Network Working Group H. Schulzrinne
Internet-Draft Columbia U.
Expires: December 21, 2003 June 22, 2003
Location Objects and Location Privacy Information for Presence
Information
draft-schulzrinne-geopriv-presence-lo-00
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
Location information is a natural extension of presence information.
This document describes how the Presence Information Data Format
(PIDF) can be extended to deliver geospatial and civil location
information, as well as privacy policy information. The privacy
policy information can be used both within the presence agent (PA) as
well as the presence document.
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Privacy Rules . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2 Area Description . . . . . . . . . . . . . . . . . . . . . . . 6
4.3 Disclosure . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.4 Retention . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Location Information . . . . . . . . . . . . . . . . . . . . . 10
5.1 Geospatial Locations . . . . . . . . . . . . . . . . . . . . . 10
5.2 Civil Locations . . . . . . . . . . . . . . . . . . . . . . . 10
5.3 Heading . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Composition Rules . . . . . . . . . . . . . . . . . . . . . . 12
7. Notes on Requirements . . . . . . . . . . . . . . . . . . . . 13
8. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 14
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15
References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . 18
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1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. Introduction
The draft [I-D.morris-geopriv-core] describes a set of privacy
protections and rules that a location object (LO) must contain. This
document implements the notions set forth in the draft, albeit with
differences in details.
The draft [I-D.peterson-geopriv-pres] makes the case that presence
systems already offer many of the features required from a using
protocol. Thus, this document extends presence information encoded in
the CPIM-compliant PIDF format to express the location of tuples
describing a presentity. Such tuples may represent a human being
named by the 'entity' attribute in the 'presence' element of the
presence document or it may describe the location of a communications
device associated with the presentity. Presentities do not need to
refer to humans, so the same mechanism is applicable to tracking the
location of animals, vehicles or other assets.
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3. Architecture
The LO described here is a small, but crucial, component in an
overall location service. As motivated in the introduction, a
location service based on presence can leverage a number of other
existing and emerging pieces of the presence infrastructure. For
example, location recipients (i.e., presence subscribers or watchers)
need to satisfy the policy requirements before they are allowed to
subscribe. The watcher information event package
[I-D.ietf-simple-winfo-package] allows authorization agents to be
notified when potential location recipients request subscriptions to
presence information.
Filters [I-D.ietf-simple-pres-filter-reqs] can be used by subscribers
to limit the amount of information that they receive, for example to
avoid taxing limited subscriber bandwidth. Conceptually, the
subscription filter is applied to the information after it has been
tailored by the rules described in this specification, Section 4.
The geospatial and civil coordinates described in this document
extend the RPIDS [I-D.schulzrinne-simple-rpids] presence using the
RPIDS composition rules to merge tuples and to 'pivot' (i.e., to
compose tuples along a certain attribute axis).
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4. Privacy Rules
4.1 Introduction
Privacy rules describe how participants in a location system may
access, distribute and retain location information. We also allow
other components to use these privacy rules. For example, elements
within Rich Presence Information (RPIDS) may be protected by these
rules.
Privacy rules are found in two places: they are contained in
location objects delivered as part of presence information and they
are stored in presence agents. We believe that there is much to be
gained by making these two the same. Among other advantages, a
simple presence agent can just copy the rules into location objects
that it delivers. However, this is not always advisable since the
privacy rules may well reveal private information that is at least as
sensitive as the location information itself, e.g., the target's list
of friends and less-trusted acquaintances. The privacy rules defined
here are capable of restricting the delivery of the privacy rules
themselves, so that the presentity can achieve fine-grained control
over its visibility. We also mitigate this exposure by introducing
hashed versions of identifiers which are sufficient for the watcher
to determine whether another entity may receive location information,
but does not reveal the identity itself.
Privacy rules are uploaded and manipulated by the presentity, or an
agent acting on its behalf, to the presence agent, e.g., using XCAP.
They complement and refine the subscription rules. While
subscription rules govern who can subscribe to the presentity, the
privacy rules contained in this document restrict the information
that is being delivered to the successful subscriber.
When a watcher receives presence information containing these privacy
rules, it can propagate the presence object according to these rules
and may itself include rules in the presence information it divulges
to third parties. However, these rules MUST NOT be any less
restrictive than the rules contained in the presence information
received. This applies even if, for example, the accuracy of data is
also degraded.
4.2 Area Description
The area description provides a labeled geographic area that can be
referenced from other rules. It uses the same geospatial or civil
coordinates defined in Sections Section 5.1, respectively.
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4.3 Disclosure
An example of a disclosure description is shown in Figure 1.
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:p="urn:ietf:params:xml:ns:geo-privacy"
entity="pres:alice@example.com">
...
<p:disclosure rule="http://example.com/disclosure.xml">
<p:rule uri="sip:bob@example.com">
<p:match>
<p:area>home</p:area>
<p:rrule freq="daily" until="20031224T000000Z" count="10"/>
</p:match>
<p:action>
<p:include>a1</p:include>
<p:include>a2</p:include>
<p:exclude></exclude>
<p:resolution latitude="9" longitude="10" altitude="3"/>
<p:notify uri="mailto:alice@example.com"/>
</p:action>
</p:rule>
<p:rule subject="C=US ST=Washington L=Seattle O=Amazon.com, Inc
OU=Software CN=www.amazon.com"/>
<p:rule hash-uri="6e8c81b2f0de5e5957871354761b56c5"/>
<p:rule until="2004-05-31T13:20:00.000-05:00" duration="3600"/>
</p:disclosure>
Figure 1
A disclosure specification consists of any number of rules, where
each rule consists of a 'match' description that determines when the
rule applies and an 'action' element that enumerates which elements
of the LO to include and exclude and whether the target needs to be
notified.
While the disclosure information could be organized along any number
of matching rules, this document chooses to make the recipient of the
information the principal selection criteria. Among other reasons,
it is easier to compare than the time and area selectors and seems
most likely to be the most common criteria for allowing or
disallowing disclosure. TBD: The destination could easily be made a
peer of the other selection criteria.
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A rule with no 'uri' attribute matches any destination. Like the
'default' tag in C switches, it is only used if no other rule matches
according to the 'uri' tag.
Instead of a constant URI, simple 'glob' expressions can also be used
for user@domain-style URIs such as SIP and mailto URIs. Only two
wildcards are permitted: a '*' instead of the user name indicates
that any user in the domain matches the rule, while a '*.'
immediately following the '@' sign indicates that any subdomain
within the domain matches. The '*' MUST NOT appear anywhere else. For
example, 'alice@example.*.com' is invalid. (TBD: '*' is a legitimate
user name, so an escaping rule is needed, strictly speaking.)
Instead of a literal URI, a rule can contain a hashed URI that is
compared to the MD5 hash of the potential destination the holder of
presence information wants to deliver data to. Hashed URIs can only
be used for schemes that support a canonical form. Examples include
SIP URIs [RFC3261]. Using hashed URIs avoids exposing the identity
of favored or disfavored individuals to the watcher. Naturally, the
watcher can still play a game of 'I wonder if the presentity likes
Alice' by checking hashed URIs against a guessed list of friends and
enemies.
As a third type of identifier, X.509 subject identities are
supported, applicable when the location requestor can be verified
using a X.509-using authentication protocol, such as CMS (S/MIME) or
TLS.
Each 'to' element can specify a set of time restrictions during which
disclosure is permitted.
The time recurrence rules are specified using the iCal notation in
RFC 2445 [RFC2445], translated into XML schema format, roughly
following the (expired) Internet draft
draft-ietf-calsch-many-xcal-00. 'exdate' 4.8.5.2, 'rdate' 4.8.5.3,
'rrule', 4.8.5.4.0
The same 'uri' can appear multiple times. Disclosure is permitted if
any of the matching rules allow disclosure. A rule matches if all
elements of the rule match. If a rule contains an attribute that is
unknown to the receiver, the rule does not match.
One or more 'include' elements enumerate, as XPath expressions, the
elements that should be included in transmission, while the exclude
explicitly removes elements from that list. If there is no 'include'
element, all elements are included and need to be removed explicitly.
This mechanism is sufficient to limit the accuracy for civil
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coordinates, but does not suffice for geospatial coordinates. The
'resolution' element restricts the resolution for geospatial
coordinates and is measured in bits, similar to the LaRes, LoRes and
AltRes parameters in draft-ietf-geopriv-dhcp-lo-option.
A target can request that all disclosures to a particular destination
cause a notification to be sent to the target, using the 'uri'
specified. The notification could be sent, for example, using
instant messaging (im:), email (mailto:) or an HTTP request. This
clearly has security implications, since a malicious target could use
this mechanism to cause messages to be sent to third parties,
introducing a new form of 'open proxy' spamming. Thus, such
notification is only appropriate if the notifying party can convince
itself that the address indeed belongs to the presentity.
Unfortunately, there is no fool-proof way of ensuring that, but a
recipient of this information may compare the non-schema part of the
notification URI with the presentity and only allow notification on
equality. Given these constraints and the inherent unreliability and
delays in most current notification mechanisms, a target cannot rely
on receiving notification.
4.4 Retention
<retention until="2004-05-31T13:20:00.000-05:00" duration="3600"/>
The 'until' attribute determines the absolute time until the
recipient may retain this information. The 'duration' attribute
determines the time duration, measured in seconds, counting from the
time the location recipient has obtained the location object. [TBD:
should this be a schema duration, in ISO 8601 format? Seconds seems
easier and in line with other duration indications.]
Note that a location recipient that passes a LO to a third party MUST
decrement the 'duration' attribute by the time it has held the
location object.
If no attribute is specified, a default of one hour is assumed. If
both 'until' and 'duration' attributes are specified, the shorter
duration governs retention.
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5. Location Information
Each tuple can have zero or more 'location' elements, each containing
an alternate representation of a location for the tuple. PIDF allows
tuples to have no contact element. We take this to represent the
location of the presentity itself, if a single location can be
unambiguously assigned to a presentity.
5.1 Geospatial Locations
Geospatial coordinates, multiple sightings and headings can be
readily specified using the OpenGIS GML format. An example is shown
in Figure 3.
<?xml version="1.0" encoding="UTF-8"?>
<presence ... xmlns:gml='http://www.opengis.net/gml'
xmlns:loc='urn:ietf:params:xml:ns:geopriv-loc'
entity='pres:alice@example.com'...>
<tuple id="123">
<status>
<basic>open</basic>
<status>
<loc:location>
<gml:Point>
<gml:pos>40.85790 73.98857</gml:pos>
</gml:Point>
</loc:location>
</tuple>
</presence>
Figure 3
5.2 Civil Locations
Civil locations use a hierarchy similar to
[I-D.schulzrinne-geopriv-dhcp-civil]. An example is shown in Figure
4.
<?xml version="1.0" encoding="UTF-8"?>
<presence ... xmlns:loc='urn:ietf:params:xml:ns:geopriv-loc'
xmlns:c='urn:ietf:params:xml:ns:geopriv-civil'
entity='pres:alice@example.com'...>
<tuple id="123">
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<loc:location>
<c:c>US</c:c>
<c:a1>NJ</c:a1>
<c:a2>Bergen</c:a2>
<c:a3>Leonia</c:a3>
<c:a6>Westview</c:a6>
<c:sts>Ave</c:sts>
<c:hno>313</c:hno>
<c:zip>10027</c:zip>
</loc:location>
</tuple>
</presence>
Figure 4
5.3 Heading
Both civil and geospatial coordinates can contain heading vectors.
TBD: how can GML speed, bearing, etc. be combined with civil
coordinates?
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6. Composition Rules
Composition is 'union' by default, i.e., all location objects are
enumerated.
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7. Notes on Requirements
This draft satisfies most of the requirements of
draft-morris-geopriv-core. However, in a few instances, it
intentionally deviates from the suggestions made. Below, we motivate
our design choices.
In Section 3.2, Rule 4, the location seeker is identified simply by a
URI. Unfortunately, this is insufficient, since there is no universal
personal identifier. (There is no guarantee We qualify this
'user@domain' identifier with a URI scheme.
In Section 3.2, Rule 4, the accuracy requirement indicates
kilometers. However, this is impossible to implement for civil
coordinates and difficult for geospatial coordinates, as it requires
spherical geometry. For values 'D' (local or municipial) and 'E'
(state or regional), experience indicates that these nomenclatures
are not used uniformly across countries. Thus, the explicit labeling
by element chosen above appears to be more amenable to machine
interpretation.
This document does not directly support consent. However, this can be
emulated by having a one-time subscription and making the
subscription itself require explicit consent from the presentity.
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8. Open Issues
o Should the retention and disclosure rules apply to all RPIDS
elements, not just location information?
o Given the security risks outlined above, is notification on
disclosure realistic and appropriate?
o Default 'notify' element?
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9. Security Considerations
See [I-D.ietf-geopriv-reqs].
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References
[I-D.ietf-geopriv-reqs]
Cuellar, J., Morris, J. and D. Mulligan, "Geopriv
requirements", draft-ietf-geopriv-reqs-03 (work in
progress), March 2003.
[I-D.ietf-simple-pres-filter-reqs]
Moran, T., "Requirements for Presence Specific Event
Notification Filtering",
draft-ietf-simple-pres-filter-reqs-01 (work in progress),
June 2003.
[I-D.ietf-simple-winfo-package]
Rosenberg, J., "A Watcher Information Event
Template-Package for the Session Initiation Protocol
(SIP)", draft-ietf-simple-winfo-package-05 (work in
progress), January 2003.
[I-D.morris-geopriv-core]
Morris, J., "Core Privacy Protections for Geopriv Location
Object", draft-morris-geopriv-core-01 (work in progress),
March 2003.
[I-D.peterson-geopriv-pres]
Peterson, J., "A Presence Architecture for the
Distribution of Geopriv Location Objects",
draft-peterson-geopriv-pres-00 (work in progress),
February 2003.
[I-D.schulzrinne-geopriv-dhcp-civil]
Schulzrinne, H., "DHCP Option for Civil Location",
draft-schulzrinne-geopriv-dhcp-civil-01 (work in
progress), February 2003.
[I-D.schulzrinne-simple-rpids]
Schulzrinne, H., "RPIDS -- Rich Presence Information Data
Format for Presence Based on the Session Initiation
Protocol (SIP)", draft-schulzrinne-simple-rpids-01 (work
in progress), February 2003.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2445] Dawson, F. and Stenerson, D., "Internet Calendaring and
Scheduling Core Object Specification (iCalendar)", RFC
2445, November 1998.
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[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M. and E. Schooler,
"SIP: Session Initiation Protocol", RFC 3261, June 2002.
Author's Address
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US
Phone: +1 212 939 7042
EMail: hgs+nsis@cs.columbia.edu
URI: http://www.cs.columbia.edu
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