854023f054
Obtained from: OpenBSD Reviewed by: trasz MFC after: 1 month Differential Revision: https://reviews.freebsd.org/D7280
93 lines
2.4 KiB
Groff
93 lines
2.4 KiB
Groff
.\" $OpenBSD: timingsafe_bcmp.3,v 1.2 2014/06/21 20:22:15 tedu Exp $
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.\"
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.\" Copyright (c) 2014 Google Inc.
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\"
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.\" $FreeBSD$
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.Dd August 15, 2016
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.Dt TIMINGSAFE_BCMP 3
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.Os
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.Sh NAME
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.Nm timingsafe_bcmp ,
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.Nm timingsafe_memcmp
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.Nd timing-safe byte sequence comparisons
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.Sh SYNOPSIS
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.In string.h
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.Ft int
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.Fn timingsafe_bcmp "const void *b1" "const void *b2" "size_t len"
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.Ft int
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.Fn timingsafe_memcmp "const void *b1" "const void *b2" "size_t len"
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.Sh DESCRIPTION
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The
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.Fn timingsafe_bcmp
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and
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.Fn timingsafe_memcmp
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functions lexicographically compare the first
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.Fa len
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bytes (each interpreted as an
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.Vt unsigned char )
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pointed to by
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.Fa b1
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and
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.Fa b2 .
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.Pp
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Additionally, their running times are independent of the byte sequences compared,
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making them safe to use for comparing secret values such as cryptographic MACs.
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In contrast,
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.Xr bcmp 3
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and
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.Xr memcmp 3
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may short-circuit after finding the first differing byte.
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.Sh RETURN VALUES
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The
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.Fn timingsafe_bcmp
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function returns 0 or not zero if the byte sequence pointed to by
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.Fa b1
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compares equal to or not equal to (respectively)
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the byte sequence pointed to by
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.Fa b2 .
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.Pp
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The
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.Fn timingsafe_memcmp
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function returns a negative value, 0, or positive value if the byte sequence
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pointed to by
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.Fa b1
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compares less than, equal to, or greater than (respectively)
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the byte sequence pointed to by
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.Fa b2 .
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.Sh SEE ALSO
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.Xr bcmp 3 ,
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.Xr memcmp 3
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.Sh STANDARDS
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The
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.Fn timingsafe_bcmp
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and
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.Fn timingsafe_memcmp
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functions are
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.Fx
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extensions.
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.Sh HISTORY
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The
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.Fn timingsafe_bcmp
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function first appeared in
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.Ox 4.9 .
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.Pp
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The
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.Fn timingsafe_memcmp
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function first appeared in
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.Ox 5.6 .
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.Pp
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Both functions first appeared in
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.Fx 12.0 .
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