Date: Sun, 23 Jun 2013 14:31:25 +0000 (UTC)
From: chris...@astron.com (Christos Zoulas)
In article <20130623142023.6e4c760...@jupiter.mumble.net>,
Taylor R Campbell <riastr...@netbsd.org> wrote:
>We ought to have a man page for explicit_bzero and consttime_bcmp.
>I didn't realize we lacked one since they were added last year.
We should not be creating new interfaces based on obsolete ones. I'd
rather we have consttime_memcmp() and explicit_memset().
I don't care if we rename them to consttime_memeq and explicit_memzero
instead, but these are absolutely the operations that real crypto
applications need. consttime_memcmp and explicit_memset are not, and
are needlessly complicated.
How do the attached man pages look? We ought to add cross-references
in memcmp(3) and memset(3) too, perhaps.
.\" $NetBSD$
.\"
.\" Copyright (c) 2013 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This documentation is derived from text contributed to The NetBSD
.\" Foundation by Taylor R. Campbell.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd June 23, 2013
.Dt EXPLICIT_BZERO 3
.Os
.Sh NAME
.Nm explicit_bzero
.Nd guarantee zeroing a buffer in memory
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In string.h
.Ft void
.Fn explicit_bzero "void *ptr" "size_t len"
.Sh DESCRIPTION
The
.Fn explicit_bzero
function writes
.Fa len
zeros to the memory pointed to by
.Fa ptr .
It is guaranteed not to be optimized away by the compiler even if
.Fa ptr
is no longer used and is about to be freed or go out of scope.
.Sh EXAMPLES
Create a buffer on the stack for a secret key, use it, and then zero it
in memory before throwing it away.
.Bd -literal -offset indent
void
f(void)
{
uint8_t key[32];
crypto_random(key, sizeof(key));
do_crypto_stuff(key, sizeof(key));
\&...
explicit_bzero(key, sizeof(key));
}
.Ed
.Sh SEE ALSO
.Xr consttime_bcmp 3 ,
.Xr memset 3
.Sh HISTORY
The
.Fn explicit_bzero
function appeared in
.Nx 7.0 .
.\" $NetBSD$
.\"
.\" Copyright (c) 2013 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This documentation is derived from text contributed to The NetBSD
.\" Foundation by Taylor R. Campbell.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd June 23, 2013
.Dt CONSTTIME_BCMP 3
.Os
.Sh NAME
.Nm consttime_bcmp
.Nd compare byte strings for equality without timing leaks
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In string.h
.Ft int
.Fn consttime_bcmp "void *b1" "void *b2" "size_t len"
.Sh DESCRIPTION
The
.Fn consttime_bcmp
function compares
.Fa len
bytes of memory at
.Fa b1
and
.Fa b2
for equality, returning zero if they are identical and nonzero
otherwise.
.Pp
The time taken by
.Fn consttime_bcmp
depends on
.Fa len ,
but not on the data at
.Fa b1
or
.Fa b2 .
Thus,
.Fn consttime_bcmp
is appropriate for comparing cryptographic secrets, hashes, message
authentication codes, etc., without leaking information about them
through a timing side channel.
In crypto literature,
.Fn consttime_bcmp
is said to take
.Sq constant time ,
meaning time that does not vary depending on the data it processes.
.Pp
Note that unlike
.Xr memcmp 3 ,
.Fn consttime_bcmp
does not return a lexicographic ordering on the data at
.Fa b1
and
.Fa b2 ;
it tells only whether they are equal.
.Sh SEE ALSO
.Xr explicit_bzero 3 ,
.Xr memcmp 3
.Sh HISTORY
The
.Fn consttime_bcmp
function appeared in
.Nx 7.0 .
