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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2016 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 "sigcache.h"
#include "memusage.h"
#include "pubkey.h"
#include "random.h"
#include "uint256.h"
#include "util.h"
#include "cuckoocache.h"
#include <boost/thread.hpp>
namespace {
/**
* We're hashing a nonce into the entries themselves, so we don't need extra
* blinding in the set hash computation.
*
* This may exhibit platform endian dependent behavior but because these are
* nonced hashes (random) and this state is only ever used locally it is safe.
* All that matters is local consistency.
*/
class SignatureCacheHasher
{
public:
template <uint8_t hash_select>
uint32_t operator()(const uint256& key) const
{
static_assert(hash_select <8, "SignatureCacheHasher only has 8 hashes available.");
uint32_t u;
std::memcpy(&u, key.begin()+4*hash_select, 4);
return u;
}
};
/**
* 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):
uint256 nonce;
typedef CuckooCache::cache<uint256, SignatureCacheHasher> map_type;
map_type setValid;
boost::shared_mutex cs_sigcache;
public:
CSignatureCache()
{
GetRandBytes(nonce.begin(), 32);
}
void
ComputeEntry(uint256& entry, const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubkey)
{
CSHA256().Write(nonce.begin(), 32).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;
}
// To be called once in AppInit2/TestingSetup to initialize the signatureCache
void InitSignatureCache()
{
size_t nMaxCacheSize = GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
if (nMaxCacheSize <= 0) return;
size_t nElems = signatureCache.setup_bytes(nMaxCacheSize);
LogPrintf("Using %zu MiB out of %zu requested for signature cache, able to store %zu elements\n",
(nElems*sizeof(uint256)) >>20, nMaxCacheSize>>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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