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 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