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>
uint32_t
arc4random(void);
void
arc4random_buf(void *buffer, size_t length);
uint32_t
arc4random_uniform(uint32_t upper_bound);
void
arc4random_stir(void);
void
arc4random_addrandom(u_char *dat, int datlen);
DESCRIPTION
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 rnd(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 rnd(4) versus the fast but poor quality interfaces described in
rand(3), random(3), and drand48(3).
The arc4random_buf() function fills the buffer with length bytes of
ARC4-derived random data.
The arc4random_uniform() function returns a uniformly distributed random
number less than upper_bound avoiding 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(),
since arc4random() automatically initializes itself.
SEE ALSOrand(3), rand48(3), random(3)HISTORY
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 situ‐
ation, 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.
BSD February 4, 2011 BSD
