Bernard, All,
Comments inline. ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Bernard Aboba Sent: Tuesday, December 08, 2009 12:33 AM To: [email protected] Subject: Re: [Emu] Working Group Last Call for draft-ietf-emu-chbind-04.txt (part 3) Section 9.2 Additional network entities (such as proxies) might be on the communication path between peer and server and may attempt to manipulate the channel binding protocol. If these entities do not possess the keying material used for integrity protection of the channel binding messages, the same threat analysis applies as for the dishonest authenticators. Hence, such entities can neither manipulate single channel binding messages nor the outcome. On the other hand, entities with access to the keying material must be treated like a server in a threat analysis. Hence such entities are able to manipulate the channel binding protocol without being detected. However, the required knowledge of keying material is unlikely since channel binding is executed before the EAP method is completed, and thus before keying material is typically transported to other entities. [BA] Unless the transient EAP keys used for integrity protection are derivable from the MSK, possession of the MSK would not be sufficient to enable an authenticator to modify the channel bindings. As a result, the only entities relevant to the threat analysis are those that possess the TEKs, not just those that possess the MSK or other derived keys. [KH] I assume you have a problem with the last sentence that suggests that integrity protected keys are derived from the MSK. The rest of the paragraph talks very generally about “keying material used for integrity-protection”. For this reason I suggest changing the last sentence to “However, the required knowledge of keying material is unlikely even if the keys are derived from the MSK because channel binding is executed before the EAP method is completed, and thus before the MSK is transported to other entities.” <http://im.live.com/Messenger/IM/Home/?source=EML_WLHM_GreaterGood>
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