Re: [rtcweb] Identity and PSTN gateways

It seems the same problem exists when a TURN relay is involved in an inter-browser call. The endpoints cannot verify each other's identity directly. They need to trust the relay to interconnect them and not to do anything evil, such as snooping.

Huilan

> -----Original Message-----
> From: rtcweb-bounces@ietf.org [mailto:rtcweb-bounces@ietf.org] On Behalf Of
> Olle E. Johansson
> Sent: Tuesday, April 03, 2012 9:05 AM
> To: Harald Alvestrand
> Cc: rtcweb@ietf.org
> Subject: Re: [rtcweb] Identity and PSTN gateways
> 
> 
> 3 apr 2012 kl. 14:58 skrev Harald Alvestrand:
> 
> > One thing that has come up repeatedly in the discussion is the claim that
> "you can't have a verified identity when you talk to someone via a
> telephone gateway" (and therefore <insert your favourite security mechanism
> here> is not needed / not an added benefit / other claim).
> >
> > I think this is a fallacy.
> >
> > Sure, as people have commented numerous times, telephone numbers are
> identities; they're being used as such every time someone prints them on a
> business card or a billboard.
> >
> > When you're connecting via a gateway to the PSTN, the gateway operator
> gives you a guarantee that you're being connected to the right person;
> that's what gateways are for.
> >
> > This makes for a fairly simple mapping to the "identity / identity
> provider" model we've been bandying about for the "full-blown" IdP /
> endpoint case:
> >
> > The identity is the telephone number.
> > The identity provider (one of many possible ones for the number) is the
> gateway operator.
> >
> > Thus - if you call a telephone number via a gateway, you would perform a
> DTLS key exchange with the gateway, and an identity verification exchange
> with the gateway operator; you would then guarantee that the gateway
> operator vouches for this being a legitimate gateway function that you can
> reach for that number.
> >
> > That's just about the best guarantee you can get when talking to the
> telephone system. But if we're using the IdP + DTLS-SRTP version, the
> exchange guarantees you that:
> > a) nobody is listening in between you and the gateway (even if they
> snooped your signalling)
> > b) the gateway operator vouches for the gateway being the right gateway
> to reach that number
> >
> > Seems like a little bit better than what you get with SDES. Only a little.
> 
> Now we will have to separate "PSTN-emulating" gateways that accept calls to
> all phone numbers but play a prompt saying "You gotta be kidding me -
> calling a phone number?" from REAL gateways that have a connection to the
> PSTN world.
> 
> Will guys connecting with SS7 have a certificate signed by the ITU as a
> "TRUE" PSTN provider and the voip guy in the basement next door just have a
> "Best effort fourth-tier PSTN service" certificate?
> 
> I think that any identity of any PSTN gateway just identifies the gateway
> as a server. Not as a service.
> 
> /O
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