libbrandt/smc.c

/* This file is part of libbrandt.
 * Copyright (C) 2016 GNUnet e.V.
 *
 * libbrandt 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.
 *
 * libbrandt 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
 * libbrandt.  If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * @file smc.c
 * @brief Implementation of the smc primitives.
 */

#include <gcrypt.h>

#include "crypto.h"
#include "util.h"
#include "smc.h"

extern gcry_ctx_t ec_ctx;

void
smc_zkp_dl (gcry_mpi_point_t v, gcry_mpi_point_t g, gcry_mpi_t x, gcry_mpi_point_t *a, gcry_mpi_t *c, gcry_mpi_t *r)
{
	gcry_mpi_t z = gcry_mpi_new(0);

	brandt_ec_keypair_create_base(a, &z, g);
	/**TODO: generate c from HASH(g,v,a) and don't output it */
	brandt_ec_skey_create(c);
	*r = gcry_mpi_new(0);
	gcry_mpi_mul(*r, *c, x);
	gcry_mpi_add(*r, *r, z);

	gcry_mpi_release(z);
}

int
smc_zkp_dl_check (gcry_mpi_point_t v, gcry_mpi_point_t g, gcry_mpi_point_t a, gcry_mpi_t c, gcry_mpi_t r)
{
	int ret;
	gcry_mpi_point_t left = gcry_mpi_point_new(0);
	gcry_mpi_point_t right = gcry_mpi_point_new(0);

	gcry_mpi_ec_mul(left, r, g, ec_ctx);
	gcry_mpi_ec_mul(right, c, v, ec_ctx);
	gcry_mpi_ec_add(right, a, right, ec_ctx);

	ret = brandt_ec_point_cmp(left, right);
	gcry_mpi_point_release(left);
	gcry_mpi_point_release(right);

	return ret;
}

/*
GEN
smc_hextodec (const char *s)
{
	size_t i;
	char c;
	pari_sp ltop = avma;
	GEN ret = gen_0;

	for (i = 0; i < strlen (s); i++)
	{
		errno = 0;
		if (1 != sscanf (&s[i], "%1hhx", &c))
		{
			brandt_eprintf ("failed to parse hex (\"%s\") to decimal:", s);
			return NULL;
		}
		ret = addis (shifti (ret, 4), c);
	}
	return gerepilecopy (ltop, ret);
}
*/