Network Working Group                                        J. Peterson
Request for Comments: 4119                                       NeuStar
Category: Standards Track                                  December 2005
            A Presence-based GEOPRIV Location Object Format
Status of This Memo
   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.
Copyright Notice
   Copyright (C) The Internet Society (2005).
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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RFC 4119                GEOPRIV Location Object            December 2005
Table of Contents
   1. Introduction ....................................................2
      1.1. Conventions Used in This Document ..........................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 ..................................14
   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
   7. Acknowledgements ...............................................19
   A. Appendix: NENA Provided-by Schema ..............................20
      A.1. dataProvider XML Schema ...................................21
   Normative References ..............................................22
   Informative References ............................................22
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 issues 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
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RFC 4119                GEOPRIV Location Object            December 2005
   communicating and securing presence information on the Internet.
   Presence (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 civic location,
   geographic coordinates, and the like, have been developed in other
   standards fora.  Instead, this document defines an object that is
   suitable both for identifying and encapsulating preexisting 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 [14]) would
   natively accommodate the location object format defined in this
   document, and be capable of composing location information with other
   presence information, because 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
   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.
1.1.  Conventions Used in This Document
   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 [1].
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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:  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,
   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'.
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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, which describes
   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).  Because it satisfies REQ
   2.5.1, this document works from the assumption that Geography Markup
   Language (GML) 3.0 [15] shall be this mandatory format (a MUST
   implement for all PIDF implementations supporting the 'geopriv'
   element).
   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
   information is the 'feature.xsd' schema.  Although 'feature.xsd' can
   express complicated geographical concepts, it requires very little
   markup to provide basic coordinate points for the most commonly used
   cases.  Various format descriptions (including latitude/longitude
   based location information) are supported by Feature (see section
   7.4.1.4 of [15] for examples), which resides here:
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      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 civic location format (civicLoc)
   defined in Section 2.2.5.  civicLoc 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)                 |                     |
   |                      |                      |                     |
   | A5                   | neighborhood, block  | Morningside Heights |
   |                      |                      |                     |
   | A6                   | street               | Broadway            |
   |                      |                      |                     |
   | PRD                  | Leading street       | N, W                |
   |                      | direction            |                     |
   |                      |                      |                     |
   | POD                  | Trailing street      | SW                  |
   |                      | suffix               |                     |
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   |                      |                      |                     |
   | 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 ('civicLoc') defined in this document, MAY
   appear 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 civicLoc 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
   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
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   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 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 the value MUST be
      assumed to be 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
      unable to decrypt the external MIME body will not learn the HTTPS
      URI unless they are able to decrypt the MIME body.
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   '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 Peterson Standards Track [Page 18] RFC 4119 GEOPRIV Location Object December 2005 RFC4119.
END 7. Acknowledgements This document was produced with the assistance of many members of the GEOPRIV IETF working group. Special thanks to Carl Reed of OpenGIS for a close read of the document. The civic location format described in this document was proposed by Henning Schulzrinne for communicating location information in DHCP, and has been appropriated in its entirety for this document. James M. Polk provided the text related to the 'method' element, and much of the text for the 'provided-by' element. The text of Appendix A was written by Nadine Abbott. Peterson Standards Track [Page 19] RFC 4119 GEOPRIV Location Object December 2005 A. Appendix: NENA Provided-By Schema The following registers the XML namespace urn:ietf:params:xml:ns:pidf:geopriv10:dataProvider and the associated schema below, for usage within the 'provided-by' element of PIDF-LO. The dataProvider namespace was developed by the US National Emergency Number Administration (NENA) for next-generation emergency communications needs. This appendix is non-normative for implementers of PIDF-LO implementations and MAY support the dataProvider namespace. Other registrants of 'provided-by' namespaces are invited to use the registration below as an informative example. URI: The URI for this namespace is urn:ietf:params:xml:ns:pidf:geopriv10:dataProvider Registrant Contact: NENA, VoIP working group & IETF, GEOPRIV working group, (geopriv@ietf.org), Nadine Abbott (nabbott@telcordia.com). XML: BEGINSee RFC4119.
END Peterson Standards Track [Page 20] RFC 4119 GEOPRIV Location Object December 2005 A.1. dataProvider XML Schema