Columbia crypto box

[Trei, Peter]

> Matthew Byng-Maddick[SMTP:cryptography at lists.colondot.net] writes:
> 
> 
> On Sun, Feb 09, 2003 at 11:43:55PM -0500, Donald Eastlake 3rd wrote:
> > been that you either throw away the first 256 bytes of stream key output
> 
> > or use a different key on every message. WEP does neither. TKIP, the new
> 
> 
> You NEVER, EVER, re-use the key for a stream cipher, if you do, you might
> as well just give up. By re-using the key, I can get
> plaintext (combinator) plaintext, which is easier to solve than
> plaintext (combinator) cipherstream.
> 
> It's one of those things, like re-using a pad.
> 
> MBM
> 
The weird thing about WEP was its choice of cipher. It used RC4, a 
stream cipher, and re-keyed for every block. . RC4 is
not really intended for this application. Today we'd
have used a block cipher with varying IVs if neccessary

I suspect that RC4 was chosen for other reasons - ease of
export, smallness of code, or something like that. It runs fast,
but rekeying every block loses most of that advantage.

Just my personal musings....

Peter Trei




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