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/*
* Copyright (C) 2011-2012 Free Software Foundation, Inc.
*
* This file is part of GNUTLS.
*
* The GNUTLS 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.
*
* This 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 this program. If not, see <http://www.gnu.org/licenses/>
*
*/
/* Based on public domain code of LibTomCrypt by Tom St Denis.
* Adapted to gmp and nettle by Nikos Mavrogiannopoulos.
*/
#include "ecc.h"
/*
@file ecc_mulmod_timing.c
ECC Crypto, Tom St Denis
*/
/*
Perform a point multiplication (timing resistant)
@param k The scalar to multiply by
@param G The base point
@param R [out] Destination for kG
@param a The a value of the curve
@param modulus The modulus of the field the ECC curve is in
@param map Boolean whether to map back to affine or not (1==map, 0 == leave in projective)
@return 0 on success
*/
int
ecc_mulmod_timing (mpz_t k, ecc_point * G, ecc_point * R, mpz_t a, mpz_t modulus,
int map)
{
ecc_point *tG, *M[3];
int i, j, err;
int bit_to_read;
int mode;
if (k == NULL || G == NULL || R == NULL || modulus == NULL)
return -1;
/* alloc ram for window temps */
for (i = 0; i < 3; i++)
{
M[i] = ecc_new_point ();
if (M[i] == NULL)
{
for (j = 0; j < i; j++)
{
ecc_del_point (M[j]);
}
return -1;
}
}
/* make a copy of G incase R==G */
tG = ecc_new_point ();
if (tG == NULL)
{
err = -1;
goto done;
}
/* tG = G and convert to montgomery */
mpz_set (tG->x, G->x);
mpz_set (tG->y, G->y);
mpz_set (tG->z, G->z);
/* calc the M tab */
/* M[0] == G */
mpz_set (M[0]->x, tG->x);
mpz_set (M[0]->y, tG->y);
mpz_set (M[0]->z, tG->z);
/* M[1] == 2G */
if ((err = ecc_projective_dbl_point (tG, M[1], a, modulus)) != 0)
{
goto done;
}
/* setup sliding window */
mode = 0;
bit_to_read = mpz_size (k) * GMP_NUMB_BITS - 1;
/* perform ops */
for (;;)
{
/* grab next digit as required */
if (bit_to_read == -1)
break;
i = mpz_tstbit (k, bit_to_read--);
if (mode == 0 && i == 0)
{
/* dummy operations */
if ((err =
ecc_projective_add_point (M[0], M[1], M[2], a,
modulus)) != 0)
{
goto done;
}
if ((err =
ecc_projective_dbl_point (M[1], M[2], a, modulus)) != 0)
{
goto done;
}
continue;
}
if (mode == 0 && i == 1)
{
mode = 1;
/* dummy operations */
if ((err =
ecc_projective_add_point (M[0], M[1], M[2], a,
modulus)) != 0)
{
goto done;
}
if ((err =
ecc_projective_dbl_point (M[1], M[2], a, modulus)) != 0)
{
goto done;
}
continue;
}
if ((err =
ecc_projective_add_point (M[0], M[1], M[i ^ 1], a,
modulus)) != 0)
{
goto done;
}
if ((err = ecc_projective_dbl_point (M[i], M[i], a, modulus)) != 0)
{
goto done;
}
}
/* copy result out */
mpz_set (R->x, M[0]->x);
mpz_set (R->y, M[0]->y);
mpz_set (R->z, M[0]->z);
/* map R back from projective space */
if (map)
{
err = ecc_map (R, modulus);
}
else
{
err = 0;
}
done:
ecc_del_point (tG);
for (i = 0; i < 3; i++)
{
ecc_del_point (M[i]);
}
return err;
}
/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_mulmod_timing.c,v $ */
/* $Revision: 1.13 $ */
/* $Date: 2007/05/12 14:32:35 $ */
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