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/* ecc-mul-g.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 <assert.h>
#include "ecc.h"
#include "ecc-internal.h"
mp_size_t
ecc_mul_g_itch (const struct ecc_curve *ecc)
{
/* Needs 3*ecc->size + scratch for ecc_add_jja. */
return ECC_MUL_G_ITCH (ecc->size);
}
void
ecc_mul_g (const struct ecc_curve *ecc, mp_limb_t *r,
const mp_limb_t *np, mp_limb_t *scratch)
{
/* Scratch need determined by the ecc_add_jja call. Current total is
9 * ecc->size, at most 648 bytes. */
#define tp scratch
#define scratch_out (scratch + 3*ecc->size)
unsigned k, c;
unsigned i, j;
unsigned bit_rows;
int is_zero;
k = ecc->pippenger_k;
c = ecc->pippenger_c;
bit_rows = (ecc->bit_size + k - 1) / k;
mpn_zero (r, 3*ecc->size);
for (i = k, is_zero = 1; i-- > 0; )
{
ecc_dup_jj (ecc, r, r, scratch);
for (j = 0; j * c < bit_rows; j++)
{
unsigned bits;
/* Avoid the mp_bitcnt_t type for compatibility with older GMP
versions. */
unsigned bit_index;
/* Extract c bits from n, stride k, starting at i + kcj,
ending at i + k (cj + c - 1)*/
for (bits = 0, bit_index = i + k*(c*j+c); bit_index > i + k*c*j; )
{
mp_size_t limb_index;
unsigned shift;
bit_index -= k;
limb_index = bit_index / GMP_NUMB_BITS;
if (limb_index >= ecc->size)
continue;
shift = bit_index % GMP_NUMB_BITS;
bits = (bits << 1) | ((np[limb_index] >> shift) & 1);
}
sec_tabselect (tp, 2*ecc->size,
(ecc->pippenger_table
+ (2*ecc->size * (mp_size_t) j << c)),
1<<c, bits);
cnd_copy (is_zero, r, tp, 2*ecc->size);
cnd_copy (is_zero, r + 2*ecc->size, ecc->unit, ecc->size);
ecc_add_jja (ecc, tp, r, tp, scratch_out);
/* Use the sum when valid. ecc_add_jja produced garbage if
is_zero != 0 or bits == 0, . */
cnd_copy (bits & (is_zero - 1), r, tp, 3*ecc->size);
is_zero &= (bits == 0);
}
}
#undef tp
#undef scratch_out
}
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