Differential D7280 Diff 18655 lib/libc/string/timingsafe_bcmp.3

Changeset View

Standalone View

lib/libc/string/timingsafe_bcmp.3

This file was added.

Property	Old Value	New Value
svn:eol-style	null	native \ No newline at end of property
svn:keywords	null	FreeBSD=%H \ No newline at end of property
svn:mime-type	null	text/plain \ No newline at end of property

				.\" $OpenBSD: timingsafe_bcmp.3,v 1.2 2014/06/21 20:22:15 tedu Exp $
				.\"
				.\" Copyright (c) 2014 Google Inc.
				.\"
				.\" Permission to use, copy, modify, and distribute this software for any
				.\" purpose with or without fee is hereby granted, provided that the above
				.\" copyright notice and this permission notice appear in all copies.
				.\"
				.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
				.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
				.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
				.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
				.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
				.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
				.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
				.\"
				.\" $FreeBSD$
				.Dd $Mdocdate: June 13 2014 $
				.Dt TIMINGSAFE_BCMP 3
				bjkUnsubmitted Done Inline Actions Is this a target merge date? ;) bjk: Is this a target merge date? ;)
				delphijAuthorUnsubmitted Not Done Inline Actions Yes. delphij: Yes.
				.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 not zero 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 a negative value, 0, or positive value if the byte sequence
				pointed to by
				.Fa b1
				compares less than, equal to, or greater than (respectively)
				the byte sequence pointed to by
				bjkUnsubmitted Not Done Inline Actions I slightly worry that future advances in compiler optimizers will make these semantics hard to support, but have no real objection. bjk: I slightly worry that future advances in compiler optimizers will make these semantics hard to…
				delphijAuthorUnsubmitted Not Done Inline Actions That's possible, but I think we can always hint compiler not to optimize a select subset of library functions when this become a problem? delphij: That's possible, but I think we can always hint compiler not to optimize a select subset of…
				.Fa b2 .
				.Sh SEE ALSO
				.Xr bcmp 3 ,
				.Xr memcmp 3
				.Sh STANDARDS
				The
				.Fn timingsafe_bcmp
				and
				.Fn timingsafe_memcmp
				functions are
				.Fx
				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 .
				Both functions first appeared in
				.Fx 12.0 .