1 /**
2 * @file mem/secure.c Secure memory functions
3 *
4 * Copyright (C) 2010 Creytiv.com
5 */
6
7 #include <re_types.h>
8 #include <re_mem.h>
9
10
11 /**
12 * Compare two byte strings in constant time. This function can be used
13 * by secure code to compare secret data, such as authentication tags,
14 * to avoid side-channel attacks.
15 *
16 * @param s1 First byte string
17 * @param s2 Second byte string
18 * @param n Number of bytes
19 *
20 * @return a negative number if argument errors
21 * 0 if both byte strings matching
22 * a positive number if not matching
23 */
mem_seccmp(const volatile uint8_t * volatile s1,const volatile uint8_t * volatile s2,size_t n)24 int mem_seccmp(const volatile uint8_t *volatile s1,
25 const volatile uint8_t *volatile s2,
26 size_t n)
27 {
28 uint8_t val = 0;
29
30 if (!s1 || !s2)
31 return -1;
32
33 while (n--)
34 val |= *s1++ ^ *s2++;
35
36 return val;
37 }
38