secp256k1-zkp/src/modules/extrakeys/main_impl.h

/**********************************************************************
 * Copyright (c) 2020 Jonas Nick                                      *
 * Distributed under the MIT software license, see the accompanying   *
 * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
 **********************************************************************/

#ifndef _SECP256K1_MODULE_EXTRAKEYS_MAIN_
#define _SECP256K1_MODULE_EXTRAKEYS_MAIN_

#include "include/secp256k1.h"
#include "include/secp256k1_extrakeys.h"

static SECP256K1_INLINE int secp256k1_xonly_pubkey_load(const secp256k1_context* ctx, secp256k1_ge *ge, const secp256k1_xonly_pubkey *pubkey) {
    return secp256k1_pubkey_load(ctx, ge, (const secp256k1_pubkey *) pubkey);
}

static SECP256K1_INLINE void secp256k1_xonly_pubkey_save(secp256k1_xonly_pubkey *pubkey, secp256k1_ge *ge) {
    secp256k1_pubkey_save((secp256k1_pubkey *) pubkey, ge);
}

int secp256k1_xonly_pubkey_parse(const secp256k1_context* ctx, secp256k1_xonly_pubkey *pubkey, const unsigned char *input32) {
    secp256k1_ge pk;
    secp256k1_fe x;

    VERIFY_CHECK(ctx != NULL);
    ARG_CHECK(pubkey != NULL);
    memset(pubkey, 0, sizeof(*pubkey));
    ARG_CHECK(input32 != NULL);

    if (!secp256k1_fe_set_b32(&x, input32)) {
        return 0;
    }
    if (!secp256k1_ge_set_xo_var(&pk, &x, 0)) {
        return 0;
    }
    secp256k1_xonly_pubkey_save(pubkey, &pk);
    return 1;
}

int secp256k1_xonly_pubkey_serialize(const secp256k1_context* ctx, unsigned char *output32, const secp256k1_xonly_pubkey *pubkey) {
    secp256k1_ge pk;

    VERIFY_CHECK(ctx != NULL);
    ARG_CHECK(output32 != NULL);
    memset(output32, 0, 32);
    ARG_CHECK(pubkey != NULL);

    if (!secp256k1_xonly_pubkey_load(ctx, &pk, pubkey)) {
        return 0;
    }
    secp256k1_fe_get_b32(output32, &pk.x);
    return 1;
}

/** Keeps a group element as is if it has an even Y and otherwise negates it.
 *  y_parity is set to 0 in the former case and to 1 in the latter case.
 *  Requires that the coordinates of r are normalized. */
static int secp256k1_extrakeys_ge_even_y(secp256k1_ge *r) {
    int y_parity = 0;
    VERIFY_CHECK(!secp256k1_ge_is_infinity(r));

    if (secp256k1_fe_is_odd(&r->y)) {
        secp256k1_fe_negate(&r->y, &r->y, 1);
        y_parity = 1;
    }
    return y_parity;
}

int secp256k1_xonly_pubkey_from_pubkey(const secp256k1_context* ctx, secp256k1_xonly_pubkey *xonly_pubkey, int *pk_parity, const secp256k1_pubkey *pubkey) {
    secp256k1_ge pk;
    int tmp;

    VERIFY_CHECK(ctx != NULL);
    ARG_CHECK(xonly_pubkey != NULL);
    ARG_CHECK(pubkey != NULL);

    if (!secp256k1_pubkey_load(ctx, &pk, pubkey)) {
        return 0;
    }
    tmp = secp256k1_extrakeys_ge_even_y(&pk);
    if (pk_parity != NULL) {
        *pk_parity = tmp;
    }
    secp256k1_xonly_pubkey_save(xonly_pubkey, &pk);
    return 1;
}

#endif