From: "David F. Ogren" <ogren@cris.com>
Date: Sun, 21 Jul 1996 10:04:24 +0800
To: cypherpunks@toad.com
Subject: ITAR's 40 bit limit
Message-ID: <199607202345.TAA01019@darius.cris.com>
MIME-Version: 1.0
Content-Type: text/plain


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To: cypherpunks@toad.com
Date: Sat Jul 20 19:41:41 1996

Another paradox of the US export regulations.

The NSA is allowing 40 bit crypto exports.  So as a hypothetical example 
assume that I write a crypto program that uses 40 bit RC4 to encode data 
(licensing from RSA).  I then get an export license using the accelerated 
process for 40 bit RC4.

I then export my program to Alice who wants to use it to transmit messages 
to Bob.

If she uses my program to encrypt messages to Bob, any reasonably powerful 
attacker can decrypt her messages.

However, what if she runs the program three times with three different 
passwords.  (Ignore the problems of Inner-CBC and Outer-CBC for now.)  Now 
the file is triple RC4 encoded with the equivalent of 80 bit security.  
Alice and Bob now have strong crypto.  And if they run the program five 
times they have 120 bits of effective protection.

The problem of using Inner-CBC is a little tricky, but if we assume that I 
can export in a DLL format, a Windows program could be written that calls 
the DLL repeatedly to layer it into triple or pentuple CBC RC4.

The entire above discussion is entirely theoretical.  I realize that it's a 
moot point since strong crypto is already perfectly accessible outside of 
the US.  And that strong crypto algorithms can be exported in non-machine 
readable format (another paradox).  (And that running 5-layer RC4 is a 
really inefficient block cipher.)

I just wanted to point out yet another reason why ITAR regulations over 
crypto are not effectively preventing strong crypto.  They are merely 
making it difficult for American business.

- --
David F. Ogren                |
ogren@concentric.net          | "A man without religion is like a fish
PGP Key ID: 0x6458EB29        |  without a bicycle"
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