Subject: RE: Last Call: 'Guidance for AAA Key Management' to BCP (draft-housley-aaa-key-mgmt)

From: "Joseph Salowey \(jsalowey\)" <[email-masked]>
Date: Wed, 8 Nov 2006 08:34:20 -0800

Hi Russ and Bernard,

I'm not really clear on the purpose of the document.  What does it apply
to?  Does it require changes to existing AAA protocols? Does it add new
requirements to EAP methods that are not in RFC3748? It would probably
be good to reference 3748 when it applies to a requirement in this
document (such as replay protection, strong fresh session keys, etc.).

What does AAA key management protocol refer to?  Is it the combination
of EAP, AAA and Security Association Protocol?  

A few comments on this document

1. Section 3 states "This section provides guidance to AAA protocol
designers and EAP method designers."

This should include designers of "security association protocols" as
well since many of the requirements apply to them.

2. Strong fresh session keys

In this section it is not clear what the subject session keys are.  It
is not clear to me what role the AAA protocol plays in "ensure that the
keying material supplied as an input to session key derivation is fresh"

Also wouldn't key caching be relevant on the EAP server rather than the
"AAA server"?

3.  Authenticate all parties

What is the AAA key management protocol?  It seems that some of this
section is about validating keys are used within they correct context
and not necessarily authentication.  Maybe part of this section should
belong with the context binding section. 

4. Keying material confidentiality

It seems that a system should also preserve key material integrity
(perhaps this is assumed in confidentiality). 

5. Unique Key Names

This section states "the key name MUST NOT be based on the keying
material itself." 802.11i uses this technique; are there vulnerabilities
associated with this?  

6. Bind key to its context

In this section it is not clear what the "protocol" is or how the
binding would occur.  What is meant by "The manner in which the keying
material is expected to be used." 
 
7. Security considerations

The first paragraph is difficult to understand.  It seems to be stating
that the authenticator can be separated from a AAA client as long as the
context of the request is communicated correctly between parties. Is
this it? 

Joe

> -----Original Message-----
> From: Russ Housley [mailto:[email-masked]] 
> Sent: Tuesday, November 07, 2006 8:00 AM
> To: Narayanan, Vidya; [email-masked]
> Subject: RE: Last Call: 'Guidance for AAA Key Management' to 
> BCP (draft-housley-aaa-key-mgmt) 
> 
> Vidya:
> 
> > > I agree, the document is really addressing AAA/EAP key management.
> >
> >Why would the scope be limited to EAP? It seems to me that 
> most, if not 
> >all, of the requirements would be applicable to just about any 
> >AAA-based key management protocol. Would it not be useful to 
> generalize it?
> 
> You are right.  It is about AAA key management protocols, 
> which includes various features of EAP, RADIUS, Diameter, and 
> secure association protocols.
> 
> Is the document introduction clear about the scope?
> 
> Russ
> 
> 
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---

From: Russ Housley <[email-masked]>
Date: Wed, 08 Nov 2006 13:47:37 -0500

>document (such as replay protection, strong fresh session keys, etc.).

This is really asking for two things, if I am reading it properly.

First, you seem to want some additional text in the Introduction 
about the things to which the BCP will apply.  The intent was broad 
applicability.  It is intended to become a BCP.

Second, you seem to want a tighter coupling to EAP.  While EAP is 
clearly an important aspect of AAA, the requirements are intended to 
be met by the system as a whole.  Maybe I am missing something in 
your comment, but I do not want a tighter binding than necessary.

>of EAP, AAA and Security Association Protocol?

Other Last Call comments suggest that a broad interpretation is 
appropriate.  All three of these are certainly included, but other 
things might be included too.

>well since many of the requirements apply to them.

Good point.  I'll add "security association protocol designers" too.

>keying material supplied as an input to session key derivation is fresh"

Bernard and I discussed this at great length with Sam before IETF 
Last Call.  In this context, "session" is a vague.  I think it is 
vague because of the large number of places where AAA is 
employed.  This document inherits this purposeful vagueness too.

>Also wouldn't key caching be relevant on the EAP server rather than the

Is "AAA/EAP server" better?

>belong with the context binding section.

I do not understand your point here.

>(perhaps this is assumed in confidentiality).

Good point.  (confidentially certainly does not automatically assume 
integrity).  I'll update it.

>material itself." 802.11i uses this technique; are there vulnerabilities

Maybe I have forgotten too much about 802.11i.  Please give your example.

Yes, there are several way to base the name on the key value that 
discloses information about the key value.  We do not want the key 
name to aid the attacker in a brute force search by trimming the search space.

>material is expected to be used."

Is it an integrity key, an encryption key, a key derivation key, a 
key-encrypting key, etc?  In which protocol will the key perform this role?

>context of the request is communicated correctly between parties. Is

I think so. Also, the split would need to be done in such a way that 
naming ambiguities are not introduced.

Russ