]> Andrew Corporation

PO Box U40 University of Wollongong NSW 2500 AU +61 242 212938 james.winterbottom@andrew.com http://www.andrew.com/products/geometrix

Nokia Siemens Networks

Linnoitustie 6 Espoo 02600 Finland +358 (50) 4871445 Hannes.Tschofenig@gmx.net http://www.tschofenig.priv.at

Columbia University

Department of Computer Science 450 Computer Science Building New York, NY 10027 US +1 212 939 7004 hgs@cs.columbia.edu http://www.cs.columbia.edu

Andrew Corporation

PO Box U40 University of Wollongong NSW 2500 AU martin.thomson@andrew.com

Andrew Corporation

PO Box U40 University of Wollongong NSW 2500 AU martin.dawson@andrew.com

RAI GEOPRIV Internet-Draft HELD Dereference lbyr HTTP Location GEOPRIV 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.

Provision of location information by reference involves the creation of a resource that is identified by a "location URI". A "location URI" identifies resource that contains the location of an entity. A location URI might be a temporary resource, created in response to a HTTP-Enabled Location Delivery (HELD) 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. The HELD protocol, as described in , 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 location object in the form of a Presence Information Data Format - Location Object (PIDF-LO) document. A constrained set of HELD features are defined such that it is suitable for use as a location dereference protocol. Use as a location dereference protocol requires use of the Transport Layer Security (TLS) binding for HTTP 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 . 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 for the HTTP binding of HELD. 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 . This diagram shows how a location dereference protocol fits with location configuration and conveyance. contains more information on this scenario and others like it.

| . | : | | : Location | . | locationResponse | . Configuration | : |<-----(location URI)-----| : Protocol | . | | . | `- + - - - - - - - - - - - - + -' | | | | | Location Conveyance | |~ ~ ~ ~ ~ ~ ~ ~ ~ ~(location URI)~ ~ ~ ~ ~ ~ ~ ~ ~>| | | | | .- + - - - - - - - - - - - - + -. | : | locationRequest | : | . |<--------(civic)---------| . | Dereferencing : | | : | Protocol . | locationResponse | . | : |--------(PIDF-LO)------->| : | . | | . | `- + - - - - - - - - - - - - + -' | | | ]]>

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 . This document uses key terminology from several sources: terms for the GEOPRIV reference model defined in and ; the term Location Information Server (LIS), from , is a node in the access network that provides location information to an end point; a LIS provides location URIs; the term Location Server (LS), from , is used to identify the server that responds to a location dereference request; this might be the same entity as the LIS, but the model in allows for the existence of separate - but related - entities; and the term location URI is coined in .

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. These two models can, however, be used in combination in a real deployment. , from , shows the model applicable to location configuration, conveyance and dereference.

It is important to note that this document does not mandate a specific authorization model, nor does it constrain the usage with regard to these models in any way. Additionally, it is possible to combine certain parts of both models. For either authorization model, the overall process is similar. The following steps are followed, with minor alterations: The Target acquires a location URI from the LIS. This might use HELD as a location configuration protocol (LCP). The Target then conveys the location URI to a third party, the Location Recipient (for example using SIP as described in ). This step is shown in (2) of . 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 document. In this final step, the Location Server (LS) or LIS makes an authorization decision. How this decision is reached depends on the authorization model.

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 ) 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 or S/MIME, protects the information from eavesdroppers. Use of authorization by possession location URIs in a hop-by-hop protocol such as SIP 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 indefinitely. 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, as is the case with .

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 , 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 and Geolocation 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 the identity of Location Recipients, constrain the accuracy and form of location information, and to control other aspects of the authorization process.

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 resource. 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 . 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. Given that a location URI does not indicate the authorization model used, the Location Recipient MUST be prepared to provide authentication information unless it has external information on the authorization model used by the URI. This document does not specify how the LS authenticates the Location Recipient; however, a Location Recipient MUST support provision of a client certificate during TLS session creation and HTTP digest authentication, unless these authentication methods are known to be inapplicable.

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 . 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). Other specifications MUST explicitly describe whether other requests or parameters apply to dereference requests and how they are to be interpreted if they are permitted. The LS MUST ignore any parameters that it does not understand unless it knows the parameters to be invalid, such as those defined in . If parameters are known to be invalid, the LS MAY generate a HELD error response. The LS MUST NOT generate any 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. This document requires additional HTTP features from Location Recipients that are not required of Devices in HELD. HTTP digest authentication MUST be supported by Location Recipients, unless there is no means to provide such authentication information.

The example in shows the simplest form of dereferencing request using HELD to the location URI https://ls.example.com:49152/uri/w3g61nf5n66p0. The only way that this differs from the example in Section 10.1 of is in the request URI and the source of the URI.

]]>

shows the response to the previous request listing both civic and geodetic location information of the Target's location. If this looks similar to the response in Section 10.1 of , that is no coincidence - unless policy specfies otherwise, the Location Recipient receives the same information as the Device.

-34.407 150.88001 2006-01-11T03:42:28+00:00 Wiremap 2006-01-10T03:42:28+00:00 ]]>

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: , . Use of TLS for the dereferencing of location URIs is strongly RECOMMENDED, as discussed in . 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 . Local policy determines what a Location Recipient does is authentication fails, or is not attempted. The authorization by possession model 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 references. This 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 Location Recipient MUST be prepared to provide authentication credentials when making a dereference request. To comply with identity protection requirements in , the LS MUST NOT include any information that could be used to identify a Target, unless policy is provided that allows this. To this end, an unlinked pseudonym MUST be provided in the entity attribute of the PIDF-LO document. Further security considerations and requirements relating to the use of location URIs are described in .

This document makes no request of IANA. [[IANA/RFC-EDITOR: Please remove this section before publication.]]

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.

&RFC2119; &RFC2616; &RFC2617; &RFC2818; &RFC3986; &RFC4119; &RFC4395; &RFC5234; &RFC5491; &I-D.ietf-geopriv-http-location-delivery; &RFC3261; &RFC3693; &RFC3851; &RFC4745; &RFC4825; &RFC5246; &I-D.ietf-geopriv-lbyr-requirements; &I-D.ietf-geopriv-l7-lcp-ps; &I-D.ietf-geopriv-policy; &I-D.ietf-geopriv-lis-discovery; &I-D.ietf-sip-location-conveyance; &I-D.winterbottom-geopriv-held-context; &I-D.winterbottom-geopriv-held-identity-extensions; &I-D.barnes-geopriv-lo-sec;

This section describes how use of HELD as a location dereference protocol complies with the GEOPRIV requirements described in . (Location Object generalities): This section relates to the PIDF-LO document, which is used by HELD. These requirements are addressed by and . (Location Object fields): This section relates to the PIDF-LO document, which is used by HELD. These requirements are addressed by and . (Location Data Types): This section relates to the PIDF-LO document, which is used by HELD. These requirements are addressed by and . Section 7.2 of details the requirements of a "Using Protocol". These requirements are repeated here for reference, followed by a statement of compliance: "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 LIS to the Location Recipient. The sending and receiving parties must obey the instructions carried inside the object. "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. Location Recipient is accomplished using certificates exchanged using TLS, or through HTTP digest authentication. Authentication of Location Recipients as specified in this document requires pre-arrangement; further key establishment methods are left to later work. "(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." Not Compliant: The XML encoding specified in is not suited to single packet transfers. It is not the goal of this document to define a new Location Object format. Section 7.3 of details the requirements of a "Rule based Location Data Transfer". These requirements are repeated where they are applicable to this document: "(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." Compliance or Not Applicable: 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 outside the scope of this document. (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. "(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 is used to convey authorization policies from Rule Maker to LS, this is possible using the parameters specified in . (Full Rule language) Not Applicable: Note however that Geopriv has defined a rule language capable of expressing a wide range of privacy rules (see and . (Limited Rule language) Not Applicable: This requirement applies to (and is addressed by) PIDF-LO. Section 7.4 of details the requirements of "Location Object Privacy and Security". These requirements are repeated where they are applicable to this document: (Identity Protection) Potentially Compliant: Identity protection of the Target is provided as long as both of the following conditions are true: the location URI is not associated with the identity of the Target in any context, and if 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. recommends that an unlinked pseudonym is used by the LS. (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. (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 these requirements. (Minimal Crypto) Compliant: The mandatory to implement ciphersuite is provided in the TLS layer security specification.

This section describes how HELD complies to the location reference requirements stipulated in . Compliance to the Location Configuration Protocol are included in this document. 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 held: location URIs that are acquired by other means.

"location URI support: The configuration protocol MUST support a location reference in URI form." Compliant: HELD only provides location references in URI form. "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. HELD contexts also expire, and an explicit indication is included in the context response; a Device is able to specify limits on the life time of a HELD context. "location URI cancellation: The location configuration protocol MUST support the ability to request a cancellation of a specific location URI." Compliant conditional on on the source of the location URI: HELD contexts can be explicitly removed. HELD does not provide a method for cancelling location URIs. "Location Information Masking: The location URI form MUST, through randomization and uniqueness, ensure that any location specific information embedded within the location URI itself is kept obscure during location configuration." Compliant: The HELD specification explicitly references this requirement in providing guidance on the format of the location URI. "User Identity Protection: The location URI MUST NOT contain any user identifying information that identifies the user, device or address of record, (e.g., which includes phone extensions, badge numbers, first or last names, etc.), within the URI form." Compliant: The HELD specification provides specific guidance on the anonymity of the Target with regards to the generation of location URIs. expands on this guidance. "Reuse indicator: There SHOULD be a way to allow a client to control whether a location URI can be resolved once only, or multiple times." Compliant: The default semantics of location URIs in HELD place no limits on the number of times that a location URI can be dereferenced. "Validity Interval Indication: A location configuration protocol MUST provide an indication of the location URI validity interval (i.e., expiry time) when present." Duplicate Requirement: As above. "Location only: The location URI MUST NOT point to any information about the Target other than it's location." Compliance depends on implementation: A PIDF-LO document can contain information other than location, but no protocol semantics exist that allow for or encourage inclusion of other information. "Location URI Not guessable: Where location URIs are used publicly, any location URI MUST be constructed using properties of uniqueness and cryptographically random sequences so that it is not guessable." Compliant: HELD specifies that location URIs conform to this requirement. "Location URI Optional: In the case of user-provided authorization policies, where anonymous or non-guessable location URIs are not warranted, the location configuration protocol MAY support optional location URI forms." Not Compliant: HELD does not support Device-specified location URI forms. "Location URI Authorization Model: The location configuration protocol SHOULD indicate whether the requested location URI conforms to the access control authorization model or the possession authorization model." Compliant: HELD explicitly indicates that the possession model applies to all URIs. "Location URI Lifetime: A location URI SHOULD have an associated expiration lifetime (i.e., validity interval), and MUST have an validity interval if used with the possession authorization model." Duplicate Requirement: As above.

"Location URI support: The location dereference protocol MUST support a location reference in URI form." Compliant: HELD only provides location references in URI form. "Validity Interval Indication: A location dereference protocol MUST provide an indication of the location URI validity interval (i.e., expiry time) when present." Invalid Requirement: not applicable to location dereference protocols. "Authentication: The location dereference protocol MUST include mechanisms to authenticate both the client and the server." Compliant: TLS provides means for mutual authentication. This document only specifies the required mechanism for server authentication. "Dereferenced Location Form: The value returned by the dereference protocol MUST contain a well-formed PIDF-LO document." Compliant: HELD requires that location objects are in the form of a PIDF-LO that complies with . "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 configuration." 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. "Validity Interval Indication: A dereference protocol MUST provide an indication of the location URI validity interval (i.e., expiry time) when present." Not Compliant: This document does not provide this indication - this information is arguably useful to a Location Recipient, but it also reveals something about the policy associated with the location URI. Without also providing a mechanism to suppress this capability and hide the expiry time, this might reveal more information than a Rule Maker is willing to share. "Location URI anonymized: Any location URI whose dereference will not be subject to authentication and access control MUST be anonymized." Not applicable to location dereference protocols - applies to the creation of the URI. "Location Information Masking: The location URI form MUST, through randomization and uniqueness, ensure that any location specific information embedded within the location URI itself is kept obscure during location URI dereferencing." Not applicable to location dereference protocols - applies to the creation of the URI. "Location Privacy: The location dereference protocol MUST support the application of privacy rules to the dissemination of a requested location object." Compliant: Authorization policy must be applied by the LS for all attempts at dereferencing. Note that in the case of authorization by possession, this authorization policy grants access to location information based on proof of knowledge of the location URI. "Location Confidentiality: The dereference protocol MUST support encryption of messages sent between the location dereference client and the location dereference server, and MAY alternatively provide messaging unencrypted." Compliant: This document strongly recommends the use of TLS for confidentiality. Unsecured HTTP is permitted, and some of the associated risks are described in . "Location URI Authorization Model: The location dereference protocol SHOULD indicate whether the requested location URI conforms to the access control authorization model or the possession authorization model." Not Compliant: The basis of an authorization decision is potentially private information; this document does not provide this indication. Note that the recipient of a location URI is expected to respect the confidentiality of a location URI as if it were secret, even if it is not.