arc4random(3)

NAME

arc4random, arc4random_stir, arc4random_addrandom - arc4

random number
generator

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <stdlib.h>
u_int32_t
arc4random(void);
void
arc4random_stir(void);
void
arc4random_addrandom(unsigned char *dat, int datlen);

DESCRIPTION

The arc4random() function uses the key stream generator em

ployed by the
arc4 cipher, which uses 8*8 8 bit S-Boxes. The S-Boxes can

be in about
(2**1700) states. The arc4random() function returns pseudo

random numbers in the range of 0 to (2**32)-1, and therefore has twice

the range of
rand(3) and random(3).

The arc4random_stir() function reads data from /dev/urandom

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.

EXAMPLES

The following produces a drop-in replacement for the tradi

tional rand()
and random() functions using arc4random():

#define foo4random() (arc4random() % ((un

signed)RAND_MAX + 1))

SEE ALSO

rand(3), random(3), srandomdev(3)

HISTORY

RC4 has been designed by RSA Data Security, Inc. It was

posted anonymously to the USENET and was confirmed to be equivalent by

several
sources who had access to the original cipher. Since RC4

used to be a
trade secret, the cipher is now referred to as ARC4.

BSD April 15, 1997

BSD