Subject: [eap] issue: aaa-key confusion (review of eap-keying-08 by mats naslund)

From: Jari Arkko <[email-masked]>
Date: Thu, 01 Dec 2005 07:29:31 +0200

Submitter name: Mats Naslund
Submitter email address: [email-masked]
Reference: (this email)
Document: Keying Framework
Comment type: T
Priority: 1
Section: multiple
Rationale/Explanation of issue:

AAA-Key
     A key derived by the peer and EAP server, used by the peer and
     authenticator in the derivation of Transient Session Keys (TSKs).
     Where a backend authentication server is present, the AAA-Key is
     transported from the backend authentication server to the
     authenticator.  In existing usage, the AAA-Key is always derived
     from the MSK and so can be referred to using the MSK name.  AAA-Key
     = MSK(0,63).

MN: Isn't it the case that we MUST
have AAAk = MSK for mode independence?? Why does it only say
"in existing usage..."

The purpose of the PMK is a bit unclear to me...

   Within EAP, the primary function of the AAA protocol is to maintain
   the principle of Mode Independence, so that as far as the EAP peer is
   concerned, its conversation with the EAP authenticator, and all
   consequences of that conversation, are identical, regardless of the
   authenticator mode of operation.

MN: Doesn't this imply that AAAk MUST be equal to MSK?

   An additional step (phase 1b) is required in deployments which
   include a backend authentication server, in order to transport keying
   material from the backend authentication server to the authenticator.
   In order to obey the principle of Mode Independence, where a backend
   server is present AAA Key transport needs to provide the exported EAP
   keying material and/or derived keys required for derivation of the
   TSKs.  Since existing TSK derivation techniques depend solely on the
   MSK, in existing AAA implementations, this is the only keying
   material replicated in the AAA key transport phase 1b.

MN: again does this imply that MSK = AAAk? How else get mode independence?

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From: "Bernard Aboba" <[email-masked]>
Date: Wed, 30 Nov 2005 22:04:22 -0800

Since existing EAP lower layers only make use of the MSK, the MSK must be 
transported from the server to  authenticator in order to provide for mode 
independence. Currently it is not necessary to transport other keys, since 
existing lower layers don't use them. However, it does not necessarily 
follow that only the MSK can be transported.

So yes, the MSK must be transported as a consequence of mode independence. 
And yes, AAA-Key = MSK, but this is a tautology, not a consequence of any 
principle.  I think it is more correct to say that "all keys which are 
required by the lower layer need to be transported  from the server to the 
authenticator", and leave the term "AAA-Key" out of it.

>From: Jari Arkko <[email-masked]>
>To: [email-masked]
>CC: "Mats Näslund (KI/EAB)" <[email-masked]>
>Subject: [eap] issue: aaa-key confusion (review of eap-keying-08 by 
>matsnaslund)
>Date: Thu, 01 Dec 2005 07:29:31 +0200
>

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From: Jari Arkko <[email-masked]>
Date: Thu, 01 Dec 2005 08:07:18 +0200

> So yes, the MSK must be transported as a consequence of mode 
> independence. And yes, AAA-Key = MSK, but this is a tautology, not a 
> consequence of any principle. 

Yes.

> I think it is more correct to say that "all keys which are required by 
> the lower layer need to be transported  from the server to the 

Works for me.

--Jari

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From: Yoshihiro Ohba <[email-masked]>
Date: Thu, 01 Dec 2005 02:49:54 -0500

On Wed, Nov 30, 2005 at 10:04:22PM -0800, Bernard Aboba wrote:
> principle.  

I think AAA-Key=MSK is not a requirement for mode independence.
Other AAA-Key derivation algorithm described in
draft-ohba-eap-aaakey-binding can also provide mode independence.

> I think it is more correct to say that "all keys which are 

This looks good.

> >CC: "Mats N?slund (KI/EAB)" <[email-masked]>