2 * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
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:
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
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
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
)
37 * 'mlen' is the length of m[] expressed in bytes (including
38 * the "bit length" first field).
40 mlen
= ((m
[0] + 63) >> 5) * sizeof m
[0];
43 * Throughout the algorithm:
44 * -- t1[] is in Montgomery representation; it contains x, x^2,
46 * -- The result is accumulated, in normal representation, in
48 * -- t2[] is used as destination buffer for each multiplication.
50 * Note that there is no need to call br_i32_from_monty().
53 br_i32_to_monty(t1
, m
);
56 for (k
= 0; k
< ((uint32_t)elen
<< 3); k
++) {
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
);