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Revision 1.9, Sat Feb 5 00:24:08 2011 UTC (3 years, 11 months ago) by wiz
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.\" $NetBSD: arc4random.3,v 1.9 2011/02/05 00:24:08 wiz Exp $ .\" $OpenBSD: arc4random.3,v 1.17 2000/12/21 14:07:41 aaron Exp $ .\" .\" Copyright 1997 Niels Provos <firstname.lastname@example.org> .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by Niels Provos. .\" 4. The name of the author may not be used to endorse or promote products .\" derived from this software without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .\" Manual page, using -mandoc macros .\" .Dd February 4, 2011 .Dt ARC4RANDOM 3 .Os .Sh NAME .Nm arc4random , .Nm arc4random_buf , .Nm arc4random_uniform , .Nm arc4random_stir , .Nm arc4random_addrandom .Nd arc4 random number generator .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In stdlib.h .Ft uint32_t .Fn arc4random "void" .Ft void .Fn arc4random_buf "void *buffer" "size_t length" .Ft uint32_t .Fn arc4random_uniform "uint32_t upper_bound" .Ft void .Fn arc4random_stir "void" .Ft void .Fn arc4random_addrandom "u_char *dat" "int datlen" .Sh DESCRIPTION The .Fn arc4random function provides a high quality 32-bit pseudo-random number very quickly. .Fn arc4random seeds itself on a regular basis from the kernel strong random number subsystem described in .Xr rnd 4 . On each call, an ARC4 generator is used to generate a new result. The .Fn arc4random function uses the ARC4 cipher key stream generator, which uses 8*8 8 bit S-Boxes. The S-Boxes can be in about (2**1700) states. .Pp .Fn arc4random fits into a middle ground not covered by other subsystems such as the strong, slow, and resource expensive random devices described in .Xr rnd 4 versus the fast but poor quality interfaces described in .Xr rand 3 , .Xr random 3 , and .Xr drand48 3 . .Pp The .Fn arc4random_buf function fills the .Fa buffer with .Fa length bytes of ARC4-derived random data. .Pp The .Fn arc4random_uniform function returns a uniformly distributed random number less than .Fa upper_bound avoiding modulo bias when the upper bound is not a power of two. .Pp The .Fn arc4random_stir function reads data from .Pa /dev/urandom and uses it to permute the S-Boxes via .Fn arc4random_addrandom . .Pp There is no need to call .Fn arc4random_stir before using .Fn arc4random , since .Fn arc4random automatically initializes itself. .Sh SEE ALSO .Xr rand 3 , .Xr rand48 3 , .Xr random 3 .Sh HISTORY An algorithm called .Pa RC4 was designed by RSA Data Security, Inc. It was considered a trade secret, but not trademarked. Because it was a trade secret, it obviously could not be patented. A clone of this was posted anonymously to USENET and confirmed to be equivalent by several sources who had access to the original cipher. Because of the trade secret situation, RSA Data Security, Inc. can do nothing about the release of the ARC4 algorithm. Since .Pa RC4 used to be a trade secret, the cipher is now referred to as .Pa ARC4 . .Pp These functions first appeared in .Ox 2.1 .