// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

/** Multiply point by scalar in constant time.
 *  Returns: 1: multiplication was successful
 *           0: scalar was invalid (zero or overflow)
 *  Args:    ctx:      pointer to a context object (cannot be NULL)
 *  Out:     point:    the multiplied point (usually secret)
 *  In:      point:    pointer to a 64-byte bytepublic point,
                       encoded as two 256bit big-endian numbers.
 *           scalar:   a 32-byte scalar with which to multiply the point
 */
int secp256k1_pubkey_scalar_mul(const secp256k1_context* ctx, unsigned char *point, const unsigned char *scalar) {
    int ret = 0;
    int overflow = 0;
    secp256k1_fe feX, feY;
    secp256k1_gej res;
    secp256k1_ge ge;
    secp256k1_scalar s;
    ARG_CHECK(point != NULL);
    ARG_CHECK(scalar != NULL);
    (void)ctx;

    secp256k1_fe_set_b32(&feX, point);
    secp256k1_fe_set_b32(&feY, point+32);
    secp256k1_ge_set_xy(&ge, &feX, &feY);
    secp256k1_scalar_set_b32(&s, scalar, &overflow);
    if (overflow || secp256k1_scalar_is_zero(&s)) {
        ret = 0;
    } else {
        secp256k1_ecmult_const(&res, &ge, &s);
        secp256k1_ge_set_gej(&ge, &res);
        /* Note: can't use secp256k1_pubkey_save here because it is not constant time. */
        secp256k1_fe_normalize(&ge.x);
        secp256k1_fe_normalize(&ge.y);
        secp256k1_fe_get_b32(point, &ge.x);
        secp256k1_fe_get_b32(point+32, &ge.y);
        ret = 1;
    }
    secp256k1_scalar_clear(&s);
    return ret;
}