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// 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;
}
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