr) const override
     {
         return m_fuzzed_data_provider.ConsumeBool();
     }