1 /* $OpenBSD: timingsafe_memcmp.c,v 1.2 2015/08/31 02:53:57 guenther Exp $ */ 2 /* 3 * Copyright (c) 2014 Google Inc. 4 * 5 * Permission to use, copy, modify, and distribute this software for any 6 * purpose with or without fee is hereby granted, provided that the above 7 * copyright notice and this permission notice appear in all copies. 8 * 9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16 */ 17 18 #include <sys/cdefs.h> 19 __FBSDID("$FreeBSD$"); 20 21 #include <limits.h> 22 #include <string.h> 23 24 int __timingsafe_memcmp(const void *, const void *, size_t); 25 26 int 27 __timingsafe_memcmp(const void *b1, const void *b2, size_t len) 28 { 29 const unsigned char *p1 = b1, *p2 = b2; 30 size_t i; 31 int res = 0, done = 0; 32 33 for (i = 0; i < len; i++) { 34 /* lt is -1 if p1[i] < p2[i]; else 0. */ 35 int lt = (p1[i] - p2[i]) >> CHAR_BIT; 36 37 /* gt is -1 if p1[i] > p2[i]; else 0. */ 38 int gt = (p2[i] - p1[i]) >> CHAR_BIT; 39 40 /* cmp is 1 if p1[i] > p2[i]; -1 if p1[i] < p2[i]; else 0. */ 41 int cmp = lt - gt; 42 43 /* set res = cmp if !done. */ 44 res |= cmp & ~done; 45 46 /* set done if p1[i] != p2[i]. */ 47 done |= lt | gt; 48 } 49 50 return (res); 51 } 52 53 __weak_reference(__timingsafe_memcmp, timingsafe_memcmp); 54