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/* ecc-384.c.c */
/* Compile time constant (but machine dependent) tables. */
/* 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 <assert.h>
#include "ecc-internal.h"
#define USE_REDC 0
#include "ecc-384.h"
#if HAVE_NATIVE_ecc_384_modp
#define ecc_384_modp nettle_ecc_384_modp
void
ecc_384_modp (const struct ecc_curve *ecc, mp_limb_t *rp);
#elif GMP_NUMB_BITS == 32
/* Use that 2^{384} = 2^{128} + 2^{96} - 2^{32} + 1, and eliminate 256
bits at a time.
We can get carry == 2 in the first iteration, and I think *only* in
the first iteration. */
/* p is 12 limbs, and B^12 - p = B^4 + B^3 - B + 1. We can eliminate
almost 8 at a time. Do only 7, to avoid additional carry
propagation, followed by 5. */
static void
ecc_384_modp (const struct ecc_curve *ecc, mp_limb_t *rp)
{
mp_limb_t cy, bw;
/* Reduce from 24 to 17 limbs. */
cy = mpn_add_n (rp + 4, rp + 4, rp + 16, 8);
cy = sec_add_1 (rp + 12, rp + 12, 3, cy);
bw = mpn_sub_n (rp + 5, rp + 5, rp + 16, 8);
bw = sec_sub_1 (rp + 13, rp + 13, 3, bw);
cy += mpn_add_n (rp + 7, rp + 7, rp + 16, 8);
cy = sec_add_1 (rp + 15, rp + 15, 1, cy);
cy += mpn_add_n (rp + 8, rp + 8, rp + 16, 8);
assert (bw <= cy);
cy -= bw;
assert (cy <= 2);
rp[16] = cy;
/* Reduce from 17 to 12 limbs */
cy = mpn_add_n (rp, rp, rp + 12, 5);
cy = sec_add_1 (rp + 5, rp + 5, 3, cy);
bw = mpn_sub_n (rp + 1, rp + 1, rp + 12, 5);
bw = sec_sub_1 (rp + 6, rp + 6, 6, bw);
cy += mpn_add_n (rp + 3, rp + 3, rp + 12, 5);
cy = sec_add_1 (rp + 8, rp + 8, 1, cy);
cy += mpn_add_n (rp + 4, rp + 4, rp + 12, 5);
cy = sec_add_1 (rp + 9, rp + 9, 3, cy);
assert (cy >= bw);
cy -= bw;
assert (cy <= 1);
cy = cnd_add_n (cy, rp, ecc->Bmodp, ECC_LIMB_SIZE);
assert (cy == 0);
}
#elif GMP_NUMB_BITS == 64
/* p is 6 limbs, and B^6 - p = B^2 + 2^32 (B - 1) + 1. Eliminate 3
(almost 4) limbs at a time. */
static void
ecc_384_modp (const struct ecc_curve *ecc, mp_limb_t *rp)
{
mp_limb_t tp[6];
mp_limb_t cy;
/* Reduce from 12 to 9 limbs */
tp[0] = 0; /* FIXME: Could use mpn_sub_nc */
mpn_copyi (tp + 1, rp + 8, 3);
tp[4] = rp[11] - mpn_sub_n (tp, tp, rp + 8, 4);
tp[5] = mpn_lshift (tp, tp, 5, 32);
cy = mpn_add_n (rp + 2, rp + 2, rp + 8, 4);
cy = sec_add_1 (rp + 6, rp + 6, 2, cy);
cy += mpn_add_n (rp + 2, rp + 2, tp, 6);
cy += mpn_add_n (rp + 4, rp + 4, rp + 8, 4);
assert (cy <= 2);
rp[8] = cy;
/* Reduce from 9 to 6 limbs */
tp[0] = 0;
mpn_copyi (tp + 1, rp + 6, 2);
tp[3] = rp[8] - mpn_sub_n (tp, tp, rp + 6, 3);
tp[4] = mpn_lshift (tp, tp, 4, 32);
cy = mpn_add_n (rp, rp, rp + 6, 3);
cy = sec_add_1 (rp + 3, rp + 3, 2, cy);
cy += mpn_add_n (rp, rp, tp, 5);
cy += mpn_add_n (rp + 2, rp + 2, rp + 6, 3);
cy = sec_add_1 (rp + 5, rp + 5, 1, cy);
assert (cy <= 1);
cy = cnd_add_n (cy, rp, ecc->Bmodp, ECC_LIMB_SIZE);
assert (cy == 0);
}
#else
#define ecc_384_modp ecc_generic_modp
#endif
const struct ecc_curve nettle_secp_384r1 =
{
384,
ECC_LIMB_SIZE,
ECC_BMODP_SIZE,
ECC_BMODQ_SIZE,
USE_REDC,
ECC_REDC_SIZE,
ECC_PIPPENGER_K,
ECC_PIPPENGER_C,
ecc_p,
ecc_b,
ecc_q,
ecc_g,
ecc_redc_g,
ecc_384_modp,
ECC_REDC_SIZE != 0 ? ecc_generic_redc : NULL,
ecc_384_modp,
ecc_generic_modq,
ecc_Bmodp,
ecc_Bmodp_shifted,
ecc_pp1h,
ecc_redc_ppm1,
ecc_unit,
ecc_Bmodq,
ecc_Bmodq_shifted,
ecc_qp1h,
ecc_table
};
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