Repository: bitcoin/bitcoin
File: src/key.cpp (C++)

Code before:
    // Additional verification step to prevent using a potentially corrupted signature
    secp256k1_pubkey epk, rpk;
    ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &epk, UCharCast(begin()));
    assert(ret);
    ret = secp256k1_ecdsa_recover(secp256k1_context_static, &rpk, &rsig, hash.begin());
    assert(ret);
    ret = secp256k1_ec_pubkey_cmp(secp256k1_context_static, &epk, &rpk);
    assert(ret == 0);
    return true;
}

bool CKey::SignSchnorr(const uint256& hash, Span<unsigned char> sig, const uint256* merkle_root, const uint256& aux) const
{
    assert(sig.size() == 64);
    bool ret = 1;
    secp256k1_keypair keypair;
    if (!secp256k1_keypair_create(secp256k1_context_sign, &keypair, UCharCast(begin()))) return false;
    if (merkle_root) {
        secp256k1_xonly_pubkey pubkey;
        ret &= secp256k1_keypair_xonly_pub(secp256k1_context_sign, &pubkey, nullptr, &keypair);
        unsigned char pubkey_bytes[32];
        ret &= secp256k1_xonly_pubkey_serialize(secp256k1_context_sign, pubkey_bytes, &pubkey);
        uint256 tweak = XOnlyPubKey(pubkey_bytes).ComputeTapTweakHash(merkle_root->IsNull() ? nullptr : merkle_root);
        ret &= secp256k1_keypair_xonly_tweak_add(secp256k1_context_static, &keypair, tweak.data());
    }
    if (!ret) return false;
    ret &= secp256k1_schnorrsig_sign32(secp256k1_context_sign, sig.data(), hash.data(), &keypair, aux.data());
    if (ret) {
        // Additional verification step to prevent using a potentially corrupted signature
        secp256k1_xonly_pubkey pubkey_verify;
        ret &= secp256k1_keypair_xonly_pub(secp256k1_context_static, &pubkey_verify, nullptr, &keypair);
        ret &= secp256k1_schnorrsig_verify(secp256k1_context_static, sig.data(), hash.begin(), 32, &pubkey_verify);
    }
    if (!ret) memory_cleanse(sig.data(), sig.size());
    memory_cleanse(&keypair, sizeof(keypair));
    return ret;
}

bool CKey::Load(const CPrivKey &seckey, const CPubKey &vchPubKey, bool fSkipCheck=false) {
    MakeKeyData();
    if (!ec_seckey_import_der(secp256k1_context_sign, (unsigned char*)begin(), seckey.data(), seckey.size())) {
        ClearKeyData();
        return false;
    }
    fCompressed = vchPubKey.IsCompressed();

    if (fSkipCheck)
        return true;

    return VerifyPubKey(vchPubKey);
}

Review comment (bug):
> we do not change behavior by exiting early before attempting to sign if there is a failure with the merkle_root logic.

Previously, when an error occurred, subsequent calculations weren't performed. 
Since `&=` doesn't short-circuit (and even if it did, `pubkey_bytes` would be allocated and `ComputeTapTweakHash` would run even if `secp256k1_keypair_xonly_pub` failed), the methods could be called even though a previous dependency failed.
Are you sure this is just a refactoring and not a behavior change?

Code after:
    // Additional verification step to prevent using a potentially corrupted signature
    secp256k1_pubkey epk, rpk;
    ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &epk, UCharCast(begin()));
    assert(ret);
    ret = secp256k1_ecdsa_recover(secp256k1_context_static, &rpk, &rsig, hash.begin());
    assert(ret);
    ret = secp256k1_ec_pubkey_cmp(secp256k1_context_static, &epk, &rpk);
    assert(ret == 0);
    return true;
}

bool CKey::SignSchnorr(const uint256& hash, Span<unsigned char> sig, const uint256* merkle_root, const uint256& aux) const
{
    KeyPair kp = ComputeKeyPair(merkle_root);
    return kp.SignSchnorr(hash, sig, aux);
}

bool CKey::Load(const CPrivKey &seckey, const CPubKey &vchPubKey, bool fSkipCheck=false) {
    MakeKeyData();
    if (!ec_seckey_import_der(secp256k1_context_sign, (unsigned char*)begin(), seckey.data(), seckey.size())) {
        ClearKeyData();
        return false;
    }
    fCompressed = vchPubKey.IsCompressed();

    if (fSkipCheck)
        return true;

    return VerifyPubKey(vchPubKey);
}

bool CKey::Derive(CKey& keyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const {
    assert(IsValid());
    assert(IsCompressed());
    std::vector<unsigned char, secure_allocator<unsigned char>> vout(64);
    if ((nChild >> 31) == 0) {
        CPubKey pubkey = GetPubKey();
        assert(pubkey.size() == CPubKey::COMPRESSED_SIZE);
        BIP32Hash(cc, nChild, *pubkey.begin(), pubkey.begin()+1, vout.data());
    } else {
        assert(size() == 32);
        BIP32Hash(cc, nChild, 0, UCharCast(begin()), vout.data());
    }
    memcpy(ccChild.begin(), vout.data()+32, 32);
    keyChild.Set(begin(), begin() + 32, true);
    bool ret = secp256k1_ec_seckey_tweak_add(secp256k1_context_sign, (unsigned char*)keyChild.begin(), vout.data());
    if (!ret) keyChild.ClearKeyData();
    return ret;
}

EllSwiftPubKey CKey::EllSwiftCreate(Span<const std::byte> ent32) const