AES, RC4

[PETER SCHWEITZER]

Referring to your note of August 1: I haven't found anything about  
breaking RC4 if used with a newly randomly generated key (unrelated to  
any others) for every communication session. I would appreciate being  
enlightened!

(Of course one should throw away initial parts of the stream. I  
suggested doing this to Ron Rivest & RSA in the early 1980s,  
legitimately knowing about the still-secret RC4 cipher-logic from a  
client, to whom I made the same suggestion. But even if one doesn't,  
the result isn't what I would call "breaking" RC4.) I should say that  
I was appalled when I first learned of people using RC4 with related  
keys; its structure certainly suggested to me that there would be  
vulnerabilities.

Is your partly negative recommendation for AES' "...for most new  
protocol purposes" to do with the recent related-key attack? Which I  
would certainly agree is very disquieting, even though, as you say, it  
has no current negative consequences.

I may speculate elsewhere about who knew what & why before the recent  
publication.

Thank you!

P.
(Peter Schweitzer)


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