From 5c1e798a8e9df15f8fbd120e57fc67e585f13843 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Wed, 10 Sep 2014 16:16:09 +0200
Subject: Make signature cache optional

---
 src/script/interpreter.cpp | 74 ++++------------------------------------------
 1 file changed, 6 insertions(+), 68 deletions(-)

(limited to 'src/script/interpreter.cpp')

diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
index 048d298f0b..f0b4268390 100644
--- a/src/script/interpreter.cpp
+++ b/src/script/interpreter.cpp
@@ -9,14 +9,10 @@
 #include "crypto/ripemd160.h"
 #include "crypto/sha1.h"
 #include "crypto/sha2.h"
-#include "random.h"
 #include "script/script.h"
 #include "uint256.h"
 #include "util.h"
 
-#include <boost/thread.hpp>
-#include <boost/tuple/tuple_comparison.hpp>
-
 using namespace std;
 
 typedef vector<unsigned char> valtype;
@@ -132,7 +128,7 @@ bool IsCanonicalSignature(const valtype &vchSig, unsigned int flags) {
     return true;
 }
 
-bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const SignatureChecker& checker)
+bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const BaseSignatureChecker& checker)
 {
     CScript::const_iterator pc = script.begin();
     CScript::const_iterator pend = script.end();
@@ -921,65 +917,13 @@ uint256 SignatureHash(const CScript& scriptCode, const CTransaction& txTo, unsig
     return ss.GetHash();
 }
 
-// Valid signature cache, to avoid doing expensive ECDSA signature checking
-// twice for every transaction (once when accepted into memory pool, and
-// again when accepted into the block chain)
-class CSignatureCache
+bool SignatureChecker::VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash, int flags) const
 {
-private:
-     // sigdata_type is (signature hash, signature, public key):
-    typedef boost::tuple<uint256, std::vector<unsigned char>, CPubKey> sigdata_type;
-    std::set< sigdata_type> setValid;
-    boost::shared_mutex cs_sigcache;
-
-public:
-    bool
-    Get(const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubKey)
-    {
-        boost::shared_lock<boost::shared_mutex> lock(cs_sigcache);
-
-        sigdata_type k(hash, vchSig, pubKey);
-        std::set<sigdata_type>::iterator mi = setValid.find(k);
-        if (mi != setValid.end())
-            return true;
-        return false;
-    }
-
-    void Set(const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubKey)
-    {
-        // DoS prevention: limit cache size to less than 10MB
-        // (~200 bytes per cache entry times 50,000 entries)
-        // Since there are a maximum of 20,000 signature operations per block
-        // 50,000 is a reasonable default.
-        int64_t nMaxCacheSize = GetArg("-maxsigcachesize", 50000);
-        if (nMaxCacheSize <= 0) return;
-
-        boost::unique_lock<boost::shared_mutex> lock(cs_sigcache);
-
-        while (static_cast<int64_t>(setValid.size()) > nMaxCacheSize)
-        {
-            // Evict a random entry. Random because that helps
-            // foil would-be DoS attackers who might try to pre-generate
-            // and re-use a set of valid signatures just-slightly-greater
-            // than our cache size.
-            uint256 randomHash = GetRandHash();
-            std::vector<unsigned char> unused;
-            std::set<sigdata_type>::iterator it =
-                setValid.lower_bound(sigdata_type(randomHash, unused, unused));
-            if (it == setValid.end())
-                it = setValid.begin();
-            setValid.erase(*it);
-        }
-
-        sigdata_type k(hash, vchSig, pubKey);
-        setValid.insert(k);
-    }
-};
+    return pubkey.Verify(sighash, vchSig);
+}
 
 bool SignatureChecker::CheckSig(const vector<unsigned char>& vchSigIn, const vector<unsigned char>& vchPubKey, const CScript& scriptCode, int flags) const
 {
-    static CSignatureCache signatureCache;
-
     CPubKey pubkey(vchPubKey);
     if (!pubkey.IsValid())
         return false;
@@ -993,19 +937,13 @@ bool SignatureChecker::CheckSig(const vector<unsigned char>& vchSigIn, const vec
 
     uint256 sighash = SignatureHash(scriptCode, txTo, nIn, nHashType);
 
-    if (signatureCache.Get(sighash, vchSig, pubkey))
-        return true;
-
-    if (!pubkey.Verify(sighash, vchSig))
+    if (!VerifySignature(vchSig, pubkey, sighash, flags))
         return false;
 
-    if (!(flags & SCRIPT_VERIFY_NOCACHE))
-        signatureCache.Set(sighash, vchSig, pubkey);
-
     return true;
 }
 
-bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, unsigned int flags, const SignatureChecker& checker)
+bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, unsigned int flags, const BaseSignatureChecker& checker)
 {
     vector<vector<unsigned char> > stack, stackCopy;
     if (!EvalScript(stack, scriptSig, flags, checker))
-- 
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