1.\" $OpenBSD: arc4random.3,v 1.2 1997/04/27 22:40:25 angelos Exp $ 2.\" Copyright 1997 Niels Provos <provos@physnet.uni-hamburg.de> 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 3. All advertising materials mentioning features or use of this software 14.\" must display the following acknowledgement: 15.\" This product includes software developed by Niels Provos. 16.\" 4. The name of the author may not be used to endorse or promote products 17.\" derived from this software without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 20.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 21.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 22.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 23.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 24.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 25.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 26.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 27.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 28.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29.\" 30.\" Manual page, using -mandoc macros 31.\" $FreeBSD: src/lib/libc/gen/arc4random.3,v 1.8.2.5 2003/05/06 21:40:19 trhodes Exp $ 32.\" $DragonFly: src/lib/libc/gen/arc4random.3,v 1.3 2005/04/26 10:16:16 joerg Exp $ 33.\" 34.Dd April 15, 1997 35.Dt ARC4RANDOM 3 36.Os 37.Sh NAME 38.Nm arc4random , 39.Nm arc4random_stir , 40.Nm arc4random_addrandom 41.Nd arc4 random number generator 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In stdlib.h 46.Ft uint32_t 47.Fn arc4random "void" 48.Ft void 49.Fn arc4random_stir "void" 50.Ft void 51.Fn arc4random_addrandom "uint8_t *dat" "size_t datlen" 52.Sh DESCRIPTION 53The 54.Fn arc4random 55function uses the key stream generator employed by the 56arc4 cipher, which uses 8*8 8 bit S-Boxes. 57The S-Boxes 58can be in about 59.if t 2\u\s71700\s10\d 60.if n (2**1700) 61states. The 62.Fn arc4random 63function returns pseudo-random numbers in the range of 0 to 64.if t 2\u\s731\s10\d\(mi1, 65.if n (2**31)\(mi1, 66and therefore has twice the range of 67.Dv RAND_MAX . 68.Pp 69The 70.Fn arc4random_stir 71function reads data from 72.Pa /dev/urandom 73and uses it to permute the S-Boxes via 74.Fn arc4random_addrandom . 75.Pp 76There is no need to call 77.Fn arc4random_stir 78before using 79.Fn arc4random , 80since 81.Fn arc4random 82automatically initializes itself. 83.Sh EXAMPLES 84The following produces a drop-in replacement for the traditional 85.Fn rand 86and 87.Fn random 88functions using 89.Fn arc4random : 90.Pp 91.Dl #define foo4random() (arc4random() % ((unsigned)RAND_MAX + 1)) 92.Sh SEE ALSO 93.Xr rand 3 , 94.Xr random 3 , 95.Xr srandomdev 3 96.Sh HISTORY 97.Pa RC4 98has been designed by RSA Data Security, Inc. 99It was posted anonymously 100to the USENET and was confirmed to be equivalent by several sources who 101had access to the original cipher. 102Since 103.Pa RC4 104used to be a trade secret, the cipher is now referred to as 105.Pa ARC4 . 106