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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2021 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 <algorithm>
#include <mutex>
#include <optional>
#include <shared_mutex>
#include <vector>
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 || 'E' or 'S' || 31 zero bytes || signature hash || public key || signature):
CSHA256 m_salted_hasher_ecdsa;
CSHA256 m_salted_hasher_schnorr;
typedef CuckooCache::cache<uint256, SignatureCacheHasher> map_type;
map_type setValid;
std::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, and then pad with 'E' for ECDSA and
// 'S' for Schnorr (followed by 0 bytes).
static constexpr unsigned char PADDING_ECDSA[32] = {'E'};
static constexpr unsigned char PADDING_SCHNORR[32] = {'S'};
m_salted_hasher_ecdsa.Write(nonce.begin(), 32);
m_salted_hasher_ecdsa.Write(PADDING_ECDSA, 32);
m_salted_hasher_schnorr.Write(nonce.begin(), 32);
m_salted_hasher_schnorr.Write(PADDING_SCHNORR, 32);
}
void
ComputeEntryECDSA(uint256& entry, const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubkey) const
{
CSHA256 hasher = m_salted_hasher_ecdsa;
hasher.Write(hash.begin(), 32).Write(pubkey.data(), pubkey.size()).Write(vchSig.data(), vchSig.size()).Finalize(entry.begin());
}
void
ComputeEntrySchnorr(uint256& entry, const uint256 &hash, Span<const unsigned char> sig, const XOnlyPubKey& pubkey) const
{
CSHA256 hasher = m_salted_hasher_schnorr;
hasher.Write(hash.begin(), 32).Write(pubkey.data(), pubkey.size()).Write(sig.data(), sig.size()).Finalize(entry.begin());
}
bool
Get(const uint256& entry, const bool erase)
{
std::shared_lock<std::shared_mutex> lock(cs_sigcache);
return setValid.contains(entry, erase);
}
void Set(const uint256& entry)
{
std::unique_lock<std::shared_mutex> lock(cs_sigcache);
setValid.insert(entry);
}
std::optional<std::pair<uint32_t, size_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.
bool InitSignatureCache()
{
// nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,
// setup_bytes creates the minimum possible cache (2 elements).
size_t nMaxCacheSize = std::max((int64_t)0, gArgs.GetIntArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2) * ((size_t) 1 << 20);
auto setup_results = signatureCache.setup_bytes(nMaxCacheSize);
if (!setup_results) return false;
const auto [num_elems, approx_size_bytes] = *setup_results;
LogPrintf("Using %zu MiB out of %zu/2 requested for signature cache, able to store %zu elements\n",
approx_size_bytes >> 20, (nMaxCacheSize * 2) >> 20, num_elems);
return true;
}
bool CachingTransactionSignatureChecker::VerifyECDSASignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
{
uint256 entry;
signatureCache.ComputeEntryECDSA(entry, sighash, vchSig, pubkey);
if (signatureCache.Get(entry, !store))
return true;
if (!TransactionSignatureChecker::VerifyECDSASignature(vchSig, pubkey, sighash))
return false;
if (store)
signatureCache.Set(entry);
return true;
}
bool CachingTransactionSignatureChecker::VerifySchnorrSignature(Span<const unsigned char> sig, const XOnlyPubKey& pubkey, const uint256& sighash) const
{
uint256 entry;
signatureCache.ComputeEntrySchnorr(entry, sighash, sig, pubkey);
if (signatureCache.Get(entry, !store)) return true;
if (!TransactionSignatureChecker::VerifySchnorrSignature(sig, pubkey, sighash)) return false;
if (store) signatureCache.Set(entry);
return true;
}
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