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.\" $FreeBSD$ 32.\" 33.Dd April 15, 1997 34.Dt ARC4RANDOM 3 35.Os 36.Sh NAME 37.Nm arc4random , 38.Nm arc4random_stir , 39.Nm arc4random_addrandom 40.Nd arc4 random number generator 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In stdlib.h 45.Ft u_int32_t 46.Fn arc4random "void" 47.Ft void 48.Fn arc4random_stir "void" 49.Ft void 50.Fn arc4random_addrandom "unsigned char *dat" "int datlen" 51.Sh DESCRIPTION 52The 53.Fn arc4random 54function uses the key stream generator employed by the 55arc4 cipher, which uses 8*8 8 bit S-Boxes. 56The S-Boxes 57can be in about 58.if t 2\u\s71700\s10\d 59.if n (2**1700) 60states. The 61.Fn arc4random 62function returns pseudo-random numbers in the range of 0 to 63.if t 2\u\s731\s10\d\(mi1, 64.if n (2**31)\(mi1, 65and therefore has twice the range of 66.Dv RAND_MAX . 67.Pp 68The 69.Fn arc4random_stir 70function reads data from 71.Pa /dev/urandom 72and uses it to permute the S-Boxes via 73.Fn arc4random_addrandom . 74.Pp 75There is no need to call 76.Fn arc4random_stir 77before using 78.Fn arc4random , 79since 80.Fn arc4random 81automatically initializes itself. 82.Sh EXAMPLES 83The following produces a drop-in replacement for the traditional 84.Fn rand 85and 86.Fn random 87functions using 88.Fn arc4random : 89.Pp 90.Dl #define foo4random() (arc4random() % ((unsigned)RAND_MAX + 1)) 91.Sh SEE ALSO 92.Xr rand 3 , 93.Xr random 3 , 94.Xr srandomdev 3 95.Sh HISTORY 96.Pa RC4 97has been designed by RSA Data Security, Inc. 98It was posted anonymously 99to the USENET and was confirmed to be equivalent by several sources who 100had access to the original cipher. 101Since 102.Pa RC4 103used to be a trade secret, the cipher is now referred to as 104.Pa ARC4 . 105