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/* 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;
extern gcry_mpi_point_t ec_gen;
extern gcry_mpi_point_t ec_zero;
extern gcry_mpi_t ec_n;
/**
* 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 (const gcry_mpi_point_t v,
const gcry_mpi_point_t g,
const gcry_mpi_t x,
const 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);
gcry_mpi_mod (c, c, ec_n);
gcry_mpi_mulm (r, c, x, ec_n);
gcry_mpi_addm (r, r, z, ec_n);
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 (const gcry_mpi_point_t v,
const gcry_mpi_point_t g,
const gcry_mpi_point_t a,
const gcry_mpi_t c,
const 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 (const gcry_mpi_point_t v,
const gcry_mpi_point_t w,
const gcry_mpi_point_t g1,
const gcry_mpi_point_t g2,
const 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);
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);
gcry_mpi_mod (c, c, ec_n);
gcry_mpi_mulm (r, c, x, ec_n);
gcry_mpi_addm (r, r, z, ec_n);
gcry_mpi_release (z);
}
int
smc_zkp_2dle_check (const gcry_mpi_point_t v,
const gcry_mpi_point_t w,
const gcry_mpi_point_t g1,
const gcry_mpi_point_t g2,
const gcry_mpi_point_t a,
const gcry_mpi_point_t b,
const gcry_mpi_t c,
const 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;
}
void
smc_zkp_0og (gcry_mpi_point_t alpha,
const gcry_mpi_point_t m,
const gcry_mpi_point_t y,
gcry_mpi_point_t beta,
gcry_mpi_point_t a1,
gcry_mpi_point_t a2,
gcry_mpi_point_t b1,
gcry_mpi_point_t b2,
gcry_mpi_t c,
gcry_mpi_t d1,
gcry_mpi_t d2,
gcry_mpi_t r1,
gcry_mpi_t r2)
{
gcry_mpi_t r = gcry_mpi_new (0);
gcry_mpi_t w = gcry_mpi_new (0);
int eq0 = !brandt_ec_point_cmp (m, ec_zero);
int eqg = !brandt_ec_point_cmp (m, ec_gen);
if (!(eq0 ^ eqg))
eprintf ("zero knowledge proof: m is neither 0 nor g");
/* beta = r*g */
brandt_ec_keypair_create (beta, r);
gcry_mpi_mod (r, r, ec_n);
/* alpha = m + r*y */
gcry_mpi_ec_mul (alpha, r, y, ec_ctx);
gcry_mpi_ec_add (alpha, m, alpha, ec_ctx);
if (eq0)
{ /* m == 0 */
brandt_ec_keypair_create_base (a1, d1, beta);
gcry_mpi_mod (d1, d1, ec_n);
brandt_ec_keypair_create_base (b1, r1, y);
gcry_mpi_mod (r1, r1, ec_n);
/* a1 = r1*g + d1*beta */
gcry_mpi_ec_mul (a2, r1, ec_gen, ec_ctx);
gcry_mpi_ec_add (a1, a2, a1, ec_ctx);
/* b1 = r1*y + d1*(alpha-g) */
gcry_mpi_ec_sub (b2, alpha, ec_gen, ec_ctx);
gcry_mpi_ec_mul (a2, d1, b2, ec_ctx);
gcry_mpi_ec_add (b1, b1, a2, ec_ctx);
/* a2 = w * g */
brandt_ec_keypair_create_base (a2, w, ec_gen);
gcry_mpi_mod (w, w, ec_n);
/* b2 = w * y */
gcry_mpi_ec_mul (b2, w, y, ec_ctx);
/* compute challange c */
/**TODO: generate c from HASH(alpha,beta,a1,b1,a2,b2) and don't output it */
brandt_ec_skey_create (c);
gcry_mpi_mod (c, c, ec_n);
/* d2 = c - d1 */
gcry_mpi_subm (d2, c, d1, ec_n);
/* r2 = w - r*d2 */
gcry_mpi_mulm (r2, r, d2, ec_n);
gcry_mpi_subm (r2, w, r2, ec_n);
}
else
{ /* m == g */
brandt_ec_keypair_create_base (a2, d2, beta);
gcry_mpi_mod (d2, d2, ec_n);
brandt_ec_keypair_create_base (b2, r2, y);
gcry_mpi_mod (r2, r2, ec_n);
/* a2 = r2*g + d2*beta */
gcry_mpi_ec_mul (a1, r2, ec_gen, ec_ctx);
gcry_mpi_ec_add (a2, a1, a2, ec_ctx);
/* b2 = r2*y + d2*(alpha-0) */
/* useless subtraction to have same amount of operations as in m == 0 */
gcry_mpi_ec_sub (b1, alpha, ec_zero, ec_ctx);
gcry_mpi_ec_mul (a1, d2, b1, ec_ctx);
gcry_mpi_ec_add (b2, b2, a1, ec_ctx);
/* a1 = w * g */
brandt_ec_keypair_create_base (a1, w, ec_gen);
gcry_mpi_mod (w, w, ec_n);
/* b1 = w * y */
gcry_mpi_ec_mul (b1, w, y, ec_ctx);
/* compute challange c */
/**TODO: generate c from HASH(alpha,beta,a1,b1,a2,b2) and don't output it */
brandt_ec_skey_create (c);
gcry_mpi_mod (c, c, ec_n);
/* d1 = c - d2 */
gcry_mpi_subm (d1, c, d2, ec_n);
/* r1 = w - r*d1 */
gcry_mpi_mulm (r1, r, d1, ec_n);
gcry_mpi_subm (r1, w, r1, ec_n);
}
gcry_mpi_release (r);
gcry_mpi_release (w);
}
int
smc_zkp_0og_check (const gcry_mpi_point_t alpha,
const gcry_mpi_point_t y,
const gcry_mpi_point_t beta,
const gcry_mpi_point_t a1,
const gcry_mpi_point_t a2,
const gcry_mpi_point_t b1,
const gcry_mpi_point_t b2,
const gcry_mpi_t c,
const gcry_mpi_t d1,
const gcry_mpi_t d2,
const gcry_mpi_t r1,
const gcry_mpi_t r2)
{
int ret;
gcry_mpi_t sum = gcry_mpi_new (0);
gcry_mpi_point_t right = gcry_mpi_point_new (0);
gcry_mpi_point_t tmp = gcry_mpi_point_new (0);
/* c == d1 + d2 */
gcry_mpi_addm (sum, d1, d2, ec_n);
ret = gcry_mpi_cmp (c, sum);
/* a1 == r1*g + d1*beta */
gcry_mpi_ec_mul (tmp, r1, ec_gen, ec_ctx);
gcry_mpi_ec_mul (right, d1, beta, ec_ctx);
gcry_mpi_ec_add (right, tmp, right, ec_ctx);
ret |= brandt_ec_point_cmp (a1, right) << 1;
/* b1 == r1*y + d1*(alpha-g) */
gcry_mpi_ec_sub (right, alpha, ec_gen, ec_ctx);
gcry_mpi_ec_mul (tmp, d1, right, ec_ctx);
gcry_mpi_ec_mul (right, r1, y, ec_ctx);
gcry_mpi_ec_add (right, right, tmp, ec_ctx);
ret |= brandt_ec_point_cmp (b1, right) << 2;
/* a2 == r2*g + d2*beta */
gcry_mpi_ec_mul (tmp, d2, beta, ec_ctx);
gcry_mpi_ec_mul (right, r2, ec_gen, ec_ctx);
gcry_mpi_ec_add (right, right, tmp, ec_ctx);
ret |= brandt_ec_point_cmp (a2, right) << 3;
/* b2 == r2*y + d2*alpha */
gcry_mpi_ec_mul (tmp, d2, alpha, ec_ctx);
gcry_mpi_ec_mul (right, r2, y, ec_ctx);
gcry_mpi_ec_add (right, right, tmp, ec_ctx);
ret |= brandt_ec_point_cmp (b2, right) << 4;
gcry_mpi_release (sum);
gcry_mpi_point_release (right);
gcry_mpi_point_release (tmp);
if (ret)
weprintf ("ret: 0x%x", ret);
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);
//}
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