1.\" $OpenBSD: arc4random.9,v 1.15 2020/05/29 03:19:43 deraadt Exp $ 2.\" 3.\" Copyright (c) 1996,2000 Michael Shalayeff 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25.\" 26.Dd $Mdocdate: May 29 2020 $ 27.Dt ARC4RANDOM 9 28.Os 29.Sh NAME 30.Nm arc4random , 31.Nm arc4random_buf , 32.Nm arc4random_uniform , 33.Nm enqueue_randomness 34.Nd kernel random subsystem 35.Sh SYNOPSIS 36.In sys/systm.h 37.Ft u_int32_t 38.Fn arc4random "void" 39.Ft void 40.Fn arc4random_buf "void *buf" "size_t nbytes" 41.Ft u_int32_t 42.Fn arc4random_uniform "u_int32_t upper_bound" 43.Ft void 44.Fn enqueue_randomness "int" 45.Sh DESCRIPTION 46.Fn arc4random 47and 48.Fn arc4random_buf 49provide random numbers and are intended to be called in any 50circumstance where random numbers are required. 51.Pp 52.Fn arc4random_uniform 53will return a uniformly distributed random number less than 54.Fa upper_bound , 55avoiding "modulo bias" when the upper bound is not a power of two. 56In the worst case, this function may consume multiple iterations 57to ensure uniformity; see the source code to understand the problem 58and solution. 59.Pp 60.Fn enqueue_randomness 61causes the supplied data argument to be added to the entropy pool. 62.Sh SEE ALSO 63.Xr arc4random 3 , 64.Xr random 4 65