Subject: RE: [AAA-WG]: Re: Issue 414: Keying AVPs

From: <[email-masked]>
Date: Wed, 13 Aug 2003 16:40:09 +0300

> I agree that including a list of ciphers with the AAA-Key AVP is not a
> good idea since this keying material MUST be ciphersuite independent,
> according to the Key Framework draft.  Similarly, 
> directionality is not
> useful since this is keying material, not a session key.
> 
> However, it does strike me that perhaps a key lifetime might 
> make sense,
> since overloading Session-Timeout or another equivalent AVP 
> seems like a
> bad idea.

Why? Doesn't the Session-Timeout really mean that after expiration 
full (re-)authentication must be done and thus new keys must be 
derived?

Diameter has Session-Timeout and Authorization-Lifetime AVPs (see 
also Termination-Action (NASREQ) and Re-Auth-Request-Type AVPs). 
I don't know why, but NASREQ recommends to use Authorization-Lifetime 
AVP only. No need for Session-Timeout? Then it's not overloading I 
guess.

I'm just confused with all these lifetime AVPs and recommendations.

- Dan

> 
> One issue which is still open is whether the Key-Name should 
> be included
> along with the key.  IEEE 802.11i has a new PMK naming 
> proposal in D5.0
> which essentially names keys based on the key itself as well as
> Called-Station-Id and Calling-Station-Id.  However, I'm not 
> clear how the
> station knows which algorithm was used to generate the key 
> (could be one
> of several).
>

---

From: Bernard Aboba <[email-masked]>
Date: Wed, 13 Aug 2003 06:49:52 -0700 (PDT)

> full (re-)authentication must be done and thus new keys must be

In RADIUS, Session-Timeout can be used to indicate the maximum amount of
time that the user can have (with Termination-Action not specified or set
to default), or the maximum time to re-authentication (if
Termination-Action = RADIUS).  While it is true that a re-authentication
implies a re-key, the reverse is not true; a re-key can be done without
re-authenticating (e.g. rerun the 4-way handshake in 802.11).  Also
typically a re-key is done after a certain amount of data is sent.  For
example in block ciphers this is related to the birthday attack
probability.  For a credible cipher (e.g. AES) this is typically quite a
large number.  For WEP it was small due to its flaws and so people have
set Session-Timeout to 10 minutes or less.  In general it would be useful
to be able to set the re-key and re-authentication timers independently.

> AVP only. No need for Session-Timeout? Then it's not overloading I

The Authorization-Lifetime AVP specifies when the NAS needs to
re-authorize the session.  This is still not the same thing as specifying
when a rekey is required.

> I'm just confused with all these lifetime AVPs and recommendations.

Yes, it is confusing.  I've never been convinced that
Authorization-Lifetime AVP really adds any value to Diameter other than
requiring more logic in a RADIUS/Diameter gateway.