Make signature cache optional

src/script/sigcache.cpp

@@ -0,0 +1,88 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2013 The Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "sigcache.h"
+
+#include "key.h"
+#include "random.h"
+#include "uint256.h"
+#include "util.h"
+
+#include <boost/thread.hpp>
+#include <boost/tuple/tuple_comparison.hpp>
+
+namespace {
+
+// 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
+{
+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);
+    }
+};
+
+}
+
+bool CachingSignatureChecker::VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash, int flags) const
+{
+    static CSignatureCache signatureCache;
+
+    if (signatureCache.Get(sighash, vchSig, pubkey))
+        return true;
+
+    if (!SignatureChecker::VerifySignature(vchSig, pubkey, sighash, flags))
+        return false;
+
+    if (!(flags & SCRIPT_VERIFY_NOCACHE))
+        signatureCache.Set(sighash, vchSig, pubkey);
+    return true;
+}