cryptographic ergodic sequence generators?

John S. Denker jsd at av8n.com
Sat Sep 6 14:30:36 EDT 2003


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.

The counter provably has a cycle of 2^n.
The encryption is provably 1-to-1.
Choose the encryption key randomly and keep it secret.


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