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/* ecc-mul-a.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_a_itch (const struct ecc_curve *ecc)
{
/* Binary algorithm needs 6*ecc->size + scratch for ecc_add_jja.
Current total is 12 ecc->size, at most 864 bytes.
Window algorithm needs (3<<w) * ecc->size for the table,
3*ecc->size for a temporary point, and scratch for
ecc_add_jjj. */
return ECC_MUL_A_ITCH (ecc->size);
}
#if ECC_MUL_A_WBITS == 0
void
ecc_mul_a (const struct ecc_curve *ecc,
int initial, mp_limb_t *r,
const mp_limb_t *np, const mp_limb_t *p,
mp_limb_t *scratch)
{
#define tp scratch
#define pj (scratch + 3*ecc->size)
#define scratch_out (scratch + 6*ecc->size)
int is_zero;
unsigned i;
ecc_a_to_j (ecc, initial, pj, p);
mpn_zero (r, 3*ecc->size);
for (i = ecc->size, is_zero = 1; i-- > 0; )
{
mp_limb_t w = np[i];
mp_limb_t bit;
for (bit = (mp_limb_t) 1 << (GMP_NUMB_BITS - 1);
bit > 0;
bit >>= 1)
{
int digit;
ecc_dup_jj (ecc, r, r, scratch_out);
ecc_add_jja (ecc, tp, r, pj, scratch_out);
digit = (w & bit) > 0;
/* If is_zero is set, r is the zero point,
and ecc_add_jja produced garbage. */
cnd_copy (is_zero, tp, pj, 3*ecc->size);
is_zero &= ~digit;
/* If we had a one-bit, use the sum. */
cnd_copy (digit, r, tp, 3*ecc->size);
}
}
}
#else /* ECC_MUL_A_WBITS > 1 */
#define TABLE_SIZE (1U << ECC_MUL_A_WBITS)
#define TABLE_MASK (TABLE_SIZE - 1)
#define TABLE(j) (table + (j) * 3*ecc->size)
static void
table_init (const struct ecc_curve *ecc,
mp_limb_t *table, unsigned bits,
int initial, const mp_limb_t *p,
mp_limb_t *scratch)
{
unsigned size = 1 << bits;
unsigned j;
mpn_zero (TABLE(0), 3*ecc->size);
ecc_a_to_j (ecc, initial, TABLE(1), p);
for (j = 2; j < size; j += 2)
{
ecc_dup_jj (ecc, TABLE(j), TABLE(j/2), scratch);
ecc_add_jja (ecc, TABLE(j+1), TABLE(j), TABLE(1), scratch);
}
}
void
ecc_mul_a (const struct ecc_curve *ecc,
int initial, mp_limb_t *r,
const mp_limb_t *np, const mp_limb_t *p,
mp_limb_t *scratch)
{
#define tp scratch
#define table (scratch + 3*ecc->size)
mp_limb_t *scratch_out = table + (3*ecc->size << ECC_MUL_A_WBITS);
int is_zero = 0;
/* Avoid the mp_bitcnt_t type for compatibility with older GMP
versions. */
unsigned blocks = (ecc->bit_size + ECC_MUL_A_WBITS - 1) / ECC_MUL_A_WBITS;
unsigned bit_index = (blocks-1) * ECC_MUL_A_WBITS;
mp_size_t limb_index = bit_index / GMP_NUMB_BITS;
unsigned shift = bit_index % GMP_NUMB_BITS;
mp_limb_t w, bits;
table_init (ecc, table, ECC_MUL_A_WBITS, initial, p, scratch_out);
w = np[limb_index];
bits = w >> shift;
if (limb_index < ecc->size - 1)
bits |= np[limb_index + 1] << (GMP_NUMB_BITS - shift);
assert (bits < TABLE_SIZE);
sec_tabselect (r, 3*ecc->size, table, TABLE_SIZE, bits);
is_zero = (bits == 0);
for (;;)
{
unsigned j;
if (shift >= ECC_MUL_A_WBITS)
{
shift -= ECC_MUL_A_WBITS;
bits = w >> shift;
}
else
{
if (limb_index == 0)
{
assert (shift == 0);
break;
}
bits = w << (ECC_MUL_A_WBITS - shift);
w = np[--limb_index];
shift = shift + GMP_NUMB_BITS - ECC_MUL_A_WBITS;
bits |= w >> shift;
}
for (j = 0; j < ECC_MUL_A_WBITS; j++)
ecc_dup_jj (ecc, r, r, scratch_out);
bits &= TABLE_MASK;
sec_tabselect (tp, 3*ecc->size, table, TABLE_SIZE, bits);
cnd_copy (is_zero, r, tp, 3*ecc->size);
ecc_add_jjj (ecc, tp, tp, r, 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 table
#undef tp
}
#endif /* ECC_MUL_A_WBITS > 1 */
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