full-disclosure - RC4 and Lotus Notes

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From: derek at ihtfp.com (Derek Atkins)
Subject: RC4 and Lotus Notes

While RC4 does have some weaknesses in its key scheduling, that alone
does not make it a weak cipher.  Indeed, the WEP break was not due
solely to RC4 -- most of the problem was that WEP used RC4
incorrectly.  It is perfectly reasonable to use RC4-256 (are you SURE
it's using a 256-bit key?) in a "secure" application.  You just need
to be careful to:

        a) use real, unique IVs
        b) use different, unique, random keys in both directions
        c) discard the first N bytes of the cipher (IIRC 256-1024)
        d) never.. EVER re-use a key

WEP's problem was that it violated all four of these rules, which is
why it was broken.  The fact that WEP's IV was only 24 bits didn't
help -- 24 bits wraps around pretty quickly on a busy network.  Worse,
the IV gets re-set if the AP gets rebooted.

So, don't fear RC4 just because it's RC4..  Fear RC4 because most people
don't know how to _use_ it properly.  :)

-derek

aliver@...il.com writes:

> 	While developing something boring using the Lotus C API for Linux.
> I noticed while using valgrind that functions like NSFNoteDecrypt()  and
> NSFNoteIsSignedOrSealed() are still making use of RC4 encryption with a
> 256 bit key even when I use "strong" encryption settings in it's lame
> windows MegaGUI. IIRC, RC4 is known to have some weaknesses in it's key
> scheduling that have yielded some interesting results (WEP, Winnt, etc..).
> 	I'm pretty sure my libnotes.so is up to date. Am I misinformed
> about the choice of crypto in Lotus Notes? Anyone know of plans to change
> this? I guess it doesn't matter since nobody is masochistic enough to work
> on a brute forcer for something as nasty as LN. It's what you call
> "security-through-being-so-disgusting-no-one-will-play-with-you" or "the
> hagfish method."
> 
> aliver
> 
> 
> _______________________________________________
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-- 
       Derek Atkins
       Computer and Internet Security Consultant
       derek@...fp.com             www.ihtfp.com