James,
I do believe that the intent of Ted (as well as others in the GEOPRIV
working group, including myself) is that if a UAC specifies
"recipient=endpoint" then a compliant proxy will not 'read' the location
body. In particular, "recipient=endpoint" indicates that a SIP proxy in
the signaling path does not have permission to store the location (or
any derived information) for longer than is necessary to forward the SIP
message and does not have permission to send the location to any third
party (for any reason including location-based routing) other than the
next-hop SIP proxy. That is, the intent of "recipient=endpoint" that if
a call requires location-based routing in order to succeed, then the
call should fail.
Personally, I believe (and I think this is a point Ted was trying to
make) that a UAC must have a way to indicate that a location is to be
read by the endpoint and no one else. This goes back to RFC 3693 which
dictates that a target must have a way of articulating privacy rules and
that using protocols must enforce those rules. In particular, see
requirements 7, 10 and 11 in RFC 3693. (Note that RFC 3693 explicitly
makes an exception for the emergency case, and so this discussion is in
the context of non-emergency conveyance of location information ... e.g.
Pizza Hut.)
(Also note: there is always the issue that a malicious proxy might not
obey the wishes expressed by the UAC, but SIP is an architecture in
which there is implicit trust by the UAC that the proxy acting on his
behave properly and comply with all relevant specifications.
Implications of the SIP trust model are a topic for another thread ...
See for example:
http://www1.ietf.org/mail-archive/web/sip/current/msg20319.html)
Clearly, there are many mechanisms that satisfy the desideratum that a
target be able to indicate that its location is to be read only by the
SIP endpoint. For example, this desire could be encoded as a privacy
rule within the PIDF-LO and each SIP proxy could parse the privacy rules
in a PIDF-LO to determine the target's intent. Alternatively, a
location-by-value could be encrypted end-to-end; or location could be
conveyed by-reference using an LIS with certificate-based access
controls. The GEOPRIV working group discussed various mechanisms last
May (See the thread beginning with:
http://www1.ietf.org/mail-archive/web/geopriv/current/msg03521.html) and
I believe there was rough consensus that the "recipient=endpoint"
mechanism described in the current conveyance draft was the best
mechanism for achieving the above desideratum.
This seems to leave us with three options going forward:
1) Deny the UAC the opertunity to indicate that location is to be read
only by the SIP endpoint. (That is, declare that SIP is not a GEOPRIV
using protocol in sense of RFC 3693).
2) Revisit the mechanism discussion and attempt to reach consensus on a
better mechanism for indicating that location is to be read only by the
SIP endpoint.
3) Craft text explaining that when the "recipient=endpoint" parameter is
used that a compliant SIP proxy is not to 'read' the location
information. (Note that this text should also indicate that when
"recipient=endpoint" is used that calls requiring location-based routing
will fail, and thus should only be used when call failure is preferred
over disclosure of location information to a routing entity.)
- Matt Lepinski
James M. Polk wrote:
This also gets back to one of my original points, does SIP expect a
UAC to understand the topology of a message's path to the ultimate
destination?
Is Ted's intent of the "recipient=endpoint" parameter to prevent
proxies from reading location in a message *and* a "recipient=server"
parameter to prevent endpoints from reading location in a message?
Does the UAC always know that there are only proxies between it and
the destination UAS?
Does the UAC always understand a particular message does or does not
need to be routed based on the location within the request?
Emergency services is an example of, always allow proxy routing when
the UAC knows this is an emergency request. But will this be true for
all applications of location conveyance in the (relatively near-term)
future? I'm not so sure.
The UAC has a mechanism for making location not readable by proxies if
it doesn't want them to, use encryption e2e. But this has interesting
properties in at least one case, the a user calls the nearest Pizza Hut.
A UAC can encrypt its location in the first INVITE, but if Pizza Hut
has a national or regional number, that routes on the location of the
caller, the message will probably return a 493 (undecipherable).
Does the UAC then send location to PizzaHut.com unencrypted, knowing
this is required to get the INVITE to the right store?
There are other usages of this, other than Pizza Hut.
Does anyone have a suggestion for informative text that can address
each of these two (or more) situations?
At the moment, all text around "recipient=" is suggestive, and not
definitive, because of what Dean says below.
That said, I could put something in like "unless a future standards
track RFC says otherwise, the use of "recipient=" parameter within any
locationValue is informative in nature", thus leaving the door open
for ECRIT's phoneBCP doc to refine usage in the emergency context, as
well as any other service defining document to do the same type of
refinement.
James
At 08:28 AM 11/26/2007, DRAGE, Keith \(Keith\) wrote:
This just seems to me to be an inappropriate change of RFC 2119
language.
If we really mean either of these, then we should be specifying that
the message is encrypted in the first place.
What we probably mean is something informative (because we cannot
make a normative statement on what applications do with the data),
stating that usage of the message so tagged is inappropriate because
the sender did not intend it to be used for this purpose.
Regards
Keith
> -----Original Message-----
> From: daniel grotti [mailto:[EMAIL PROTECTED]
> Sent: Saturday, November 24, 2007 11:38 AM
> To: Dean Willis
> Cc: IETF SIP List; James M. Polk
> Subject: R: R: R: [Sip] a question about IETF draft location
> conveyance 09
>
> I know.
> May be SHOULD NOT instead MUST NOT could be better.
>
> daniel
>
>
> ----------------------------------
> Daniel Grotti
> D.E.I.S. - University of Bologna
> ----------------------------------
> Via Venezia, 52
> 47023 Cesena (FC) - ITALY
> ----------------------------------
> e-mail: [EMAIL PROTECTED]
> ----------------------------------
>
>
>
> -----Messaggio originale-----
> Da: Dean Willis [mailto:[EMAIL PROTECTED]
> Inviato: sab 24/11/2007 2.32
> A: daniel grotti
> Cc: Hannes Tschofenig; IETF SIP List; James M. Polk
> Oggetto: Re: R: R: [Sip] a question about IETF draft location
> conveyance 09
>
>
> On Nov 22, 2007, at 12:08 PM, daniel grotti wrote:
>
> > Hi all,
> > so why don't emphasize this point in the next draft, saying :
> > "Proxy server MUST not read messages with "recipient=endpoint"
> > paramenter setted".
> > This is my point of you.
> >
> >
>
>
> because from a security standpoint, this prohibition is meaningless.
> Intermediate nodes can and will read anything that's in
> plaintext, and SOMEBODY will come up with a rationale, in
> some context or another, for doing so.
>
> And has been pointed out, doing so does not appear to create
> a compatibility problem. It doesn't break the protocol. It
> might defeat security-through-obscurity. It might be rude, or
> otherwise socially unacceptable. But those don't qualify for
> a MUST level protocol prohibition.
>
> --
> Dean
>
>
>
>
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