TIMINGSAFE_BCMP(3)

NAME
timingsafe_bcmp, timingsafe_memcmp - timing-safe byte sequence comparisons

LIBRARY
libc

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
bcmp(3), memcmp(3)

STANDARDS
The timingsafe_bcmp() and timingsafe_memcmp() functions are OpenBSD extensions.

HISTORY
The timingsafe_bcmp() function first appeared in OpenBSD 4.9 and DragonFly 5.6.

The timingsafe_memcmp() function first appeared in OpenBSD 5.5 and DragonFly 5.6.