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Diffstat (limited to 'ecc-mul-a.c')
| -rw-r--r-- | ecc-mul-a.c | 181 |
1 files changed, 181 insertions, 0 deletions
diff --git a/ecc-mul-a.c b/ecc-mul-a.c new file mode 100644 index 00000000..0b347162 --- /dev/null +++ b/ecc-mul-a.c @@ -0,0 +1,181 @@ +/* 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 Internetfonden. */ + +#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; + + mp_bitcnt_t blocks = (ecc->bit_size + ECC_MUL_A_WBITS - 1) / ECC_MUL_A_WBITS; + mp_bitcnt_t 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 */ |