[14050] in cryptography@c2.net mail archive
Re: cryptographic ergodic sequence generators?
daemon@ATHENA.MIT.EDU (Perry E. Metzger)
Sat Sep 6 19:18:45 2003
X-Original-To: cryptography@metzdowd.com
X-Original-To: cryptography@metzdowd.com
To: Victor.Duchovni@morganstanley.com
Cc: cryptography@metzdowd.com
From: "Perry E. Metzger" <perry@piermont.com>
Date: 06 Sep 2003 19:07:17 -0400
In-Reply-To: <Pine.SOL.4.56.200309061550110.20535@sasas1.ms.com>
Victor.Duchovni@morganstanley.com writes:
> Why does it need to be strictly non repeating?
For applications like block numbers in protocols, it is highly
desirable to avoid overlap for as long as possible.
I've noted to others on this before that for an application like
the IP fragmentation id, it might be even better if no repeats
occurred in any block of 2^31 (n being 32) but the sequence did not
repeat itself (or at least could be harmlessly reseeded at very very
long intervals). However, doing that might be even harder than
producing a more standard ergodic sequence...
> Is 2^n always large enough that sequences of length > 2^n are
> uninteresting?
I don't understand the question.
> If sequences longer than 2^n are practical and *every* subsequence
> of 2^n elements is free of duplicates the entire thing is periodic,
> this may or may not be a problem...
Re-keying is of course an option, but I'll admit that produces
problems of its own.
--
Perry E. Metzger perry@piermont.com
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