cryptographic ergodic sequence generators?

[Tim Dierks]

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'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.

  - Tim



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