GEOPRIV WG J. Peterson
Internet-Draft NeuStar
Expires: March 10, 2005 September 9, 2004
A Presence-based GEOPRIV Location Object Format
draft-ietf-geopriv-pidf-lo-03
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Abstract
This document describes an object format for carrying geographical
information on the Internet. This location object extends the
Presence Information Data Format (PIDF), which was designed for
communicating privacy-sensitive presence information and which has
similar properties.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Location Object Format . . . . . . . . . . . . . . . . . . . . 4
2.1 Baseline PIDF Usage . . . . . . . . . . . . . . . . . . . 4
2.2 Extensions to PIDF for Location and Usage Rules . . . . . 5
2.2.1 'location-info' element . . . . . . . . . . . . . . . 5
2.2.2 'usage-rules' element . . . . . . . . . . . . . . . . 7
2.2.3 'method' element . . . . . . . . . . . . . . . . . . . 9
2.2.4 'provided-by' element . . . . . . . . . . . . . . . . 9
2.2.5 Schema definitions . . . . . . . . . . . . . . . . . . 10
2.3 Example Location Objects . . . . . . . . . . . . . . . . . 13
3. Carrying PIDF in a Using Protocol . . . . . . . . . . . . . . 15
4. Securing PIDF . . . . . . . . . . . . . . . . . . . . . . . . 15
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
6.1 'method' tokens . . . . . . . . . . . . . . . . . . . . . 17
6.2 'provided-by' elements . . . . . . . . . . . . . . . . . . 18
6.3 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:pidf:geopriv10 . . . . . . . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 21
A. NENA Provided-By Schema . . . . . . . . . . . . . . . . . . . 21
A.1 dataProvider XML Schema . . . . . . . . . . . . . . . . . 22
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1 Normative References . . . . . . . . . . . . . . . . . . . . 19
7.2 Informative References . . . . . . . . . . . . . . . . . . . 20
B. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
Intellectual Property and Copyright Statements . . . . . . . . 24
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1. Introduction
Geographical location information describes a physical position in
the world that may correspond to the past, present or future location
of a person, event or device. Numerous applications used in the
Internet today benefit from sharing location information (including
mapping/navigation applications, 'friend finders' on cell phones, and
so on). However, such applications may disclose the whereabouts of a
person in a manner contrary to the user's preferences. Privacy
lapses may result from poor protocol security (which permits
eavesdroppers to capture location information), inability to
articulate or accommodate user preferences, or similar defects common
in existing systems. The privacy concerns surrounding the unwanted
disclosure of a person's physical location are among the more serious
that confront users on the Internet.
Consequently, a need has been identified to convey geographical
location information within an object that includes a user's privacy
and disclosure preferences and which is protected by strong
cryptographic security. Previous work [13] has observed that this
problem bears some resemblance to the general problem of
communicating and securing presence information on the Internet.
Presence (which is defined in [12]) provides a real-time
communications disposition for a user, and thus has similar
requirements for selective distribution and security.
Therefore, this document extends the XML-based Presence Information
Data Format (PIDF [2]) to allow the encapsulation of location
information within a presence document.
This document does not invent any format for location information
itself. Numerous existing formats based on civil location,
geographic coordinates, and the like have been developed in other
standards fora. Instead, this document defines an object that is
suitable for both identifying and encapsulating pre-existing location
information formats, and for providing adequate security and policy
controls to regulate the distribution of location information over
the Internet.
The location object described in this document can be used
independently of any 'using protocol', as the term is defined in the
GEOPRIV requirements [10]. It is considered an advantage of this
proposal that existing presence protocols (such as [15]) would
natively accommodate the location object format defined in this
document, and be capable of composing location information with other
presence information, since this location object is an extension of
PIDF. However, the usage of this location object format is not
limited to presence using protocols - any protocol that can carry XML
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or MIME types can carry PIDF.
Some of the requirements in [10] and [11] concern data collection and
usage policies associated with location objects. This document
provides only the minimum markup necessary for a user to express the
necessary privacy preferences as specified by the GEOPRIV
requirements (the three basic elements in [11]). However, this
document does not demonstrate how a full XML-based ruleset
accommodating the needs of Location Servers could be embedded in PIDF
- it is assumed that other protocols (such as HTTP) will be used to
move rules between Rule Holders and Location Servers, and that full
rulesets will be defined in a separate document.
2. Location Object Format
2.1 Baseline PIDF Usage
The GEOPRIV requirements [10] (or REQ for short) specify the need for
a name for the person, place or thing that location information
describes (REQ 2.1). PIDF has such an identifier already, since
every PIDF document has an "entity" attribute of the 'presence'
element that signifies the URI of the entity whose presence the
document describes. Consequently, if location information is
contained in a PIDF document, the URI in the "entity" attribute of
the 'presence' element indicates the target of that location
information (the 'presentity'). The URI in the "entity" attribute
generally uses the "pres" URI scheme defined in [3]. Such URIs can
serve as unlinkable pseudonyms (per REQ 12).
PIDF optionally contains a 'contact' element that provides a URI
where the presentity can be reached by some means of communication
(usually, the URI scheme in the value of the 'contact' element gives
some sense of how the presentity can be reached: if it uses the SIP
URI scheme, for example, SIP can be used, and so on). Location
information can be provided without any associated means of
communication - thus, the 'contact' element may or may not be
present, as desired by the creator of the PIDF document.
PIDF optionally contains a 'timestamp' element that designates the
time at which the PIDF document was created. This element
corresponds to REQ 2.7a.
PIDF contains a 'status' element, which is mandatory. 'status'
contains an optional child element 'basic' that describes the
presentity's communications disposition (in very broad terms: either
OPEN or CLOSED). For the purposes of this document, it is not
necessary for 'basic' status to be included. If, however,
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communications disposition is included in a PIDF document above and
beyond geolocation, then 'basic' status may appear in a PIDF document
that uses these extensions.
PIDF also contains a 'tuple' umbrella element, which holds an "id"
element used to uniquely identify a segment of presence information
so that changes to this information can be tracked over time (as
multiple notifications of presence are received). 'timestamp',
'status', and 'contact' are composed under 'tuple'.
2.2 Extensions to PIDF for Location and Usage Rules
This XML Schema extends the 'status' element of PIDF with a complex
element called 'geopriv'. There are two major subelements that are
encapsulated within geopriv: one for location information, and one
for usage rules. Both of these subelements are mandatory, and are
described in subsequent sections. By composing these two subelements
under 'geopriv', the usage rules are clearly and explicitly
associated with the location information.
For extensibility (see REQ 1.4), the schema allows any other
subelements to appear under the 'geopriv' element. Two other
optional subelements are included in this document: one that
indicates the method by which geographical location was determined,
and one that allows an explicit designation of the entity that
provided the information.
2.2.1 'location-info' element
Each 'geopriv' element MUST contain one 'location-info' element. A
'location-info' element consists of one or more chunks of location
information (per REQ 2.5). The format of the location information
(REQ 2.6) is identified by the imported XML Schema describing the
namespace in question. All PIDF documents that contain a 'geopriv'
element MUST contain one or more import directives indicating the XML
Schema(s) that are used for geographic location formats.
In order to ensure interoperability of GEOPRIV implementations, it is
necessary to select a baseline location format that all compliant
implementations support (see REQ 3.1). Since it satisfies REQ 2.5.1,
this document works from the assumption that GML 3.0 [16] shall be
this mandatory format (a MUST implement for all PIDF implementations
supporting the 'geopriv' element).
The Geography Markup Language (GML) is an extraordinarily thorough
and versatile system for modeling all manner of geographic object
types, topologies, metadata, coordinate reference systems and units
of measurement. The simplest package for GML supporting location
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information is the 'feature.xsd' schema. Although 'feature.xsd' can
express complicated geographical concepts, it requires very little
markup to provide basic coordinates points for the most common use
cases. Various format descriptions (including latitude/longitude
based location information) are supported by Feature (see section
7.4.1.4 of [16] for examples), which resides here:
urn:opengis:specification:gml:schema-xsd:feature:v3.0
Note that by importing the Feature schema, necessary GML baseline
schemas are transitively imported.
Complex features (such as modeling topologies and polygons,
directions and vectors, temporal indications of the time for which a
particular location is valid for a target) are also available in GML,
but require importing additional schemas. For the purposes of
baseline interoperability as defined by this document, only support
for the 'feature.xsd' GML schema is REQUIRED.
Implementations MAY support the civil location format (civilLoc)
defined in Section 2.2.5. civilLoc provides the following elements:
+----------------------+----------------------+---------------------+
| Label | Description | Example |
+----------------------+----------------------+---------------------+
| country | The country is | US |
| | identified by the | |
| | two-letter ISO 3166 | |
| | code. | |
| | | |
| A1 | national | New York |
| | subdivisions (state, | |
| | region, province, | |
| | prefecture) | |
| | | |
| A2 | county, parish, gun | King's County |
| | (JP), district (IN) | |
| | | |
| A3 | city, township, shi | New York |
| | (JP) | |
| | | |
| A4 | city division, | Manhattan |
| | borough, city | |
| | district, ward, chou | |
| | (JP) | |
| | | |
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| A5 | neighborhood, block | Morningside Heights |
| | | |
| A6 | street | Broadway |
| | | |
| PRD | Leading street | N, W |
| | direction | |
| | | |
| POD | Trailing street | SW |
| | suffix | |
| | | |
| STS | Street suffix | Avenue, Platz, |
| | | Street |
| | | |
| HNO | House number, | 123 |
| | numeric part only. | |
| | | |
| HNS | House number suffix | A, 1/2 |
| | | |
| LMK | Landmark or vanity | Low Library |
| | address | |
| | | |
| LOC | Additional location | Room 543 |
| | information | |
| | | |
| FLR | Floor | 5 |
| | | |
| NAM | Name (residence, | Joe's Barbershop |
| | business or office | |
| | occupant) | |
| | | |
| PC | Postal code | 10027-0401 |
+----------------------+----------------------+---------------------+
Either the GML 3.0 geographical information format element, or the
location format element ('civilLoc') defined in this document, MAY
appear in in a 'location-info' element. Both MAY also be used in the
same 'location-info' element. In summary, the feature.xsd schema of
GML 3.0 MUST be supported by implementations compliant with this
specification, and the civilLoc format MAY be supported by
implementations compliant with this specification.
2.2.2 'usage-rules' element
At the time this document was written, the policy requirements for
GEOPRIV objects were not definitively completed. However, the
'usage-rules' element exists to satisfy REQ 2.8, and the requirements
of the GEOPRIV policy requirements [11] document. Each 'geopriv'
element MUST contain one 'usage-rules' element, even if the Rule
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Maker has requested that all subelements be given their default
values.
Following the policy requirements document (Section 3.1), there are
three fields that need to be expressible in Location Objects
throughout their lifecycle (from Generator to Recipient): one field
that limits retransmission, one that limits retention, and one that
contains a reference to external rulesets. Those three fields are
instantiated here by the first three elements. The fourth element
provides a generic space for human-readable policy directives. Any
of these fields MAY be present in a Location Object 'usage-rules'
element; none are required to be.
'retransmission-allowed': When the value of this element is 'no',
the Recipient of this Location Object is not permitted to share
the enclosed Location Information, or the object as a whole, with
other parties. When the value of this element is 'yes',
distributing this Location is permitted (barring an existing
out-of-band agreement or obligation to the contrary). By default,
the value MUST be assumed to be 'no'. Implementations MUST
include this field, with a value of 'no', if the Rule Maker
specifies no preference.
'retention-expires': This field specifies an absolute date at
which time the Recipient is no longer permitted to possess the
location information and its encapsulating Location Object - both
may be retained only up until the time specified by this field.
By default, the value MUST be assumed to be twenty-four hours from
the 'timestamp' element in the PIDF document, if present; if the
'timestamp' element is also not present, then twenty-four hours
from the time at which the Location Object is received by the
Location Recipient. If the value in the 'retention-expires'
element has already passed when the Location Recipient receives
the Location Object, the Recipient MUST discard the Location
Object immediately.
'ruleset-reference': This field contains a URI that indicates
where a fuller ruleset of policies related to this object can be
found. This URI SHOULD use the HTTPS URI scheme, and if it does,
the server that holds these rules MUST authenticate any attempt to
access these rules - usage rules themselves may divulge private
information about a Target or Rule Maker. The URI MAY
alternatively use the CID URI scheme [7], in which case it MUST
denote a MIME body carried with the Location Object by the using
protocol. Rulesets carried as MIME bodies SHOULD be encrypted and
signed by the Rule Maker; unsigned rulesets SHOULD NOT be honored
by Location Servers or Location Recipients. Note that in order to
avoid network lookups that result in an authorization failure,
creators of Location Objects MAY put HTTPS-based
ruleset-references into an encrypted external MIME body referenced
by a CID; in this way, recipients of the Location Object that are
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unable to decrypt the external MIME body will not learn the HTTPS
URI unless they are able to decrypt the MIME body.
'note-well': This field contains a block of text containing
further generic privacy directives. These directives are intended
to be human-readable only, not to be processed by any automaton.
2.2.3 'method' element
The optional 'method' element describes the way that the location
information was derived or discovered. An example of this element
(for a geographical position system) is:
See RFCXXXX.
END 7. References 7.1 Normative References [1] Bradner, S., "Key words for use in RFCs to indicate requirement levels", RFC 2119, March 1997. [2] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and J. Peterson, "Presence Information Data Format (PIDF)", RFC 3863, August 2004. [3] Peterson, J., "Common Profile for Presence (CPP)", RFC 3859, October 2003. [4] Mealling, M., "The IETF XML Registry", RFC 3688, BCP 81, January 2004. [5] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions (S/ MIME) Version 3.1 Message Specification", RFC 3851, July 2004. [6] Housley, R., "Cryptographic Message Syntax", RFC RFC3852, July 2004. [7] Levinson, E., "Content-ID and Message-ID Uniform Resource Locators", RFC 2392, August 1998. [8] Schaad, J., "Use of the Advanced Encryption Standard (AES) Encryption Algorithm in Cryptographic Message Syntax (CMS)", RFC 3565, July 2003. Peterson Expires March 10, 2005 [Page 19] Internet-Draft GEOPRIV Location Obj September 2004 [9] Gutmann, P., "Password-based Encryption for CMS", RFC 3211, December 2001. 7.2 Informative References [10] Cuellar, J., Morris, J., Mulligan, D., Peterson, J. and J. Polk, "Geopriv requirements", draft-ietf-geopriv-reqs-03 (work in progress), February 2003. [11] Morris, J., Mulligan, D. and J. Cuellar, "Core Privacy Protections for Geopriv Location Object", draft-morris-geopriv-core-02 (work in progress), June 2003. [12] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000. [13] Peterson, J., "A Presence Architecture for the Distribution of Geopriv Location Objects", draft-peterson-geopriv-pres-00 (work in progress), February 20003. [14] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. [15] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, May 2002. [16] OpenGIS, "Open Geography Markup Language (GML) Implementation Specification", OGC 02-023r4, January 2003,See RFCXXXX.
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