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 } 51