[Geopriv] Multiple URIs for LIS discovery

From: Richard Barnes ^lt;rbarnes@bbn.com>
Date: Wed Apr 01 2009 - 01:08:19 EDT

PROPOSAL: Modify the DHCP option formats in lis-discovery so that more
than one URI can be provided.


The sense in the room on draft-ietf-geopriv-lis-discovery (since
reflected in the draft) was to remove the certificate fingerprint
portion. This means that the client has to be pre-provisioned with
information about the server's credentials, e.g., a pre-shared key or a
list of default trust anchors.

On the other hand, the DHCP options in the draft don't allow for the
DHCP server to provide both an HTTP URI and an HTTPS URI.

The combination of these facts means that security in LIS-discovery is
(All) DHCP offers HTTPS and client can authenticate LIS
(Nothing) DHCP offers HTTP
(Worse) DHCP offers HTTPS and client can't authenticate LIS

"Worse" is worse because in that case, it's not just that there's no
security, there's no HELD at all. So things like emergency calling do
not work.

The "Worse" case concerns me, mainly because it seems like clients are
likely to end up there frequently -- unless the whole Internet agrees on
a single, small set of CAs, it's unlikely that the LIS will present a
cert that is valid from the client's perspective. This happens with
some regularity even in the web context, where things are reasonably
well consolidated. Obviously this is not the level of reliability you
want for some things, most notably emergency calling.

(You might think that this is not such a huge issue, since the HELD
client can just decide not to care about authentication. However, HELD
clients are likely to be embedded down in operating systems, a few
layers away from applications, so they may not even know that
circumstances require them to ignore authentication.)

This all gets better if the discovery option can carry multiple URIs.
In that case, the document can say that "Server: if you provide an HTTPS
URI, you SHOULD also provide an HTTP URI." That way, a client can fall
back to HTTP if HTTPS fails. ISTM that the minor additional complexity
of multiple URIs is worth it, given that it prevents HELD from failing


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Received on Wed, 01 Apr 2009 01:08:19 -0400

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