GeoPriv R. Marshall, Ed. Internet-Draft TCS Intended status: Informational
February 25,July 9, 2008 Expires: August 28, 2008January 10, 2009 Requirements for a Location-by-Reference Mechanism draft-ietf-geopriv-lbyr-requirements-02draft-ietf-geopriv-lbyr-requirements-03 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 28, 2008. Copyright Notice Copyright (C) The IETF Trust (2008).January 10, 2009. Abstract This document defines terminology and provides requirements relating to Location-by-Reference approach using a location URI to handle location information within signaling and other Internet messaging. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview of Location-by-Reference . . . . . . . . . . . . . . 6 4. High-Level Requirements . . . . . . . . . . . . . . . . . . . 9 4.1. Requirements for a Location Configuration Protocol . . . 9 4.2. Requirements for a Location Dereference Protocol . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1. Normative References . . . . . . . . . . . . . . . . . . . 17 8.2. Informative References . . . . . . . . . . . . . . . . . . 17 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 18 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 1920 Intellectual Property and Copyright Statements . . . . . . . . . . 2021 1. Introduction Location-based services rely on ready access to location information, which can be through a direct or indirect mechanism. While there are mechanisms for providing location directly, (e.g., as part of the SIP signaling protocol), an alternative mechanism has been developed for handling location indirectly, via a location reference, a pointer to the actual location information. This reference is called a location URI, and is used by the mechanism we generally call the Location-by- Reference mechanism, or simply, LbyR. The use of a location URI is generally applied in one of the following ways: 1. Creation/allocation of a location URI, by a location server based on some request mechanism. 2. As part of a Location Configuration Protocol, between a target and location server*. 3. The location dereference process, (between a dereference client and dereference server). 4. Cancellation/expiration of a location URI, by a location server based on either a direct target request or some other action (e.g., timer). *In this document, we make no differentiation between a LS, per RFC3693, and a LIS, but may refer to either of them as a location server interchangeably. These four things fall under two general protocol mechanisms, location configuration protocols and location dereference protocols. A fifth use of location URI is within the context of what is called location conveyance. Location conveyance is defined as part of the SIP protocol, and is out of scope for this document. (see [I-D.ietf-sip-location-conveyance] for an explanation of conveyance of location using a location URI. The issues around location configuration protocols have been documented in a location configuration protocol problem statement and requirements document [I-D.ietf-geopriv-l7-lcp-ps]. There are currently a several examples of a location configuration protocol. These include DHCP, LLDP-MED, and HELD [I-D.ietf-geopriv-http-location-delivery]) protocols. The structure of this document includes terminology, Section 2, followed by a discussion of the basic elements that surround how a location URI is used. These elements, or actors, are discussed in an overview section, Section 3, accompanied by a graph and associated processing steps. Requirements are outlined accordingly, separated as location configuration requirements, Section 4.1, and location dereference requirements, Section 4.2. In contrast to using a location URI as the mechanism to support a Location-by-Reference model, it may be worth mentioning the common alternative model, that of Location-by-Value (LbyV), which provides location directly. LbyV uses a location object, (e.g., a PIDF-LO, [RFC4119]) within SIP signaling. Using the LbyV model for location configuration is considered out of scope for this document (see [I-D.ietf-sip-location-conveyance] for an explanation of location conveyance for either LbyR or LbyV scenarios. Location determination, different than location configuration or dereferencing, often includes topics related to manual provisioning processes, automated measurements, and/or location transformations, (e.g., geo-coding), and are beyond the scope of this document. 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 RFC 2119 [RFC2119]. This document reuses the terminology of [RFC3693], such as Location Server (LS), Location Recipient (LR), Rule Maker (RM), Target, Location Generator (LG), Location Object (LO), and Using Protocol: Location-by-Value (LbyV): The mechanism of representing location either in configuration or conveyance protocols, (i.e., the actual included location value). Location-by-Reference (LbyR): The mechanism of representing location by means of a location URI for use in either a location configuration, conveyance, or dereferencing protocol, and which refers to a fully specified location. Location Configuration Protocol: A protocol which is used by a client to acquire either location or a location URI from a location configuration server, based on information unique to the client. Location Dereference Protocol: A protocol which is used by a client to query a location dereference server, based on location URI input and which returns location information. Location URI: An identifier which serves as a pointer to a location record on a remote host (e.g., LIS). Used within an Location-by- Reference mechanism, a location URI is provided by a location configuration server, and is used as input by a dereference protocol to retrieve location from a dereference server. 3. Overview of Location-by-Reference In mobile wireless networks it is not efficient for the end host to periodically query the LIS for up-to-date location information. This is especially the case when power is a constraint or a location update is not immediately needed. Furthermore, the end host might want to delegate the task of retrieving and publishing location information to a third party, such as to a presence server. Finally, in some deployments, the network operator may not want to make location information widely available. Different location scenarios, such as whether a Target is mobile and whether a mobile device needs to be located on demand or according to some pre-determined interval motivated the introduction of the LbyR concept. Depending on the type of reference, such as HTTP/HTTPS or SIP Presence URI, different operations can be performed. While an HTTP/HTTPS URI can be resolved to location information, a SIP Presence URI provides further benefits from the SUBSCRIBE/NOTIFY concept that can additionally be combined with location filters [I-D.ietf-geopriv-loc-filters]. +-----------+ Geopriv +-----------+ | | Location | Location | | LIS +---------------+ Recipient | | | Dereference | | +-+---+-----+ Protocol (3) +----+------+ * | -- Rulemaker * | Geopriv -- Policy * | Location -- Exchange * | Configuration -- (1b) * | Protocol -- * | (1a) -- Geopriv * | -- Using Protocol + - - - -*- - - - - -|- - - -+ -- (e.g., SIP) |+------+----+ +-----+-----+ |-- (2) | Rulemaker | | Target / |-- || / owner | | End Host + | | | | | |+-----------+ +-----------+ | | User of Target | + - - - - - - - - - - - - - -+ Figure 1: Shows the assumed communication model for both a layer 7 location configuration protocol and a dereference protocol: Figure 1: Shows the assumed communication model for both a layer 7 location configuration protocol and a location dereference protocol. (1a). Target requests reference from server; and receives back, a location URI in server response (1b). Rulemaker policy is consulted (interface out of scope) (2). Target conveys reference to recipient (out of scope) (3). Recipient dereferences location URI, by a choice of methods, including a request/response (e.g., HTTP) or publish/subscription (e.g., SIP SUBSCRIBE/NOTIFY) Note A. There is no requirement for using the same protocol in (1a) and (3). Note B. Figure 1 includes the interaction between the owner of the Target and the LIS to establish Rulemaker policies. This is communications path (1b). This interaction needs to be done before the LIS will authorize anything of than default policies to a dereference request for location of the Target. Note C. that the Target may take on the role of the Location Recipient whereby it would dereference the location URI to obtain its own location information. An example scenario of how this might work, is where the Target obtains a location URI in the form of a subscription URI (e.g., a SIP URI) via HELD, (a Geopriv layer 7 location configuration protocol). Since, in this case the Target equals Recipient, then the Target can subscribe to the URI in order to be notified of its current location based on subscription parameters (see [I-D.ietf-geopriv-loc-filters]). Additionally, a geospatial boundary can be expressed (ref. [I-D.ietf-geopriv-policy]), so that the Target/Recipient will get its updated location notification once it crosses the specified boundary. Location URIs may have an life expirationexpiry associated to them, so that the LIS needs to beis able to keep track of the location URIs that have been handed out, in addition,to alsoknow about validity information for eachwhether a location URI. Location URIs need to expire to preventURI is still valid once the LIS receives it in a request, and in order for a recipient of such a URI from being able to (in some cases) permanently track a host. Another exampleOther justifications for expiration of location URIs include the usefulness of an expiration mechanism isability for a LIS to offerdo garbage collection capabilitiescollection. Because a location URI is a pointer to the LIS. ItTarget's location, it is important that it be constructed in such a way that it does not unintentionally reveal any usable information about the Target it represents. For example, it is important to prevent adversaries from obtaining any information that may be revealed about a Target throughby direct examination of the location URI itself, (e.g., names, identifiers, etc.), some determinable pattern or even a Target's location if the ownersyntax (e.g., sequence of the Target wants to protect it.numbers), or guessable codes (e.g., weak encryption). Therefore, each location URI must be constructed with security safeguards in mind. There are two general cases assumed, both having to do withHow a location URI is will ultimately be used within the form ofdereference step is an important consideration at the time that the location URI whenis requested via a location configuration protocol. Since dereferencing of location URIs could be done according to one of two models, an "access control" model or a "possession" model (see below), it is created. Caseimportant that location configuration protocols indicate the type of a location URI that is being requested, (and also which type is returned). Dereference protocols must support both types. 1. Where accessAccess control use type: Access to the location URI is limited by policy:policy. This is the case wherewhere, for location configuration, the LIS applies (server side) authentication and access control at the location configuration stepstep, and again at therepeats authentication and authorization for each dereference step. In this case, the URI can beoperation of any form chosen by the LIS. Casethat location URI. 2. Access limited by distribution:Possession use type: The LIS does not applypossession use type is described as having no authentication and access control atand/or authorization requirement aside from only possessing the time thatlocation URI itself (in this case, possession implies authorization). Access to the location URI is dereferenced.limited by distribution only. Whoever possesses the location URI has the ability to dereference it. Possession use types may be used within specified domains only, or might be used across wide open public networks. In this case,either of the above cases, a location URI mustneeds to be constructed is such a way as to make it difficult to guess (soguess. The form of the URI is constrained by the degree of randomness and uniqueness applied to it. It is important to protect the actual location information from an intermediate node (despite the fact that in the possession canmodel there would be usednothing to imply authorization).prevent an interceptor from seeking to dereference the location URI). Obfuscating the location URI safeguards against the undetected stripping off of what would otherwise be evident location information, since it forces a dereference operation by the location dereference server, an important step for the purpose of providing statistics, audit trails, and general logging for many different kinds of location based services. 4. High-Level Requirements This document outlines the requirements for an Location by Reference mechanism which can be used by a number of underlying protocols. Requirements here address two general types of such protocols, a general location configuration protocol, and a general location dereferencing protocol. Given that eitherEach of these two general protocols can take the form of different protocols implementations for either locationhas multiple specific protocol implementations. Location configuration vs.protocols include, HELD, DHCP, and LLDP-MED, whereas current location dereference, (e.g., HELD/DHCP/LLDP-MED, vs.dereferencing protocols include HELD Deref, HTTP GET/SIP SUBSCRIBE/NOTIFY, respectively).GET, and SIP SUBSCRIBE/NOTIFY. Because each of these specific protocol implementations has its own unique client and server interactions, the requirements here are not intended to state what a client or server is expected to do, but rather which requirements must be met separately by either aany location configuration protocol,protocol or alocation dereference protocol, for the purposes of using a location URI. The requirements are broken into two sections. 4.1. Requirements for a Location Configuration Protocol Below, we summarize high-level design requirements needed for a location-by-reference mechanism as used within the location configuration protocol. C1. Location URI support: The configuration protocol MUST support a location reference in URI form. Motivation: It is helpful to have a consistent form of key for the LbyR mechanism. C2. Location URI expiration: When a location URI has a limited validity interval, its lifetime MUST be indicated. Motivation: A location URI may not intend to represent a location forever, and the identifier eventually may need to be recycled, or may be subject to a specific window of validity, after which the location reference fails to yield a location, or the location is determined to be kept confidential. C3. Location URI cancellation: The location configuration protocol SHOULD support the ability to request a cancellation of a specific location URI. Motivation: If the client determines that in its best interest to destroy the ability for a location URI to effectively be used to dereference a location, then there should be a way to nullify the location URI. C4. [Deleted, replaced by C8,C9,C10]: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. Motivation: It is important to keep any location information masked from a casual observing node. C5. 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. Motivation: It is important to protect caller identity or contact address from being included in the form of the location URI itself when it is generated. C6. 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. Motivation: The client requesting a location URI may request a location URI which has a 'one-time-use' only characteristic, as opposed to a location URI having multiple reuse capability. C7. Location URI Valid-for: A location URI validity interval, if used, MUST include the validity time, in seconds, as an indication of how long the client can consider a location URI to be valid. Motivation: It is important to be able to determine how long a location URI is to remain useful for, and when it must be refreshed. C8. Location URI Anonymous: The location URI MUST NOT revealpoint to any information about the Target other than it's location. Motivation: A user should have the option to control how much information is revealed about them. This provides that control by not forcing the inclusion of other information with location, (e.g., to not include any identification information in the location URI.) C9. Location URI Not guessable: LocationWhere location URIs that do not require authentication and authorizationare used publicly, any location URI MUST NOTbe guessable, based on the useconstructed using properties of auniqueness and cryptographically random sequence somewhere within the URI.sequences so that it is not guessable. (Note that the number of bits depends to some extent on the number of active location URIs that might exist at the one time; 128-bit is most likely enough for the shortnear term.) Motivation: Location URIs without access control reveal private information, and a guessable location URI could be easily exploitedneed to obtain private information.guard against any observing node or individual stripping off meaningful information about the Target. C10. 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. Motivation: Users don't always have such strict privacy requirements, but may opt to specify their own location URI, or components thereof. C11. Location URI Use Type: The location configuration protocol MUST indicate whether the requested location URI conforms to the access control model or the possession model. Motivation: Downstream dereference clients and servers need to know whether a location URI provided by the location configuration protocol conforms to an access control model or a possession model. 4.2. Requirements for a Location Dereference Protocol Below, we summarize high-level design requirements needed for a location-by-reference mechanism as used within the location dereference protocol. D1. Location URI support: The location dereference protocol MUST support a location reference in URI form. Motivation: It is required that there be consistency of use between location URI formats used in an configuration protocol and those used by a dereference protocol. D2. Location URI expiration indicator: The location dereference protocol MUST support an indicator showing that, if it is the case, that a location URI is no longer valid due to expiration. Motivation: Location URIs are expected to expire, based on location configuration protocol parameters, and it is therefore useful to convey the expired status of the location URI in the location dereference protocol. D3. Authentication: The location dereference protocol MUST include mechanisms to authenticate both the client and the server. Motivation: Although the implementations must support authentication of both parties, any given transaction has the option not to authenticate one or both parties. D4. Dereferenced Location Form: The value returned by the dereference protocol MUST contain a well-formed PIDF-LO document. Motivation: This is in order to ensure that adequate privacy rules can be adhered to, since the PIDF-LO format comprises the necessary structures to maintain location privacy. D5. 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. Motivation: Through dereference server configuration, for example, it may be useful to not only allow more than one dereference request, but, in some cases, to also limit the number of dereferencing attempts by a client. D6. Location URI Valid-for: A location URI validity interval, if used, MUST include the validity time, in seconds, as an indication of how long the client can consider a location URI to be valid. Motivation: It is important to be able to determine how long a location URI is to remain useful when dereferencing a location URI. D7. Location URI anonymized: Any location URI whose dereference will not be subject to authentication and access control MUST be anonymized. Motivation: The dereference protocol must define an anonymized format for location URIs. This format must identify the desired location information via a random token with at least 128 bits of entropy (rather than some kind of explicit identifier, such as an IP address). D8. Location URI non-anonymized:Information Masking: The dereference protocol MAY define a more general, non-anonymizedlocation URI form MUST, through randomization and uniqueness, ensure that any location specific information embedded within the location URI format.itself is kept obscure during location URI dereferencing. Motivation: OnlyIt is important to keep any location URIs for whichinformation masked from a casual observing node, requiring instead a discrete dereference is subjectoperation in order to access-control policy by the LIS may use this format.return location information. D9. Location Privacy: The location dereference protocol MUST support the application of privacy rules to the dissemination of a requested location object. Motivation: The dereference server must obey all provisioned privacy rules that apply to a requested location object. D10. 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. Motivation: Environmental and local configuration policy will guide the requirement for encryption for certain transactions. In some cases, encryption may be the rule, in others, it may be acceptable to send and receive messages without encryption. D11. Location URI Use Type: The location dereference protocol MUST indicate whether the requested location URI conforms to the access control model or the possession model. Motivation: Downstream dereference clients need to know whether a location URI provided by the location configuration protocol conforms to an access control model or a possession model in order to save time processing dereference attempts. 5. Security Considerations The LbyR mechanism currently addresses security issues as follows. A location URI, regardless of its construction, if public, by itself, implies no safeguard against anyone being able to dereference and get the location. The method of constructing athe location URI in its namingform to include randomization along with encryption does help prevent some potential guessing, according to some defined pattern.pattern guessing. In the instancecase of one-time-useone time use location URIs, which function similarly(referred to as a pawn ticket,ticket), the argument can be made that with a pawn ticket,possession implies permission, and location URIs whichthat are public are protected only by privacy rules enforced at the dereference server. 6. IANA Considerations This document does not require actions by the IANA. 7. Acknowledgements We would like to thank the IETF GEOPRIV working group chairs, Andy Newton, Allison Mankin and Randall Gellens, for creating the design team which initiated this requirements work. We'd also like to thank those design team participants for their inputs, comments, and reviews. The design team included the following folks: Richard Barnes; Martin Dawson; Keith Drage; Randall Gellens; Ted Hardie; Cullen Jennings; Marc Linsner; Rohan Mahy; Allison Mankin; Roger Marshall; Andrew Newton; Jon Peterson; James M. Polk; Brian Rosen; John Schnizlein; Henning Schulzrinne; Barbara Stark; Hannes Tschofenig; Martin Thomson; and James Winterbottom. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 8.2. Informative References [I-D.ietf-geopriv-http-location-delivery] Barnes, M., Winterbottom, J., Thomson, M., and B. Stark, "HTTP Enabled Location Delivery (HELD)", draft-ietf-geopriv-http-location-delivery-05draft-ietf-geopriv-http-location-delivery-07 (work in progress), FebruaryApril 2008. [I-D.ietf-geopriv-l7-lcp-ps] Tschofenig, H. and H. Schulzrinne, "GEOPRIV Layer 7 Location Configuration Protocol; Problem Statement and Requirements", draft-ietf-geopriv-l7-lcp-ps-06draft-ietf-geopriv-l7-lcp-ps-08 (work in progress), November 2007.June 2008. [I-D.ietf-geopriv-loc-filters] Mahy, R., "A Document Format for Filtering and Reporting Location Notications in the Presence Information Document Format Location Object (PIDF-LO)", draft-ietf-geopriv-loc-filters-01 (work in progress), March 2007. [I-D.ietf-geopriv-policy] 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-14draft-ietf-geopriv-policy-17 (work in progress), FebruaryJune 2008. [I-D.ietf-sip-location-conveyance] Polk, J. and B. Rosen, "Location Conveyance for the Session Initiation Protocol", draft-ietf-sip-location-conveyance-09draft-ietf-sip-location-conveyance-10 (work in progress), November 2007.February 2008. [RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. Polk, "Geopriv Requirements", RFC 3693, February 2004. [RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object Format", RFC 4119, December 2005. Appendix A. Change log Changes to this draft in comparison to the previous version (-03 vs. -02): 1. Changed wording of section 3 "Overview of Location-by-Reference" (Polk, Thomson, Winterbottom ~ 4/1/08 list comments). 2. Added new requirement C4. "Location Information Masking:", based on (Thomson ~4/1/08 list comment). 3. Added new requirement C11. "Location URI Use Type:", based on (~4/1/08 list comments). 4. Added new requirement D11. "Location URI Use Type:", for deref. based on (~4/1/08 list comments). 5. Replaced requirement D8. "Location URI Non-Anonymized" with "Location Information Masking:". Changes to this draft in comparison to the previous version (-02 vs. -01): 1. Reworded Introduction (Barnes 12/6 list comments). 2. Changed name of "Basic Actors" section to "Overview of Location by Reference" (Barnes). 3. Keeping the LCP term away (for now) since it is used as Link Control Protocol elsewhere (IETF). 4. Changed formatting of Terminology section (Barnes). 5. Requirement C2. changed to indicate that if the URI has a lifetime, it has to have an expiry (Barnes) 6. C7. Changed title and wording based on suggested text and dhcp- uri-option example (Polk). 7. The new C2 req. describing valid-for, was also added into the deref section, as D6 8. Changed C4 based on much list discussion - replaced by 3 new requirements... 9. Reworded C5 based on the follow-on C4 thread/discussion on list (~2/18). 10. Changed wording of D3 based on suggestion (Barnes). 11. Reworded D4 per suggestion (Barnes). 12. Changed D5 based on comment (Barnes), and additional title and text changes for clarity. 13. Added D9 and D10 per Richard Barnes suggestions - something needed in addition to his own security doc. 14. Deleted reference to individual Barnes-loc-sec draft per wg list suggestion (Barnes), but need more text for this draft's security section. Author's Address Roger Marshall (editor) TeleCommunication Systems, Inc. 2401 Elliott Avenue 2nd Floor Seattle, WA 98121 US Phone: +1 206 792 2424 Email: email@example.com URI: http://www.telecomsys.com Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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