NAME

     arc4random, arc4random_buf, arc4random_uniform, arc4random_stir, arc4random_addrandom — arc4
     random number generator

LIBRARY

     library “libbsd”

SYNOPSIS

     #include <bsd/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 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 automatically 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 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.