146 lines
4.0 KiB
Groff
146 lines
4.0 KiB
Groff
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.\" $NetBSD: randomid.3,v 1.1 2003/09/09 22:10:34 itojun Exp $
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.\"
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.\" Copyright (C) 2003 WIDE Project.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the project nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd September 9, 2003
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.Dt RANDOMID 3
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.Os
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.Sh NAME
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.Nm randomid
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.Nm randomid_new ,
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.Nm randomid_delete ,
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.Nd make a copy of a struct passwd
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <randomid.h>
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.Ft u_int32_t
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.Fn randomid "randomid_t ctx"
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.Ft randomid_t
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.Fn randomid_new "int bits" "long timeo"
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.Ft void
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.Fn randomid_delete "randomid_t ctx"
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.Sh DESCRIPTION
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The
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.Fn randomid
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function provides pseudo-random data stream,
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which is guaranteed not to generate the same number twice during
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a certain duration.
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.Fa ctx
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is the context which holds internal state for the random number generator.
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.Pp
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To initialize context
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.Fa randomid_new
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is used.
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.Fa bits
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specifies the bitwidth of value generated by
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.Fn randomid .
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Currently 32, 20 and 16 are supported.
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.Fa timeo
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specifies reinitialization interval in seconds.
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.Fa timeo
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has to be bigger than
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.Dv RANDOMID_TIMEO_MIN .
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Return value of
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.Fa randomid_new
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is a dynamically-allocated memory region allocated by
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.Xr malloc 3 .
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.Pp
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.Fn randomid_delete
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will
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.Xr free 3
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the internal state,
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.Fa ctx .
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.Pp
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Same number may appear after two reinitialization events of the internal state,
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.Fa ctx .
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Reinitialization happens when the random number generator cycle is exhausted,
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or
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.Fa timeo
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seconds have passed since the last reinitialization.
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For instance,
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.Fa ctx
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configured to generate 16 bit data stream will reinitialize its internal state
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every 18000 calls to
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.Fn randomid
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.Po
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or after
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.Fa timeo
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seconds
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.Pc ,
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therefore same data will not appear until after 36000 calls to
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.Fn randomid
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.Po
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or after 2 times
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.Fa timeo
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seconds
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.Pc .
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.Pp
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The internal state,
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.Fa ctx ,
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determines the data stream generated by
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.Fn randomid .
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.Fa ctx
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must be allocated per data stream
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.Pq such as a specific data field .
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It must not be shared among multiple data streams with different usage.
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.\"
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.Sh EXAMPLES
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.Bd -literal -offset indent
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#include <sys/types.h>
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#include <randomid.h>
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u_int32_t
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genid(void)
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{
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static randomid_t ctx = NULL;
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if (!ctx)
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ctx = randomid_new(16, (long)3600);
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return randomid(ctx);
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}
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.Ed
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.\"
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.Sh ERRORS
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.Fn randomid_new
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returns
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.Dv NULL
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on error and set the external variable
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.Va errno .
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.\"
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.Sh SEE ALSO
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.Xr arc4random 3
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.\"
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.Sh HISTORY
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The pseudo-random data stream generator was designed by Niels Provos for
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.Ox
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IPv4 fragment ID generation.
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.Fn randomid
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is a generalized version of the generator, reworked by Jun-ichiro itojun Hagino,
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and was introduced in
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.Nx 2.0 .
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