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Suppose one uses AES in CTR mode to generate a keystream, but every $l$ bytes the $n$ bits that would follow are used as a new AES key.

Assuming that AES is a secure PRP:

  • Is this a secure stream cipher?
  • How does it compare to standard AES-CTR?
  • Suppose the (original) key is mixed back in at each rekeying useing a one-way pseudorandom compression: what changes?

Note that AES is used as an example secure block cipher.

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  • $\begingroup$ I think this will eventually fall into a cycle after about $2^{k/2}$ new keys, where $k$ is the length of the key in bits. $\endgroup$ – user13741 Mar 3 '16 at 14:34
  • $\begingroup$ Until then, is it harder (vs. AES) to distinguish from a PRP? $\endgroup$ – Demi Mar 3 '16 at 16:59

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