1.\" $NetBSD: arc4random.3,v 1.5 2002/05/28 11:38:29 itojun Exp $ 2.\" $OpenBSD: arc4random.3,v 1.17 2000/12/21 14:07:41 aaron Exp $ 3.\" 4.\" Copyright 1997 Niels Provos <provos@physnet.uni-hamburg.de> 5.\" All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed by Niels Provos. 18.\" 4. The name of the author may not be used to endorse or promote products 19.\" derived from this software without specific prior written permission. 20.\" 21.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 22.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 23.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 24.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 25.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 26.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 27.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 28.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 29.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 30.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 31.\" 32.\" Manual page, using -mandoc macros 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.Fd #include \*[Lt]stdlib.h\*[Gt] 46.Ft u_int32_t 47.Fn arc4random "void" 48.Ft void 49.Fn arc4random_stir "void" 50.Ft void 51.Fn arc4random_addrandom "u_char *dat" "int datlen" 52.Sh DESCRIPTION 53The 54.Fn arc4random 55function provides a high quality 32-bit pseudo-random 56number very quickly. 57.Fn arc4random 58seeds itself on a regular basis from the kernel strong random number 59subsystem described in 60.Xr rnd 4 . 61On each call, an ARC4 generator is used to generate a new result. 62The 63.Fn arc4random 64function uses the ARC4 cipher key stream generator, 65which uses 8*8 8 bit S-Boxes. 66The S-Boxes can be in about (2**1700) states. 67.Pp 68.Fn arc4random 69fits into a middle ground not covered by other subsystems such as 70the strong, slow, and resource expensive random 71devices described in 72.Xr rnd 4 73versus the fast but poor quality interfaces described in 74.Xr rand 3 , 75.Xr random 3 , 76and 77.Xr drand48 3 . 78.Pp 79The 80.Fn arc4random_stir 81function reads data from 82.Pa /dev/urandom 83and uses it to permute the S-Boxes via 84.Fn arc4random_addrandom . 85.Pp 86There is no need to call 87.Fn arc4random_stir 88before using 89.Fn arc4random , 90since 91.Fn arc4random 92automatically initializes itself. 93.Sh SEE ALSO 94.Xr rand 3 , 95.Xr rand48 3 , 96.Xr random 3 97.Sh HISTORY 98An algorithm called 99.Pa RC4 100was designed by RSA Data Security, Inc. 101It was considered a trade secret, but not trademarked. 102Because it was a trade secret, it obviously could not be patented. 103A clone of this was posted anonymously to USENET and confirmed to 104be equivalent by several sources who had access to the original cipher. 105Because of the trade secret situation, RSA Data Security, Inc. can do 106nothing about the release of the ARC4 algorithm. 107Since 108.Pa RC4 109used to be a trade secret, the cipher is now referred to as 110.Pa ARC4 . 111.Pp 112These functions first appeared in 113.Ox 2.1 . 114