cryptographic ergodic sequence generators?

[Perry E. Metzger]

Tim Dierks <tim at 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 at piermont.com

---------------------------------------------------------------------
The Cryptography Mailing List
Unsubscribe by sending "unsubscribe cryptography" to majordomo at metzdowd.com