/*
 * This file is part of the Flowee project
 * Copyright (c) 2009-2015 The Bitcoin Core developers
 * Copyright (C) 2019-2025 Tom Zander <tom@flowee.org>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "PublicKey.h"
#include <hash.h>

#include <secp256k1.h>
#include <secp256k1_recovery.h>
#include <secp256k1_schnorr.h>

namespace
{
/* Global secp256k1_context object used for verification. */
secp256k1_context* secp256k1_context_verify = nullptr;
}

/** This function is taken from the libsecp256k1 distribution and implements
 *  DER parsing for ECDSA signatures, while supporting an arbitrary subset of
 *  format violations.
 *
 *  Supported violations include negative integers, excessive padding, garbage
 *  at the end, and overly long length descriptors. This is safe to use in
 *  Bitcoin because since the activation of BIP66, signatures are verified to be
 *  strict DER before being passed to this module, and we know it supports all
 *  violations present in the blockchain before that point.
 */
static int ecdsa_signature_parse_der_lax(const secp256k1_context* ctx, secp256k1_ecdsa_signature* sig, const unsigned char *input, size_t inputlen) {
    size_t rpos, rlen, spos, slen;
    size_t pos = 0;
    size_t lenbyte;
    unsigned char tmpsig[64] = {0};
    int overflow = 0;

    /* Hack to initialize sig with a correctly-parsed but invalid signature. */
    secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig);

    /* Sequence tag byte */
    if (pos == inputlen || input[pos] != 0x30) {
        return 0;
    }
    pos++;

    /* Sequence length bytes */
    if (pos == inputlen) {
        return 0;
    }
    lenbyte = input[pos++];
    if (lenbyte & 0x80) {
        lenbyte -= 0x80;
        if (pos + lenbyte > inputlen) {
            return 0;
        }
        pos += lenbyte;
    }

    /* Integer tag byte for R */
    if (pos == inputlen || input[pos] != 0x02) {
        return 0;
    }
    pos++;

    /* Integer length for R */
    if (pos == inputlen) {
        return 0;
    }
    lenbyte = input[pos++];
    if (lenbyte & 0x80) {
        lenbyte -= 0x80;
        if (pos + lenbyte > inputlen) {
            return 0;
        }
        while (lenbyte > 0 && input[pos] == 0) {
            pos++;
            lenbyte--;
        }
        if (lenbyte >= sizeof(size_t)) {
            return 0;
        }
        rlen = 0;
        while (lenbyte > 0) {
            rlen = (rlen << 8) + input[pos];
            pos++;
            lenbyte--;
        }
    } else {
        rlen = lenbyte;
    }
    if (rlen > inputlen - pos) {
        return 0;
    }
    rpos = pos;
    pos += rlen;

    /* Integer tag byte for S */
    if (pos == inputlen || input[pos] != 0x02) {
        return 0;
    }
    pos++;

    /* Integer length for S */
    if (pos == inputlen) {
        return 0;
    }
    lenbyte = input[pos++];
    if (lenbyte & 0x80) {
        lenbyte -= 0x80;
        if (pos + lenbyte > inputlen) {
            return 0;
        }
        while (lenbyte > 0 && input[pos] == 0) {
            pos++;
            lenbyte--;
        }
        if (lenbyte >= sizeof(size_t)) {
            return 0;
        }
        slen = 0;
        while (lenbyte > 0) {
            slen = (slen << 8) + input[pos];
            pos++;
            lenbyte--;
        }
    } else {
        slen = lenbyte;
    }
    if (slen > inputlen - pos) {
        return 0;
    }
    spos = pos;
    pos += slen;

    /* Ignore leading zeroes in R */
    while (rlen > 0 && input[rpos] == 0) {
        rlen--;
        rpos++;
    }
    /* Copy R value */
    if (rlen > 32) {
        overflow = 1;
    } else {
        memcpy(tmpsig + 32 - rlen, input + rpos, rlen);
    }

    /* Ignore leading zeroes in S */
    while (slen > 0 && input[spos] == 0) {
        slen--;
        spos++;
    }
    /* Copy S value */
    if (slen > 32) {
        overflow = 1;
    } else {
        memcpy(tmpsig + 64 - slen, input + spos, slen);
    }

    if (!overflow) {
        overflow = !secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig);
    }
    if (overflow) {
        /* Overwrite the result again with a correctly-parsed but invalid
           signature if parsing failed. */
        memset(tmpsig, 0, 64);
        secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig);
    }
    return 1;
}

bool PublicKey::verifyECDSA(const uint256 &hash, const std::vector<unsigned char>& vchSig) const {
    if (!isValid())
        return false;
    secp256k1_pubkey pubkey;
    secp256k1_ecdsa_signature sig;
    if (!secp256k1_ec_pubkey_parse(secp256k1_context_verify, &pubkey, &(*this)[0], size())) {
        return false;
    }
    if (vchSig.size() == 0) {
        return false;
    }
    if (!ecdsa_signature_parse_der_lax(secp256k1_context_verify, &sig, &vchSig[0], vchSig.size())) {
        return false;
    }
    /* libsecp256k1's ECDSA verification requires lower-S signatures, which have
     * not historically been enforced in Bitcoin, so normalize them first. */
    secp256k1_ecdsa_signature_normalize(secp256k1_context_verify, &sig, &sig);
    return secp256k1_ecdsa_verify(secp256k1_context_verify, &sig, hash.begin(), &pubkey) == 1;
}

bool PublicKey::verifyCompact(const uint256 &hash, const std::vector<unsigned char> &vchSig) const
{
    if (!isValid() || vchSig.size() != 65)
        return false;

    secp256k1_ecdsa_recoverable_signature sig;
    const int recid = (vchSig[0] - 27) & 3;
    if (!secp256k1_ecdsa_recoverable_signature_parse_compact(secp256k1_context_verify, &sig, &vchSig[1], recid)) {
        return false;
    }
    secp256k1_ecdsa_signature convertedSig;
    if (!secp256k1_ecdsa_recoverable_signature_convert(secp256k1_context_verify, &convertedSig, &sig))
        return false;

    secp256k1_pubkey pubkey;
    if (!secp256k1_ec_pubkey_parse(secp256k1_context_verify, &pubkey, &(*this)[0], size()))
        return false;

    return secp256k1_ecdsa_verify(secp256k1_context_verify, &convertedSig, hash.begin(), &pubkey) == 1;
}

bool PublicKey::verifySchnorr(const uint256 &hash, const std::vector<uint8_t> &vchSig) const
{
    if (!isValid())
        return false;
    if (vchSig.size() != 64)
        return false;
    secp256k1_pubkey pubkey;
    if (!secp256k1_ec_pubkey_parse(secp256k1_context_verify, &pubkey, &(*this)[0], size()))
        return false;

    return secp256k1_schnorr_verify(secp256k1_context_verify, &vchSig[0], hash.begin(), &pubkey);
}

bool PublicKey::recoverCompact(const uint256 &hash, const std::vector<unsigned char>& vchSig) {
    if (vchSig.size() != 65)
        return false;
    int recid = (vchSig[0] - 27) & 3;
    bool fComp = ((vchSig[0] - 27) & 4) != 0;
    secp256k1_pubkey pubkey;
    secp256k1_ecdsa_recoverable_signature sig;
    if (!secp256k1_ecdsa_recoverable_signature_parse_compact(secp256k1_context_verify, &sig, &vchSig[1], recid)) {
        return false;
    }
    if (!secp256k1_ecdsa_recover(secp256k1_context_verify, &pubkey, &sig, hash.begin())) {
        return false;
    }
    unsigned char pub[65];
    size_t publen = 65;
    secp256k1_ec_pubkey_serialize(secp256k1_context_verify, pub, &publen, &pubkey, fComp ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
    setData(pub, pub + publen);
    return true;
}

bool PublicKey::isFullyValid() const {
    if (!isValid())
        return false;
    secp256k1_pubkey pubkey;
    return secp256k1_ec_pubkey_parse(secp256k1_context_verify, &pubkey, &(*this)[0], size());
}

bool PublicKey::isCompressed() const
{
    return size() == 33;
}

bool PublicKey::decompress() {
    if (!isValid())
        return false;
    secp256k1_pubkey pubkey;
    if (!secp256k1_ec_pubkey_parse(secp256k1_context_verify, &pubkey, &(*this)[0], size())) {
        return false;
    }
    unsigned char pub[65];
    size_t publen = 65;
    secp256k1_ec_pubkey_serialize(secp256k1_context_verify, pub, &publen, &pubkey, SECP256K1_EC_UNCOMPRESSED);
    setData(pub, pub + publen);
    return true;
}

bool PublicKey::derive(PublicKey& pubkeyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const {
    assert(isValid());
    assert((nChild >> 31) == 0);
    assert(begin() + 33 == end());
    unsigned char out[64];
    BIP32Hash(cc, nChild, *begin(), begin()+1, out);
    memcpy(ccChild.begin(), out+32, 32);
    secp256k1_pubkey pubkey;
    if (!secp256k1_ec_pubkey_parse(secp256k1_context_verify, &pubkey, &(*this)[0], size())) {
        return false;
    }
    if (!secp256k1_ec_pubkey_tweak_add(secp256k1_context_verify, &pubkey, out)) {
        return false;
    }
    unsigned char pub[33];
    size_t publen = 33;
    secp256k1_ec_pubkey_serialize(secp256k1_context_verify, pub, &publen, &pubkey, SECP256K1_EC_COMPRESSED);
    pubkeyChild.setData(pub, pub + publen);
    return true;
}

KeyId PublicKey::getKeyId() const
{
    return KeyId(Hash160(vch, vch + size()));
}

uint256 PublicKey::createHash() const
{
    return Hash(vch, vch + size());
}

bool PublicKey::isValid() const
{
    return size() > 0;
}

bool PublicKey::checkLowS(const std::vector<unsigned char>& vchSig) {
    secp256k1_ecdsa_signature sig;
    if (!ecdsa_signature_parse_der_lax(secp256k1_context_verify, &sig, &vchSig[0], vchSig.size())) {
        return false;
    }
    return (!secp256k1_ecdsa_signature_normalize(secp256k1_context_verify, nullptr, &sig));
}

/* static */ int ECCVerifyHandle::refcount = 0;

ECCVerifyHandle::ECCVerifyHandle()
{
    if (refcount == 0) {
        assert(secp256k1_context_verify == nullptr);
        secp256k1_context_verify = secp256k1_context_create(SECP256K1_CONTEXT_VERIFY);
        assert(secp256k1_context_verify != nullptr);
    }
    refcount++;
}

ECCVerifyHandle::~ECCVerifyHandle()
{
    refcount--;
    if (refcount == 0) {
        assert(secp256k1_context_verify != nullptr);
        secp256k1_context_destroy(secp256k1_context_verify);
        secp256k1_context_verify = nullptr;
    }
}