gen/FreeBSD/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 1.16 2003/07/31 06:18:24 das Exp $
  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
  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 The
  62 .Fn arc4random
  63 function returns pseudo-random numbers in the range of 0 to
  64 .if t 2\u\s731\s10\d\(mi1,
  65 .if n (2**32)\(mi1,
  66 and therefore has twice the range of
  67 .Xr rand 3
  68 and
  69 .Xr random 3 .
  70 .Pp
  71 The
  72 .Fn arc4random_stir
  73 function reads data from
  74 .Pa /dev/urandom
  75 and uses it to permute the S-Boxes via
  76 .Fn arc4random_addrandom .
  77 .Pp
  78 There is no need to call
  79 .Fn arc4random_stir
  80 before using
  81 .Fn arc4random ,
  82 since
  83 .Fn arc4random
  84 automatically initializes itself.
  85 .Sh EXAMPLES
  86 The following produces a drop-in replacement for the traditional
  87 .Fn rand
  88 and
  89 .Fn random
  90 functions using
  91 .Fn arc4random :
  92 .Pp
  93 .Dl "#define foo4random() (arc4random() % ((unsigned)RAND_MAX + 1))"
  94 .Sh SEE ALSO
  95 .Xr rand 3 ,
  96 .Xr random 3 ,
  97 .Xr srandomdev 3
  98 .Sh HISTORY
  99 .Pa RC4
 100 has been designed by RSA Data Security, Inc.
 101 It was posted anonymously
 102 to the USENET and was confirmed to be equivalent by several sources who
 103 had access to the original cipher.
 104 Since
 105 .Pa RC4
 106 used to be a trade secret, the cipher is now referred to as
 107 .Pa ARC4 .