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.

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.