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/* ecc-modp.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 Internetfonden. */
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include <assert.h>
#include "ecc-internal.h"
/* Routines for modp arithmetic. All values are ecc->size limbs, but
not necessarily < p. */
void
ecc_modp_add (const struct ecc_curve *ecc, mp_limb_t *rp,
const mp_limb_t *ap, const mp_limb_t *bp)
{
mp_limb_t cy;
cy = mpn_add_n (rp, ap, bp, ecc->size);
cy = cnd_add_n (cy, rp, ecc->Bmodp, ecc->size);
cy = cnd_add_n (cy, rp, ecc->Bmodp, ecc->size);
assert (cy == 0);
}
void
ecc_modp_sub (const struct ecc_curve *ecc, mp_limb_t *rp,
const mp_limb_t *ap, const mp_limb_t *bp)
{
mp_limb_t cy;
cy = mpn_sub_n (rp, ap, bp, ecc->size);
cy = cnd_sub_n (cy, rp, ecc->Bmodp, ecc->size);
cy = cnd_sub_n (cy, rp, ecc->Bmodp, ecc->size);
assert (cy == 0);
}
void
ecc_modp_sub_1 (const struct ecc_curve *ecc, mp_limb_t *rp,
const mp_limb_t *ap, mp_limb_t b)
{
mp_size_t i;
for (i = 0; i < ecc->size; i++)
{
mp_limb_t cy = ap[i] < b;
rp[i] = ap[i] - b;
b = cy;
}
b = cnd_sub_n (b, rp, ecc->Bmodp, ecc->size);
assert (b == 0);
}
void
ecc_modp_mul_1 (const struct ecc_curve *ecc, mp_limb_t *rp,
const mp_limb_t *ap, mp_limb_t b)
{
mp_limb_t hi;
assert (b <= 0xffffffff);
hi = mpn_mul_1 (rp, ap, ecc->size, b);
hi = mpn_addmul_1 (rp, ecc->Bmodp, ecc->size, hi);
assert (hi <= 1);
hi = cnd_add_n (hi, rp, ecc->Bmodp, ecc->size);
/* Sufficient if b < B^size / p */
assert (hi == 0);
}
void
ecc_modp_addmul_1 (const struct ecc_curve *ecc, mp_limb_t *rp,
const mp_limb_t *ap, mp_limb_t b)
{
mp_limb_t hi;
assert (b <= 0xffffffff);
hi = mpn_addmul_1 (rp, ap, ecc->size, b);
hi = mpn_addmul_1 (rp, ecc->Bmodp, ecc->size, hi);
assert (hi <= 1);
hi = cnd_add_n (hi, rp, ecc->Bmodp, ecc->size);
/* Sufficient roughly if b < B^size / p */
assert (hi == 0);
}
void
ecc_modp_submul_1 (const struct ecc_curve *ecc, mp_limb_t *rp,
const mp_limb_t *ap, mp_limb_t b)
{
mp_limb_t hi;
assert (b <= 0xffffffff);
hi = mpn_submul_1 (rp, ap, ecc->size, b);
hi = mpn_submul_1 (rp, ecc->Bmodp, ecc->size, hi);
assert (hi <= 1);
hi = cnd_sub_n (hi, rp, ecc->Bmodp, ecc->size);
/* Sufficient roughly if b < B^size / p */
assert (hi == 0);
}
/* NOTE: mul and sqr needs 2*ecc->size limbs at rp */
void
ecc_modp_mul (const struct ecc_curve *ecc, mp_limb_t *rp,
const mp_limb_t *ap, const mp_limb_t *bp)
{
mpn_mul_n (rp, ap, bp, ecc->size);
ecc->reduce (ecc, rp);
}
void
ecc_modp_sqr (const struct ecc_curve *ecc, mp_limb_t *rp,
const mp_limb_t *ap)
{
mpn_sqr (rp, ap, ecc->size);
ecc->reduce (ecc, rp);
}
void
ecc_modp_inv (const struct ecc_curve *ecc, mp_limb_t *rp, mp_limb_t *ap,
mp_limb_t *scratch)
{
sec_modinv (rp, ap, ecc->size, ecc->p, ecc->pp1h, ecc->bit_size, scratch);
}
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