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+.\" $OpenBSD: arc4random.3,v 1.19 2005/07/17 08:50:55 jaredy Exp $
+.\"
+.\" Copyright 1997 Niels Provos <provos@physnet.uni-hamburg.de>
+.\" All rights reserved.
+.\"
+.\" 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.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"      This product includes software developed by Niels Provos.
+.\" 4. The name of the author may not be used to endorse or promote products
+.\"    derived from this software without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
+.\"
+.\" Manual page, using -mandoc macros
+.\"
+.Dd April 15, 1997
+.Dt ARC4RANDOM 3
+.Os
+.Sh NAME
+.Nm arc4random ,
+.Nm arc4random_stir ,
+.Nm arc4random_addrandom
+.Nd arc4 random number generator
+.Sh SYNOPSIS
+.Fd #include <stdlib.h>
+.Ft uint32_t
+.Fn arc4random "void"
+.Ft void
+.Fn arc4random_stir "void"
+.Ft void
+.Fn arc4random_addrandom "u_char *dat" "int datlen"
+.Sh DESCRIPTION
+The
+.Fn arc4random
+function provides a high quality 32-bit pseudo-random
+number very quickly.
+.Fn arc4random
+seeds itself on a regular basis from the kernel strong random number
+subsystem described in
+.Xr random 4 .
+On each call, an ARC4 generator is used to generate a new result.
+The
+.Fn arc4random
+function uses the ARC4 cipher key stream generator,
+which uses 8*8 8-bit S-Boxes.
+The S-Boxes can be in about (2**1700) states.
+.Pp
+.Fn arc4random
+fits into a middle ground not covered by other subsystems such as
+the strong, slow, and resource expensive random
+devices described in
+.Xr random 4
+versus the fast but poor quality interfaces described in
+.Xr rand 3 ,
+.Xr random 3 ,
+and
+.Xr drand48 3 .
+.Pp
+The
+.Fn arc4random_stir
+function reads data from a pseudo-random device, usually
+.Pa /dev/urandom,
+and uses it to permute the S-Boxes via
+.Fn arc4random_addrandom .
+.Pp
+There is no need to call
+.Fn arc4random_stir
+before using
+.Fn arc4random ,
+since
+.Fn arc4random
+automatically initializes itself.
+.Sh SEE ALSO
+.Xr rand 3 ,
+.Xr rand48 3 ,
+.Xr random 3
+.Sh HISTORY
+An algorithm called
+.Pa RC4
+was designed by RSA Data Security, Inc.
+It was considered a trade secret.
+Because it was a trade secret, it obviously could not be patented.
+A clone of this was posted anonymously to USENET and confirmed to
+be equivalent by several sources who had access to the original cipher.
+Because of the trade secret situation, RSA Data Security, Inc. can do
+nothing about the release of the ARC4 algorithm.
+Since
+.Pa RC4
+used to be a trade secret, the cipher is now referred to as
+.Pa ARC4 .
+.Pp
+These functions first appeared in
+.Ox 2.1 .