NAME
memcmp —
compare byte string
LIBRARY
library “libc”
SYNOPSIS
#include
<string.h>
int
memcmp(const
void *b1, const void
*b2, size_t
len);
DESCRIPTION
Thememcmp()
function compares byte string b1 against byte string
b2. Both strings are assumed to be
len bytes long.
RETURN VALUES
The memcmp() function returns zero if the
two strings are identical, otherwise returns the difference between the
first two differing bytes (treated as unsigned char values, so that
‘\200’ is greater than
‘\0’, for example). Zero-length
strings are always identical.
Do not use memcmp() to compare
cryptographic secrets, because the time it takes varies depending on how
many bytes are the same, and thus leaks information about the two strings by
a timing side channel. To compare secrets, hashes, message authentication
codes, etc., use
consttime_memequal(3) instead.
SEE ALSO
bcmp(3), consttime_memequal(3), strcasecmp(3), strcmp(3), strcoll(3), strxfrm(3)
STANDARDS
The memcmp() function conforms to
ANSI X3.159-1989
(“ANSI C89”).