DragonFly On-Line Manual Pages
ARC4RANDOM(3) DragonFly Library Functions Manual ARC4RANDOM(3)
arc4random, arc4random_buf, arc4random_uniform, arc4random_stir,
arc4random_addrandom -- arc4 random number generator
Standard C Library (libc, -lc)
arc4random_buf(void *buf, size_t nbytes);
arc4random_addrandom(uint8_t *dat, size_t datlen);
The arc4random() function uses the key stream generator employed by the
arc4 cipher, which uses 256 8 bit S-Boxes. The S-Boxes can be in about
(2**1700) states. The arc4random() function returns pseudo-random num-
bers 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 con-
structions 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.
The following produces a drop-in replacement for the traditional rand()
and random() functions using arc4random():
#define foo4random() (arc4random() % ((unsigned)RAND_MAX + 1))
rand(3), random(3), srandomdev(3), urandom(4)
RC4 has been designed by RSA Data Security, Inc. It was posted anony-
mously 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.
DragonFly 4.7 April 15, 1997 DragonFly 4.7