thoughts on RC4

[Carl Ellison]

>Date: Thu, 15 Sep 94 10:52:03 EDT
>From: perry at imsi.com (Perry E. Metzger)

>Can anyone see any reason why one could not change RC4 to
>being a word oriented stream cipher, call it "ERC4"?

Alleged-RC4 (1) requires that the table be a permutation and (2) might base
security on the fact that the table is itself permuted beyond recognition
after a small number of inputs.

(1) You could conceivably go to an array of 65K short values and retain the
permutation but I wouldn't try to go to an array of longs.  I don't have
32GB of RAM on my workstation.

(2) With a longer array, the amount of input until the array is
indistinguishable from the one with which you started is proportionally
longer.  I don't know if that means that shorter arrays are more secure,
but it's worth taking a look at.

 - Carl