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

extern gcry_ctx_t ec_ctx;

/**
 * smc_zkp_dl
 *
 * @param v TODO
 * @param g TODO
 * @param x TODO
 * @param a TODO
 * @param c TODO
 * @param r TODO
 */
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);

	/* compute challange c */
	/**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);
}


/**
 * smc_zkp_dl_check
 *
 * @param v TODO
 * @param g TODO
 * @param a TODO
 * @param c TODO
 * @param r TODO
 * @return 0 if the proof is correct, something else otherwise
 */
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;
}


void
smc_zkp_2dle (gcry_mpi_point_t v, gcry_mpi_point_t w, gcry_mpi_point_t g1, gcry_mpi_point_t g2, gcry_mpi_t x, gcry_mpi_point_t *a, gcry_mpi_point_t *b, gcry_mpi_t *c, gcry_mpi_t *r)
{
	gcry_mpi_t z = gcry_mpi_new (0);

	brandt_ec_keypair_create_base (a, &z, g1);
	*b = gcry_mpi_point_new(0);
	gcry_mpi_ec_mul(*b, z, g2, ec_ctx);

	/* compute challange c */
	/**TODO: generate c from HASH(g1,g2,v,w,a,b) 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_2dle_check (gcry_mpi_point_t v, gcry_mpi_point_t w, gcry_mpi_point_t g1, gcry_mpi_point_t g2, gcry_mpi_point_t a, gcry_mpi_point_t b, 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, g1, 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_ec_mul (left, r, g2, ec_ctx);
	gcry_mpi_ec_mul (right, c, w, ec_ctx);
	gcry_mpi_ec_add (right, b, 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);
//}