Subject: [6tisch-security] question on (D)TLS support for piggy-backed info

From: Rene Struik <[email-masked]>
Date: Thu, 10 Apr 2014 11:37:27 -0400

Dear colleagues:

I had a look at the (D)TLS protocol suites, so as to find out if one can
realize authenticated key agreement with piggy-backed info, i.e., where
both client and server would optionally add some additional strings to
the key confirmation messages. This would be similar to the MAC tag
provided over Text_U and Text_V with NIST SP 800-56a-2012 (Section 6.3.3
- key confirmation). This functionality would be useful esp. in
constrained settings, where one would like to "tag along" additional
info if this would save in the number of message exchanges required.

BTW - I looked into this in the context of 6TiSCH security discussions
and device enrollment aspects. Here, the joining node would be the
client, the network representative would be the server, and the
additional text string the server may wish to "stuff" into the key
confirmation flow would correspond to an object codifying resource
allocation (time schedule related info, authorization info, and such).

It seems that none of the TLS and DTLS versions supports this
functionality, but I may have missed something here. If you could also
give this a look, that would be great.

If TLS does not provide this functionality, it seems to me that some of
the efforts of the ACE WG may also become more communication-heavy,
since now authorization info cannot hitch-hike on the back of the key
confirmation messages one already has. With avg time slots being spaced
out quite sparsely (e.g., 1s spacing), this comes at a considerable
delay penalty.

I am not sure whether there has been any attempt in the past to see
how TLS and other IETF protocols could potentially implement
NIST SP 800-56a and -56b (which do have the piggy-back facility
and strong security).

As a final note, coap currently stipulates the use of DTLS, without
too much detail on how to instantiate this in real-life applications.

Best regards, Rene

-- 
email: [email-masked] | Skype: rstruik
cell: +1 (647) 867-5658 | US: +1 (415) 690-7363