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To: "'CIPE-list'" <cipe-l,AT,inka,DOT,de>
Subject: RE: Data integrity check in CIPE - Please explain me the necessityor benefit of a larger checksum.
From: "Mark Smith" <mark.smith,AT,avcosystems,DOT,co,DOT,uk>
Date: Mon, 29 Sep 2003 11:01:41 +0100
Importance: Normal
In-reply-to: <000b01c3865f$f66d9e20$d620a8c0@pcw_hans.hnsasd.priv>

Two items quickly:

Has anyone else had any thoughts about a second list, and if so could anyone
host it?  I'm in the process if finding out if I can get permission, it
appears to be technically possible.

Second, has anyone thought about the just as serious problem of message
replay?  Message deletion for UDP means nothing to me as UDP can drop a
packet just as easily on it's own.  Replay either of existing or modified
packets provides another security hole.  I believe any change should attempt
to address this as well since even I could figure out how to exploit it.

As for CRC itself - can I ask, is the checksum calculated pre- or post-
encryption?  Could a copy of the checksum be included in the payload for
comparison to ensure it hasn't been altered, but without compromising the
encryption key?  I'd imagine that if the checksum was then compressed it
would be 'harder' to compromise.  Would this be enough, perhaps for both
vulnerabilities?

I'm guessing, feel free to explain if you know better.

--
Mark Smith - Avco Systems Ltd
email: mark.smith,AT,avcosystems,DOT,co,DOT,uk
Tel: +44 (0)1784 430996 Fax: +44 (0)1784 431078


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