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Re: thoughts on RC4



Hal says:
> [email protected] (Perry E. Metzger) writes:
> 
> >Unlike most ciphers, RC4 doesn't seem to have any particular word
> >length dependancies in its principles.
[...]
> I'm not sure exactly how you would generalize it.  Right now it has a 256
> entry table which holds a permutation of the values in 0..255.  A byte is
> selected from this table and xor'd with the data stream.  To increase to
> four bytes per entry and keep it as a permutation we would have to have 4
> billion entries taking up 16 GB of memory which seems a bit much.
> Altenatively we could still have 256 entries but have them four bytes
> each, but then it's not clear that you keep the cryptographic properties
> since you no longer have a permutation.

Am I being thick? If you simply do all array indexes modulo the length
of the table, wouldn't you still have a permutation? (Its true,
however, that one could slow down the algorithm quite a bit if one
isn't careful with how one does this...)

.pm