1.\" $OpenBSD: arc4random.3,v 1.17 2000/12/21 14:07:41 aaron Exp $ 2.\" 3.\" Copyright 1997 Niels Provos <provos@physnet.uni-hamburg.de> 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.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by Niels Provos. 17.\" 4. The name of the author may not be used to endorse or promote products 18.\" derived from this software without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 21.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 22.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 23.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 24.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 25.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 29.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30.\" 31.\" Manual page, using -mandoc macros 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 SYNOPSIS 42.Fd #include <stdlib.h> 43.Ft u_int32_t 44.Fn arc4random "void" 45.Ft void 46.Fn arc4random_stir "void" 47.Ft void 48.Fn arc4random_addrandom "u_char *dat" "int datlen" 49.Sh DESCRIPTION 50The 51.Fn arc4random 52function provides a high quality 32-bit pseudo-random 53number very quickly. 54.Fn arc4random 55seeds itself on a regular basis from the kernel strong random number 56subsystem described in 57.Xr random 4 . 58On each call, an ARC4 generator is used to generate a new result. 59The 60.Fn arc4random 61function uses the ARC4 cipher key stream generator, 62which uses 8*8 8 bit S-Boxes. 63The S-Boxes can be in about (2**1700) states. 64.Pp 65.Fn arc4random 66fits into a middle ground not covered by other subsystems such as 67the strong, slow, and resource expensive random 68devices described in 69.Xr random 4 70versus the fast but poor quality interfaces described in 71.Xr rand 3 , 72.Xr random 3 , 73and 74.Xr drand48 3 . 75.Pp 76The 77.Fn arc4random_stir 78function reads data from 79.Pa /dev/arandom 80and uses it to permute the S-Boxes via 81.Fn arc4random_addrandom . 82.Pp 83There is no need to call 84.Fn arc4random_stir 85before using 86.Fn arc4random , 87since 88.Fn arc4random 89automatically initializes itself. 90.Sh SEE ALSO 91.Xr rand 3 , 92.Xr rand48 3 , 93.Xr random 3 94.Sh HISTORY 95An algorithm called 96.Pa RC4 97was designed by RSA Data Security, Inc. 98It was considered a trade secret, but not trademarked. 99Because it was a trade secret, it obviously could not be patented. 100A clone of this was posted anonymously to USENET and confirmed to 101be equivalent by several sources who had access to the original cipher. 102Because of the trade secret situation, RSA Data Security, Inc. can do 103nothing about the release of the ARC4 algorithm. 104Since 105.Pa RC4 106used to be a trade secret, the cipher is now referred to as 107.Pa ARC4 . 108.Pp 109These functions first appeared in 110.Ox 2.1 . 111