Internet Engineering Task Force (IETF) J. Winterbottom

Internet Engineering Task Force (IETF) J. Winterbottom
Request for Comments: 6155 M. Thomson
Category: Standards Track Andrew Corporation
ISSN: 2070-1721 H. Tschofenig
Nokia Siemens Networks
R. Barnes
BBN Technologies
March 2011

Use of Device Identity in HTTP-Enabled Location Delivery (HELD)

Abstract

When a Location Information Server receives a request for location
information (using the locationRequest message), described in the
base HTTP-Enabled Location Delivery (HELD) specification, it uses the
source IP address of the arriving message as a pointer to the
location determination process. This is sufficient in environments
where the location of a Device can be determined based on its IP
address.

Two additional use cases are addressed by this document. In the
first, location configuration requires additional or alternative
identifiers from the source IP address provided in the request. In
the second, an entity other than the Device requests the location of
the Device.

This document extends the HELD protocol to allow the location request
message to carry Device identifiers. Privacy and security
considerations describe the conditions where requests containing
identifiers are permitted.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6155.

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Copyright Notice

Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Applications . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2. Device Identity . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Identifier Suitability . . . . . . . . . . . . . . . . . . 7
2.1.1. Subjective Network Views . . . . . . . . . . . . . . . 7
2.1.2. Transient Identifiers . . . . . . . . . . . . . . . . 9
2.1.3. Network Interfaces and Devices . . . . . . . . . . . . 9
2.2. Identifier Format and Protocol Details . . . . . . . . . . 9
3. Identifiers . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. IP Address . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2. MAC Address . . . . . . . . . . . . . . . . . . . . . . . 11
3.3. Port Numbers . . . . . . . . . . . . . . . . . . . . . . . 12
3.4. Network Access Identifier . . . . . . . . . . . . . . . . 12
3.4.1. Using NAI for Location Configuration . . . . . . . . . 13
3.5. URI . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.6. Fully Qualified Domain Name . . . . . . . . . . . . . . . 14
3.7. Cellular Telephony Identifiers . . . . . . . . . . . . . . 14
3.8. DHCP Unique Identifier . . . . . . . . . . . . . . . . . . 15
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 15
4.1. Targets Requesting Their Own Location . . . . . . . . . . 16
4.2. Third-Party Requests . . . . . . . . . . . . . . . . . . . 17
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
5.1. Identifier Suitability . . . . . . . . . . . . . . . . . . 18
5.2. Targets Requesting Their Own Location . . . . . . . . . . 18
5.3. Third-Party Requests . . . . . . . . . . . . . . . . . . . 19
6. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
7.1. URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:geopriv:held:id . . . . . . . . . . 21
7.2. XML Schema Registration . . . . . . . . . . . . . . . . . 22
7.3. Registration of HELD 'badIdentifier' Error Code . . . . . 22
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.1. Normative References . . . . . . . . . . . . . . . . . . . 23
9.2. Informative References . . . . . . . . . . . . . . . . . . 25

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1. Introduction

Protocols for requesting and providing location information require a
way for the requestor to specify the location that should be
returned. In a Location Configuration Protocol (LCP), the location
being requested is the requestor's location. This fact can make the
problem of identifying the Device simple, since IP datagrams that
carry the request already carry an identifier for the Device --
namely, the source IP address of an incoming request. Existing LCPs,
such as HTTP-Enabled Location Delivery (HELD) [RFC5985] and DHCP
([RFC3825], [RFC4776]) rely on the source IP address or other
information present in protocol datagrams to identify a Device.

Aside from the datagrams that form a request, a Location Information
Server (LIS) does not necessarily have access to information that
could further identify the Device. In some circumstances, as shown
in [RFC5687], additional identification information can be included
in a request to identify a Device.

This document extends the HELD protocol to support the inclusion of
additional identifiers for the Device in HELD location requests. An
XML schema is defined that provides a structure for including these
identifiers in HELD requests.

An important characteristic of this addition is that the HELD
protocol with identity extensions implemented is not considered an
LCP. The scope of an LCP is limited to the interaction between a
Device and a LIS, and LCPs can guarantee the identity of Devices
without additional authorization checks. A LIS identifies the Device
making the LCP request using the source addressing on the request
packets, using return routability to ensure that these identifiers
are not spoofed.

HELD with identity extensions allows a requestor to explicitly
provide identification details in the body of a location request.
This means that location requests can be made in cases where
additional Device identity checks are necessary, and in cases where
the requestor is not the Device itself. Third-party Location
Recipients (LRs) are able to make requests that include identifiers
to retrieve location information about a particular Device.

The usage of identifiers in HELD introduces a new set of privacy
concerns. In an LCP, the requestor can be implicitly authorized to
access the requested location information, because it is their own
location. In contrast, a third-party LR must be explicitly
authorized when requesting the location of a Device. Establishing
appropriate authorization and other related privacy concerns are
discussed in Section 4.

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1.1. Applications

This document defines a means to explicitly include Device identity
information in the body of a HELD location request. This identity
information is used to identify the Device that is the subject (or
Target) of the location request. If Device identity is present, the
identity of the requestor in the form of the source IP address is not
used to identify the subject of the request.

Device identifiers in HELD can be used for two purposes:

Location configuration: A Device can use these parameters to
identify itself to a LIS. Identification information other than
an IP address might be needed to determine the location of a
Device.

A LIS can authorize location configuration requests using a policy
that allows Devices to acquire their own location (see
Section 4.1). If an unauthorized third party falsifies addressing
on request packets to match the provided Device identity, the
request might be erroneously authorized under this policy.
Requests containing Device identity MUST NOT be authorized using
this policy unless specific measures are taken to prevent this
type of attack.

This document describes a mechanism that provides assurances that
the requestor and included Device identity are the same for the
Network Access Identifier (NAI) in a WiMAX network. The LIS MUST
treat requests containing other identifiers as third-party
requests, unless it is able to ensure that the provided Device
identity is uniquely attributable to the requestor.

Third-party requests: A third-party Location Recipient can be
granted authorization to make requests for a given Device. In
particular, network services can be permitted to retrieve location
for a Device that is unable to acquire location information for
itself (see Section 6.3 of [EMERGENCY-CALLING]). This allows use
of location-dependent applications -- particularly essential
services like emergency calling -- where Devices do not support a
location configuration protocol or they are unable to successfully
retrieve location information.

This document does not describe how a third party acquires an
identifier for a Device, nor how that third party is authorized by
a LIS. It is critical that these issues are resolved before
permitting a third-party request. A pre-arranged contract between
the third party, a Rule Maker, and the LIS operator is necessary
to use Device identifiers in this fashion. This contract must

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include how the request is authenticated and the set of
identifiers (and types of identifiers) that the third party is
authorized to use in requests.

Automated mechanisms to ensure that privacy constraints are
respected are possible. For instance, a policy rules document
could be used to express the agreed policy. Formal policy
documents, such as the common policy [RFC4745], can be applied in
an automated fashion by a LIS.

1.2. Terminology

This document uses the term Location Information Server (LIS) and
Location Configuration Protocol (LCP) as described in [RFC5687] and
[GEOPRIV-ARCH].

The term Device is used specifically as the subject of an LCP,
consistent with [RFC5985]. This document also uses the term Target
to refer to any entity that might be a subject of the same location
information. Target is used in a more general sense, including the
Device, but also any nearby entity, such as the user of a Device.

A Target has a stake in setting authorization policy on the use of
location information. A Rule Maker is the term used for the role
that makes policy decisions about authorization, determining what
entities are permitted to receive location and how that information
is provided.

Device, Target, and Rule Maker are defined in [GEOPRIV-ARCH].

The term "requestor" is used in this document to refer to the entity
making a HELD request.

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].

2. Device Identity

Identifiers are used as the starting point in location determination.
Identifiers might be associated with a different Device over time,
but their purpose is to identify the Device, not to describe its
environment or network attachment.

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2.1. Identifier Suitability

Use of any identifier MUST only be allowed if it identifies a single
Device at the time that location is determined. The LIS is
responsible for ensuring that location information is correct for the
Device, which includes ensuring that the identifier is uniquely
attributable to the Device.

Some identifiers can be either temporary or could potentially
identify multiple Devices. Identifiers that are transient or
ambiguous could be exploited by an attacker to either gain
information about another Device or to coerce the LIS into producing
misleading information.

The identifiers described in this document MUST only be used where
that identifier is used as the basis for location determination.
Considerations relating to the use of identifiers for a Device
requesting its own location are discussed in Section 5 of [RFC5687];
this section discusses use of identifiers for authorized third-party
requests.

It is tempting for a LIS implementation to allow alternative
identifiers for convenience or some other perceived benefit. The
LIS is responsible for ensuring that the identifier used in the
request does not refer to a Device other than the one for which it
determines location.

Some identifiers are always uniquely attributable to a single Device.
However, other identifiers can have a different meaning to different
entities on a network. This is especially true for IP addresses
[RFC2101], but this can be true for other identifiers to varying
degrees. Non-uniqueness arises from both topology (all network
entities have a subjective view of the network) and time (the network
changes over time).

2.1.1. Subjective Network Views

Subjective views of the network mean that the identifier a requestor
uses to refer to one physical entity could actually apply to a
different physical entity when used in a different network context.
Unless an authorized third-party requestor and LIS operate in the
same network context, each could have a different subjective view of
the meaning of the identifier.

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Where subjective views differ, the third party receives information
that is correct only within the network context of the LIS. The
location information provided by the LIS is probably misleading: the
requestor believes that the information relates to a different entity
than it was generated for.

Authorization policy can be affected by a subjective network view if
it is applied based on an identifier or if its application depends on
identifiers. The subjective view presented to the LIS and Rule Maker
need to agree for the two entities to understand policy on the same
terms. For instance, it is possible that the LIS could apply the
incorrect authorization policy if it selects the policy using a
subjective identifier. Alternatively, it may use the correct policy
but apply it incorrectly if subjective identifiers are used.

In IP networks, network address translation (NAT) and other forms
of address modification create network contexts. Entities on
either side of the point where modification occurs have a
different view of the network. Private use addresses [RFC1918]
are the most easily recognizable identifiers that have limited
scope.

A LIS can be configured to recognize scenarios where the subjective
view of a requestor or Rule Maker might not coincide with the view of
the LIS. The LIS can either provide location information that takes
the view of the requestor into account, or it can reject the request.

For instance, a LIS might operate within a network that uses a
private address space, with NAT between that network and other
networks. A third-party request that originates in an external
network with an IP address from the private address space might
not be valid -- it could be identifying an entity within another
address space. The LIS can be configured to reject such requests,
unless it knows by other means that the request is valid.

In the same example, the requestor might include an address from
the external space in an attempt to identify a host within the
network. The LIS could use knowledge about how the external
address is mapped to a private address, if that mapping is fixed,
to determine an appropriate response.

The residential gateway scenario in Section 3.1 of [RFC5687] is a
particular example of where a subjective view is permitted. The LIS
knowingly provides Devices on the remote side of the residential
gateway with location information. The LIS provides location
information with appropriate uncertainty to allow for the fact that
the residential gateway serves a small geographical area.

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2.1.2. Transient Identifiers

Some identifiers are temporary and can, over the course of time, be
assigned to different physical entities. An identifier that is
reassigned between the time that a request is formulated by a
requestor and when the request is received by the LIS causes the LIS
to locate a different entity than the requestor intended. The
response from the LIS might be accurate, but the request incorrectly
associates this information with the wrong subject.

A LIS should be configured with information about any potentially
temporary identifiers. It can use this information to identify when
changes have occurred. A LIS must not provide location information
if the identifier it uses might refer to a different Device. If an
identifier might have been reassigned recently, or it is likely to be
reassigned, it is not suitable as an identifier.

It's possible that some degree of uncertainty could persist where
identifiers are reassigned frequently; the extent to which errors
arising from using transient identifiers are tolerated is a matter
for local policy.

2.1.3. Network Interfaces and Devices

Several of the identifiers in this document are used to identify a
network interface. A Device can have multiple network interfaces.
Uniquely identifying any network interface is assumed to be
sufficient to identify the Device. When a network interface is
identified, the goal is to identify the Device that is immediately
attached to the network interface.

Most network interfaces remain physically attached to a particular
Device, though a network interface might be physically separable from
the Device. By identifying a network interface, any Device that is
intended to be identified could change.

2.2. Identifier Format and Protocol Details

XML elements are used to express the Device identity. The "device"
element is used as a general container for identity information.
This document defines a basic set of identifiers. An example HELD
request, shown in Figure 1, includes an IP version 4 address.

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<locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held"
responseTime="8">
<locationType exact="true">geodetic</locationType>
<device xmlns="urn:ietf:params:xml:ns:geopriv:held:id">
<ip v="4">192.0.2.5</ip>
</device>
</locationRequest>

Figure 1: HELD Request with Device Identity

A LIS that supports this specification echoes the "device" element in
a successful HELD response, including the identifiers that were used
as the basis for location determination. Absence of this indication
means that the location information was generated using the source IP
address in the request.

A "badIdentifier" HELD error code indicates that the requestor is not
authorized to use that identifier or that the request contains an
identifier that is badly formatted or not supported by the LIS. This
code is registered in Section 7.3.

If the LIS requires an identifier that is not provided in the
request, the desired identifiers MAY be identified in the HELD error
response, using the "requiredIdentifiers" element. This element
contains a list of XML qualified names [W3C.REC-xml-names11-20060816]
that identify the identifier elements required by the LIS. Namespace
prefix bindings for the qualified names are taken from document
context. Figure 2 shows an example error indicating that the
requestor needs to include a media access control (MAC) address
(Section 3.2) and IP address (Section 3.1) if the request is to
succeed.

<error xmlns="urn:ietf:params:xml:ns:geopriv:held"
code="badIdentifier">
<message xml:lang="en">MAC address required</message>
<requiredIdentifiers
xmlns="urn:ietf:params:xml:ns:geopriv:held:id">
mac ip
</requiredIdentifiers>
</error>

Figure 2: HELD Error Requesting Device Identifiers

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3. Identifiers

A limited selection of identifiers are included in this document.
The basic Device identity schema allows for the inclusion of elements
from any namespace; therefore, additional elements can be defined
using different XML namespaces.

3.1. IP Address

The "ip" element can express a Device identity as an IP address
([RFC0791], [RFC4291]). The "v" attribute identifies the IP version
with a single hexadecimal digit. The element uses the textual format
specific to the indicated IP version. The textual format for IP
version 4 and version 6 addresses MUST conform to the grammar defined
in [RFC3986] ("IPv4address" and "IPv6address", respectively). IP
version 6 addresses SHOULD conform to the formatting conventions in
[RFC5952].

<device xmlns="urn:ietf:params:xml:ns:geopriv:held:id">
<ip v="6">2001:db8::1:ea7:fee1:d1e</ip>
</device>

In situations where location configuration does not require
additional identifiers, using an IP address as an identifier enables
authorized third-party requests.

3.2. MAC Address

The MAC address used by network interfaces attached to the IEEE LAN
[IEEE802]. A MAC address is a unique sequence that is either
assigned at the time of manufacture of the interface, or assigned by
a local administrator. A MAC address is an appropriate identifier
for the Device that uses the network interface as long as the two
remain together (see Section 2.1.3).

A MAC address can be represented as a MAC-48, EUI-48, or EUI-64
address ([IEEE802], or an extended unique identifier [EUI64]) using
the hexadecimal representation defined in [IEEE802].

<device xmlns="urn:ietf:params:xml:ns:geopriv:held:id">
<mac>A0-12-34-56-78-90</mac>
</device>

A locally assigned MAC address is not guaranteed to be unique outside
the administrative domain where it is assigned. Locally assigned MAC
addresses can only be used within this domain.

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3.3. Port Numbers

A host might only be known by a flow of packets that it is sending or
receiving. On its own, a port number is insufficient to uniquely
identify a single host. In combination with an IP address, a port
number can be used to uniquely identify a Device in some
circumstances.

Use of a particular port number can be transient; often significantly
more than use of any given IP address. However, widespread use of
network address translation (NAT) means that some Devices cannot be
uniquely identified by IP address alone. An individual Device might
be identified by a flow of packets that it generates. Providing that
a LIS has sufficient knowledge of the mappings used by the NAT, an
individual target on the remote side of the NAT might be able to be
identified uniquely.

Port numbers are defined for UDP [RFC0768], TCP [RFC0793], SCTP
[RFC4960], and DCCP [RFC4340].

<device xmlns="urn:ietf:params:xml:ns:geopriv:held:id">
<ip v="4">192.0.2.75</ip>
<udpport>51393</udpport>
</device>

Use of port numbers is especially reliant on the value remaining
consistent over time.

3.4. Network Access Identifier

A Network Access Identifier (NAI) [RFC4282] is an identifier used in
network authentication in a range of networks. The identifier
establishes a user identity within a particular domain. Often,
network services use an NAI in relation to location records, tying
network access to user authentication and authorization.

<device xmlns="urn:ietf:params:xml:ns:geopriv:held:id">
<nai>[email protected]</nai>
</device>

The formal grammar for NAI [RFC4282] permits sequences of octets that
are not valid UTF-8 [RFC3629] sequences. These sequences cannot be
expressed using XML. Therefore, this expression of NAI permits
escaping. Sequences of octets that do not represent a valid UTF-8
encoding can be expressed using a backslash ('\') followed by two
case-insensitive hexadecimal digits representing the value of a
single octet.

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The canonical representation of an NAI is the sequence of octets that
is produced from the concatenation of UTF-8 encoded sequences of
unescaped characters and octets derived from escaped components. The
resulting sequence of octets MUST conform to the constraints in
[RFC4282].

For example, the NAI "f<U+FC>\<0xFF>@bar.com" that includes the UTF-8
encoded u-umlaut character (U+FC) and an invalid UTF-8 octet (0xFF)
might be represented as "f\c3\bc\5c\[email protected]", though the u-umlaut
character might be included directly.

3.4.1. Using NAI for Location Configuration

An NAI in WiMAX is uniquely attributable to a single Device at any
one time. An NAI either identifies a Device or a service
subscription, neither of which can have multiple active sessions.

In a WiMAX network, an IP address is not sufficient information for a
LIS to locate a Device. The following procedure relies on an NAI to
identify the Device. This procedure and the messages and parameters
is relies upon are defined in [WiMAX-T33-110-R015v01-B].

Location requests in a WiMAX network always require the inclusion of
an NAI. However, if a LIS receives a request that does not come from
an authenticated and authorized third-party requestor, it can treat
this request as a location configuration request.

After receiving a location request that includes an NAI, the LIS
sends a "Location-Requestor-Authentication-Protocol" access request
message to the Authentication, Authorization, and Accounting (AAA)
server. This request includes an "MS-Identity-Assertion" parameter
containing the NAI.

The AAA server consults network policy, and if the request is
permitted, the response includes the IP address that is currently
assigned to the Device. If this IP address matches the source IP
address of the HELD location request, the location request can be
authorized under the LCP policy (see Section 4.1). Otherwise, the
request must be treated as a third-party request.

This relies on the same protections against IP address spoofing that
are required by [RFC5985]. In addition, the request made of the AAA
uses either Diameter [RFC3588] or RADIUS [RFC2865], and therefore
relies on the protections provided by those protocols. In order to
rely on the access request, the AAA server MUST be authenticated to
be a trusted entity for the purpose of providing a link between the

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NAI and IP address. The AAA protocol MUST also provide protection
from modification and replay attacks to ensure that data cannot be
altered by an attacker.

3.5. URI

A Device can be identified by a URI [RFC3986]. Any URI can be used
providing that the requestor and LIS have a common understanding of
the semantics implied by use of the URI.

<device xmlns="urn:ietf:params:xml:ns:geopriv:held:id">
<uri>sip:[email protected];gr=kjh29x97us97d</uri>
</device>

Particular care needs to be taken in ensuring that a particular URI
only refers to a single Device. In many cases, a URI can resolve to
multiple destinations. For example, a SIP address of record URI can
correspond to a service subscription rather than a single Device.

A "tel:" URI [RFC3966] can be used to identify a Device by telephone
number:

<device xmlns="urn:ietf:params:xml:ns:geopriv:held:id">
<uri>tel:800-555-1111;extension=1234;phone-context=+1</uri>
</device>

3.6. Fully Qualified Domain Name

A fully qualified domain name can be used as the basis for
identification using the "fqdn" element.

<device xmlns="urn:ietf:params:xml:ns:geopriv:held:id">
<fqdn>host.example.net</fqdn>
</device>

This domain name slot, which is aware of Internationalized Domain
Names for Applications (IDNA) [RFC5890], is formed from any sequence
of valid U-labels or NR-LDH-labels.

A domain name does not always correspond to a single IP address or
host. If this is the case, a domain name is not a suitable
identifier.

3.7. Cellular Telephony Identifiers

A range of different forms of mobile station identifiers are used for
different cellular telephony systems. Elements are defined for these
identifiers. The following identifiers are defined:

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msisdn: The Mobile Station International Subscriber Dial Number
(MSISDN) [E.213] is an E.164 number [E.164] between 6 and 15
digits long.

imsi: The International Mobile Subscriber Identity (IMSI)
[TS.3GPP.23.003] is an identifier associated with all GSM (Global
System for Mobile Communications) and UMTS (Universal Mobile
Telecommunications System) mobile subscribers between 6 and 15
digits in length.

imei: The International Mobile Equipment Identifier (IMEI)
[TS.3GPP.23.003] is a unique device serial number up to 15 digits
long.

min: The Mobile Identification Number (MIN) [TIA.EIA.IS-2000-6] is a
10-digit unique number assigned to CDMA handsets.

mdn: The Mobile Directory Number (MDN) is an E.164 number [E.164],
with usage similar to MSISDN.

Each identifier contains a string of decimal digits with a length as
specified.

<device xmlns="urn:ietf:params:xml:ns:geopriv:held:id">
<msisdn>11235550123</msisdn>
</device>

3.8. DHCP Unique Identifier

The Dynamic Host Configuration Protocol (DHCP) uses a binary
identifier for its clients. The DHCP Unique Identifier (DUID) is
expressed in Option 61 of DHCPv4 (see [RFC4361]) or Option 1 of
DHCPv6 and follows the format defined in Section 9 of [RFC3315]. The
"duid" element includes the binary value of the DUID expressed in
hexadecimal.

<device xmlns="urn:ietf:params:xml:ns:geopriv:held:id">
<duid>1234567890AaBbCcDdEeFf</duid>
</device>

4. Privacy Considerations

Location configuration protocols can make use of an authorization
model known as "LCP policy", which permits only Targets to be the
recipients of their own locations. In effect, an LCP server (that
is, the LIS) follows a single-rule policy that states that the Target
is the only authorized Location Recipient.

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The security and privacy considerations of the base HELD protocol
[RFC5985] are applicable. However, the considerations relating to
return routability do not apply to third-party requests. Return
routability may also not apply to requests from Targets for their own
location, depending on the anti-spoofing mechanisms employed for the
identifier.

4.1. Targets Requesting Their Own Location

When a Target uses identity extensions to obtain its own location,
HELD can no longer be considered an LCP. The authorization policy
that the LIS uses to respond to these requests must be provisioned by
one or more Rule Makers.

In the case that the LIS exclusively provides Targets with their own
locations, the LIS can still be said to be following the "LCP
policy". The "LCP policy" concept and further security and privacy
considerations can be found in [GEOPRIV-ARCH].

The spoofing protections provided when using HELD with identity
extensions to provide Targets with their own locations differ from
the protections inherent in an LCP. For an LCP, return routability
is considered sufficient protection against spoofing. For a similar
policy to be used, specific measures MUST be defined to protect
against spoofing of the alternative identifier. This document
defines this for an NAI when used in WiMAX networks (see
Section 3.4.1), but for no other identifier.

A Rule Maker might require an assurance that the identifier is owned
by the requestor. Any multi-stage verification process that includes
a return routability test cannot provide any stronger assurance than
return routability alone; therefore, policy might require the use of
additional, independent methods of verification.

Care is required where a direct one-to-one relationship between
requestor and Device identity does not exist. If identifiers are not
uniquely attributable to a single Device, the use of HELD identity
extensions to provide Targets with their own locations could be
exploited by an attacker.

It might be possible in some networks to establish multiple
concurrent sessions using the same credentials. For instance,
Devices with different MAC addresses might be granted concurrent
access to a network using the same NAI. It is not appropriate to
provide Targets with their own locations based on the NAI in this
case. Neither is it appropriate to authenticate a Device using
NAI and allow that Device to provide an unauthenticated MAC
address as a Device identifier, even if the MAC address is

Winterbottom, et al. Standards Track [Page 16]

RFC 6155 HELD Identity March 2011

registered to the NAI. The MAC address potentially identifies a
different Device than the one that is making the request. The
correct way of gaining authorization is to establish a policy that
permits this particular request as a third-party request.

Section 3.4.1 discusses the implications of using an NAI as an
identifier for location requests made of a LIS serving a WiMAX
network. Additional security considerations are discussed in
[WiMAX-T33-110-R015v01-B].

4.2. Third-Party Requests

The "LCP policy" does not allow requests made by third parties. If a
LIS permits requests from third parties using Device identity, it
assumes the rule of a Location Server (LS). As a Location Server,
the LIS MUST explicitly authorize requests according to the policies
that are provided by Rule Makers, including the Target. The LIS MUST
also authenticate requestors according to any agreed-upon
authorization policy.

An organization that provides a LIS that allows third-party requests
must provide a means for a Rule Maker to specify authorization
policies as part of the LIS implementation (e.g, in the form of
access control lists). Authorization must be established before
allowing third-party requests for the location of any Target. Until
an authorization policy is established, the LIS MUST reject requests
by third parties (that is, the default policy is "deny all").

When the LIS is operated by an access network, the relationship
between the Target and the LIS can be transient. As the Target is a
potential Rule Maker, this presents a problem. However, the process
of establishing network access usually results in a form of agreement
between the Target and the network provider. This process offers a
natural vehicle for establishing location privacy policies.
Establishing authorization policy might be a manual process, an
explicit part of the terms of service for the network, or an
automated system that accepts formal authorization policies (see
[RFC4745] and [RFC4825]). This document does not mandate any
particular mechanism for establishing an authorization policy.

5. Security Considerations

The security considerations in [RFC5985] describe the use of
Transport Layer Security (TLS) [RFC5246] for server authentication,
confidentiality, and protection from modification. These protections
apply to both Target requests for their own locations and requests
made by third parties.

Winterbottom, et al. Standards Track [Page 17]

RFC 6155 HELD Identity March 2011

All HELD requests containing identity MUST be authenticated by the
LIS. How authentication is accomplished and what assurances are
desired is a matter for policy.

The base HELD protocol uses return reachability of an IP address
implied by the requestor being able to successfully complete a TCP
handshake. It is RECOMMENDED that any means of authentication
provide at least this degree of assurance. For requests that include
Device identity, the requestor MUST support HTTP digest
authentication [RFC2617]. Unauthenticated location requests
containing Device identity can be challenged with an HTTP 401
(Unauthorized) response or rejected with an HTTP 403 (Forbidden)
response.

HELD [RFC5985] does not mandate that Devices implement
authentication. A LIS SHOULD NOT send a HTTP 401 response if the
Device does not include Device identity.

5.1. Identifier Suitability

Transient and ambiguous identifiers can be exploited by malicious
requests and are not suitable as a basis for identifying a Device.
Section 2.1 provides further discussion on this subject.

Identifier transience can lead to incorrect location information
being provided. An attacker could exploit the use of transient
identifiers. In this attack, the attacker either knows of a
re-allocation of that identifier or is able to force the identifier
to be re-allocated during the processing of the request.

An attacker could use this to acquire location information for
another Device or to coerce the LIS to lie on its behalf if this
re-allocation occurs between the time where authorization is granted
and location information is granted.

Ambiguous identifiers present a similar problem. An attacker could
legitimately gain authorization to use a particular identifier.
Since an ambiguous identifier potentially refers to multiple Devices,
if authorization is granted for one of those Devices, an attacker
potentially gains access to location information for all of those
Devices.

5.2. Targets Requesting Their Own Location

Requests made by a Device for its own location are covered by the
same set of protections offered by HELD. These requests might be
authorized under a policy similar to the "LCP policy" that permits a
Target access to location information about itself.

Winterbottom, et al. Standards Track [Page 18]

RFC 6155 HELD Identity March 2011

Identity information provided by the Device is private data that
might be sensitive. The Device provides this information in the
expectation that it assists the LIS in providing the Device a
service. The LIS MUST NOT use identity information for any other
purpose other than serving the request that includes that
information.

5.3. Third-Party Requests

Requests from third parties have the same requirements for server
authentication, confidentiality, and protection from modification as
Target requests for their own locations. However, because the third
party needs to be authorized, the requestor MUST be authenticated by
the LIS. In addition, third-party requests MUST be explicitly
authorized by a policy that is established by a Rule Maker.

More detail on the privacy implications of third-party requests are
covered in Section 4.

6. XML Schema

<xs:schema
targetNamespace="urn:ietf:params:xml:ns:geopriv:held:id"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:id="urn:ietf:params:xml:ns:geopriv:held:id"
elementFormDefault="qualified"
attributeFormDefault="unqualified">

<xs:annotation>
<xs:appinfo
source="urn:ietf:params:xml:schema:geopriv:held:id">
HELD Device Identity
</xs:appinfo>
<xs:documentation
source="http://www.rfc-editor.org/rfc/rfc6155.txt">
This document defines Device identity elements for HELD.
</xs:documentation>
</xs:annotation>

<xs:element name="device" type="id:deviceIdentity"/>
<xs:complexType name="deviceIdentity">
<xs:sequence>
<xs:any namespace="##any" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>

<xs:element name="requiredIdentifiers" type="id:qnameList"/>

Winterbottom, et al. Standards Track [Page 19]

RFC 6155 HELD Identity March 2011

<xs:simpleType name="qnameList">
<xs:list itemType="xs:QName"/>
</xs:simpleType>

<xs:element name="ip" type="id:ipAddress"/>
<xs:complexType name="ipAddress">
<xs:simpleContent>
<xs:extension base="xs:token">
<xs:attribute name="v" use="required">
<xs:simpleType>
<xs:restriction base="xs:token">
<xs:pattern value="[\da-fA-F]"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:extension>
</xs:simpleContent>
</xs:complexType>

<xs:element name="mac" type="id:macAddress"/>
<xs:simpleType name="macAddress">
<xs:restriction base="xs:token">
<xs:pattern
value="[\da-fA-F]{2}(-[\da-fA-F]{2}){5}((-[\da-fA-F]{2}){2})?"/>
</xs:restriction>
</xs:simpleType>

<xs:element name="udpport" type="id:portNumber"/>
<xs:element name="tcpport" type="id:portNumber"/>
<xs:element name="sctpport" type="id:portNumber"/>
<xs:element name="dccpport" type="id:portNumber"/>
<xs:simpleType name="portNumber">
<xs:restriction base="xs:nonNegativeInteger">
<xs:maxInclusive value="65535"/>
</xs:restriction>
</xs:simpleType>

<xs:element name="nai" type="id:naiType"/>
<xs:simpleType name="naiType">
<xs:restriction base="xs:token">
<xs:pattern
value="([^\\]|\\[\dA-Fa-f]{2})*
(@([A-Za-z\d]([A-Za-z\d\-]*[A-Za-z\d])*\.)+
[A-Za-z\d]([A-Za-z\d\-]*[A-Za-z\d])*)?"/>
</xs:restriction>
</xs:simpleType>

<xs:element name="uri" type="xs:anyURI"/>

Winterbottom, et al. Standards Track [Page 20]

RFC 6155 HELD Identity March 2011

<xs:element name="fqdn" type="xs:token"/>

<xs:element name="duid" type="xs:hexBinary"/>

<xs:element name="msisdn" type="id:e164"/>
<xs:element name="imsi" type="id:e164"/>
<xs:element name="imei" type="id:digit15"/>
<xs:element name="min" type="id:digit10"/>
<xs:element name="mdn" type="id:e164"/>
<xs:simpleType name="digits">
<xs:restriction base="xs:token">
<xs:pattern value="[\d]+"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="e164">
<xs:restriction base="id:digit15">
<xs:minLength value="6"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="digit15">
<xs:restriction base="id:digits">
<xs:maxLength value="15"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="digit10">
<xs:restriction base="id:digits">
<xs:length value="10"/>
</xs:restriction>
</xs:simpleType>

</xs:schema>

7. IANA Considerations

This document registers an XML namespace and schema with IANA in
accordance with guidelines in [RFC3688].

7.1. URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:geopriv:held:id

This section registers a new XML namespace,
"urn:ietf:params:xml:ns:geopriv:held:id", as per the guidelines in
[RFC3688].

URI: urn:ietf:params:xml:ns:geopriv:held:id

Registrant Contact: IETF, GEOPRIV working group ([email protected]),
James Winterbottom ([email protected]).

Winterbottom, et al. Standards Track [Page 21]

RFC 6155 HELD Identity March 2011

XML:

BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<title>HELD Device Identity Parameters</title>
</head>
<body>
<h1>Namespace for HELD Device Identity Parameters</h1>
<h2>urn:ietf:params:xml:ns:geopriv:held:id</h2>
<p>See <a href="http://www.rfc-editor.org/rfc/rfc6155.txt">
RFC 6155</a>.</p>
</body>
</html>
END

7.2. XML Schema Registration

This section registers an XML schema as per the guidelines in
[RFC3688].

URI: urn:ietf:params:xml:schema:geopriv:held:id

Registrant Contact: IETF, GEOPRIV working group ([email protected]),
James Winterbottom ([email protected]).

Schema: The XML for this schema can be found as the entirety of
Section 6 of this document.

7.3. Registration of HELD 'badIdentifier' Error Code

This section registers the "badIdentifier" error code in the IANA
maintained "HELD Error Codes" sub-registry of the "Geopriv HTTP
Enabled Location Delivery (HELD) Parameters" registry.

badIdentifier This error code indicates that a Device identifier
used in the HELD request was either: not supported by the LIS,
badly formatted, or not one for which the requestor was authorized
to make a request.

8. Acknowledgements

The National Emergency Number Association (NENA) VoIP location
working group provided assistance in the definition of the schema
used in this document. Special thanks go to Barbara Stark, Guy

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RFC 6155 HELD Identity March 2011

Caron, Nadine Abbott, Jerome Grenier, and Martin Dawson. Bob Sherry
provided input on use of URIs. Thanks to Adam Muhlbauer and Eddy
Corbett for providing further corrections. Bernard Aboba provided
excellent feedback on use cases and the security model; Bernard,
along with Alan DeKok, also helped resolve an issue with NAIs. Ray
Bellis provided motivation for the protocol port parameters. Marc
Linsner and Alissa Cooper provided guidance and text (respectively)
that greatly clarified the discussion relating to LCPs. Thanks to
Jon Peterson and Cullen Jennings for forcing this to be practical.

9. References

9.1. Normative References

[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.

[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.

[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.

[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.

[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.

[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.

[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.

Winterbottom, et al. Standards Track [Page 23]

RFC 6155 HELD Identity March 2011

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.

[RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
Network Access Identifier", RFC 4282, December 2005.

[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.

[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340, March 2006.

[RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client
Identifiers for Dynamic Host Configuration Protocol
Version Four (DHCPv4)", RFC 4361, February 2006.

[RFC4960] Stewart, R., "Stream Control Transmission Protocol",
RFC 4960, September 2007.

[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.

[RFC5985] Barnes, M., "HTTP-Enabled Location Delivery (HELD)",
RFC 5985, September 2010.

[W3C.REC-xml-names11-20060816]
Hollander, D., Tobin, R., Layman, A., and T. Bray,
"Namespaces in XML 1.1 (Second Edition)", World Wide Web
Consortium Recommendation REC-xml-names11-20060816,
August 2006,
<http://www.w3.org/TR/2006/REC-xml-names11-20060816>.

[IEEE802] IEEE, "IEEE Standard for Local and Metropolitan Area
Networks: Overview and Architecture", IEEE 802,
February 2002.

[EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority", March 1997,
<http://standards.ieee.org/regauth/oui/tutorials/
EUI64.html>.

[E.164] ITU-T, "E.164 : The international public telecommunication
numbering plan", ITU-T Recommendation E.164,
February 2005,
<http://www.itu.int/rec/T-REC-E.164-200502-I/en>.

Winterbottom, et al. Standards Track [Page 24]

RFC 6155 HELD Identity March 2011

[E.213] ITU-T, "E.213 : Telephone and ISDN numbering plan for land
mobile stations in public land mobile networks (PLMN)",
ITU-T Recommendation E.213, November 1988,
<http://www.itu.int/rec/T-REC-E.213-198811-I/en>.

[TS.3GPP.23.003]
3GPP, "Numbering, addressing and identification", 3GPP
TS 23.003 9.4.0, September 2010,
<http://www.3gpp.org/ftp/Specs/html-info/23003.htm>.

[TIA.EIA.IS-2000-6]
TIA/EIA, "Analog Signaling Standard for CDMA 2000 Spread
Spectrum Systems", TIA/EIA/IS-2000-6-C, May 2002.

[WiMAX-T33-110-R015v01-B]
WiMAX Forum, "Protocols and Procedures for Location Based
Services", WiMAX Forum Network Architecture T33-110-
R015v01-B, May 2009.

[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952, August 2010.

9.2. Informative References

[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.

[RFC2101] Carpenter, B., Crowcroft, J., and Y. Rekhter, "IPv4
Address Behaviour Today", RFC 2101, February 1997.

[RFC3825] Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based
Location Configuration Information", RFC 3825, July 2004.

[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
RFC 3966, December 2004.

[RFC4745] Schulzrinne, H., Tschofenig, H., Morris, J., Cuellar, J.,
Polk, J., and J. Rosenberg, "Common Policy: A Document
Format for Expressing Privacy Preferences", RFC 4745,
February 2007.

[RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol
(DHCPv4 and DHCPv6) Option for Civic Addresses
Configuration Information", RFC 4776, November 2006.

Winterbottom, et al. Standards Track [Page 25]

RFC 6155 HELD Identity March 2011

[RFC4825] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)", RFC 4825, May 2007.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.

[RFC5687] Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7
Location Configuration Protocol: Problem Statement and
Requirements", RFC 5687, March 2010.

[GEOPRIV-ARCH]
Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
Tschofenig, H., and H. Schulzrinne, "An Architecture for
Location and Location Privacy in Internet Applications",
Work in Progress, October 2010.

[EMERGENCY-CALLING]
Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in support of Emergency Calling",
Work in Progress, October 2010.

Winterbottom, et al. Standards Track [Page 26]

RFC 6155 HELD Identity March 2011

Authors' Addresses

James Winterbottom
Andrew Corporation
Andrew Building (39)
Wollongong University Campus
Northfields Avenue
Wollongong, NSW 2522
AU

Phone: +61 2 4221 2938
EMail: [email protected]

Martin Thomson
Andrew Corporation
Andrew Building (39)
Wollongong University Campus
Northfields Avenue
Wollongong, NSW 2522
AU

Phone: +61 2 4221 2915
EMail: [email protected]

Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland

Phone: +358 (50) 4871445
EMail: [email protected]
URI: http://www.tschofenig.priv.at

Richard Barnes
BBN Technologies
9861 Broken Land Pkwy, Suite 400
Columbia, MD 21046
USA

Phone: +1 410 290 6169
EMail: [email protected]

Winterbottom, et al. Standards Track [Page 27]