Subject: [AAA-WG]: [issue] NAS-Key-Binding and Ciphersuite Negotiation

From: [email-masked]
Date: Thu, 27 Sep 2001 15:50:46 +0300

Submitter name: Henry Haverinen
Submitter email address: [email-masked]
Date first submitted: 2001-09-27
Reference: 
Document: nasreq
Comment type: T
Priority: S
Section: 2.1.6
Rationale/Explanation of issue: 

The NAS-Key-Binding AVP specifies the purpose of the 
session key. The AVP MUST be included if the NAS-Session-Key 
AVP is included. The key binding specifies which ciphersuite 
will be used between the NAS and the user. The problem is that 
the ciphersuite may not have been selected yet. 

In PPP, ECP is used to negotiate the ciphersuite and it occurs 
between the user and the NAS after authentication.
In IEEE 802.11, the ciphesuite negotiation may as well 
occur after authentication.

In addition, the NAS-Key-Binding AVP makes AAA servers
dependent on and aware of different ciphersuites, so they
need to be updated if a new ciphersuite is specified.

Even if the ciphersuite hasn't been selected, the AAA server
can still transport keying material to the NAS in the 
NAS-Session-Key AVP. For example, it can include large
session keys which the NAS can truncate as necessary for use 
with a given ciphersuite. 

Requested change: 

The NAS-Key-Binding AVP should not be mandatory even if the 
NAS-Session-Key AVP is included. Do we need the NAS-Key-Binding
AVP at all?