[14048] in cryptography@c2.net mail archive
Re: cryptographic ergodic sequence generators?
daemon@ATHENA.MIT.EDU (Perry E. Metzger)
Sat Sep 6 19:17:43 2003
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To: Tim Dierks <tim@dierks.org>
Cc: cryptography@metzdowd.com
From: "Perry E. Metzger" <perry@piermont.com>
Date: 06 Sep 2003 18:54:11 -0400
In-Reply-To: <6.0.0.21.2.20030906142617.04598b68@127.0.0.1>
Tim Dierks <tim@dierks.org> writes:
> At 02:09 PM 9/6/2003, Perry E. Metzger wrote:
> >For making things like IP fragmentation ids and other similar protocol
> >elements unpredictable, it would be useful to have what I'll call a
> >cryptographic ergodic sequence generator -- that is, a generator that
> >will produce a sequence of n bit numbers such that there are no
> >repeats until you pass the 2^nth number in the sequence.
> >
> >Anyone know how to produce such a thing?
>
> It seems to me that this could be constructed with a block cipher with
> a block size n bits long by encrypting the values 0..2^n sequentially
> with a random key.
I've thought that. Unfortunately, I don't know that there are good
block ciphers out there with 32 bit block sizes, and some uses (for
example, IP fragment ids) are 32 bits.
> I'm sure that it would be possible to design a Feistel-based block
> cipher with variable block size, supporting some range of even values
> of n.
Perhaps -- I don't know of a good one.
--
Perry E. Metzger perry@piermont.com
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