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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 2.1 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_map.c
ECC Crypto, Tom St Denis
*/
/*
Map a projective jacobian point back to affine space
@param P [in/out] The point to map
@param modulus The modulus of the field the ECC curve is in
@param mp The "b" value from montgomery_setup()
@return 0 on success
*/
int
ecc_map (ecc_point * P, mpz_t modulus)
{
mpz_t t1, t2;
int err;
if (P == NULL)
return -1;
if ((err = mp_init_multi (&t1, &t2, NULL)) != 0)
{
return -1;
}
mpz_mod (P->z, P->z, modulus);
/* get 1/z */
mpz_invert (t1, P->z, modulus);
/* get 1/z^2 and 1/z^3 */
mpz_mul (t2, t1, t1);
mpz_mod (t2, t2, modulus);
mpz_mul (t1, t1, t2);
mpz_mod (t1, t1, modulus);
/* multiply against x/y */
mpz_mul (P->x, P->x, t2);
mpz_mod (P->x, P->x, modulus);
mpz_mul (P->y, P->y, t1);
mpz_mod (P->y, P->y, modulus);
mpz_set_ui (P->z, 1);
err = 0;
mp_clear_multi (&t1, &t2, NULL);
return err;
}
/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_map.c,v $ */
/* $Revision: 1.7 $ */
/* $Date: 2007/05/12 14:32:35 $ */
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