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comparison libtomcrypt/src/misc/mem_neq.c @ 1471:6dba84798cd5

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Update to libtomcrypt 1.18.1, merged with Dropbear changes
author Matt Johnston <matt@ucc.asn.au>
date Fri, 09 Feb 2018 21:44:05 +0800
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1470:8bba51a55704 1471:6dba84798cd5
1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 */
9 #include "tomcrypt.h"
10
11 /**
12 @file mem_neq.c
13 Compare two blocks of memory for inequality in constant time.
14 Steffen Jaeckel
15 */
16
17 /**
18 Compare two blocks of memory for inequality in constant time.
19
20 The usage is similar to that of standard memcmp, but you can only test
21 if the memory is equal or not - you can not determine by how much the
22 first different byte differs.
23
24 This function shall be used to compare results of cryptographic
25 operations where inequality means most likely usage of a wrong key.
26 The execution time has therefore to be constant as otherwise
27 timing attacks could be possible.
28
29 @param a The first memory region
30 @param b The second memory region
31 @param len The length of the area to compare (octets)
32
33 @return 0 when a and b are equal for len bytes, 1 they are not equal.
34 */
35 int mem_neq(const void *a, const void *b, size_t len)
36 {
37 unsigned char ret = 0;
38 const unsigned char* pa;
39 const unsigned char* pb;
40
41 LTC_ARGCHK(a != NULL);
42 LTC_ARGCHK(b != NULL);
43
44 pa = a;
45 pb = b;
46
47 while (len-- > 0) {
48 ret |= *pa ^ *pb;
49 ++pa;
50 ++pb;
51 }
52
53 ret |= ret >> 4;
54 ret |= ret >> 2;
55 ret |= ret >> 1;
56 ret &= 1;
57
58 return ret;
59 }
60
61 /* ref: $Format:%D$ */
62 /* git commit: $Format:%H$ */
63 /* commit time: $Format:%ai$ */