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commit 8c7c7084b7ff813f1b7d012ddaa5d11d0eb55875
parent 41baeebc284edb331f96fb43abe25f533a0ea1f3
Author: Duncaen <mail@duncano.de>
Date:   Fri, 19 May 2017 18:14:45 +0200

lib/libopenbsd: add arc4random(3) man page

lib/libopenbsd/crypt/arc4random.3 | 114+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 114 insertions(+), 0 deletions(-)

diff --git a/lib/libopenbsd/crypt/arc4random.3 b/lib/libopenbsd/crypt/arc4random.3 @@ -0,0 +1,114 @@ +.\" $OpenBSD: arc4random.3,v 1.35 2014/11/25 16:45:24 millert 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 $Mdocdate: November 25 2014 $ +.Dt ARC4RANDOM 3 +.Os +.Sh NAME +.Nm arc4random , +.Nm arc4random_buf , +.Nm arc4random_uniform +.Nd random number generator +.Sh SYNOPSIS +.In stdlib.h +.Ft uint32_t +.Fn arc4random "void" +.Ft void +.Fn arc4random_buf "void *buf" "size_t nbytes" +.Ft uint32_t +.Fn arc4random_uniform "uint32_t upper_bound" +.Sh DESCRIPTION +This family of functions provides higher quality data than those +described in +.Xr rand 3 , +.Xr random 3 , +and +.Xr rand48 3 . +.Pp +Use of these functions is encouraged for almost all random number +consumption because the other interfaces are deficient in either +quality, portability, standardization, or availability. +These functions can be called in almost all coding environments, +including +.Xr pthreads 3 +and +.Xr chroot 2 . +.Pp +High quality 32-bit pseudo-random numbers are generated very quickly. +On each call, a cryptographic pseudo-random number generator is used +to generate a new result. +One data pool is used for all consumers in a process, so that consumption +under program flow can act as additional stirring. +The subsystem is re-seeded from the kernel random number subsystem using +.Xr getentropy 2 +on a regular basis, and also upon +.Xr fork 2 . +.Pp +The +.Fn arc4random +function returns a single 32-bit value. +.Pp +.Fn arc4random_buf +fills the region +.Fa buf +of length +.Fa nbytes +with random data. +.Pp +.Fn arc4random_uniform +will return a single 32-bit value, uniformly distributed but less than +.Fa upper_bound . +This is recommended over constructions like +.Dq Li arc4random() % upper_bound +as it avoids "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. +.Sh RETURN VALUES +These functions are always successful, and no return value is +reserved to indicate an error. +.Sh SEE ALSO +.Xr rand 3 , +.Xr rand48 3 , +.Xr random 3 +.Sh HISTORY +These functions first appeared in +.Ox 2.1 . +.Pp +The original version of this random number generator used the +RC4 (also known as ARC4) algorithm. +In +.Ox 5.5 +it was replaced with the ChaCha20 cipher, and it may be replaced +again in the future as cryptographic techniques advance. +A good mnemonic is +.Dq A Replacement Call for Random .