cryptographic ergodic sequence generators?

[Perry E. Metzger]

"John S. Denker" <jsd at av8n.com> writes:
> On 09/06/2003 02:09 PM, 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
>  > (that is, the sequence is a permutation of all 2^n bit numbers) and
>  > such that it is very difficult to predict what the next number in the
>  > sequence might be beyond the fact that it will not be one of the
>  > numbers seen earlier in the sequence. It is also rather important
>  > that the generator be computationally inexpensive.
>  >
>  > Anyone know how to produce such a thing?
> 
> Encrypted counter.

I'd thought of that, but encrypting with a stream cipher would not
work for this application -- it would not produce an ergodic sequence
-- and encrypting with a block cipher would require that the block
cipher use unusually small block sizes for many such applications.

Perry

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