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.\" $OpenBSD: arc4random.9,v 1.15 2020/05/29 03:19:43 deraadt Exp $
.\"
.\" Copyright (c) 1996,2000 Michael Shalayeff
.\" 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.
.\"
.\" 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.
.\"
.Dd $Mdocdate: May 29 2020 $
.Dt ARC4RANDOM 9
.Os
.Sh NAME
.Nm arc4random ,
.Nm arc4random_buf ,
.Nm arc4random_uniform ,
.Nm enqueue_randomness
.Nd kernel random subsystem
.Sh SYNOPSIS
.In sys/systm.h
.Ft u_int32_t
.Fn arc4random "void"
.Ft void
.Fn arc4random_buf "void *buf" "size_t nbytes"
.Ft u_int32_t
.Fn arc4random_uniform "u_int32_t upper_bound"
.Ft void
.Fn enqueue_randomness "int"
.Sh DESCRIPTION
.Fn arc4random
and
.Fn arc4random_buf
provide random numbers and are intended to be called in any
circumstance where random numbers are required.
.Pp
.Fn arc4random_uniform
will return a uniformly distributed random number less than
.Fa upper_bound ,
avoiding "modulo bias" when the upper bound is not a power of two.
In the worst case, this function may consume multiple iterations
to ensure uniformity; see the source code to understand the problem
and solution.
.Pp
.Fn enqueue_randomness
causes the supplied data argument to be added to the entropy pool.
.Sh SEE ALSO
.Xr arc4random 3 ,
.Xr random 4
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