/* ecc-25519.c
Arithmetic and tables for curve25519,
Copyright (C) 2014 Niels MÃ¶ller
This file is part of GNU Nettle.
GNU Nettle is free software: you can redistribute it and/or
modify it under the terms of either:
* 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.
or
* the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your
option) any later version.
or both in parallel, as here.
GNU Nettle 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 copies of the GNU General Public License and
the GNU Lesser General Public License along with this program. If
not, see http://www.gnu.org/licenses/.
*/
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include "ecc-internal.h"
#define USE_REDC 0
#include "ecc-25519.h"
#define HIGH_BITS (GMP_NUMB_BITS * ECC_LIMB_SIZE - 255)
#if HIGH_BITS == 0
#error Unsupported limb size */
#endif
static void
ecc_25519_modp(const struct ecc_curve *ecc UNUSED, mp_limb_t *rp)
{
mp_limb_t hi, cy;
cy = mpn_addmul_1 (rp, rp + ECC_LIMB_SIZE, ECC_LIMB_SIZE,
(mp_limb_t) 19 << HIGH_BITS);
hi = rp[ECC_LIMB_SIZE-1];
cy = (cy << HIGH_BITS) + (hi >> (GMP_NUMB_BITS - HIGH_BITS));
rp[ECC_LIMB_SIZE-1] = (hi & (GMP_NUMB_MASK >> HIGH_BITS))
+ sec_add_1 (rp, rp, ECC_LIMB_SIZE - 1, 19 * cy);
}
/* We'll also need square roots, see
http://www.math.vt.edu/people/brown/doc/sqrts.pdf for a description
of Shanks-Tonelli. A quadratic non-residue is 2. */
const struct ecc_curve nettle_curve25519 =
{
255,
ECC_LIMB_SIZE,
ECC_BMODP_SIZE,
ECC_BMODQ_SIZE,
0, /* No redc */
0,
ECC_PIPPENGER_K,
ECC_PIPPENGER_C,
ecc_p,
ecc_d, /* Use the Edwards curve constant. */
ecc_q,
ecc_g,
ecc_redc_g,
ecc_edwards,
ecc_25519_modp,
NULL,
ecc_25519_modp,
NULL,
ecc_Bmodp,
ecc_Bmodp_shifted,
ecc_pp1h,
ecc_redc_ppm1,
ecc_unit,
ecc_Bmodq,
ecc_Bmodq_shifted,
ecc_qp1h,
ecc_table
};