1 /*
2 * Copyright (c) 2016 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
br_i32_modpow(uint32_t * x,const unsigned char * e,size_t elen,const uint32_t * m,uint32_t m0i,uint32_t * t1,uint32_t * t2)29 br_i32_modpow(uint32_t *x,
30 const unsigned char *e, size_t elen,
31 const uint32_t *m, uint32_t m0i, uint32_t *t1, uint32_t *t2)
32 {
33 size_t mlen;
34 uint32_t k;
35
36 /*
37 * 'mlen' is the length of m[] expressed in bytes (including
38 * the "bit length" first field).
39 */
40 mlen = ((m[0] + 63) >> 5) * sizeof m[0];
41
42 /*
43 * Throughout the algorithm:
44 * -- t1[] is in Montgomery representation; it contains x, x^2,
45 * x^4, x^8...
46 * -- The result is accumulated, in normal representation, in
47 * the x[] array.
48 * -- t2[] is used as destination buffer for each multiplication.
49 *
50 * Note that there is no need to call br_i32_from_monty().
51 */
52 memcpy(t1, x, mlen);
53 br_i32_to_monty(t1, m);
54 br_i32_zero(x, m[0]);
55 x[1] = 1;
56 for (k = 0; k < ((uint32_t)elen << 3); k ++) {
57 uint32_t ctl;
58
59 ctl = (e[elen - 1 - (k >> 3)] >> (k & 7)) & 1;
60 br_i32_montymul(t2, x, t1, m, m0i);
61 CCOPY(ctl, x, t2, mlen);
62 br_i32_montymul(t2, t1, t1, m, m0i);
63 memcpy(t1, t2, mlen);
64 }
65 }
66