NAME
arc4random —
kernel random subsystem
SYNOPSIS
#include
<sys/systm.h>
u_int32_t
arc4random(void);
void
arc4random_buf(void
*buf, size_t
nbytes);
u_int32_t
arc4random_uniform(u_int32_t
upper_bound);
#include
<dev/rndvar.h>
void
add_true_randomness(int);
void
add_timer_randomness(int);
void
add_mouse_randomness(int);
void
add_tty_randomness(int);
void
add_net_randomness(int);
void
add_disk_randomness(int);
void
add_audio_randomness(int);
DESCRIPTION
The
add_random()
functions below mix input into the system entropy pool, which is then used
to create a key for the ChaCha stream cipher used in the
arc4random() series of functions.
The
add_mouse_randomness(),
add_tty_randomness(),
add_net_randomness(),
add_disk_randomness()
and
add_audio_randomness()
routines are used to supply data for the random data source device for
further processing. The processing involves calculating inter-event
timedelta and inserting it into a pool which is cryptographically mixed
multiple times.
add_true_randomness()
does not involve the usual timing calculations, and causes the supplied data
argument to be added to the entropy pool, increasing the entropy counter by
32 bits.
add_timer_randomness()
will not cause the entropy counter to rise. It is used to change the state
of the pool periodically, mostly by means of timing the random driver's
operations.
arc4random()
and
arc4random_buf()
provide random numbers and are intended to be called in any circumstance
where random numbers are required.
arc4random_uniform()
will return a uniformly distributed random number less than
upper_bound, avoiding "modulo bias" when the
upper bound is not a power of two. In the worst case, this function may
consume multiple iterations to ensure uniformity; see the source code to
understand the problem and solution.
arc4random(),
arc4random_buf(),
and arc4random_uniform() may be called in nearly any
kernel context.