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1994-09-15 - Re: thoughts on RC4

Header Data

From: “Perry E. Metzger” <perry@imsi.com>
To: Hal <hfinney@shell.portal.com>
Message Hash: 1932f342aca36c800b18b34b71fa0a9b08f41b87a3e4607dd9d42a0dae94bb08
Message ID: <9409151606.AA04784@snark.imsi.com>
Reply To: <199409151546.IAA02879@jobe.shell.portal.com>
UTC Datetime: 1994-09-15 16:06:23 UTC
Raw Date: Thu, 15 Sep 94 09:06:23 PDT

Raw message

From: "Perry E. Metzger" <perry@imsi.com>
Date: Thu, 15 Sep 94 09:06:23 PDT
To: Hal <hfinney@shell.portal.com>
Subject: Re: thoughts on RC4
In-Reply-To: <199409151546.IAA02879@jobe.shell.portal.com>
Message-ID: <9409151606.AA04784@snark.imsi.com>
MIME-Version: 1.0
Content-Type: text/plain



Hal says:
> perry@imsi.com (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

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