ct.c revision 233294 
1/*
2 * Copyright (c) 2009 Kungliga Tekniska H��gskolan
3 * (Royal Institute of Technology, Stockholm, Sweden).
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 *
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 *
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 *
17 * 3. Neither the name of the Institute nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34#include <config.h>
35#include "roken.h"
36
37/**
38 * Constant time compare to memory regions. The reason for making it
39 * constant time is to make sure that timeing information leak from
40 * where in the function the diffrence is.
41 *
42 * ct_memcmp() can't be used to order memory regions like memcmp(),
43 * for example, use ct_memcmp() with qsort().
44 *
45 * @param p1 memory region 1 to compare
46 * @param p2 memory region 2 to compare
47 * @param len length of memory
48 *
49 * @return 0 when the memory regions are equal, non zero if not
50 *
51 * @ingroup roken
52 */
53
54int
55ct_memcmp(const void *p1, const void *p2, size_t len)
56{
57    const unsigned char *s1 = p1, *s2 = p2;
58    size_t i;
59    int r = 0;
60
61    for (i = 0; i < len; i++)
62	r |= (s1[i] ^ s2[i]);
63    return !!r;
64}
65