Added generic API for date range validation (with callbacks).
[BearSSL] / int / i15_modpow.c
1 /*
2 * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
6 * "Software"), to deal in the Software without restriction, including
7 * without limitation the rights to use, copy, modify, merge, publish,
8 * distribute, sublicense, and/or sell copies of the Software, and to
9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
11 *
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22 * SOFTWARE.
23 */
24
25 #include "inner.h"
26
27 /* see inner.h */
28 void
29 br_i15_modpow(uint16_t *x,
30 const unsigned char *e, size_t elen,
31 const uint16_t *m, uint16_t m0i, uint16_t *t1, uint16_t *t2)
32 {
33 size_t mlen;
34 unsigned k;
35
36 mlen = ((m[0] + 31) >> 4) * sizeof m[0];
37 memcpy(t1, x, mlen);
38 br_i15_to_monty(t1, m);
39 br_i15_zero(x, m[0]);
40 x[1] = 1;
41 for (k = 0; k < ((unsigned)elen << 3); k ++) {
42 uint32_t ctl;
43
44 ctl = (e[elen - 1 - (k >> 3)] >> (k & 7)) & 1;
45 br_i15_montymul(t2, x, t1, m, m0i);
46 CCOPY(ctl, x, t2, mlen);
47 br_i15_montymul(t2, t1, t1, m, m0i);
48 memcpy(t1, t2, mlen);
49 }
50 }