A variation of RC4

From: Mok-Kong Shen (mok-kong.shen_at_t-online.de)
Date: 02/23/04 

Date: Mon, 23 Feb 2004 09:54:17 +0100

In producing each output byte, RC4 modifies its 8*8 S-box
by swapping two elements indexed by two counters. A higher
rate of modification of the S-box could evidently be
achieved in a similar fashion thru employing more counters.
A version using three counters i, j and m (initialized to
zero) would run as follows:

      i = (i + 1) mod 256
      j = (j + S_i) mod 256
      m = (m + S_j) mod 256
      rotate (S_i, S_j, S_m)
      t = (S_i + S_j + S_m) mod 256
      K = S_t

Question: Would such a variation be benefical or counter-
productive? (Of course, it's less efficient than the
original. Intuitively, its output could be better.)

Thanks.

M. K. Shen

Relevant Pages

  • Differential Cryptanalysis of DES
    ... "counting algorithm" instead of saving 2^30 counters for the possible ... I need 2^30 counters for all subkeys? ... My idea is, to count for each S-box ...
    (sci.crypt)
  • Re: A variation of RC4
    ... > rate of modification of the S-box could evidently be ... > achieved in a similar fashion thru employing more counters. ... The rotate() should then reduce to a simple swap. ...
    (sci.crypt)