NAME    [Toc]    [Back]

     arc4random,  arc4random_stir,  arc4random_addrandom  -  arc4
random number
     generator

SYNOPSIS    [Toc]    [Back]

     #include <stdlib.h>

     u_int32_t
     arc4random(void);

     void
     arc4random_stir(void);

     void
     arc4random_addrandom(u_char *dat, int datlen);

DESCRIPTION    [Toc]    [Back]

     The  arc4random()  function  provides  a high quality 32-bit
pseudo-random
     number very quickly.  arc4random() seeds itself on a regular
basis from
     the  kernel strong random number subsystem described in random(4).  On
     each call, an ARC4 generator is used to generate a  new  result.  The
     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.

     arc4random()  fits into a middle ground not covered by other
subsystems
     such as the strong, slow, and resource expensive random  devices described
     in random(4) versus the fast but poor quality interfaces described in
     rand(3), random(3), and drand48(3).

     The arc4random_stir() function reads data from  /dev/arandom
and uses it
     to permute the S-Boxes via arc4random_addrandom().

     There  is  no  need  to  call arc4random_stir() before using
arc4random(),
     since arc4random() automatically initializes itself.

SEE ALSO    [Toc]    [Back]

     rand(3), rand48(3), random(3)

HISTORY    [Toc]    [Back]

     An algorithm called 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 RC4 used to be a  trade  secret,  the
cipher is now
     referred to as ARC4.

     These functions first appeared in OpenBSD 2.1.

OpenBSD      3.6                          April      15,     1997