Subject: RE: [Capwap] State machine issues with LWAPP over DTLS

From: "Susan Hares" <[email-masked]>
Date: Mon, 21 Nov 2005 10:51:29 -0700

Ekr:

My point is that your draft was not sufficient in it's descriptions.
As a friend of my says "I can neither confirm nor deny" whether the DTLS
can work.  Your draft is insufficient to determine that.   My first
slide was the text I found in your draft that indicated how you would
plug DTLS into LWAPP. 

I've attached a power point slide.   If you are simply using DTLS as
transport, your document needs to describe the transitions at the
arrows.

If you want to support key distribution, please add additional
information to the draft. 

Sue

-----Original Message-----
From: Eric Rescorla [mailto:[email-masked]] 
Sent: Friday, November 18, 2005 1:43 PM
To: [email-masked]
Subject: [Capwap] State machine issues with LWAPP over DTLS

At the meeting in Vancouver, Sue Hares raised a question regarding
state machine coordination between DTLS and LWAPP. I must confess,
I didn't really understand what the issue was. Sue, do you think
you could explain your concern in a little more detail here?

Thanks,
-Ekr

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From: Scott G Kelly <[email-masked]>
Date: Tue, 22 Nov 2005 07:35:20 -0800

Hi Sue,

Comments inline below...

> slide was the text I found in your draft that indicated how you would

The main reason the draft is so sparse is that it was quickly put 
together very close to the submission deadline prior to the last IETF 
meeting, which encouraged ...a certain economy (think of it as 
Hemingway-esque :-))

> transport, your document needs to describe the transitions at the

Echoing Mani's comments here, ascii is preferable and sufficient. I had 
intended to cut, paste, and modify the state diagram from the lwapp 
draft into the document, but ran out of time. I can add this for clarity.

> information to the draft. 

I'm not sure I understand which keys you are referring to. The keys 
distribued in your diagram are for the lwapp session itself, and this is 
taken care of entirely by DTLS as part of the handshake.

I think we need to be careful about calling DTLS "a transport" for 
lwapp. I understand what is meant in one sense, but in another, it seems 
to imply that lwapp is somehow disjoint (maybe even unaware) of the dtls 
layer - and this is not my view of how this should work.

On the contrary, I think lwapp must be aware of the dtls connection and 
its properties in order to meet its configured security requirements, 
and that our choice to use dtls (vs some other internal lwapp security 
mechanism) should be transparent (as much as possible) to 
administrators. In this respect, the integration is closer than 
"transport" would seem to imply.

I'll try to spend some time editing over the weekend, and maybe we can 
submit an update early next week.

--Scott

> ------------------------------------------------------------------------
>

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From: "T. Charles Clancy" <[email-masked]>
Date: Tue, 22 Nov 2005 10:45:06 -0500 (EST)

> taken care of entirely by DTLS as part of the handshake.

I think there are a few issues here:

1. Is EAP executed over DTLS
2. Is the 11i four-way handshake executed over DTLS
3. Are TKs distributed to APs over DTLS

IMHO, (1) and (2) are simply data packets, and should go over the 
unencrypted data channels.  These packets already have sufficient 
cryptographic protection, in that they are authentication protocols 
expected to be executed over a plaintext channel.

However (3) is part of the LWAPP control protocol.  Thus, it will be going 
over DTLS.  We need to make sure there aren't any security concerns with 
sending these keys unencrypted (sort of) over DTLS.  First of all, if we 
were going to provide additional crypto, we'd need to get 
application-layer keys from somewhere.  DTLS doesn't provide them, so we'd 
need to drive them (yuck).  Fortunately, I really don't think they're 
necessary.  DTLS provides all the security we need for key transport.  As 
long as we don't treat DTLS as a modular transport layer, we'll be fine.

[ t. charles clancy ]--[ [email-masked] ]--[ www.cs.umd.edu/~clancy ]
[ computer science ]-----[ university of maryland | college park ]
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