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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