gen/arc4random.3

   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>
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  15 .\"      This product includes software developed by Niels Provos.
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  30 .\" Manual page, using -mandoc macros
  31 .\" $FreeBSD: src/lib/libc/gen/arc4random.3,v 1.12 2001/10/01 16:08:50 ru Exp $
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  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
  52 The
  53 .Fn arc4random
  54 function uses the key stream generator employed by the
  55 arc4 cipher, which uses 8*8 8 bit S-Boxes.
  56 The S-Boxes
  57 can be in about
  58 .if t 2\u\s71700\s10\d
  59 .if n (2**1700)
  60 states.
  61 .Pp
  62 The
  63 .Fn arc4random_stir
  64 function reads data from
  65 .Pa /dev/urandom
  66 and uses it to permute the S-Boxes via
  67 .Fn arc4random_addrandom .
  68 .Pp
  69 There is no need to call
  70 .Fn arc4random_stir
  71 before using
  72 .Fn arc4random ,
  73 since
  74 .Fn arc4random
  75 automatically initializes itself.
  76 .Sh SEE ALSO
  77 .Xr rand 3 ,
  78 .Xr random 3 ,
  79 .Xr srandomdev 3
  80 .Sh HISTORY
  81 .Pa RC4
  82 has been designed by RSA Data Security, Inc.
  83 It was posted anonymously
  84 to the USENET and was confirmed to be equivalent by several sources who
  85 had access to the original cipher.
  86 Since
  87 .Pa RC4
  88 used to be a trade secret, the cipher is now referred to as
  89 .Pa ARC4 .