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Re: [Dan Harkins] comments on draft-houseley-aaa-key-mgmt-07.txt

2007-03-07 15:54:08
Hi Sam,

Many thanks for the opportunity to comment on the proposed text before approval.

I do have concerns with the proposed text. Some of the new requirements are overly burdensome. In other places, it is not clear what is expected.

Some notes below:

Sam Hartman wrote:
Hi, folks.  The following last call comment was received and based on
discussion the draft was updated.  This comment never seems to have
made it to the ietf list though.


The following text was added to address the comment.  Please confirm
that this text addresses the comment and that from the following text
it is clear that these requirements prohibit authenticator
impersonination:

      Peer and authenticator authorization

         Peer and authenticator authorization MUST be performed.  These
         entities MUST demonstrate possession of the appropriate keying
         material, without disclosing it.  Authorization is REQUIRED
         whenever a peer associates with a new authenticator.  The
         authorization checking prevents an elevation of privilege
         attack, and it ensures that an unauthorized authenticator is
         detected.

I must say I do not fully understand the paragraph above. I took a quick look at 2906 and that RFC has a more nuanced take on authorization. If we are going to require something we need to be more specific.

Specifically, what does it mean to say "Peer and authenticator authorization MUST be performed?" Who is authorizing whom to do what?

Is proof of possession of keying material proof of authorization? Not according to the text below (on the 4-way exchange etc.).


         Authorizations SHOULD be synchronized between the peer, NAS,
         and backend authentication server.  Once the AAA key management
         protocol exchanges are complete, all of these parties should
         hold a common view of the authorizations associated the other
         parties.

This is better.  (Nit: There is an editorial mistake in the last sentence.)


         In addition to authenticating all parties, key management
         protocols need to demonstrate that the parties are authorized
to possess keying material.

What does this mean? How do key management protocols demonstrate that the parties are authorized to possess keying material? Does this mean that key management protocols must facilitate carrying authorization information? Or must carry authorization information? Or that a party requesting a key must prove that it is authorized to possess that keying material?

Note that proof of possession of
         keying material does not necessarily prove authorization to
         hold that keying material.  For example, within an IEEE
         802.11i, the 4-way handshake demonstrates that both the peer
         and authenticator possess the same EAP keying material.
         However, by itself, this possession proof does not demonstrate
         that the authenticator was authorized by the backend
authentication server to possess that keying material.

The example is helpful, but are we then saying that 802.11i and the 4-way handshake are non-compliant? Or put differently, how do we fix the 4-way handshake so that the authenticator can prove to the peer that it was authorized to possess the keying material it has? Does the peer need to prove to the authenticator of its authorization to hold the same keying material?

As
         noted in RFC 3579 in section 4.3.7, where AAA proxies are
         present, it is possible for one authenticator to impersonate
         another, unless each link in the AAA chain implements checks
         against impersonation.  Even with these checks in place, an
         authenticator may still claim different identities to the peer
         and the backend authentication server.  As described in RFC
         3748 in section 7.15, channel binding is required to enable the
         peer to verify that the authenticator claim of identity is both
         consistent and correct.

Consistent sure, but why is correctness of the claim of identity necessary? Put another way, is there a way to solve the problem of the authenticator providing the same incorrect identity to the peer and the server. I think there is in a number of usage scenarios, and therefore propose that the requirement on correctness should be relaxed. More specifically, I think we should stick to the guidance level of RFC 3579.



If no serious objections are raised, I'll finally be able to approve
this draft next week

Once again thanks for the opportunity. Please do consider this as an objection to the new text.

regards,
Lakshminath

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