NAME
timingsafe_bcmp,
timingsafe_memcmp —
timing-safe byte sequence
comparisons
SYNOPSIS
#include
<string.h>
int
timingsafe_bcmp(const
void *b1, const void
*b2, size_t
len);
int
timingsafe_memcmp(const
void *b1, const void
*b2, size_t
len);
DESCRIPTION
The
timingsafe_bcmp()
and
timingsafe_memcmp()
functions lexicographically compare the first len
bytes (each interpreted as an unsigned char) pointed
to by b1 and b2.
Additionally, their running times are independent of the byte sequences compared, making them safe to use for comparing secret values such as cryptographic MACs. In contrast, bcmp(3) and memcmp(3) may short-circuit after finding the first differing byte.
RETURN VALUES
The timingsafe_bcmp() function returns 0
or not zero if the byte sequence pointed to by b1
compares equal to or not equal to (respectively) the byte sequence pointed
to by b2.
The timingsafe_memcmp() function returns a
negative value, 0, or positive value if the byte sequence pointed to by
b1 compares less than, equal to, or greater than
(respectively) the byte sequence pointed to by b2.
SEE ALSO
STANDARDS
The timingsafe_bcmp() and
timingsafe_memcmp() functions are
OpenBSD extensions.
HISTORY
The timingsafe_bcmp() function first
appeared in OpenBSD 4.9.
The timingsafe_memcmp() function first
appeared in OpenBSD 5.6.