Geopriv J. Winterbottom
Internet-Draft Andrew Corporation
Intended status: Standards Track H. Tschofenig
Expires: January 15, 2009 Nokia Siemens Networks
H. Schulzrinne
Columbia University
M. Thomson
M. Dawson
Andrew Corporation
July 14, 2008
An HTTPS Location Dereferencing Protocol Using HELD
draft-winterbottom-geopriv-deref-protocol-02.txt
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Abstract
This document describes how to use the Hypertext Transfer Protocol
(HTTP) over Transport Layer Security (TLS) as a dereferencing
protocol to resolve a reference into 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Authorization Models . . . . . . . . . . . . . . . . . . . . . 6
3.1. Authorization by Possession . . . . . . . . . . . . . . . 6
3.2. Authorization via Access Control Lists . . . . . . . . . . 8
4. Steps for Retrieval . . . . . . . . . . . . . . . . . . . . . 9
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . . 17
9.2. Informative references . . . . . . . . . . . . . . . . . . 17
Appendix A. GEOPRIV Using Protocol Compliance . . . . . . . . . . 19
Appendix B. HELD Compliance to IETF Location Reference
Requirements . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
Intellectual Property and Copyright Statements . . . . . . . . . . 29
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1. Introduction
This document describes how to transport Presence Information Data
Format Location Object (PIDF-LO) when dereferencing a location URI in
the form of a secure HELD URI (held: URI scheme) [1]. This held:
URI indicates that the XML-based HELD messages are carried on top of
the Hypertext Transfer Protocol (HTTP), which is secured using
Transport Layer Security (TLS) ([2] and [3]).
The document describes how HELD [1] is used to request and to receive
location information in a way that also satisfies the requirements
laid out in [7]. HELD provides location information in the form of a
PIDF-LO (see [4]) which, as part of its definition, complies with the
requirements of a location object as described in [8].
To use 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 [1]. 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.
The general usage scenario envisioned by this document is shown in
Figure 1. While the figure shows a typical HELD location request
being made to initially obtain the location URI. As Figure 1
indicates, an alternative Location Configuration Protocol (LCP) that
can provide a HELD URI can be used.
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+-----------+
+------------+ | Location | +-----------+
| End Device | |Information| | Location |
| (Target) | | Server | | Recipient |
+-----+------+ +----+------+ +-----+-----+
| | |
+--+--------------------------+--+ |
| | | | |
| |===locationRequest(URI)==>0 | |
| | | | Location |
| | | | Configuration |
| 0<==locationResponse(URI)==| | Protocol |
| | | | |
+--+--------------------------+--+ |
| | |
| | |
|~~~~~~~~~~~~Location Conveyance (URI)~~~~~~~~~~~~~~~~~~>0
| | |
| +--+-----------------------------+--+
| | | | |
| | 0<===locationRequest(Civic)===| |
| Dereferencing | | | |
| Protocol | | | |
| | |==locationResponse(PIDF-LO)=>0 |
| | | | |
| +--+-----------------------------+--+
| | |
| | |
Figure 1: Example of Dereference Protocol Exchange
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2. Terminology
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 [5].
The key conventions and terminology used in this document are defined
as follows:
This document reuses the term Target, as defined in [8].
This document uses the term Location Information Server, LIS, as the
node in the access network providing location information to an end
point, or to the node dereferencing a location URI. This term is
also used in [9].
The Location Recipient acts as a HELD client and the LIS as a HELD
server in the context of this document.
Many architectural descriptions related to the updated terminology of
RFC 3693 can be found in [10].
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3. Authorization Models
This section discusses two extreme types of authorization models for
dereferencing with HELD URIs, namely "Authorization by Possession"
and "Authorization via Access Control Lists". In the subsequent
subsections we discuss the properties of these two models. These two
models can, however, be used in combination in a real deployment.
Figure 2 shows the communication model relevant for this discussion.
It is a simplified version of Figure 1 from [7].
+--------+ Dereferencing +-----------+
| | Protocol (3) | |
| LIS +---------------+ Location |
| | | Recipient |
+---+----+ | |
| +----+------+
| --
| Location --
| Configuration --
| Protocol ---
| (1) -- Geopriv
| --- Using
| -- Protocol
+----+-----+ -- (2)
| Target / +--
| End Host |
+----------+
Figure 2: Communication Model
It is important to note that this document does not mandate a
specific authorization model nor does it constraint the usage with
regard to these models in any way. Additionally, it is possible to
combine certain parts of both models.
3.1. Authorization by Possession
With this type of authorization model the communication steps with
respect to Figure 2 are as follows. We focus on the description of
the case where the Location URI is dereferenced by an entity other
than the Target.
1. The Target discovers the LIS.
2. The Target sends a request to the LIS asking for a location-by-
reference, as shown in (1) of Figure 2.
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3. The LIS responds to the request and returns a Location URI. This
reference fullfills the requirements indicated in [7], in
particular it must be non-guessable (see requirement C9 of [7]).
4. The Target then conveys the Location URI to a third party, the
Location Recipient (for example using SIP as described in [11]).
This step is shown in (2) of Figure 2.
5. The Location Recipient then needs to dereference the Location URI
in order to obtain the Location Object. Depending on the URI
scheme of the Location URI this might, for example in case of a
HELD URI, be done as described in this document.
The last step where the LIS has to decide whether to resolve the
reference and to return the Location Object to the entity asking for
it is important. With this authorization model there is the
assumption that the possession of the Location URI by the Location
Recipient alone is sufficient, from an authorization point of view,
to grant access to the Location Object that is being referenced by
the Location URI. As such, the Location Recipient authenticates the
LIS using TLS server-side authentication but no authentication from
the Location Recipient point of view is demanded.
A few aspects are worth further discussion when the Target would like
to avoid unrestricted disclosure of it's location information.
o First, the Target is able to control the disclosure of location
information by making the Location URI available only to selected
entities.
o Second, in order to deal with adversary along the signaling path
between the Target and the Location Recipient the properties of
the using protocol need to be taken advantage of. For example,
the Location URI may be encrypted end-to-end using S/MIME and
consequently only the entity that is able to decrypt the protected
object can resolve the reference. 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 [11].
o Finally, the Target can place restrictions on the URI itself. For
example, the Target may put rules around how long the URI can live
for, how many times the URI may be dereferences, or indeed,
precisely what the URI will reveal when accessed. That is, the
properties or the URI and policies invoked by the URI determine
what the recipient receives, regardless of any identification that
the recipient may present to the LIS.
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3.2. Authorization via Access Control Lists
In this model the communication steps are slightly different, as
shown below.
1. The procedure again starts with the Target performing the LIS
discovery procedure.
2. The Target sends a request to the LIS asking for a location-by-
reference, as shown in (1) of Figure 2.
3. Before handing out the reference the Target uploads authorization
policies to the LIS that aim to control access to the
dereferencing step. A possible format for these authorization
policies is available with GEOPRIV Common Policy [12] and
Geolocation Policy [13]. Additional policies are described in
[14] that allow constraints to be placed on the dereferencing
procedure to limit the location information being exposed to
Location Recipients.
4. The LIS responds to the request and returns a Location URI. With
the uploaded authorization policies in place there are no
requirements for the Location URI to be non-guessable.
5. The Target then conveys the Location URI to a third party, the
Location Recipient (for example using SIP as described in [11]).
This step is shown in (2) of Figure 2.
6. The Location Recipient then needs to dereference the Location URI
in order to obtain the Location Object. Depending on the
specific content of the authorization policies (such as identity-
based conditions in the policy rule set) the Location Recipient
has to be authenticated in order to allow the authorization check
to continue.
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4. Steps for Retrieval
When a Location Recipient obtains a Location URI with the "held:" URI
scheme then the following steps for dereferencing the Location URI
are being executed:
1. The Location Recipient, acting as a HELD client, determines the
IP address of the LIS based on the obtained Location URI
following the procedure described in Section 3 of [15].
2. The HELD client establishes a TLS connection to the LIS, as
described in [3]. The TLS ciphersuite TLS_NULL_WITH_NULL_NULL
MUST NOT be used.
3. When certificate based authentication is used the client
authenticates the server and compares the domain part of the
Location URI with the identity information in the certificate.
4. The server MAY require the client to be authenticated. This
could, for example, be useful in deployment environments where
certain Location Recipients are granted access to location
information only or where access control rules have to be
executed as part of the authorization procedure. Various
authentication mechanisms for HTTP exist and this document does
not restrict them in any way since the preferred mechanism may be
deployment specific.
5. The client retrieves the PIDF-LO document encapsulated into the
HELD locationResponse or an error message conveyed in a HELD
error message.
The subsequent text describes how HELD protected by TLS can be used
to qualify location requests to the LIS. Only a subset of HELD
functionality is required and is described in the following
paragraphs. The HELD based dereferencing step provides ways to tell
the LIS what information is desired and allows the LIS to communicate
additional information back to the client.
The <locationType> element allows location to be requested in a
specific form, such as civic or geodetic location information. The
Location Recipient SHOULD NOT request location as a locationURI. The
LIS MUST respond with a "requestError" if it receives a request for a
locationURI where HELD is being used as a dereference protocol.
Location information provided by the LIS MUST correspond to the rules
and guidelines in [6]. If the requested form of location violates
any authorization policies known to the LIS, then the LIS MUST
respond with a "cannotProvideLiType" error.
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The LIS will provide location information on request even if the
location information does not fit the form requested. This stems
from the premise that some location is better than no location. HELD
provides a means for the requestor to modify this behaviour and
instruct the LIS to return an error if location information is not
available in the form requested. This is done using the "exact"
attribute.
Location systems often have more than one location determination
mechanism at their disposal. Differing determination techniques
provide different degrees of accuracy over differing periods of time.
Generally, more accurate determination techniques require more time.
HELD addresses this trade-off by allowing the requestor to specify
how long they are prepared to wait for a location result. This
allows the LIS to select the most accurate determination technique at
its disposal that can return a result in the specified time. The
HELD attribute for specifying this value is the "responseTime"
attribute and MAY be used by a Location Recipient to specify their
preference for the accuracy-time trade-off.
The LIS MUST support the HELD locationRequest semantic using an HTTP
GET as described in [1]. The usage of HTTP POST is optional.
Where the LIS is unable to process the Location Recipient's request,
it MUST return the appropriate error from the existing HELD error set
defined in [1].
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5. Examples
This example in Figure 3 shows the most basic rereferencing request
for a LO. This uses the GET feature described by the HTTP binding
from Section 9 of [1]. This example assumes that the LO is available
for retrieval at the URL
"https://lis.example.com/357yc6s64ceyoiuy5ax3o".
GET held://lis.example.com:80/357yc6s64ceyoiuy5ax3o HTTP/1.1
Host: lis.example.com
Accept:application/held+xml,
application/xml;q=0.8,
text/xml;q=0.7
Accept-Charset: UTF-8,*
Figure 3: Minimal GET Dereferencing Request
The GET request is exactly identical to a minimal POST request that
includes an empty "locationRequest" element.
POST held://lis.example.com:80/357yc6s64ceyoiuy5ax3o HTTP/1.1
Host: lis.example.com
Accept: application/held+xml,
application/xml;q=0.8,
text/xml;q=0.7
Accept-Charset: UTF-8,*
Content-Type: application/held+xml
Content-Length: 83
<?xml version="1.0"?>
<locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held"/>
Figure 4: Minimal POST Dereferencing Request
Figure 5 shows a request indicating that both civic and geodetic
location information has to be returned. If it cannot be provided,
the request fails.
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POST held://lis.example.com:80/357yc6s64ceyoiuy5ax3o HTTP/1.1
Host: lis.example.com
Accept: application/held+xml,
application/xml;q=0.8,
text/xml;q=0.7
Accept-Charset: UTF-8,*
Content-Type: application/held+xml
Content-Length: 168
<?xml version="1.0"?>
<locationRequest xmlns="urn:ietf:params:xml:ns:geopriv:held">
<locationType exact="true">
civic
geodetic
</locationType>
</locationRequest>
Figure 5: Dereferencing POST Request for Civic and Geodetic Location
Information
Figure 6 shows the response to the previous request listing both
civic and geodetic location information of the Target's location.
HTTP/1.x 200 OK
Server: Example LIS
Date: Tue, 10 Jan 2006 03:42:29 GMT
Expires: Tue, 10 Jan 2006 03:49:20 GMT
Content-Type: application/held+xml
Content-Length: 1660
<?xml version="1.0"?>
<locationResponse xmlns="urn:ietf:params:xml:ns:geopriv:held">
<presence xmlns="urn:ietf:params:xml:ns:pidf:geopriv10"
entity="pres:ae3be8585902e2253ce2@10.102.23.9">
<tuple id="lisLocation">
<status>
<geopriv>
<location-info>
<gs:Circle
xmlns:gs="http://www.opengis.net/pidflo/1.0"
xmlns:gml="http://www.opengis.net/gml"
srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>-34.407242 150.882518</gml:pos>
<gs:radius uom="urn:ogc:def:uom:EPSG::9001">30
</gs:radius>
</gs:Circle>
<ca:civicAddress
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ca="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xml:lang="en-au">
<ca:country>AU</ca:country>
<ca:A1>NSW</ca:A1>
<ca:A3>Wollongong</ca:A3>
<ca:A4>Gwynneville</ca:A4>
<ca:STS>Northfield Avenue</ca:STS>
<ca:LMK>University of Wollongong</ca:LMK>
<ca:FLR>2</ca:FLR>
<ca:NAM>Andrew Corporation</ca:NAM>
<ca:PC>2500</ca:PC>
<ca:BLD>39</ca:BLD>
<ca:SEAT>WS-183</ca:SEAT>
<ca:POBOX>U40</ca:POBOX>
</ca:civicAddress>
</location-info>
<usage-rules>
<retransmission-allowed>false</retransmission-allowed>
<retention-expiry>2007-05-25T12:35:02+10:00
</retention-expiry>
</usage-rules>
<method>Wiremap</method>
</geopriv>
</status>
<timestamp>2007-05-24T12:35:02+10:00</timestamp>
</tuple>
</presence>
</locationResponse>
Figure 6: Response with Civic and Geodetic Location Information
Figure 7 shows an error message returned in response to a request.
HTTP/1.x 200 OK
Server: Example LIS
Expires: Tue, 10 Jan 2006 03:49:20 GMT
Content-Type: application/held+xml
Content-Length: 172
<error xmlns="urn:ietf:params:xml:ns:geopriv:held"
code="cannotProvideLiType"
message="Authorization policies do not permit
location information to be disclosed."/>
Figure 7: Error Message
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6. Security Considerations
This document assumes that the use of TLS to protect HTTP is
sufficient to protect the privacy of the PIDF-LO content while in
flight. When access control at the LIS is not applied, as described
in Section 3.1, then the possession of the location URI is equal to
the possession of location information. When the requirements for
creating a location URI, as described in [7], are met, then the
reference provides sufficiently high security guarantees for most
location-based applications. Furthermore, the ability of the Rule
Maker to put constraints on the dereferencing step, as described in
[14], provides the ability to restrict how often location can be
accessed through a location URI, how long the URI is valid for, and
the type of location information returned when a location URI is
accessed. If this is still not sufficient then the Target is able to
put authorization policies either to the LIS or uploads the Location
URI to a presence server that hosts authorization policies, as
described in [16].
Connection establishment from the Location Recipient to the LIS will
be made using HTTP over TLS, and the location URI being dereferenced
by the Location Recipient will contain the hostname of the LIS. The
Location Recipient MUST check the FQDN of the LIS in the reference
with the identity presented in the server's certificate. A
discrepancy may indicate a possible man-in-the-middle-attack, and the
Location Recipient should take appropriate action based on
application dependent semantics. Actions may include but are not
limited to; proceeding anyway, flagging the result as suspect, or
giving up.
In some applications the Location Recipient has a pre-established
relationship with one or several Location Information Servers and
hence the LIS might authorize only certain Location Recipients might
be allowed to resolve a reference.
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7. IANA Considerations
There are no specific IANA considerations for this document.
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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.
The authors would like to thank the participants of the GEOPRIV
interim meeting 2008 for their feedback.
James Polk provided comments on a security aspects in June 2008.
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9. References
9.1. Normative References
[1] Barnes, M., Winterbottom, J., Thomson, M., and B. Stark, "HTTP
Enabled Location Delivery (HELD)",
draft-ietf-geopriv-http-location-delivery-08 (work in
progress), July 2008.
[2] 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.
[3] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[4] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
PIDF-LO Usage Clarification, Considerations and
Recommendations", draft-ietf-geopriv-pdif-lo-profile-11 (work
in progress), February 2008.
9.2. Informative references
[7] Marshall, R., "Requirements for a Location-by-Reference
Mechanism", draft-ietf-geopriv-lbyr-requirements-03 (work in
progress), July 2008.
[8] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004.
[9] Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7 Location
Configuration Protocol; Problem Statement and Requirements",
draft-ietf-geopriv-l7-lcp-ps-08 (work in progress), June 2008.
[10] Barnes, R., Lepinski, M., Tschofenig, H., and H. Schulzrinne,
"Security Requirements for the Geopriv Location System",
draft-barnes-geopriv-lo-sec-02 (work in progress),
February 2008.
[11] Polk, J. and B. Rosen, "Location Conveyance for the Session
Initiation Protocol", draft-ietf-sip-location-conveyance-10
(work in progress), February 2008.
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[12] 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.
[13] 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-17 (work in progress), June 2008.
[14] Winterbottom, J., Tschofenig, H., and M. Thomson, "HELD
Protocol Context Management Extensions",
draft-winterbottom-geopriv-held-context-02 (work in progress),
February 2008.
[15] Thomson, M. and J. Winterbottom, "Discovering the Local
Location Information Server (LIS)",
draft-ietf-geopriv-lis-discovery-02 (work in progress),
July 2008.
[16] Garcia-Martin, M., Tschofenig, H., and H. Schulzrinne,
"Indirect Presence Publication with the Session Initiation
Protocol(SIP)",
draft-garcia-simple-indirect-presence-publish-00 (work in
progress), February 2008.
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Appendix A. GEOPRIV Using Protocol Compliance
This section compares the GEOPRIV requirements described in [8] with
the approach outlined in this document.
Req. 1. (Location Object generalities):
o Regarding requirement 1.1, the Location Object has to be
understood by the Location Recipient and the Location Server, the
two communication end points. The PIDF-LO [4] allows both civic
and geospatial location information to be expressed. Combining
this with [6] ensures that location can be constructed and
interpreted in a consistent manner.
o Regarding requirement 1.2, a number of fields in the civic
location information format are optional.
o Regarding requirement 1.3, the civic location information is
defined in an extensible way.
o Regarding requirement 1.4, the location information itself is not
defined in this document.
o Regarding requirement 1.5, the protocol described in this document
allows the Location Recipient to resolve a reference to a PIDF-LO
only.
o Regarding requirement 1.6, the Location Object contains both
location information and privacy rules. Depending on the
deployment scenario, which is outside the scope of this document,
the privacy rules might have stronger or a weaker semantic.
o Regarding requirement 1.7, the Location Object is usable in a
variety of protocols.
o Regarding requirement 1.8, no change regarding with respect to the
encoding of the Location Object (see [4]) was made by this
document.
Req. 2. (Location Object fields):
o Regarding requirement 2.1, depending on the deployment scenario an
identifier pointing to the Target may be carried inside the
PIDF-LO since the PIDF object provides the ability to carry this
identifier. In some circumstances it might be desirable not to
carry information about the Target's identity in the PIDF-LO.
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o Regarding requirement 2.2, depending on the deployment scenario
the LIS might require that the Location Recipient performs an
authentication step. The security mechanisms for client and
server authentication are outside the scope of this document and
defined already for HTTPS itself.
o Regarding requirement 2.3, proof of possession of the Location
Recipient credentials is provided outside the scope of this
document. The security mechanisms defined for HTTPS are used by
this document.
o Regarding requirement 2.5, RFC 4119 defines the basis for carrying
location information in a PIDF document. The ability to extend
RFC 4119 to convey motion specific information is work in
progress.
o Regarding requirement 2.6, this document as specified only allows
the Location Recipient to resolve the reference and to indicate
which location format has to be returned.
o Regarding requirement 2.7, the PIDF-LO relevant elements and
attributes are available.
o Regarding requirement 2.8, provision exists for a reference to an
external (more detailed rule set) within the PIDF-LO to be made.
This is the <external-ruleset> element.
o Regarding requirement 2.9, security headers and trailers are
provided Transport Layer Security.
o Regarding requirement 2.10, extensibility within the PIDF-LO is
provided regarding the definition of namespaces.
Req. 3. (Location Data Types):
o Regarding requirement 3.1, [4] defines geospatial location
information as the mandatory to implement location format. [6]
describes in more detail the acceptable forms of geolocation and
its interaction with civic notations.
o With the support of civic and geodedic location information in [4]
the requirement 3.2 is fulfilled.
o Regarding requirement 3.3, rules described in [13] apply to an
absolute geodetic point. Geodetic information expressed in a
PIDF-LO that complies with [6] may express an area or volume
there-by "fuzzing" the location of the Target.
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o Regarding requirement 3.4, since the PIDF-LO format is designed to
be extensible it allows further location information types to be
defined in the future.
Section 7.2 of [8] details the requirements of a "Using Protocol".
These requirements are listed below:
Req. 4. The using protocol has to obey the privacy and security
instructions coded in the Location Object regarding the
transmission and storage of the LO. This document carries
the PIDF-LO as is via HTTPS from the LIS to the Location
Recipient. The sending and receiving parties must obey 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. This document does
not define additional security mechanisms beyond HTTPS.
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
transaction. The encoding of the RFC 4119-defined Location
Object format is not changed. Because of the verbose XML
encoding it is not tailored towards inclusion into a single
message.
Section 7.3 of [8] details the requirements of a "Rule based Location
Data Transfer". These requirements are listed below:
Req. 7. (LS Rules): Access to location information is controlled by
allowing the Target (or by an entity on behalf of the
Target) to indicate to which Location Recipients the short-
lived location URI that contains a unguessable random
component. Additionally, constraints can be put on the
dereferencing step by the Target.
Req. 8. (LG Rules): In context of location URI it is not possible
that there is no relationship between the Location Generator
and the Location Information Server. As such, the statement
made in Requirement 7 applies.
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Req. 9. (Viewer Rules): The Rule Maker might define (via mechanisms
outside the scope of this document) which policy rules are
disclosed to other entities. These mechanisms are available
with [13]. These rules are, however, best used when the
location URI is not directly provided to Location Recipients
but rather to an intermediary that stores these
authorization policies, such as a location-based presence
server.
Req. 10. (Full Rule language): Geopriv has defined a rule language
capable of expressing a wide range of privacy rules which
is applicable in the area of the distribution of Location
Objects. The format of these rules are described in [12]
and [13]. These rules may be used in a larger context but
this document does not define their usage.
Req. 11. (Limited Rule language): A limited (or basic) ruleset was
introduced with PIDF-LO [4]).
Section 7.4 of [8] details the requirements of "Location Object
Privacy and Security". These requirements are listed below:
Req. 12. (Identity Protection): Identity protection of the Target
can be provided if both the following conditions are true:
(a) the protocol used to convey the reference does not
disclose the identity of the Target and
(b) if the PIDF-LO does not contain information about the
identity about the Target.
Currently, there is no mechanism available that allows the
Target to tell the LIS which identity information to
include in the PIDF-LO.
Req. 13. (Credential Requirements): The 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.
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Req. 14. (Security Features): 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 these
requirements.
Req. 15. Minimal Crypto: The mandatory to implement ciphersuite is
provided in the TLS layer security specification.
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Appendix B. HELD Compliance to IETF Location Reference Requirements
This section describes how HELD complies to the location reference
requirements stipulated in [7].
High-level requirements for a location configuration protocol.
C1. "Location URI support - LCP: The configuration protocol MUST
support a location reference in URI form."
COMPLY. HELD only provides location references in URI form.
C2. "Location URI expiration: The LCP MUST support the ability to
specify to the server, the length of time that a location URI
will be valid."
COMPLY. basic HELD supports the LIS informing the Target of the
location URI expiry time. HELD context management extension
[14] provides the Target the ability to specify exipry times for
location URIs.
C3. "Location URI cancellation: The LCP MUST support the ability to
request the cancellation of a specific location URI."
COMPLY. HELD context management extension [14] provides the
Target the ability to void location URIs when required.
C4. "Random Generated: The location URI MUST be hard to guess, i.e.,
it MUST contain a cryptographically random component."
COMPLY. The HELD specification provides specific guidance on
the security surrounding location URI generation.
C5. "Identity Protection - LCP: The location URI MUST NOT contain
any information that identifies the user, device or address of
record within the URI form."
COMPLY. The HELD specification provides specific guidance on
the anonymity of the Target with regards to the generation of
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location URIs.
C6. "Reuse flag default: The LCP MUST support the default condition
of a requested location URI being repeatedly reused."
COMPLY. The default semantics of location URIs in HELD place no
limits on the number of times that a location URI can be
dereferenced.
C7. "One-time-use: The LCP MUST support the ability for the client
to request a 'one-time-use' location URI (e.g., via a reuse flag
setting)."
COMPLY. HELD context management extension [14] provides the
Target the ability to set the number of times that a location
URI may yield the Target's location.
High-level requirements for a location dereference protocol.
D1. "Location URI support - LDP: The LDP MUST support a location
reference in URI form."
COMPLY. HELD only provides location references in URI form.
D2. "Location URI expiration status: The LDP MUST support a message
indicating that for a location URI which is no longer valid,
that the location URI has expired."
COMPLY. HELD indicates to the requestor that location for the
URI cannot be provided by returning a locationUnknown error when
a location URI is found to have expired.
D3. "Authentication: The LDP MUST support either client-side and
server-side authentication between client and server."
COMPLY. Client authentication may be provided using a variety
of techniques. However, this document does not mandate a
specific procedure nor does it specify the format of
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authorization policies that may be in place to control access at
the LIS. The server authenticates itself using the methods
described in HTTP on TLS [3].
D4. "Dereferenced Location Form: Location URI dereferencing MUST
result in a well-formed PIDF-LO."
COMPLY. HELD when used as a dereference protocol MUST provide
location information as a PIDF-LO that complies with [6] as
described in Section 4.
D5. "Repeated use: The LDP MUST support the ability for the same
location URI to be resolved more than once, based on server
settings and LCP parameters."
COMPLY. A Location Recipient may access and use a location URI
as many times as desired until such time as the URI expires due
to age, or is made invalid by other Target policies on the LIS.
D6. "Updated location: The LDP MUST support the ability for the same
location URI to be resolved into a continuum of location values
(e.g., location updates)."
COMPLY. Using base-HELD the location of the Target is
determined each time that URI is accessed.
D7. "Location form: The LDP MUST support dereferenced location in
both coordinate and civic forms."
COMPLY. HELD provide the locationType parameter allowing the
Location Recipient the ability to specify the form of location
they require.
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Authors' Addresses
James Winterbottom
Andrew Corporation
PO Box U40
University of Wollongong, NSW 2500
AU
Phone: +61 242 212938
Email: james.winterbottom@andrew.com
URI: http://www.andrew.com/products/geometrix
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building, New York, NY 10027
US
Phone: +1 212 939 7004
Email: hgs@cs.columbia.edu
URI: http://www.cs.columbia.edu
Martin Thomson
Andrew Corporation
PO Box U40
University of Wollongong, NSW 2500
AU
Email: martin.thomson@andrew.com
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Martin Dawson
Andrew Corporation
PO Box U40
University of Wollongong, NSW 2500
AU
Email: martin.dawson@andrew.com
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