114 lines
3.8 KiB
Groff
114 lines
3.8 KiB
Groff
.\" $NetBSD: arc4random.3,v 1.5 2002/05/28 11:38:29 itojun Exp $
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.\" $OpenBSD: arc4random.3,v 1.17 2000/12/21 14:07:41 aaron Exp $
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.\"
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.\" Copyright 1997 Niels Provos <provos@physnet.uni-hamburg.de>
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.\" All rights reserved.
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by Niels Provos.
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" Manual page, using -mandoc macros
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.\"
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.Dd April 15, 1997
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.Dt ARC4RANDOM 3
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.Os
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.Sh NAME
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.Nm arc4random ,
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.Nm arc4random_stir ,
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.Nm arc4random_addrandom
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.Nd arc4 random number generator
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include \*[Lt]stdlib.h\*[Gt]
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.Ft u_int32_t
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.Fn arc4random "void"
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.Ft void
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.Fn arc4random_stir "void"
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.Ft void
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.Fn arc4random_addrandom "u_char *dat" "int datlen"
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.Sh DESCRIPTION
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The
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.Fn arc4random
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function provides a high quality 32-bit pseudo-random
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number very quickly.
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.Fn arc4random
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seeds itself on a regular basis from the kernel strong random number
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subsystem described in
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.Xr rnd 4 .
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On each call, an ARC4 generator is used to generate a new result.
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The
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.Fn arc4random
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function uses the ARC4 cipher key stream generator,
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which uses 8*8 8 bit S-Boxes.
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The S-Boxes can be in about (2**1700) states.
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.Pp
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.Fn arc4random
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fits into a middle ground not covered by other subsystems such as
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the strong, slow, and resource expensive random
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devices described in
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.Xr rnd 4
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versus the fast but poor quality interfaces described in
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.Xr rand 3 ,
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.Xr random 3 ,
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and
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.Xr drand48 3 .
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.Pp
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The
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.Fn arc4random_stir
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function reads data from
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.Pa /dev/urandom
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and uses it to permute the S-Boxes via
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.Fn arc4random_addrandom .
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.Pp
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There is no need to call
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.Fn arc4random_stir
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before using
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.Fn arc4random ,
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since
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.Fn arc4random
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automatically initializes itself.
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.Sh SEE ALSO
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.Xr rand 3 ,
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.Xr rand48 3 ,
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.Xr random 3
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.Sh HISTORY
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An algorithm called
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.Pa RC4
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was designed by RSA Data Security, Inc.
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It was considered a trade secret, but not trademarked.
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Because it was a trade secret, it obviously could not be patented.
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A clone of this was posted anonymously to USENET and confirmed to
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be equivalent by several sources who had access to the original cipher.
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Because of the trade secret situation, RSA Data Security, Inc. can do
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nothing about the release of the ARC4 algorithm.
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Since
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.Pa RC4
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used to be a trade secret, the cipher is now referred to as
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.Pa ARC4 .
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.Pp
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These functions first appeared in
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.Ox 2.1 .
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