Network Working Group J. Peterson

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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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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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:

<method>gps</method>

The possible values of the 'method' element are enumerated within an
IANA registry. Implementations MUST limit the use of this method to
the values shepherded by IANA. This document pre-populates the IANA
registry with seven possible values; see Section 6.1 for more
information.

The 'method' element is useful, for example, when multiple sources
are reporting location information for a given user, and some means
of determining location might be considered more authoritative than
others (i.e., a dynamic, real-time position system versus static
provisioning associated with a target device). However, note that
inclusion of 'method' might reveal sensitive information when the
generator is providing intentionally coarsened location information.
For example, when a LO is transmitted with 'DHCP' as the 'method',
but the location information indicates only the city in which the
generator is located, the sender has good justification to suspect
that some location information is being withheld.

2.2.4. 'provided-by' Element

The optional 'provided-by' element describes the entity or
organization that supplied this location information (beyond the
domain information that can be inferred from a signing certificate).
An example of this element (for a made-up game system) might be:

<provided-by>
<test:game>
West5
</test:game>
</provided-by>

Values for the 'provided-by' element MUST be IANA-registered XML
namespaces; see Section 6.2 for more information.

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The 'provided-by' element is not intended for use by most entities,
but rather to meet special requirements for which overhead (IANA
registration, location object size) and potential location
information leakage are acceptable choices.

In general cases, the entity that supplied location information is
communicated by the subjectAltName of the certificate with which the
location object is signed; thus, this element is unnecessary.
'Provided-by' is meaningful in particular cases when the creator of a
location object wants to designate a particular system or party
within a complex administrative domain, including situations
envisioned for providing emergency services in a diverse national
context. It might assist, for example, the recipient of a malformed
or misleading location object in identifying the particular system
that malfunctioned.

Users should be aware that this information can inadvertently provide
additional information to the receiver, increasing the effective
resolution of the geospatial or civic information, or even revealing
some location information, when it was meant to be entirely
protected. Consider if there were circumstances that influenced
Columbia University to elect to register and use the provided-by
element. If an example LO includes only state-level information,
then including the fact that the location information was provided by
Columbia University provides a strong indication that the Target is
actually located in a four-block area in Manhattan. Accordingly,
this element should be used only when organizational functions
strongly would depend on it. In all but such usages, the
subjectAltName of the certificate will suffice, and 'provided-by'
SHOULD NOT be used.

2.2.5. Schema Definitions

Note that the XML namespace [4] for this extension to PIDF contains a
version number 1.0 (as per REQ 2.10).

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
targetNamespace="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:tns="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gbp="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified" attributeFormDefault="unqualified">

<xs:import namespace=
"urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy" />



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<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>

<xs:element name="geopriv" type="tns:geopriv"/>

<xs:complexType name="geopriv">
<xs:sequence>
<xs:element name="location-info" type="tns:locInfoType"
minOccurs="1" maxOccurs="1"/>
<xs:element name="usage-rules" type="gbp:locPolicyType"
minOccurs="1" maxOccurs="1"/>
<xs:element name="method" type="tns:locMethod"
minOccurs="0" maxOccurs="1"/>
<xs:element name="provided-by" type="tns:locProvidedBy"
minOccurs="0" maxOccurs="1"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>

<xs:complexType name="locInfoType">
<xs:sequence>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>

<xs:complexType name="locMethod">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute ref="xml:lang" />
</xs:extension>
</xs:simpleContent>
</xs:complexType>

<xs:complexType name="locProvidedBy">
<xs:sequence>
<xs:any namespace="##other" processContents="skip"
minOccurs="1" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>

</xs:schema>

The 'geopriv10' schema imports, for the 'usage-rules' element, the
following policy schema. This schema has been broken out from the
basic geolocation object in order to allow for its reuse. The
semantics associated with these elements, described in Section 2.2.2,

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apply only to the use of these elements to define policy for
geolocation objects; any other use of 'usage-rules' must characterize
its own semantics for all 'usage-rules' subelements.

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
targetNamespace="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:tns="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified" attributeFormDefault="unqualified">


<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>

<xs:complexType name="locPolicyType">
<xs:sequence>
<xs:element name="retransmission-allowed" type="xs:boolean"
minOccurs="0" maxOccurs="1"/>
<xs:element name="retention-expiry" type="xs:dateTime"
minOccurs="0" maxOccurs="1"/>
<xs:element name="external-ruleset" type="xs:anyURI"
minOccurs="0" maxOccurs="1"/>
<xs:element name="note-well" type="tns:notewell"
minOccurs="0" maxOccurs="1"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>

<xs:complexType name="notewell">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute ref="xml:lang" />
</xs:extension>
</xs:simpleContent>
</xs:complexType>

</xs:schema>

The following schema is a trivial representation of civic location
that MAY be implemented by entities compliant with this
specification.

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
targetNamespace="urn:ietf:params:xml:ns:pidf:geopriv10:civicLoc"
xmlns:tns="urn:ietf:params:xml:ns:pidf:geopriv10:civicLoc"

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xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified" attributeFormDefault="unqualified">

<xs:complexType name="civicAddress">
<xs:sequence>
<xs:element name="country" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="A1" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="A2" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="A3" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="A4" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="A5" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="A6" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="PRD" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="POD" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="STS" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="HNO" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="HNS" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="LMK" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="LOC" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="FLR" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="NAM" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:element name="PC" type="xs:string"
minOccurs="0" maxOccurs="1"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>

</xs:schema>

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2.3. Example Location Objects

Note that these examples show PIDF documents without any MIME headers
or security applied to them (see Section 4 below).

The following XML instance document is an example of the use of a
simple GML 3.0 markup with a few of the policy directives specified
above within a PIDF document. The GPS coordinates given in the 'gml'
element are for San Francisco, CA.

<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gml="urn:opengis:specification:gml:schema-xsd:feature:v3.0"
entity="pres:[email protected]">
<tuple id="sg89ae">
<status>
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point gml:id="point1" srsName="epsg:4326">
<gml:coordinates>37:46:30N 122:25:10W</gml:coordinates>
</gml:Point>
</gml:location>
</gp:location-info>
<gp:usage-rules>
<gp:retransmission-allowed>no</gp:retransmission-allowed>
<gp:retention-expiry>2003-06-23T04:57:29Z</gp:retention-expiry>
</gp:usage-rules>
</gp:geopriv>
</status>
<timestamp>2003-06-22T20:57:29Z</timestamp>
</tuple>
</presence>

The following XML instance document is an example of the use of the
civicLoc object with a few of the policy directives specified above
within a PIDF document.

<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:cl=" urn:ietf:params:xml:ns:pidf:geopriv10:civicLoc"
entity="pres:[email protected]">
<tuple id="sg89ae">
<status>
<gp:geopriv>
<gp:location-info>

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<cl:civicAddress>
<cl:country>US</cl:country>
<cl:A1>New York</cl:A1>
<cl:A3>New York</cl:A3>
<cl:A6>Broadway</cl:A6>
<cl:HNO>123</cl:HNO>
<cl:LOC>Suite 75</cl:LOC>
<cl:PC>10027-0401</cl:PC>
</cl:civicAddress>
</gp:location-info>
<gp:usage-rules>
<gp:retransmission-allowed>yes</gp:retransmission-allowed>
<gp:retention-expiry>2003-06-23T04:57:29Z</gp:retention-expiry>
</gp:usage-rules>
</gp:geopriv>
</status>
<timestamp>2003-06-22T20:57:29Z</timestamp>
</tuple>
</presence>

3. Carrying PIDF in a Using Protocol

A PIDF document is an XML document; therefore, PIDF might be carried
in any protocol capable of carrying XML. A MIME type has also been
registered for PIDF: 'application/pidf+xml'. PIDF may therefore be
carried as a MIME body in protocols that use MIME (such as SMTP,
HTTP, or SIP) with an encapsulating set of MIME headers, including a
Content-Type of 'application/pidf+xml'.

Further specification of the behavior of using protocols (including
subscribing to or requesting presence information) is outside the
scope of this document.

4. Securing PIDF

There are a number of ways in which XML documents can be secured.
XML itself supports several ways of partially securing documents,
including element-level encryption and digital signature properties.

For the purposes of this document, only the securing of a PIDF
document as a whole, rather than element-by-element security, is
considered. None of the requirements [10] suggest that only part of
the information in a location object might need to be protected while
other parts are unprotected; virtually any such configuration would
introduce potentials for privacy leakage. Consequently, the use of
MIME-level security is appropriate.

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S/MIME [5] allows security properties (including confidentiality,
integrity, and authentication properties) to be applied to the
contents of a MIME body. Therefore, all PIDF implementations that
support the XML Schema extensions for location information described
in this document MUST support S/MIME; in particular, they MUST
support the CMS [6] EnvelopedData and SignedData content types, which
are used for encryption and digital signatures, respectively. It is
believed that this mechanism meets REQs 2.10, 13, 14.1, 14.2, 14.3,
and 14.4.

Additionally, all compliant applications MUST implement the AES
encryption algorithm for S/MIME, as specified in [8] (and per REQ
15.1). Of course, implementations MUST also support the baseline
encryption and digital signature algorithms described in the S/MIME
specification.

S/MIME generally entails the use of X.509 [9] certificates. In order
to encrypt a request for a particular destination end-to-end (i.e.,
to a Location Recipient), the Location Generator must possess
credentials (typically an X.509 certificate) that have been issued to
the Location Recipient. Implementations of this specification SHOULD
support X.509 certificates for S/MIME, and MUST support password-
based CMS encryption (see [6]). Any symmetric keying systems SHOULD
derive high-entropy content encoding keys (CEKs). When X.509
certificates are used to sign PIDF Location Objects, the
subjectAltName of the certificate SHOULD use the "pres" URI scheme.

One envisioned deployment model for S/MIME in PIDF documents is the
following. Location Servers hold X.509 certificates and share
secrets with Location Generators and Location Recipients. When a
Generator sends location information to a Server, it can be encrypted
with S/MIME (or any lower-layer encryption specific to the using
protocol). When a Server forwards location information to a
Recipient, location information can be encrypted with password-based
CMS encryption. This allows the use of encryption when the Location
Recipient does not possess its own X.509 certificate.

S/MIME was designed for end-to-end security between email peers that
communicate through multiple servers (i.e mail transfer agents) that
do not modify message bodies. There is, however, at least one
instance in which Location Servers modify Location Objects: when
Location Servers enforce policies on behalf of the Rule Maker. For
example, a Rule Maker may specify that Location Information should be
coarsened (made less specific) before it is transmitted to particular
recipients. If the Location Server were unable to modify a Location
Object, because it was encrypted, signed, or both, it would be unable
to accomplish this function. Consequently, when a Location Generator
wants to allow a Location Server to modify such messages, they MAY

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RFC 4119 GEOPRIV Location Object December 2005

encrypt such messages with a key that can be decrypted by the
Location Server (the digital signature, of course, can still be
created with keying material from the Location Generator's
certificate). After modifying the Location Object, the Location

Server can re-sign the Object with its own credentials (encrypting it
with any keys issued to the Location Recipient, if they are known to
the Server).

Note that policies for data collection and usage of location
information, in so far as they are carried within a location object,
are discussed in Section 2.2.2.

5. Security Considerations

The threats facing an Internet protocol that carries geolocation
information are detailed in [16]. The requirements that were
identified in that analysis of the threat model were incorporated
into [10], in particular within Section 7.4. This document aims to
be compliant with the security requirements derived from those two
undertakings, in so far as they apply to the location object itself
(as opposed to the using protocol).

Security of the location object defined in this document, including
normative requirements for implementations, is discussed in Section
4. This security focuses on end-to-end integrity and confidentiality
properties that are applied to a location object for its lifetime via
S/MIME.

Security requirements associated with using protocols (including
authentication of subscribers to geographical information, etc.) are
outside the scope of this document.

6. IANA Considerations

6.1. 'method' Tokens

This document requests that the IANA create a new registry for
'method' tokens associated with the PIDF-LO object. 'method' tokens
are text strings designating the manner in which location information
in a PIDF-LO object has been derived or discovered. Any party may
register new 'method' tokens with the IANA, as needed, on a first-
come-first-serve basis.

This section pre-registers 7 new 'method' tokens associated with the
'method' element described above in Section 2.2.3:

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GPS: Global Positioning System
A-GPS: GPS with assistance
Manual: entered manually by an operator or user, e.g., based on
subscriber billing or service location information
DHCP: provided by DHCP (used for wireline access networks, see
802.11 below)
Triangulation: triangulated from time-of-arrival, signal strength,
or similar measurements
Cell: location of the cellular radio antenna
802.11: 802.11 access point (used for DHCP-based provisioning over
wireless access networks)

6.2. 'provided-by' Elements

This document requests that IANA create a new registry of XML
namespaces for 'provided-by' elements for use with PIDF-LO objects.
Registrations of new XML namespaces that are used for 'provided-by'
MUST be reviewed by an Expert Reviewer designated by the IESG.

This document pre-registers a single XML namespace for 'provided-by',
which is given in Appendix A.

6.3. URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:pidf:geopriv10

This section registers a new XML namespace, as per the guidelines in
[4].

URI: The URI for this namespace is
urn:ietf:params:xml:ns:pidf:geopriv10.
Registrant Contact: IETF, GEOPRIV working group,
([email protected]), Jon Peterson ([email protected]).
XML:

BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>GEOPRIV PIDF Extensions</title>
</head>
<body>
<h1>PIDF Extensions of Geographical Information and Privacy</h1>
<h2>urn:ietf:params:xml:ns:pidf:geopriv10</h2>
<p>See <a href="ftp://ftp.rfc-editor.org/in-notes/rfc4119.txt">

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RFC 4119 GEOPRIV Location Object December 2005

RFC4119</a>.</p>
</body>
</html>
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.

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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, ([email protected]), Nadine Abbott
([email protected]).
XML:

BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>NENA dataProvider Schema for PIDF-LO</title>
</head>
<body>
<h1>NENA dataProvider Schema for 'provided-by' in PIDF-LO</h1>
<h2>urn:ietf:params:xml:ns:pidf:geopriv10:dataProvider</h2>
<p>See <a href="ftp://ftp.rfc-editor.org/in-notes/rfc4119.txt">
RFC4119</a>.</p>
</body>
</html>
END

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A.1. dataProvider XML Schema

<?xml version="1.0" encoding="UTF-8"?>

<xs:schema
targetNamespace="urn:ietf:params:xml:ns:pidf:geopriv10:dataProvider"
xmlns:tns="urn:ietf:params:xml:ns:pidf:geopriv10:dataProvider"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:element name="nena" type="tns:DataProviderIDType"/>
<xs:complexType name="DataProviderIDType">
<xs:annotation>
<xs:documentation>NENA registered Company ID
for Service Provider supplying location information</xs:documentation>
</xs:annotation>
<xs:all>
<xs:element name="DataProviderID"
type="tns:NENACompanyIDType" minOccurs="0"/>
<xs:element name="TelURI"
type="tns:TelURI_24x7Type" minOccurs="0"/>
<xs:element name="URL" type="xs:anyURI"
minOccurs="0"/>
</xs:all>
</xs:complexType>
<xs:simpleType name="NENACompanyIDType">
<xs:annotation>
<xs:documentation>NENA registered Company
ID.</xs:documentation>
</xs:annotation>
<xs:restriction base="xs:string">
<xs:maxLength value="5"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="TelURI_24x7Type">
<xs:annotation>
<xs:documentation>24x7 Tel URI for the
caller's [location data] service provider. To be used for contacting
service provider to resolve problems with location data. Possible
values TN number, enumerated values when not
available.</xs:documentation>
</xs:annotation>
<xs:union memberTypes="xs:anyURI">
<xs:simpleType>

<xs:restriction base="xs:string">
<xs:maxLength value="10"/>
<xs:enumeration value="NOT FOUND"/>

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RFC 4119 GEOPRIV Location Object December 2005

<xs:enumeration value="UNAVAILABLE"/>
</xs:restriction>
</xs:simpleType>
</xs:union>
</xs:simpleType>
</xs:schema>

Normative References

[1] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", BCP 14, 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 (CMS)", RFC 3852,
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.

[9] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Certificate Handling", RFC 3850, July 2004.

Informative References

[10] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004.

[11] Morris, J., Mulligan, D., and J. Cuellar, "Core Privacy
Protections for Geopriv Location Object", Work in Progress,
June 2003.

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RFC 4119 GEOPRIV Location Object December 2005

[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", Work in Progress, February 20003.

[14] 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.

[15] OpenGIS, "Open Geography Markup Language (GML) Implementation
Specification", OGC 02-023r4, January 2003,
<http://www.opengeospatial.org/specs/?page=specs>.

[16] Danley, M., Mulligan, D., Morris, J., and J. Peterson, "Threat
Analysis of the Geopriv Protocol", RFC 3694, February 2004.

Author's Address

Jon Peterson
NeuStar, Inc.
1800 Sutter St
Suite 570
Concord, CA 94520
US

Phone: +1 925/363-8720
EMail: [email protected]
URI: http://www.neustar.biz/

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RFC 4119 GEOPRIV Location Object December 2005

Full Copyright Statement

Copyright (C) The Internet Society (2005).

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.

This document and the information contained herein are provided on an
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OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
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Acknowledgement

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Internet Society.

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