3 Copyright (C) 2013 Niels Möller
5 This file is part of GNU Nettle.
7 GNU Nettle is free software: you can redistribute it and/or
8 modify it under the terms of either:
10 * the GNU Lesser General Public License as published by the Free
11 Software Foundation; either version 3 of the License, or (at your
12 option) any later version.
16 * the GNU General Public License as published by the Free
17 Software Foundation; either version 2 of the License, or (at your
18 option) any later version.
20 or both in parallel, as here.
22 GNU Nettle is distributed in the hope that it will be useful,
23 but WITHOUT ANY WARRANTY; without even the implied warranty of
24 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
25 General Public License for more details.
27 You should have received copies of the GNU General Public License and
28 the GNU Lesser General Public License along with this program. If
29 not, see http://www.gnu.org/licenses/.
32 /* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
41 #include "ecc-internal.h"
43 /* Binary algorithm needs 6*ecc->p.size + scratch for ecc_add_jja.
44 Current total is 12 ecc->p.size, at most 864 bytes.
46 Window algorithm needs (3<<w) * ecc->p.size for the table,
47 3*ecc->p.size for a temporary point, and scratch for
50 #if ECC_MUL_A_WBITS == 0
52 ecc_mul_a (const struct ecc_curve *ecc,
54 const mp_limb_t *np, const mp_limb_t *p,
58 #define pj (scratch + 3*ecc->p.size)
59 #define scratch_out (scratch + 6*ecc->p.size)
65 ecc_a_to_j (ecc, pj, p);
66 mpn_zero (r, 3*ecc->p.size);
68 for (i = ecc->p.size, is_zero = 1; i-- > 0; )
73 for (bit = (mp_limb_t) 1 << (GMP_NUMB_BITS - 1);
79 ecc_dup_jj (ecc, r, r, scratch_out);
80 ecc_add_jja (ecc, tp, r, pj, scratch_out);
82 digit = (w & bit) > 0;
83 /* If is_zero is set, r is the zero point,
84 and ecc_add_jja produced garbage. */
85 cnd_copy (is_zero, tp, pj, 3*ecc->p.size);
87 /* If we had a one-bit, use the sum. */
88 cnd_copy (digit, r, tp, 3*ecc->p.size);
92 #else /* ECC_MUL_A_WBITS > 1 */
94 #define TABLE_SIZE (1U << ECC_MUL_A_WBITS)
95 #define TABLE_MASK (TABLE_SIZE - 1)
97 #define TABLE(j) (table + (j) * 3*ecc->p.size)
100 table_init (const struct ecc_curve *ecc,
101 mp_limb_t *table, unsigned bits,
105 unsigned size = 1 << bits;
108 mpn_zero (TABLE(0), 3*ecc->p.size);
109 ecc_a_to_j (ecc, TABLE(1), p);
111 for (j = 2; j < size; j += 2)
113 ecc_dup_jj (ecc, TABLE(j), TABLE(j/2), scratch);
114 ecc_add_jja (ecc, TABLE(j+1), TABLE(j), TABLE(1), scratch);
119 ecc_mul_a (const struct ecc_curve *ecc,
121 const mp_limb_t *np, const mp_limb_t *p,
125 #define table (scratch + 3*ecc->p.size)
126 mp_limb_t *scratch_out = table + (3*ecc->p.size << ECC_MUL_A_WBITS);
129 /* Avoid the mp_bitcnt_t type for compatibility with older GMP
131 unsigned blocks = (ecc->p.bit_size + ECC_MUL_A_WBITS - 1) / ECC_MUL_A_WBITS;
132 unsigned bit_index = (blocks-1) * ECC_MUL_A_WBITS;
134 mp_size_t limb_index = bit_index / GMP_NUMB_BITS;
135 unsigned shift = bit_index % GMP_NUMB_BITS;
138 table_init (ecc, table, ECC_MUL_A_WBITS, p, scratch_out);
142 if (limb_index < ecc->p.size - 1)
143 bits |= np[limb_index + 1] << (GMP_NUMB_BITS - shift);
145 assert (bits < TABLE_SIZE);
147 sec_tabselect (r, 3*ecc->p.size, table, TABLE_SIZE, bits);
148 is_zero = (bits == 0);
153 if (shift >= ECC_MUL_A_WBITS)
155 shift -= ECC_MUL_A_WBITS;
165 bits = w << (ECC_MUL_A_WBITS - shift);
166 w = np[--limb_index];
167 shift = shift + GMP_NUMB_BITS - ECC_MUL_A_WBITS;
170 for (j = 0; j < ECC_MUL_A_WBITS; j++)
171 ecc_dup_jj (ecc, r, r, scratch_out);
174 sec_tabselect (tp, 3*ecc->p.size, table, TABLE_SIZE, bits);
175 cnd_copy (is_zero, r, tp, 3*ecc->p.size);
176 ecc_add_jjj (ecc, tp, tp, r, scratch_out);
178 /* Use the sum when valid. ecc_add_jja produced garbage if
179 is_zero != 0 or bits == 0, . */
180 cnd_copy (bits & (is_zero - 1), r, tp, 3*ecc->p.size);
181 is_zero &= (bits == 0);
187 #endif /* ECC_MUL_A_WBITS > 1 */