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ARC4RANDOM(3)            BSD Library Functions Manual            ARC4RANDOM(3)

NAME
     arc4random, arc4random_buf, arc4random_uniform, 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_buf(void *buf, size_t nbytes);

     u_int32_t
     arc4random_uniform(u_int32_t upper_bound);

     void
     arc4random_stir(void);

     void
     arc4random_addrandom(unsigned char *dat, int datlen);

DESCRIPTION
     The arc4random() function uses the key stream generator employed 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 pseudorandom
     random numbers in the range of 0 to (2**32)-1, and therefore has twice the range of rand(3) and
     random(3).

     arc4random_buf() function fills the region buf of length nbytes with ARC4-derived random data.

     arc4random_uniform() will return a uniformly distributed random number less than upper_bound.
     arc4random_uniform() is recommended over constructions like ``arc4random() % upper_bound'' as it avoids
     "modulo bias" when the upper bound is not a power of two.

     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() functions family, since they auto-matically automatically
     matically initialize themselves.

EXAMPLES
     The following produces a drop-in replacement for the traditional rand() and random() functions using
     arc4random():

           #define foo4random() (arc4random() % ((unsigned)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 con-firmed confirmed
     firmed 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

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