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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2019 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <script/sigcache.h>
#include <pubkey.h>
#include <random.h>
#include <uint256.h>
#include <util/system.h>
#include <cuckoocache.h>
#include <boost/thread.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:
//! Entries are SHA256(nonce || signature hash || public key || signature):
CSHA256 m_salted_hasher;
typedef CuckooCache::cache<uint256, SignatureCacheHasher> map_type;
map_type setValid;
boost::shared_mutex cs_sigcache;
public:
CSignatureCache()
{
uint256 nonce = GetRandHash();
// We want the nonce to be 64 bytes long to force the hasher to process
// this chunk, which makes later hash computations more efficient. We
// just write our 32-byte entropy twice to fill the 64 bytes.
m_salted_hasher.Write(nonce.begin(), 32);
m_salted_hasher.Write(nonce.begin(), 32);
}
void
ComputeEntry(uint256& entry, const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubkey)
{
CSHA256 hasher = m_salted_hasher;
hasher.Write(hash.begin(), 32).Write(&pubkey[0], pubkey.size()).Write(&vchSig[0], vchSig.size()).Finalize(entry.begin());
}
bool
Get(const uint256& entry, const bool erase)
{
boost::shared_lock<boost::shared_mutex> lock(cs_sigcache);
return setValid.contains(entry, erase);
}
void Set(uint256& entry)
{
boost::unique_lock<boost::shared_mutex> lock(cs_sigcache);
setValid.insert(entry);
}
uint32_t setup_bytes(size_t n)
{
return setValid.setup_bytes(n);
}
};
/* In previous versions of this code, signatureCache was a local static variable
* in CachingTransactionSignatureChecker::VerifySignature. We initialize
* signatureCache outside of VerifySignature to avoid the atomic operation per
* call overhead associated with local static variables even though
* signatureCache could be made local to VerifySignature.
*/
static CSignatureCache signatureCache;
} // namespace
// To be called once in AppInitMain/BasicTestingSetup to initialize the
// signatureCache.
void InitSignatureCache()
{
// nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,
// setup_bytes creates the minimum possible cache (2 elements).
size_t nMaxCacheSize = std::min(std::max((int64_t)0, gArgs.GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
size_t nElems = signatureCache.setup_bytes(nMaxCacheSize);
LogPrintf("Using %zu MiB out of %zu/2 requested for signature cache, able to store %zu elements\n",
(nElems*sizeof(uint256)) >>20, (nMaxCacheSize*2)>>20, nElems);
}
bool CachingTransactionSignatureChecker::VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
{
uint256 entry;
signatureCache.ComputeEntry(entry, sighash, vchSig, pubkey);
if (signatureCache.Get(entry, !store))
return true;
if (!TransactionSignatureChecker::VerifySignature(vchSig, pubkey, sighash))
return false;
if (store)
signatureCache.Set(entry);
return true;
}
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