Caching successful ECDSA and Schnorr verification

1// Copyright (c) 2009-2010 Satoshi Nakamoto
2// Copyright (c) 2009-present The Bitcoin Core developers
3// Distributed under the MIT software license, see the accompanying
4// file COPYING or http://www.opensource.org/licenses/mit-license.php.
5
6#include <script/sigcache.h>
7
8#include <crypto/sha256.h>
9#include <pubkey.h>
10#include <random.h>
11#include <script/interpreter.h>
12#include <uint256.h>
13#include <util/log.h>
14
15#include <mutex>
16#include <shared_mutex>
17#include <utility>
18#include <vector>
19
20SignatureCache::SignatureCache(const size_t max_size_bytes)
21{
22    uint256 nonce = GetRandHash();
23    // We want the nonce to be 64 bytes long to force the hasher to process
24    // this chunk, which makes later hash computations more efficient. We
25    // just write our 32-byte entropy, and then pad with 'E' for ECDSA and
26    // 'S' for Schnorr (followed by 0 bytes).
27    static constexpr unsigned char PADDING_ECDSA[32] = {'E'};
28    static constexpr unsigned char PADDING_SCHNORR[32] = {'S'};
29    m_salted_hasher_ecdsa.Write(nonce.begin(), 32);
30    m_salted_hasher_ecdsa.Write(PADDING_ECDSA, 32);
31    m_salted_hasher_schnorr.Write(nonce.begin(), 32);
32    m_salted_hasher_schnorr.Write(PADDING_SCHNORR, 32);
33
34    const auto [num_elems, approx_size_bytes] = setValid.setup_bytes(max_size_bytes);
35    LogInfo("Using %zu MiB out of %zu MiB requested for signature cache, able to store %zu elements",
36              approx_size_bytes >> 20, max_size_bytes >> 20, num_elems);
37}
38
39void SignatureCache::ComputeEntryECDSA(uint256& entry, const uint256& hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubkey) const
40{
41    CSHA256 hasher = m_salted_hasher_ecdsa;
42    hasher.Write(hash.begin(), 32).Write(pubkey.data(), pubkey.size()).Write(vchSig.data(), vchSig.size()).Finalize(entry.begin());
43}
44
45void SignatureCache::ComputeEntrySchnorr(uint256& entry, const uint256& hash, std::span<const unsigned char> sig, const XOnlyPubKey& pubkey) const
46{
47    CSHA256 hasher = m_salted_hasher_schnorr;
48    hasher.Write(hash.begin(), 32).Write(pubkey.data(), pubkey.size()).Write(sig.data(), sig.size()).Finalize(entry.begin());
49}
50
51bool SignatureCache::Get(const uint256& entry, const bool erase)
52{
53    std::shared_lock<std::shared_mutex> lock(cs_sigcache);
54    return setValid.contains(entry, erase);
55}
56
57void SignatureCache::Set(const uint256& entry)
58{
59    std::unique_lock<std::shared_mutex> lock(cs_sigcache);
60    setValid.insert(entry);
61}
62
63bool CachingTransactionSignatureChecker::VerifyECDSASignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
64{
65    uint256 entry;
66    m_signature_cache.ComputeEntryECDSA(entry, sighash, vchSig, pubkey);
67    if (m_signature_cache.Get(entry, !store))
68        return true;
69    if (!TransactionSignatureChecker::VerifyECDSASignature(vchSig, pubkey, sighash))
70        return false;
71    if (store)
72        m_signature_cache.Set(entry);
73    return true;
74}
75
76bool CachingTransactionSignatureChecker::VerifySchnorrSignature(std::span<const unsigned char> sig, const XOnlyPubKey& pubkey, const uint256& sighash) const
77{
78    uint256 entry;
79    m_signature_cache.ComputeEntrySchnorr(entry, sighash, sig, pubkey);
80    if (m_signature_cache.Get(entry, !store)) return true;
81    if (!TransactionSignatureChecker::VerifySchnorrSignature(sig, pubkey, sighash)) return false;
82    if (store) m_signature_cache.Set(entry);
83    return true;
84}
85