.\"	$OpenBSD: idgen32.9,v 1.1 2008/06/10 09:16:15 deraadt Exp $
.\"
.\" Copyright (c) 2008 Damien Miller <djm@mindrot.org>
.\" All rights reserved.
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: June 10 2008 $
.Dt IDGEN32 9
.Os
.Sh NAME
.Nm idgen32
.Nd non-repeating ID generation
.Sh SYNOPSIS
.Fd #include <crypto/idgen.h>
.Ft void
.Fn idgen32_init "struct idgen32_ctx *ctx"
.Ft uint32_t
.Fn idgen32 "struct idgen32_ctx *ctx"
.Sh DESCRIPTION
The
.Fn idgen32
functions provide a facility to generate a stream of 32-bit numbers
that are strongly unpredictable and have a repetition cycle close to
2^32.
Such numbers are useful as protocol identifiers where there are negative
consequences to reusing an ID within a short time period, as may happen
if they are simply assigned at random.
.Pp
The
.Fn idgen32_init
function prepares a context structure for use.
.Pp
The
.Fn idgen32
function returns a new ID in host byte order.
Note that this function will never return 0 as it often has a special
meaning in network protocols.
.Sh SEE ALSO
.Xr random 9
.Sh HISTORY
The
.Nm
functions were added in
.Ox 4.4 .