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.