89 lines
2.7 KiB
Groff
89 lines
2.7 KiB
Groff
.\" $NetBSD: consttime_bcmp.3,v 1.1 2013/06/23 16:44:06 riastradh Exp $
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.\"
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.\" Copyright (c) 2013 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This documentation is derived from text contributed to The NetBSD
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.\" Foundation by Taylor R. Campbell.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd June 23, 2013
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.Dt CONSTTIME_BCMP 3
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.Os
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.Sh NAME
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.Nm consttime_bcmp
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.Nd compare byte strings for equality without timing leaks
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In string.h
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.Ft int
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.Fn consttime_bcmp "void *b1" "void *b2" "size_t len"
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.Sh DESCRIPTION
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The
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.Fn consttime_bcmp
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function compares
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.Fa len
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bytes of memory at
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.Fa b1
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and
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.Fa b2
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for equality, returning zero if they are identical and nonzero
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otherwise.
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.Pp
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The time taken by
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.Fn consttime_bcmp
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depends on
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.Fa len ,
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but not on the data at
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.Fa b1
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or
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.Fa b2 .
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Thus,
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.Fn consttime_bcmp
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is appropriate for comparing cryptographic secrets, hashes, message
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authentication codes, etc., without leaking information about them
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through a timing side channel.
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In crypto literature,
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.Fn consttime_bcmp
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is said to take
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.Sq constant time ,
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meaning time that does not vary depending on the data it processes.
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.Pp
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Note that unlike
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.Xr memcmp 3 ,
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.Fn consttime_bcmp
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does not return a lexicographic ordering on the data at
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.Fa b1
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and
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.Fa b2 ;
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it tells only whether they are equal.
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.Sh SEE ALSO
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.Xr explicit_bzero 3 ,
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.Xr memcmp 3
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.Sh HISTORY
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The
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.Fn consttime_bcmp
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function appeared in
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.Nx 7.0 .
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