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  }