GEOPRIV                                                  J. Winterbottom
Internet-Draft                                        Andrew Corporation
Intended status: Standards Track                           H. Tschofenig
Expires: April 2, June 19, 2011                            Nokia Siemens Networks
                                                          H. Schulzrinne
                                                     Columbia University
                                                              M. Thomson
                                                               M. Dawson
                                                      Andrew Corporation
                                                      September 29,
                                                       December 16, 2010

              A Location Dereferencing Protocol Using HELD


   This document describes how to use the Hypertext Transfer Protocol
   (HTTP) over Transport Layer Security (TLS) as a dereferencing
   protocol to resolve a reference to a Presence Information Data Format
   Location Object (PIDF-LO).  The document assumes that a Location
   Recipient possesses a secure HELD URI that can be used in conjunction with the
   HELD protocol to request the location of the Target.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on April 2, June 19, 2011.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Authorization Models . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Authorization by Possession  . . . . . . . . . . . . . . .  6
     3.2.  Authorization via Access Control . . . . . . . . . . . . .  7
     3.3.  Access Control with HELD Deference . . . . . . . . . . . .  7
   4.  HELD Dereference Protocol  . . . . . . . . . . . . . . . . . .  8
     4.1.  HELD Usage Profile . . . . . . . . . . . . . . . . . . . .  9
     4.2.  HTTP GET Behavior  . . . . . . . . . . . . . . . . . . . .  9
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     9.2.  Informative references . . . . . . . . . . . . . . . . . . 15 14
   Appendix A.  GEOPRIV Using Protocol Compliance . . . . . . . . . . 16
   Appendix B.  Compliance to Location Reference Requirements . . . . 19
     B.1.  Requirements for a Location Configuration Protocol . . . . 19
     B.2.  Requirements for a Location Dereference Protocol . . . . . 21
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22

1.  Introduction

   Provision of location information by reference [RFC5808] involves the
   creation of a resource that is identified by a "location URI".  A
   "location URI" is a URI [RFC3986] that identifies a resource that contains
   containing the location of an entity.  A location URI might be identify
   a temporary resource, created in response to a HTTP-Enabled Location
   Delivery (HELD)
   [I-D.ietf-geopriv-http-location-delivery] [RFC5985] request.  A location URI does not
   intrinsically include location information, instead the URI is
   "dereferenced" by a Location Recipient to acquire location
   information.  This document specifies how a holder of a location URI
   uses that URI to retrieve location information.


   HELD protocol, as described in
   [I-D.ietf-geopriv-http-location-delivery], defines a use of HTTP that enables location configuration - the
   process where a Device acquires location information about itself.  A
   part of location configuration is the provision of a location URI.
   However, HELD does not describe how such a URI is used; this document
   provides that definition.

   This document defines how HELD is used by a Location Recipient to
   dereference a location URI and acquire location information.  The
   result of this process is a location object in the form of a Presence
   Information Data Format - Location Object (PIDF-LO) document
   [RFC4119].  A constrained set of HELD features are defined such that
   it is suitable for use as a location dereference protocol [RFC5808].
   Use as a location dereference protocol requires use of the Transport
   Layer Security (TLS) binding for HTTP [RFC2818] in order to provide
   confidentiality, authentication and protection from modification.

   Use of HELD as a dereferencing protocol has the advantage that the
   Location Recipient can indicate the type of location information it
   would like to receive.  This functionality is already available with
   the HELD base specification, described in
   [I-D.ietf-geopriv-http-location-delivery]. [RFC5985].  Furthermore,
   the HELD response from the LIS towards the Location Recipient not
   only provides the PIDF-LO but also encapsulates supplementary
   information, such as error messages, back to the Location Recipient.

   Location URIs created for use with HELD dereferencing use the
   "https:" or "http:" scheme.  The behaviour described in this document
   can be used by Location Recipients that are aware of the fact that
   the URI is a location URI.

   An example scenario envisioned by this document is shown in Figure 1.
   This diagram shows how a location dereference protocol fits with
   location configuration and conveyance.  [RFC5808] contains more
   information on this scenario and others like it.

   +------------+           |  Location   |            +-----------+
   | End Device |           | Information |            | Location  |
   |  (Target)  |           |   Server    |            | Recipient |
   +-----+------+           +------+------+            +-----+-----+
         |                         |                         |
      .- + - - - - - - - - - - - - + -.                      |
      :  |     locationRequest     |  :                      |
      .  |------(location URI)---->|  .                      |
      :  |                         |  : Location             |
      .  |     locationResponse    |  . Configuration        |
      :  |<-----(location URI)-----|  : Protocol             |
      .  |                         |  .                      |
      `- + - - - - - - - - - - - - + -'                      |
         |                         |                         |
         |                Location Conveyance                |
         |~ ~ ~ ~ ~ ~ ~ ~ ~ ~(location URI)~ ~ ~ ~ ~ ~ ~ ~ ~>|
         |                         |                         |
         |                      .- + - - - - - - - - - - - - + -.
         |                      :  |     locationRequest     |  :
         |                      .  |<--------(civic)---------|  .
         |        Dereferencing :  |                         |  :
         |        Protocol      .  |     locationResponse    |  .
         |                      :  |--------(PIDF-LO)------->|  :
         |                      .  |                         |  .
         |                      `- + - - - - - - - - - - - - + -'
         |                         |                         |

            Figure 1: Example of Dereference Protocol Exchange

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   This document uses key terminology from several sources:

   o  terms for the GEOPRIV reference model defined in

   o  the term Location Information Server (LIS), from [RFC5687], is a
      node in the access network that provides location information to
      an end point; a LIS provides location URIs;

   o  the term Location Server (LS), from [I-D.ietf-geopriv-arch], is
      used to identify the role that responds to a location dereference
      request; this might be the same entity as the LIS, but the model
      in [RFC5808] allows for the existence of separate - but related -
      entities; and

   o  the term location URI is coined in [RFC5808].

3.  Authorization Models

   This section discusses two extreme types of authorization models for
   dereferencing with HELD URIs, namely "Authorization by Possession"
   and "Authorization by Access Control".  In the subsequent subsections
   we discuss the properties of these two models.  Figure 2, from
   [RFC5808], shows the model applicable to location configuration,
   conveyance and dereference.

             +---------+--------+   Location    +-----------+
             |         |        |  Dereference  | Location  |
             |   LIS   -   LS   +---------------+ Recipient |
             |         |        |   Protocol    |           |
             +----+----+--------+      (3)      +-----+-----+
                  |         `.                        |
                  |    Policy `.                      |
    Location      |    Exchange `.                    |
    Configuration |      (*)      |                   |
    Protocol      |          +----+----+              |
      (1)         |          |  Rule   |   Location   |
                  |          |  Maker  |   Conveyance |
            +-----+----+     +---------+   Protocol   |
            |          |                      (2)     |
            |  Target  +------------------------------+
            |          |

                       Figure 2: Communication Model

   It is important to note that this document does not mandate a
   specific authorization model.  It is possible to combine aspects of
   both models.  However, no authentication framework is provided, which
   limits the policy options available when the "Authorization by Access
   Control" model is used.

   For either authorization model, the overall process is similar.  The
   following steps are followed, with minor alterations:

   1.  The Target acquires a location URI from the LIS.  This might use
       HELD as a location configuration protocol (LCP).

   2.  The Target then conveys the location URI to a third party, the
       Location Recipient (for example using SIP as described in
       [I-D.ietf-sipcore-location-conveyance]).  This step is shown in
       (2) of Figure 2.

   3.  The Location Recipient then needs to dereference the location URI
       in order to obtain the Location Object (3).  Depending on the URI
       scheme of the location URI dereferencing might, as is the case
       for "https:" or "http:" URIs, be performed as described in this

   In this final step, the Location Server (LS) or LIS makes an
   authorization decision.  How this decision is reached depends on the
   authorization model.

3.1.  Authorization by Possession

   In this model, possession - or knowledge - of the location URI is
   used to control access to location information.  A location URI is
   constructed such that it is hard to guess (see C9 of [RFC5808]) and
   the set of entities that it is disclosed to is limited.  The only
   authentication required by the LS is evidence of possession of the
   URI.  The LS is able to immediately authorize any request that
   indicates this URI.

   Authorization by possession uses a very simple policy that does not
   typically require direct interaction with a Rule Maker; it is assumed
   that the Rule Maker is able to exert control over the distribution of
   the location URI.  Therefore, the LIS can operate with limited policy
   input from a Rule Maker.

   Limited disclosure is an important aspect of this authorization
   model.  The location URI is a secret; therefore, ensuring that
   adversaries are not able to acquire this information is paramount.
   Encryption, such as might be offered by TLS [RFC5246] or S/MIME
   [RFC5751], protects the information from eavesdroppers.

   Use of authorization by possession location URIs in a hop-by-hop
   protocol such as SIP [RFC3261] adds the possibility of on-path
   adversaries.  Depending on the usage of the location URI for certain
   location based applications (e.g., emergency services, location based
   routing) specific treatment is important, as discussed in

   Using possession as a basis for authorization means that, once
   granted, authorization cannot be easily revoked.  Cancellation of a
   location URI ensures that legitimate users are also affected;
   application of additional policy is theoretically possible, but could
   be technically infeasible.  Therefore, other measures are provided to
   prevent an adversary from gaining access to location information

   A very simple policy is established at the time that the location URI
   is created.  This policy specifies that the location URI expires
   after a certain time, which limits any inadvertent exposure of
   location information to adversaries.  The expiration time of the
   location URI might be negotiated at the time of its creation, or it
   might be unilaterally set by the LIS.

3.2.  Authorization via Access Control

   Use of explicit access control provides a Rule Maker greater control
   over the behaviour of an LS.  In contrast to authorization by
   possession, possession of a this form of location URI does not imply
   authorization.  Since an explicit policy is used to authorize access
   to location information, the location URI can be distributed to many
   potential Location Recipients.

   Either before creation or dissemination of the location URI, the Rule
   Maker establishes an authorization policy with the LS.  In reference
   to Figure 2, authorization policies might be established at creation
   (Step 1), and need to be established before before the location URI
   is published (Step 2) to ensure that the policy grants access to the
   desired Location Recipients.  Depending on the mechanism used, it
   might also be possible to change authorization policies at any time.

   A possible format for these authorization policies is available with
   GEOPRIV Common Policy [RFC4745] and Geolocation Policy
   [I-D.ietf-geopriv-policy].  Additional constraints might be
   established by other means.

   The LS enforces the authorization policy when a Location Recipient
   dereferences the URI.  Explicit authorization policies allow a Rule
   Maker to specify how location information is provided to Location

3.3.  Access Control with HELD Deference

   This document does not describe a specific authentication mechanism.
   This means that authorization policies are unable to specifically
   identify authorized Location Recipients.

   In order to control access to location information based on the
   identity of the Location Recipient, use of authorization by
   possession is employed.  By controlling which Location Recipients
   receive location URIs, access to location information is controlled.

   Other policy mechanisms, such as those described in
   [I-D.ietf-geopriv-policy], can be applied to different Location
   Recipients if multiple location URIs are used.  Location Recipients
   that receive a particular location URI are granted location
   information based on the authorization policy associated with that

   Providing that knowledge of a location URI is limited, policy
   appropriate to the Location Recipients that receive the location URI
   can be assigned.  Selective disclosure used in this fashion can be
   used in place of identity-based authorization.

   How policy is associated with a location URI is not defined by this
   document.  [I-D.barnes-geopriv-policy-uri] describes one possible

   Authentication of Location Recipients and use of identity-based
   authorization policy is not precluded.  A Location Server MAY support
   an authentication mechanism that enables identity-based authorization
   policies to be used.  Future specifications might define means of
   identifying recipients.

   Note:  Policy frameworks like [RFC4745] degrade in a way that
      protects privacy if features are not supported.  If a policy
      specifies a rule that is conditional on the identity of a
      recipient and the protocol does not (or cannot) provide an
      assertion identity of the recipient, the rule has no effect and
      the policy defaults to providing less information.

4.  HELD Dereference Protocol

   This section describes how HELD can be used to dereference a location
   URI.  This process can be applied when a Location Recipient is in
   possession of a location URI with a "https:" or "http:" URI scheme.

   A Location Recipient that wishes to dereference an "https:" or
   "http:" URI performs a HELD request on HTTP to the identified

   Note:  In many cases, an "http:" URI does not provide sufficient
      security for location URIs.  The absence of the security
      mechanisms provided by TLS means that the Rule Maker has no
      control over who receives location information and the Location
      Recipient has no assurance that the information is correct.

   The Location Recipient establishes a connection to the LS, as
   described in [RFC2818].  The TLS ciphersuite TLS_NULL_WITH_NULL_NULL
   MUST NOT be used.  The LS MUST be authenticated to ensure that the
   correct server is contacted.

   A Location Server MAY reject a request and request that a Location
   Recipient provide authentication credentials if authorization is
   dependent on the Location Recipient identity.  Future specifications
   could define an authentication mechanism and a means by which
   Location Recipients are identified in authorization policies.  This
   document provides definitions for neither item.

4.1.  HELD Usage Profile

   Use of HELD as a location dereference protocol is largely the same as
   its use as a location configuration protocol.  Aside from the
   restrictions noted in this document, HELD semantics do not differ
   from those established in [I-D.ietf-geopriv-http-location-delivery]. [RFC5985].

   The HELD "locationRequest" is the only request permitted by this
   specification.  Similarly, request parameters other than the
   following MUST NOT be accepted by the LS: "responseTime",
   "locationType" (including the associated "exact" attribute).

   Parameters and requests that do not have known behaviour for
   dereference requests MUST NOT be used.  The LS MUST ignore any
   parameters that it does not understand unless it knows the parameters
   to be invalid.  If parameters are understood by the LS and known to
   be invalid, the LS MAY generate a HELD error response.  For instance,
   those defined in [I-D.ietf-geopriv-held-identity-extensions] are
   always invalid and can be rejected.

   The LS MUST NOT generate location URIs or provide a "locationUriSet"
   in response to a dereference request.  If the location request
   contains a "locationType" element that includes "locationURI", this
   parameter is either ignored or rejected as appropriate, based on the
   associated "exact" attribute.

4.2.  HTTP GET Behavior

   GET is the method assumed by generic HTTP user agents, therefore
   unless context identifies an "https:" URI as a HELD URI, such a user
   agent might simply send an HTTP GET.  Rather than providing an HTTP
   405 (Method Not Allowed) response indicating that POST is the only
   permitted method, this document describes a way for a LIS to provide
   a HELD location response if it receives an HTTP GET request.

   An HTTP GET request to a HELD URI produces a HELD response as if the
   following HELD request had been sent using HTTP POST:

     <locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held">
       <locationType exact="false">
         geodetic civic

             Figure 3: GET Request Equivalent Location Request

   HTTP GET requests must be safe and idempotent [RFC2616] - that is,
   there are no side-effects of making the request and a repeated
   request has no more effect than a single request.  Only when a
   location URI is created does HELD request have side-effects.
   Repeating a HELD request might result in a different location, but
   only as a result of a change in the state of the resource: the
   location of the Target.

   A request to a location URI can be both safe and idempotent, since a
   location URI cannot be produced in response to a request to a
   location URI.

   Note:  Idempotence does not require that the same answer be provided
      to different requests only that there are no side effects.
      Changes in the response can occur for a number of reasons,
      including a change in the value of the resource: the location of
      the Target.

   Content negotiation MAY be supported to produce a presence document
   in place of a HELD location response.  Where the presence document
   would otherwise be included in a "locationResponse" document, it can
   be included in the body of the HTTP response directly. directly by including an
   "Accept" header that includes "application/pidf+xml".

5.  Examples

   The example in Figure 4 shows the simplest form of dereferencing
   request using HELD to the location URI
   "".  The only way that
   this differs from the example in Section 10.1 of
   [I-D.ietf-geopriv-http-location-delivery] [RFC5985] is in the
   request URI and the source of the URI.

   POST /uri/w3g61nf5n66p0 HTTP/1.1
   Content-Type: application/held+xml
   Content-Length: 87

   <?xml version="1.0"?>
   <locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held"/>

                  Figure 4: Minimal Dereferencing Request

   Figure 5 shows the response to the previous request listing both
   civic and geodetic location information of the Target's location.
   Again, this is identical to the response in Section 10.1 of
   [I-D.ietf-geopriv-http-location-delivery] [RFC5985]
   - unless policy specfies otherwise, the Location Recipient receives
   the same information as the Device.

   HTTP/1.1 200 OK
   Server: Example LIS
   Date: Mon, 10 Jan 2011 03:42:29 GMT
   Expires: Tue, 11 Jan 2011 03:42:29 GMT
   Cache-control: private
   Content-Type: application/held+xml
   Content-Length: 676

   <?xml version="1.0"?>
   <locationResponse xmlns="urn:ietf:params:xml:ns:geopriv:held">
   <presence xmlns="urn:ietf:params:xml:ns:pidf"
     <tuple id="b650sf789nd">
      <geopriv xmlns="urn:ietf:params:xml:ns:pidf:geopriv10"
          <Point xmlns=""
            <pos>-34.407 150.88001</pos>

               Figure 5: Response with Location Information

   The following GET request is treated in an equivalent fashion.  The
   LS treats this request as though it were a location request of the
   form shown in Figure 3.  The same response might be provided.

   GET /uri/w3g61nf5n66p0 HTTP/1.1
   Accept: application/held+xml

                           Figure 6: GET Request

   The following GET request uses content negotiation to indicate a
   preference for a presence document.

   GET /uri/w3g61nf5n66p0 HTTP/1.1
   Accept: application/pidf+xml,application/held+xml;q=0.5

              Figure 7: GET Request with Content Negotiation

   The response only differs from a normal HELD location response to a
   POST request in that the "locationResponse" element is omitted and
   the "Content-Type" header reflects the changed content.

   HTTP/1.1 200 OK
   Server: Example LIS
   Date: Mon, 10 Jan 2011 03:42:29 GMT
   Expires: Tue, 11 Jan 2011 03:42:29 GMT
   Cache-control: private
   Content-Type: application/pidf+xml
   Content-Length: 591

   <?xml version="1.0"?>
   <presence xmlns="urn:ietf:params:xml:ns:pidf"
     ... PIDF contents are identical to the previous example ...

                    Figure 8: GET Response with PIDF-LO

6.  Security Considerations

   Privacy of location information is the most important security
   consideration for this document.  Two measures in particular are used
   to protect privacy: TLS and authorization policies.  TLS provides a
   means of ensuring confidentiality of location information through
   encryption and mutual authentication.  An authorization policy allows
   a Rule Maker to explicitly control how location information is
   provided to Location Recipients.

   The process by which a Rule Maker establishes an authorization policy
   is not covered by this document; several methods are possible, for
   instance: [I-D.barnes-geopriv-policy-uri], [RFC4825].

   Use of TLS for the dereferencing of location URIs is strongly
   RECOMMENDED, as discussed in Section 4.1. 4.  Location Recipients MUST
   authenticate the host identity using the domain name included in the
   location URI, using the procedure described in Section 3.1 of
   [RFC2818].  Local policy determines what a Location Recipient does if
   authentication fails or cannot be attempted.

   The authorization by possession model (Section 3.1) further relies on
   TLS when transmitting the location URI to protect the secrecy of the
   URI.  Possession of such a URI implies the same privacy
   considerations as possession of the PIDF-LO document that the URI

   Location URIs MUST only be disclosed to authorized Location
   Recipients.  The GEOPRIV architecture [I-D.ietf-geopriv-arch]
   identifies the Rule Maker role as being the entity that authorizes
   disclosure of this nature.

   Protection of the location URI is necessary, since the policy
   attached to such a location URI permits any who have the URI to view
   it.  This aspect of security is covered in more detail in the
   specification of location conveyance protocols, such as

   The LS MUST NOT provide any information about the Target except its
   location, unless policy from a Rule Maker allows otherwise.  In
   particular, the requirements in [RFC5808] mandate this measure to
   protect the identity of the Target.  To this end, an unlinked
   pseudonym MUST be provided in the "entity" attribute of the PIDF-LO

   Further security considerations and requirements relating to the use
   of location URIs are described in [RFC5808].

7.  IANA Considerations

   This document makes no request of IANA.

   [[IANA/RFC-EDITOR: Please remove this section before publication.]]

8.  Acknowledgements

   Thanks to Barbara Stark and Guy Caron for providing early comments.
   Thanks to Rohan Mahy for constructive comments on the scope and
   format of the document.  Thanks to Ted Hardie for his strawman
   proposal that provided assistance with the security section of this
   document.  Richard Barnes made helpful observations on the
   application of authorization policy.

   The Participants participants of the GEOPRIV interim meeting 2008 provided
   significant feedback on this document.

   James Polk provided input on security in June 2008.

9.  References

9.1.  Normative References

              Barnes, M., Winterbottom, J., Thomson, M., and B. Stark,
              "HTTP Enabled Location Delivery (HELD)",
              draft-ietf-geopriv-http-location-delivery-16 (work in
              progress), August 2009.

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

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

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

   [RFC4119]  Peterson, J., "A Presence-based GEOPRIV Location Object
              Format", RFC 4119, December 2005.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 35,
              RFC 4395, February 2006.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5491]  Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
              Presence Information Data Format Location Object (PIDF-LO)
              Usage Clarification, Considerations, and Recommendations",
              RFC 5491, March 2009.

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

9.2.  Informative references

              Barnes, R., Thomson, M., and J. Winterbottom, J., and H.
              Tschofenig, "Location Configuration Extensions for Policy
              draft-barnes-geopriv-policy-uri-01 draft-barnes-geopriv-policy-uri-02 (work in
              May November 2010.

              Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
              Tschofenig, H., and H. Schulzrinne, "An Architecture for
              Location and Location Privacy in Internet Applications",
              draft-ietf-geopriv-arch-03 (work in progress), May
              October 2010.

              Winterbottom, J., Thomson, M., Tschofenig, H., and R.
              Barnes, "Use of Device Identity in HTTP-Enabled Location
              Delivery (HELD)",
              draft-ietf-geopriv-held-identity-extensions-06 (work in
              progress), June November 2010.

              Schulzrinne, H., Tschofenig, H., Morris, J., Cuellar, J.,
              and J. Polk, "Geolocation Policy: A Document Format for
              Expressing Privacy Preferences for Location Information",
              draft-ietf-geopriv-policy-22 (work in progress),
              October 2010.

              Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
              for the Session Initiation Protocol",
              draft-ietf-sipcore-location-conveyance-04 (work in
              progress), July October 2010.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3693]  Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and
              J. Polk, "Geopriv Requirements", RFC 3693, February 2004.

   [RFC3851]  Ramsdell, B., "Secure/Multipurpose Internet Mail
              Extensions (S/MIME) Version 3.1 Message Specification",
              RFC 3851, July 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.

   [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.

   [RFC5751]  Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, January 2010.

   [RFC5808]  Marshall, R., "Requirements for a Location-by-Reference
              Mechanism", RFC 5808, May 2010.

Appendix A.  GEOPRIV Using Protocol Compliance

   This section describes how use of HELD as a location dereference
   protocol complies with the GEOPRIV requirements described in

   Req. 1.  (Location Object generalities):

            This section relates to the PIDF-LO [RFC4119] document,
            which is used by HELD.  These requirements are addressed by
            [RFC4119] and [RFC5491].

   Req. 2.  (Location Object fields):

            This section relates to the PIDF-LO [RFC4119] document,
            which is used by HELD.  These requirements are addressed by
            [RFC4119] and [RFC5491].

   Req. 3.  (Location Data Types):

            This section relates to the PIDF-LO [RFC4119] document,
            which is used by HELD.  These requirements are addressed by
            [RFC4119] and [RFC5491].

   Section 7.2 of [RFC3693] details the requirements of a "Using
   Protocol".  These requirements are restated, followed by a statement
   of compliance:

   Req. 4.  "The using protocol has to obey the privacy and security
            instructions coded in the Location Object and in the
            corresponding Rules regarding the transmission and storage
            of the LO."

            Compliant: This document carries the PIDF-LO as is via HTTPS
            from the LS to the Location Recipient.  The sending and
            receiving parties are expected to comply with the
            instructions carried inside the object.

   Req. 5.  "The using protocol will typically facilitate that the keys
            associated with the credentials are transported to the
            respective parties, that is, key establishment is the
            responsibility of the using protocol."

            Compliant: This document specifies that authentication of
            the LS uses the established public key infrastructure used
            by HTTP over TLS [RFC2818].  Authentication of Location
            Recipients is either based on distribution of a secret (the
            location URI) using a conveyance protocol (for instance,
            [I-D.ietf-sipcore-location-conveyance]), allowances are made
            for later work to define alternative methods.

   Req. 6.  "(Single Message Transfer) In particular, for tracking of
            small target devices, the design should allow a single
            message/packet transmission of location as a complete

            Not Compliant: The XML encoding specified in [RFC4119] is
            not suited to single packet transfers.  Use of compressed
            content encoding [RFC2616] might allow this condition to be

   Section 7.3 of [RFC3693] details the requirements of a "Rule based
   Location Data Transfer".  These requirements are restated where they
   are applicable to this document:

   Req. 7.   "(LS Rules) The decision of a Location Server to provide a
             Location Recipient access to Location Information MUST be
             based on Rule Maker-defined Privacy Rules."

             Compliant: This document describes two alternative methods
             by which a Rule Maker is able to control access to location
             information.  Rule Maker policy is enforced by the LS when
             a location URI is dereferenced.  However, this document
             does not describe how a location URI is created, or how a
             Rule Maker associates policy with a location URI.  These
             are covered by other specifications.

   Req. 8.   (LG Rules) Not Applicable: This relationship between LS and
             the source of its information (be that Location Generator
             (LG) or LIS) is out of scope for this document.

   Req. 9.   "(Viewer Rules) A Viewer does not need to be aware of the
             full Rules defined by the Rule Maker (because a Viewer
             SHOULD NOT retransmit Location Information), and thus a
             Viewer SHOULD receive only the subset of Privacy Rules
             necessary for the Viewer to handle the LO in compliance
             with the full Privacy Rules (such as, instruction on the
             time period for which the LO can be retained)."

             Compliant: The Rule Maker might define (via mechanisms
             outside the scope of this document) which policy rules are
             disclosed to other entities.  For instance, if [RFC4745] is
             used to convey authorization policies from Rule Maker to
             LS, this is possible using the parameters specified in

   Req. 10.  (Full Rule language) Not Applicable: Note however that
             Geopriv has defined a rule language capable of expressing a
             wide range of privacy rules (see [RFC4745] and

   Req. 11.  (Limited Rule language) Not Applicable: This requirement
             applies to (and is addressed by) PIDF-LO [RFC4119].

   Section 7.4 of [RFC3693] details the requirements of "Location Object
   Privacy and Security".  These requirements are restated where they
   are applicable to this document:

   Req. 12.  (Identity Protection) Compliant: Identity protection of the
             Target is provided as long as both of the following
             conditions are true:

             (a)  the location URI is not associated with the identity
                  of the Target in any context, and

             (b)  the PIDF-LO does not contain information about the
                  identity about the Target.

             For instance, this requirement is complied with if the
             protocol that conveys the location URI does not link the
             identity of the Target to the location URI and the LS
             doesn't include meaningful identification information in
             the PIDF-LO document.  Section 6 recommends that an
             unlinked pseudonym is used by the LS.

   Req. 13.  (Credential Requirements) Compliant: The primary security
             mechanism specified in this document is Transport Layer
             Security.  TLS offers the ability to use different types of
             credentials, including symmetric, asymmetric credentials or
             a combination of them.

   Req. 14.  (Security Features) Compliant: Geopriv defines a few
             security requirements for the protection of Location
             Objects such as mutual end-point authentication, data
             object integrity, data object confidentiality and replay
             protection.  The ability to use Transport Layer security
             fulfills most of these requirements.  Authentication of
             Location Recipients in this document relies on proof of a
             shared secret - the location URI.  This does not preclude
             the addition of more robust authentication procedures.

   Req. 15.  (Minimal Crypto) Compliant: The mandatory to implement
             ciphersuite is provided in the TLS layer security

Appendix B.  Compliance to Location Reference Requirements

   This section describes how HELD complies to the location reference
   requirements stipulated in [RFC5808].  Compliance of [RFC5985] to the
   Location Configuration Protocol are included in this document. is included.

      Note that use of HELD as a location dereference protocol does not
      necessarily imply that HELD is the corresponding LCP.  This
      document is still applicable to HTTP location URIs that are
      acquired by other means.

B.1.  Requirements for a Location Configuration Protocol

   C1.  "Location URI support: The location configuration protocol MUST
        support a location reference in URI form."

        Compliant: HELD only provides location references in URI form.

   C2.  "Location URI expiration: When a location URI has a limited
        validity interval, its lifetime MUST be indicated."

        Compliant: HELD indicates the expiry time of location URIs using
        the "expires" attribute.  [I-D.barnes-geopriv-policy-uri]
        provides a way to control expiration of a location URI; a Device
        is able to specify limits on the life time of a HELD context.

   C3.  "Location URI cancellation: The location configuration protocol
        MUST support the ability to request a cancellation of a specific
        location URI."

        Compliant with Extension: [I-D.barnes-geopriv-policy-uri]
        describes how a location URI can be cancelled through the
        application of policy.  Without extensions, HELD does not
        provide a method for cancelling location URIs.

   C4.  "Location Information Masking: The location URI MUST ensure, by
        default, through randomization and uniqueness, that the location
        URI does not contain location information specific components."

        Compliant: The HELD specification explicitly references this
        requirement in providing guidance on the format of the location

   C5.  "Target Identity Protection: The location URI MUST NOT contain
        information that identifies the Target (e.g., user or device)."

        Compliant: The HELD specification provides specific guidance on
        the anonymity of the Target with regards to the generation of
        location URIs.  Section 6 expands on this guidance.

   C6.  "Reuse indicator: There SHOULD be a way to allow a Target to
        control whether a location URI can be resolved once only, or
        multiple times."

        Not Compliant: Specific extensions to the protocol or
        authorization policy formats is needed to alter the default
        behavior, which allows unlimited resolution of the location URI.

   C7.  "Selective disclosure: The location configuration protocol MUST
        provide a mechanism that allows the Rule Maker to control what
        information is being disclosed about the Target."

        Compliant with Extension: Use of policy mechanisms and
        [I-D.barnes-geopriv-policy-uri] enable this capability.  Note
        that this document recommends that only location information be

   C8.  "Location URI Not guessable: As a default, the location
        configuration protocol MUST return location URIs that are random
        and unique throughout the indicated lifetime.  A location URI
        with 128-bits of randomness is RECOMMENDED."

        Compliant: HELD specifies that location URIs conform to this

   C9.  "Location URI Options: In the case of user-provided
        authorization policies, where anonymous or non-guessable
        location URIs are not warranted, the location configuration
        protocol MAY support a variety of optional location URI
        conventions, as requested by a Target to a location
        configuration server, (e.g., embedded location information
        within the location URI)."

        Not Compliant: HELD does not support Device-specified location
        URI forms.

B.2.  Requirements for a Location Dereference Protocol

   D1.  "Location URI support: The location dereference protocol MUST
        support a location reference in URI form."

        Compliant: HELD only provides location references in URI form.

   D2.  "Authentication: The location dereference protocol MUST include
        mechanisms to authenticate both the client and the server."

        Partially Compliant: TLS provides means for mutual
        authentication.  This document only specifies the required
        mechanism for server authentication.  Client authentication is
        not precluded.

   D3.  "Dereferenced Location Form: The value returned by the
        dereference protocol MUST contain a well-formed PIDF-LO

        Compliant: HELD requires that location objects are in the form
        of a PIDF-LO that complies with [RFC5491].

   D4.  "Location URI Repeated Use: The location dereference protocol
        MUST support the ability for the same location URI to be
        resolved more than once, based on dereference server

        Compliant: A Location Recipient may access and use a location
        URI as many times as desired until URI expiration results in the
        URI being invalidated.  Authorization policies might include
        rules that modify this behavior.

   D5.  "The location dereference protocol MUST support confidentiality
        protection of messages sent between the Location Recipient and
        the location server."

        Compliant: This document strongly recommends the use of TLS for
        confidentiality and HELD mandates its implementation.  Unsecured
        HTTP is permitted, and some of permitted: the associated risks are described in
        Section 4.1. 4.

Authors' Addresses

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

   Phone: +61 242 212938

   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600

   Phone: +358 (50) 4871445

   Henning Schulzrinne
   Columbia University
   Department of Computer Science
   450 Computer Science Building, New York, NY  10027

   Phone: +1 212 939 7004

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

   Phone: +61 2 4221 2915
   Martin Dawson
   Andrew Corporation
   Andrew Building (39)
   Wollongong University Campus
   Northfields Avenue
   Wollongong, NSW  2522

   Phone: +61 2 4221 2992