Re: Paranoid Musings

["Mark M." <markm@voicenet.com>]

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On Tue, 30 Jul 1996, Bill Frantz wrote:

> (1) Now everyone knows that 40 bit RC4 is weak, but just how weak is it? 
> We know that a university CS student can break one message in a week using
> the universities farm of workstations.  But, our foremost reputation agency
> for crypto strength, the ITAR, allows systems with RC4-40 to be exported. 
> What does this mean?
> 
> I combine the above with Whit Diffie's observation that, while crypto users
> are interested in the security of *each* message, organizations which
> monitor communications want to read *every* message.  A TLA interested in
> monitoring communications would need to crack RC4-40 much faster than
> 1/week.
> 
> Now expensive specialized cracking equipment can certainly speed up the
> process, but there may be a better way.  If cryptanalysis of RC4 yields
> techniques which make the process much easier, then it is the ideal cypher
> to certify for export.
> 
> The paranoid conclusion is that there is a significant weakness in RC4.

An FPGA can break RC4 in a few hours.  With several thousand of these, RC4
could be broken in about a second.  Besides, RC4 has been around for 9 years
and has not been successfully cryptanalyzed.  The RC4 algorithm is extremely
simple and doesn't have any obvious weaknesses.

- -- Mark

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