Re: [Geopriv] HELD and persistent TLS connections in emergency calls

[Cullen Jennings <fluffy at cisco.com>]

Few random thoughts....

Certainly session resumption might work well here - basically when  
the device connected the first time it would do the public key  
operation to set up session once then save a secret that could be  
used for future sessions without doing the expensive public key  
operations. There are extensions to allow session resumption to only  
store state on the client not server - RFC 4507 and soon to be  
approved update to it. It would be well worth having a look at the  
session resumption stuff and seeing how to specify it's usage - it is  
implemented in many TLS stacks including OpenSSL.

I also think it would be worth looking at what the time to set up a  
TLS session is. The first thing would be to look at what size keys  
should the server use - some recommendation for key size specific to  
LIS might help keep people from using things way too large. The  
information transfered over HELD is unlikely to have high long term  
value and that might change the key sizes chosen. It would then be  
good to guess what the processors might be on the very low end stuff  
by the time any of this actually gets deployed. My gut feeling is 1/2  
second does not sound quite right. Whatever the answer is, it would  
be nice to see this analysis.

I can also imagine that in some cases getting a reference might help  
in that the host that eventually fetched the reference might have a  
much faster processor than a low end mobile phone.

Cullen <with my individual hat on>

PS - I simultaneously agree with Henning that it might be possible to  
use long lived TLS connection while agreeing with Barbara that  
regardless of the feasibility, operators will hate the idea. Hows  
that for being on the fence :-)  But I hope we can avoid having to do  
this approach.


On Sep 14, 2007, at 10:34 AM, Brian Rosen wrote:

> One of the uses for HELD is for an end device to obtain its  
> location.  The
> recommendations in ecrit-phonebcp say that the end device should  
> get its
> location when it boots, periodically thereafter, and as it makes an
> emergency call.  The time to complete the operation doesn't matter  
> in the
> first two cases, but does at call time.
>
> Location sent by value should be protected from eavesdropping.  TLS  
> is of
> course the mechanism of choice for HELD. Unless we change our  
> position,
> we've stated that the security of the reference is the same as the  
> value.
> That means getting a reference doesn't help; you would want to  
> protect the
> transfer of the reference with TLS.
>
> What should the recommendation be for the TLS connection between the
> endpoint and the HELD server?  Seems like we have two bad choices:
> 1. The endpoint maintains a persistent TLS connection.  This seems
> impossible for a LIS to maintain, and wasteful for the device
> 2. We incur very long time to establish the TLS session at call  
> time.  I
> think this is currently something in the 1/2 second or more range  
> for a
> typical phone like embedded controller, sometimes much more.  That  
> is WAY
> too long for emergency call, where we're attempting to keep call  
> set up in
> the 2 seconds from dial to ring.
>
>
> I don't have an answer here.  We don't use TLS with the other LCPs;  
> we have
> other mechanisms that protect the privacy to various degrees.  TLS  
> is an
> excellent mechanism for this purpose.  I just don't know how to  
> deal with
> the setup time.
>
> Brian
>
>
>
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