Re: 16-bit Block Cipher

How is the idea of keeping the query IDs unpredictable consistent
with using the entire codebook? Anyone whose seen the first 2**15-8
generated query IDs with a given mode bit value will have an excellent
chance of predicting the remaining 8.

Well, now that you point it out, it isn't. Oops. Sorry for
suggesting something with this problem.

If the keys were refreshed and
mode bit flipped after 2**14 IDs, then the probability of guessing the
next ID is never more than 2**-14.

I think you mean the mode bit flipped after every 2^14 IDs and keys
refreshed after every 2^15 IDs. That's a good suggestion; a better
solution than what I proposed. Thanks!
.

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