From: Carl Ellison <cme@tis.com>
Date: Thu, 15 Sep 94 11:55:52 PDT
To: perry@imsi.com
Subject: Re: thoughts on RC4
In-Reply-To: <199409151735.KAA14334@comsec.com>
Message-ID: <9409151853.AA26875@tis.com>
MIME-Version: 1.0
Content-Type: text/plain


>Date: Thu, 15 Sep 94 10:52:03 EDT
>From: perry@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