.\"	$OpenBSD: timingsafe_bcmp.3,v 1.1 2014/06/13 02:12:17 matthew Exp $
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.Dd $Mdocdate: June 13 2014 $
.Dt TIMINGSAFE_BCMP 3
.Os
.Sh NAME
.Nm timingsafe_bcmp ,
.Nm timingsafe_memcmp
.Nd timing-safe byte sequence comparisons
.Sh SYNOPSIS
.In string.h
.Ft int
.Fn timingsafe_bcmp "const void *b1" "const void *b2" "size_t len"
.Ft int
.Fn timingsafe_memcmp "const void *b1" "const void *b2" "size_t len"
.Sh DESCRIPTION
The
.Fn timingsafe_bcmp
and
.Fn timingsafe_memcmp
functions lexicographically compare the first
.Fa len
bytes (each interpreted as an
.Vt unsigned char )
pointed to by
.Fa b1
and
.Fa b2 .
.Pp
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,
.Xr bcmp 3
and
.Xr memcmp 3
may short-circuit after finding the first differing byte.
.Sh RETURN VALUES
The
.Fn timingsafe_bcmp
function returns 0 or 1 if the byte sequence pointed to by
.Fa b1
compares equal to or not equal to (respectively)
the byte sequence pointed to by
.Fa b2 .
.Pp
The
.Fn timingsafe_memcmp
function returns \-1, 0, or 1 if the byte sequence pointed to by
.Fa b1
compares less than, equal to, or greater than (respectively)
the byte sequence pointed to by
.Fa b2 .
.Pp
Note that these return values are compatible with, but stricter than,
the ones specified for
.Xr bcmp 3
and
.Xr memcmp 3 .
.Sh SEE ALSO
.Xr bcmp 3 ,
.Xr memcmp 3
.Sh STANDARDS
The
.Fn timingsafe_bcmp
and
.Fn timingsafe_memcmp
functions are
.Ox
extensions.
.Sh HISTORY
The
.Fn timingsafe_bcmp
function first appeared in
.Ox 4.9 .
.Pp
The
.Fn timingsafe_memcmp
function first appeared in
.Ox 5.6 .