sigcache.cpp

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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 <script/sigcache.h>
 
#include <crypto/sha256.h>
#include <logging.h>
#include <pubkey.h>
#include <random.h>
#include <script/interpreter.h>
#include <span.h>
#include <uint256.h>
 
#include <mutex>
#include <shared_mutex>
#include <vector>
 
SignatureCache::SignatureCache(const size_t max_size_bytes) {
    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);
 
    const auto [num_elems, approx_size_bytes] =
        setValid.setup_bytes(max_size_bytes);
    LogPrintf("Using %zu MiB out of %zu MiB requested for signature cache, "
              "able to store %zu elements\n",
              approx_size_bytes >> 20, max_size_bytes >> 20, num_elems);
}
 
void SignatureCache::ComputeEntry(uint256 &entry, const uint256 &hash,
                                  const std::vector<uint8_t> &vchSig,
                                  const CPubKey &pubkey) const {
    CSHA256 hasher = m_salted_hasher;
    hasher.Write(hash.begin(), 32)
        .Write(pubkey.data(), pubkey.size())
        .Write(vchSig.data(), vchSig.size())
        .Finalize(entry.begin());
}
 
bool SignatureCache::Get(const uint256 &entry, const bool erase) {
    std::shared_lock<std::shared_mutex> lock(cs_sigcache);
    return setValid.contains(entry, erase);
}
 
void SignatureCache::Set(const uint256 &entry) {
    std::unique_lock<std::shared_mutex> lock(cs_sigcache);
    setValid.insert(entry);
}
 
template <typename F>
bool RunMemoizedCheck(SignatureCache &signatureCache,
                      const std::vector<uint8_t> &vchSig, const CPubKey &pubkey,
                      const uint256 &sighash, bool storeOrErase, const F &fun) {
    uint256 entry;
    signatureCache.ComputeEntry(entry, sighash, vchSig, pubkey);
    if (signatureCache.Get(entry, !storeOrErase)) {
        return true;
    }
    if (!fun()) {
        return false;
    }
    if (storeOrErase) {
        signatureCache.Set(entry);
    }
    return true;
}
 
bool CachingTransactionSignatureChecker::IsCached(
    const std::vector<uint8_t> &vchSig, const CPubKey &pubkey,
    const uint256 &sighash) const {
    return RunMemoizedCheck(m_signature_cache, vchSig, pubkey, sighash, true,
                            [] { return false; });
}
 
bool CachingTransactionSignatureChecker::VerifySignature(
    const std::vector<uint8_t> &vchSig, const CPubKey &pubkey,
    const uint256 &sighash) const {
    return RunMemoizedCheck(
        m_signature_cache, vchSig, pubkey, sighash, store, [&] {
            return TransactionSignatureChecker::VerifySignature(vchSig, pubkey,
                                                                sighash);
        });
}