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// 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;
}
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