.\"	$OpenBSD: random.9,v 1.25 2008/06/09 16:00:53 djm Exp $
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.\" Copyright (c) 1996,2000 Michael Shalayeff
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.Dd $Mdocdate: June 9 2008 $
.Dt RND 9
.Os
.Sh NAME
.Nm random
.Nd device kernel interface
.Sh SYNOPSIS
.Fd #include <dev/rndvar.h>
.Ft void
.Fn add_true_randomness "int"
.Ft void
.Fn add_timer_randomness "int"
.Ft void
.Fn add_mouse_randomness "int"
.Ft void
.Fn add_tty_randomness "int"
.Ft void
.Fn add_net_randomness "int"
.Ft void
.Fn add_disk_randomness "int"
.Ft void
.Fn add_audio_randomness "int"
.Ft void
.Fn get_random_bytes "void *buf" "size_t nbytes"
.Ft u_int32_t
.Fn arc4random "void"
.Ft void
.Fn arc4random_buf "void *buf" "size_t nbytes"
.Ft u_int32_t
.Fn arc4random_uniform "u_int32_t upper_bound"
.Sh DESCRIPTION
The
.Fn add_mouse_randomness ,
.Fn add_tty_randomness ,
.Fn add_net_randomness ,
.Fn add_disk_randomness
and
.Fn 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 measuring
entropy contained in the resulting delta-T; the argument data supplied
is just mixed into the pool and does not increase the entropy counter.
.Pp
.Fn 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.
.Pp
.Fn 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.
.Pp
.Fn get_random_bytes
may be used to retrieve strong random data, just
as it would by the
.Xr srandom 4
device.
.Pp
.Fn arc4random
and
.Fn arc4random_buf
will give random 32 bit numbers hashed with
the ARC4 algorithm, which appears to be faster and less abusive
to the entropy pool.
.Pp
.Fn arc4random_uniform
will return a uniformly distributed random number less than
.Fa upper_bound ,
avoiding "modulo bias" when the upper bound is not a power of two.
.Sh SEE ALSO
.Xr arc4random 3 ,
.Xr pchb 4 ,
.Xr random 4
.Sh CAVEATS
None of these functions should really be called during the
.Xr autoconf 4
process.