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/* ecc-point.c */
/* nettle, low-level cryptographics library
*
* Copyright (C) 2013 Niels Möller
*
* The nettle 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.
*
* The nettle 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 the nettle library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 02111-1301, USA.
*/
/* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include "ecc.h"
#include "ecc-internal.h"
void
ecc_point_init (struct ecc_point *p, const struct ecc_curve *ecc)
{
p->ecc = ecc;
p->p = gmp_alloc_limbs (2*ecc->size);
}
void
ecc_point_clear (struct ecc_point *p)
{
gmp_free_limbs (p->p, 2*p->ecc->size);
}
int
ecc_point_set (struct ecc_point *p, const mpz_t x, const mpz_t y)
{
mp_size_t size;
mpz_t lhs, rhs;
mpz_t t;
int res;
size = p->ecc->size;
if (mpz_sgn (x) < 0 || mpz_limbs_cmp (x, p->ecc->p, size) >= 0
|| mpz_sgn (y) < 0 || mpz_limbs_cmp (y, p->ecc->p, size) >= 0)
return 0;
mpz_init (lhs);
mpz_init (rhs);
/* Check that y^2 = x^3 - 3*x + b (mod p) */
mpz_mul (lhs, y, y);
mpz_mul (rhs, x, x);
mpz_sub_ui (rhs, rhs, 3);
mpz_mul (rhs, rhs, x);
mpz_add (rhs, rhs, mpz_roinit_n (t, p->ecc->b, size));
res = mpz_congruent_p (lhs, rhs, mpz_roinit_n (t, p->ecc->p, size));
mpz_clear (lhs);
mpz_clear (rhs);
if (!res)
return 0;
mpz_limbs_copy (p->p, x, size);
mpz_limbs_copy (p->p + size, y, size);
return 1;
}
void
ecc_point_get (const struct ecc_point *p, mpz_t x, mpz_t y)
{
mp_size_t size = p->ecc->size;
if (x)
mpz_set_n (x, p->p, size);
if (y)
mpz_set_n (y, p->p + size, size);
}
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