GEOPRIV M. Thomson Internet-Draft J. Winterbottom Intended status: Standards Track Andrew Expires: August 26, 2007 February 22, 2007 Digital Signature Methods for Location Dependability draft-thomson-geopriv-location-dependability-00.txt 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 26, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Thomson & Winterbottom Expires August 26, 2007 [Page 1] Internet-Draft Location Dependability February 2007 Abstract The dependability of location information is closely related to the degree of trust placed in the source of that information. This document describes techniques that can be used to mitigate the impact of falsifying location information. The application of digital signatures is described, relating these methods to the attacks that they address. Thomson & Winterbottom Expires August 26, 2007 [Page 2] Internet-Draft Location Dependability February 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Non-Goals . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Basic Countermeasures . . . . . . . . . . . . . . . . . . 6 2.3. Signing Location Information . . . . . . . . . . . . . . . 6 3. PIDF-LO Signature . . . . . . . . . . . . . . . . . . . . . . 7 3.1. Signature Design . . . . . . . . . . . . . . . . . . . . . 7 3.2. Signed Elements and Semantics . . . . . . . . . . . . . . 7 3.3. Signature Algorithms . . . . . . . . . . . . . . . . . . . 9 3.4. LIS/Signer Identification . . . . . . . . . . . . . . . . 9 4. Limited Validity . . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Validity Elements . . . . . . . . . . . . . . . . . . . . 10 5. Signing for a User . . . . . . . . . . . . . . . . . . . . . . 11 5.1. The 'entity' Attribute . . . . . . . . . . . . . . . . . . 11 5.2. Target Identity . . . . . . . . . . . . . . . . . . . . . 12 5.3. Protecting User Anonymity . . . . . . . . . . . . . . . . 12 5.4. Authenticated Identity . . . . . . . . . . . . . . . . . . 13 5.5. Multiple Identity Attack . . . . . . . . . . . . . . . . . 13 6. Target Identity Element . . . . . . . . . . . . . . . . . . . 14 6.1. Identity Types . . . . . . . . . . . . . . . . . . . . . . 14 6.2. Identity Hashing . . . . . . . . . . . . . . . . . . . . . 14 6.3. Authentication Indicator . . . . . . . . . . . . . . . . . 15 7. Signature Validation . . . . . . . . . . . . . . . . . . . . . 16 8. Code and Examples . . . . . . . . . . . . . . . . . . . . . . 17 8.1. Dependability Data Schema . . . . . . . . . . . . . . . . 17 8.2. PIDF-LO Transforms . . . . . . . . . . . . . . . . . . . . 18 8.2.1. PIDF-LO Tuple-only Transform . . . . . . . . . . . . . 19 8.2.2. PIDF-LO Selective Transform . . . . . . . . . . . . . 20 8.3. Example . . . . . . . . . . . . . . . . . . . . . . . . . 21 9. Location Reference Attribution . . . . . . . . . . . . . . . . 25 10. Security Considerations . . . . . . . . . . . . . . . . . . . 26 10.1. Signature Rules . . . . . . . . . . . . . . . . . . . . . 26 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 11.1. URN Sub-Namespace Registration for urn:ietf:params:xml:ns:pidf:geopriv10:dsig . . . . . . . . 27 11.2. XML Schema Registration . . . . . . . . . . . . . . . . . 27 11.3. URN Sub-Namespace Registration for urn:ietf:params:xml:ns:pidf:geopriv10:dsig:identity . . . 28 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30 13.1. Normative References . . . . . . . . . . . . . . . . . . . 30 13.2. Informative References . . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31 Intellectual Property and Copyright Statements . . . . . . . . . . 32 Thomson & Winterbottom Expires August 26, 2007 [Page 3] Internet-Draft Location Dependability February 2007 1. Introduction Location information about a particular person or device is critical to a number of applications. The integrity of this information -- whether or not it can be relied upon for correctness -- is also important to the user of the data. This is especially important if the recipient of location information expends resources based on the information. The quitessential example of an application where the veracity of location information is critical is emergency calling. Location information is used both by routing functions to determine the correct Public Safety Answering Point (PSAP) and by the selected PSAP to determine where to send personnel. If location information were faked, the call could be directed to the wrong PSAP, or personnel could be directed to an incorrect location. In either case, an attacker wastes PSAP resources and risks delaying their life-critical interventions for other legitimate emergency callers. This document details several cryptographic methods that limit the scope of attacks on location recipients based on faked or stolen location information. Methods for applying digital signatures are described so that a location recipient can identify the source of the location information, either Location Information Server (LIS) or Target. Identifying the source allows the location recipient to make a judgement on whether or not to trust the content of the location information. Ultimately, these methods are limited in practicality by the transient nature of the relationships between LIS (the access network) and the Target. Because these relationships can be arbitrary and temporary, schemes like authentication are not always feasible. The basic goal of this draft is to both limit the scope of attacks and to provide as much information to the location recipient as possible so that they can make a decision on whether or not to act on the location information they are provided. 1.1. 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 [RFC2119]. Thomson & Winterbottom Expires August 26, 2007 [Page 4] Internet-Draft Location Dependability February 2007 2. Goals This document describes several measures that can be applied to limit attacks that rely on using faked or stolen location information. These attacks leave a user of location information vulnerable to exploitation by an attacker. The measures outlined in this document are designed to limit exposure to the following attacks: Place Shifting: In place shifting, an attacker selects any location (presumably somewhere other than where they are currently located) and constructs a PIDF-LO based on that information. Time Shifting: In a time shifting, or replay, attack the attacker uses location information that was valid in the past, but is no longer valid because the attacker has moved since the location was generated. Location Theft: An attacker that is able to observe the Target's location information can replay this information and thereby appear to be at the same location. Location Swapping: Two colluding attackers can conspire to fake location by exchanging location information. One attacker can pretend to be at the other's location. These attacks are a subset of those described in [I-D.ietf-geopriv-l7-lcp-ps]. 2.1. Non-Goals The measures outlined in this document cannot hope to address all possible cases of fraud. This section outlines general areas where this document does not provide guidance; more specific limitations are included in the relevant sections. Attacks where the authenticated identity of the Target can be reliably mimicked are not included. This includes active collusion, as well as any attacks, network-based or otherwise, on the Target host that result in complete access to the Target's credentials. In addition, this includes attacks that require cooperation between the attacker and Target. If the attacker is able to gain access to the Target's private key, then to all cryptographic means the attacker can pretend to be the Target. Methods for determining trust in either LIS or Target are out of scope for this document. This document only describes the means by Thomson & Winterbottom Expires August 26, 2007 [Page 5] Internet-Draft Location Dependability February 2007 which an identity can be verified; the decision over whether or not to trust the entity is left to the location recipient. Means for establishing trust will be the topic of a separate work. Note that where certificate chains are used for authentication, a domain name-based certificate does not necessarily indicate trustworthiness in the provision of location information. Therefore, verification of LIS identity through a certificate alone is not enough to ensure that the location recipient can trust the LIS, the recipient needs to use additional criteria to decide on whether to trust the LIS. 2.2. Basic Countermeasures A good minimum requirement for the exchange of location information is that location information is protected from interception and modification by third parties in all protocol exchanges. Location protocols that use TLS [RFC4346] are able to meet this requirement. Confidentiality from third parties and integrity protection are required for all location using-protocols [RFC3693]. 2.3. Signing Location Information A digital signature provides data integrity and authentication of the source of information. This document describes how XML-Signature [RFC3275] can be applied to a Presence Information Data Format - Location Object (PIDF-LO) [RFC4119]. It also describes the benefits of signing and how signing can be practically applied. Thomson & Winterbottom Expires August 26, 2007 [Page 6] Internet-Draft Location Dependability February 2007 3. PIDF-LO Signature A location recipient can use the signature on a location object to authenticate the identity of the LIS. This is done through the certificate that the LIS attaches with the signature. The signature also ensures that the contents have not been modified since the LIS signed the location object. It is important to specify the semantics of a certificate of this nature. In essence, information that is signed SHOULD be verifiable by the LIS. However, in some cases it is expedient to include some unverifiable information (as is shown in later sections). Therefore, this document assigns a strict semantic to each signed element in the location object. 3.1. Signature Design This document uses the XML-Signature [RFC3275] enveloped signature type; that is, signature elements are included within the normal structure of the PIDF-LO document. This ensures that the location object does not appear to be any different from a regular PIDF-LO document. This permits use of the document in any protocol that carries PIDF-LO without requiring any changes to the protocol. Applications that rely on PIDF-LO can simply ignore the signature elements if they are not supported. A signature is applied to a single tuple within the PIDF document. This means that signed location information can be included in a composite presence document without destroying the signature. It is also a goal of the signature design to ensure that if unsigned elements are removed from the PIDF-LO, the document remains a valid PIDF-LO. This keeps the PIDF-LO usable if the signature and any unsigned data are stripped out. This is particularly important when the signature rules (Section 10.1) are applied. 3.2. Signed Elements and Semantics When location information is signed by a LIS, each unit of data in the signed document is given certain significance. A location recipient needs to know what significance the LIS has given to each field before it can base any decision on the contents of that field. The following list describes each of the elements that are included in a signed LO, justifies their inclusion and outlines the intended semantics of each being signed: Thomson & Winterbottom Expires August 26, 2007 [Page 7] Internet-Draft Location Dependability February 2007 presence (urn:ietf:params:xml:ns:pidf): The root element of a presence document, the "presence" element, is signed. The "entity" attribute is also signed. The "entity" attribute SHOULD contain an identifier generated by the LIS, see Section 5 and Section 5.3. tuple (urn:ietf:params:xml:ns:pidf): Only the tuple that contains location information is signed. The "id" attribute is signed to ensure a valid PIDF-LO is produced. geopriv (urn:ietf:params:xml:ns:pidf:geopriv10): The "geopriv" element is signed, along with select elements within it. location-info (urn:ietf:params:xml:ns:pidf:geopriv10): The most important element of the PIDF-LO, "location-info" contains location data. This element and all its contents are signed. usage-rules (urn:ietf:params:xml:ns:pidf:geopriv10): Usage rules are included to ensure the validity of the PIDF-LO. An empty "usage-rules" element is valid. The contents of these are not signed to allow a user to enter their preferences upon receipt of the signed LO. No decisions can be made on the unsigned content of usage rules. method (urn:ietf:params:xml:ns:pidf:geopriv10): The method parameter is included, and consequently signed, only if known. The LIS SHOULD verify the accuracy of this field, but MAY opt to include the element without validation. An unvalidated method is allowed because of the informational nature of the data it contains. Method is a metadata element and therefore is not a suitable basis for decision making, especially where a similar decision can be based on location information. A recipient SHOULD NOT use the value of this field as the basis for any decision. All elements defined in this document: This document defines a number of elements that are designed for inclusion in the tuple. These elements limit the effectiveness of certain attacks. Validity intervals and Target identity are defined in Section 4, Section 5. This document defines two transforms that can be applied to a PIDF-LO in order to limit what is signed Section 8.2. The first is a selective transform that only selects the elements listed above. The second simply selects the enveloping tuple. The LIS MAY choose not to use either transform, but in doing so, all unverified elements MUST be removed from the signed document. Thomson & Winterbottom Expires August 26, 2007 [Page 8] Internet-Draft Location Dependability February 2007 3.3. Signature Algorithms As specified in RFC 3275 [RFC3275], implementations of this specification MUST provide the following algorithms: digest algorithm: The SHA1 digest, as identified by the URN "http://www.w3.org/2000/09/xmldsig#sha1". signature algorithm: DSA with SHA1, as identified by the URN "http://www.w3.org/2000/09/xmldsig#dsa-sha1". canonicalization method: Canonical XML [RFC3076], as identified by the URN "http://www.w3.org/TR/2001/REC-xml-c14n-20010315". transforms: The enveloped signature transform, as identified by the URN "http://www.w3.org/2000/09/xmldsig#enveloped-signature"; and the transforms defined in this document: the tuple-only transform (Section 8.2.1), as identified by the URN "urn:ietf:params:xml:ns:pidf:geopriv10:dsig#tuple" and the selective transform (Section 8.2.2), as identified by the URN "urn:ietf:params:xml:ns:pidf:geopriv10:dsig#selective". It is also RECOMMENDED that the PKCS1 (RSA-SHA1) signature algorithm, as idenfied by "http://www.w3.org/2000/09/xmldsig#rsa-sha1" is also supported. 3.4. LIS/Signer Identification RFC 3275 [RFC3275] describes a number of methods for describing the key used to sign the document. For the purpose of signing a location object, the "KeyInfo" element MUST be provided in the "Signature" element. The LIS MUST include an X.509v3 certificate in the signature. This can be either by including an "X509Certificate" element, or by referencing another certificate. A reference to a certificate within the same document may be made using a fragment identifier URI. Internal references could be applicable where multiple signatures are applied to different parts of the document. The LIS SHOULD NOT reference an external source unless there is a reasonable expectation that the location recipient can successfully retrieve the certificate. A reference to an external certificate MUST be described by URI in the "RetrievalMethod" element. The scheme for the the RetrievalMethod URI MUST be "https:". Thomson & Winterbottom Expires August 26, 2007 [Page 9] Internet-Draft Location Dependability February 2007 4. Limited Validity The simplest attack to address is the Time Shifting attack. The LIS can specify a limited time period where the location information can be considered valid. Applying a signature ensures that the information is not tampered with. A known limitation of this method is that the information could become invalid at any time after the LIS signs the document. Once location is generated, the Target can move at any time, thereby invalidating the location object. Therefore, the LIS SHOULD make the time period covered by the signature as short as possible to limit the impact of such movement. The LIS can base any chosen period on any knowledge it has about the mobility or current speed of the Target. Location recipients MAY choose to implement a minimum age policy for locations, choosing to further restrict the validity interval to limit the chances of this occurring. It is RECOMMENDED that the "from" element is used in this case, since the LIS is expected to validate location before it signs location information. 4.1. Validity Elements A "validity" element is defined with two sub-elements, "from" and "until". The "from" element contains the time that the LIS signs the location information. Note that this could differ from the time that the location was generated, which is included in the PIDF "timestamp" element. The "until" element contains the last time that the signature can be considered valid. Choice of an appropriate validity interval is left to LIS implementations; however, it is RECOMMENDED that this period not exceed one day. The period chosen SHOULD also consider the type of network access in use -- location becomes invalid faster in more mobile networks. The signature MUST NOT be considered valid if the current time is outside of the interval specified in these elements. Thomson & Winterbottom Expires August 26, 2007 [Page 10] Internet-Draft Location Dependability February 2007 5. Signing for a User Signing location information alone, even with a limited validity period does not ensure that it is not reused. Signing some sort of user identifier with the location object provides an additional degree of protection. Most importantly, the location recipient is able to detect duplicate location objects for the same Target. In addition, if some extra data is included from the Target, the location recipient is also able to link the location object with a user identity. 5.1. The 'entity' Attribute The "entity" attribute of a presence document is intended to convey the identity of the Target. The LIS does not necessarily know this identity. Nor does the LIS necessarily have the means to authenticate the Target. It is RECOMMENDED that this field be generated by the LIS. The LIS SHOULD construct an "unlinked pseudonym" for the Target that does not contain any possible identifying information for the target. The simplest way to meet this requirement is to generate a "pres:" URI randomly, using a random sequence of characters and the host name of the LIS (e.g., "pres:f6pc98w1pd49s0p@lis.example.com"). An unlinked pseudonym provides a limited means of ensuring that location information is not reused or replayed. The presentity identifier used acts as a serial number for each location object, allowing each to be uniquely identified. A location recipient is able to use this identifier to detect multiple uses of the same piece of location information. This limits the effectiveness of replay attacks. Presentity identifiers can be reused for the same Target, provided that the LIS is able to verify that the Target is the same. This depends on the means by which location is acquired from the LIS; if session data that links subsequent requests exists, the LIS MAY reuse the presentity identifier. Note that the the Target can initiate a new session to ensure that a new identifier is generated and thereby ensure that their previous and current positions cannot be correlated using the presentity identifier. This does not prevent the use of a "real" presentity in this field. If the LIS is able to authenticate the Target, and the Target grants permission to the LIS to use this field, the LIS can include this information in the "entity" field. These conditions are hard to meet, which leads to two alternative means of including Target identity, described in the following sections. Thomson & Winterbottom Expires August 26, 2007 [Page 11] Internet-Draft Location Dependability February 2007 5.2. Target Identity The unlinked pseudonym used by the LIS acts as an anonymous identifier to a location recipient. The only information that this provides is that two location objects were generated for the same (anonymous) Target. The location recipient might also wish to link the location object to the identity of a particular user. For example, a PSAP might want to link the location object to the authenticated identity of a emergency caller. To achieve this linkage between location object and the Target's identity, the Target sends its identity to the LIS. The LIS includes this identifier in the signed location object, effectively linking the identity to the location information. A location recipient verifies that location information was signed for a particular Target by authenticating the Target and comparing the authenticated identity against the one in the signed location object. The LIS is not expected to authenticate this identity information, although it MAY do so. This means that an attacker within the network could request a signed location object with any identity they choose. However, the location object could only be used by an entity that can prove that they have the chosen identity, which limits the number of potential attackers. 5.3. Protecting User Anonymity The problem with sending the Target's identity to the LIS is that the Target might not wish to provide this information to the access network operator. This can be addressed by using a cryptographic hash of the user identity in place of the actual identifier. Since the LIS does not necessarily authenticate the identity, this information provides the same attributes as the real identity. Since the hash is not reversible, the LIS is unable to identify the Target, but the hash cannot be generated from any identifier other than the one used by the Target. The location recipient authenticates the Target's identity, then compares a hash of the identity to the hash that is included in the location object to verify that the identity matches. Thomson & Winterbottom Expires August 26, 2007 [Page 12] Internet-Draft Location Dependability February 2007 5.4. Authenticated Identity With the above solution, one easy collusion attack exists. One attacker at the actual location requests a location object with another attacker's identity. The second, potentially remote, attacker is able to use this object. If the first attacker is authenticated by the LIS, this attack is limited, because it requires that both attackers have access to the same authentication credentials. The effectiveness of this approach is limited by the ability of the LIS to authenticate arbitrary users in the access network. Location recipients cannot rely on the LIS performing authentication. 5.5. Multiple Identity Attack The schemes described in this section rely on the Target providing an identity. A potential attack uses a single attacker in the access network that requests location information using a number of different identities. The attacker requests multiple location objects, using a different identity each time. These objects are passed to any number of other attackers, who are each able to authenticate with the identity that is included in the location object. This potentially allows a large number of distributed attackers to use the same location information to perform a denial of service attack. In some scenarios, multiple identities can be valid. Examples in Section 3 of [I-D.ietf-geopriv-l7-lcp-ps] show that multiple hosts can appear from the same network demarcation point. Ideally, the LIS would still serve these hosts individually because they each have a valid reason to acquire location information. However, to prevent an attack where a user requests large numbers of location objects with different identity information, the LIS SHOULD limit the number of identities that can be served from any particular network point. Authenticating the Targets in this scenario could provide some additional surety that each is legitimate. If multiple Targets legitimately exist at the same location, then these Targets can authenticate with the LIS. The LIS MAY use a higher limit for authenticated Targets. Thomson & Winterbottom Expires August 26, 2007 [Page 13] Internet-Draft Location Dependability February 2007 6. Target Identity Element This document defines an XML "identity" element that can be used to include identity information in a PIDF-LO. This element is used in addition to a randomized "entity" attribute for several reasons: a randomized "entity" attribute can be used to detect replays; the identity is not necessarily authenticated; and the content can be other than a presentity identifier. 6.1. Identity Types The content of this element is dependent on the type associated with the identifier. The "type" attribute is used to define the nature of the identity that is included. Two values are provided by default: URI: A value of "urn:ietf:params:xml:ns:pidf:geopriv10:dsig:identity#uri" for the type attribute indicates that the contents are a URI. This URI can include a presentity URI, or other URI that identifies the target; for example a SIP URI. This type MUST be supported. An X.509 certificate: A value of "urn:ietf:params:xml:ns:pidf:geopriv10:dsig:identity#x509" indicates that the contents are an X.509v3 certificate [X509v3], in the format described in [RFC3275] for "X509Certificate". New identity types are identified by URNs, which means that registration is not required to add new types. A location recipient that does not support a particular identity type MUST treat the location object as if no identity information were included. 6.2. Identity Hashing To allow for anonymity, the content of the "identity" element MAY be hashed and the hash value included in this element instead. The "hash" attribute indicates whether the value has been hashed. A reserved value of "##none" indicates that the actual value is included. Otherwise, the attribute includes a hash algorithm identifier, as defined in [RFC3275]. The SHA1 algorithm MUST be supported; this is identified by the URN "http://www.w3.org/2000/09/xmldsig#sha1". Each different identity type requires a procedure for obtaining the bytes that are hashed. Thomson & Winterbottom Expires August 26, 2007 [Page 14] Internet-Draft Location Dependability February 2007 URI: For the URI type, the input to the hash algorithm is the UTF-8 bytes of the URI. X.509: For the X.509 type, the input to the hash algorithm is the binary value of the certificate; that is, after the base64 encoding [RFC2045] is decoded. If the "hash" attribute is present and set to a value other than "##none", the contents of the "identity" element are always the base64 encoded result from the hash function. 6.3. Authentication Indicator If the LIS is able to authenticate the Target, the LIS can indicate this in the "authenticated" attribute. This indicator can be used irrespective of the value of the "hash" attribute. This indicates to the location recipient that user identity included in the "identity" element was authenticated by the LIS. Thomson & Winterbottom Expires August 26, 2007 [Page 15] Internet-Draft Location Dependability February 2007 7. Signature Validation A location recipient performs the following steps to validate a signed location object: 1. Authenticate the entity that provided the location information (the sender). 2. Check the integrity of the digital certificate. 3. Extract the identity of the LIS from the digital certificate. 4. Remove all unsigned components from the location object. 5. Ensure the validity interval from the location object covers the present time. 6. Check that the authenticated identity of the sender matches the identity in the location object, or that a hash of this identity matches the hashed identity in the location object. Once this process is complete, the location recipient has the following information upon which to base any policy decision: o Whether the location object was signed. o Whether the signature on the location object was valid. o The identity of the sender. o The identity of the LIS. o Whether the LIS authenticated the sender in generating the location object. o The presentity identifier generated by the LIS that distinguishes this location object. Policies are set by individual location recipients and are dictated by a range of factors. Even a failure in signature validation does not necessarily require that the location recipient reject the location information. For instance, a PSAP might not reject an emergency call with no signature. The PSAP could instead place a lower priority on such a call so that in a busy period the call is queued behind calls that contained valid signatures. Similarly, un-authenticated calls could be given similar treatment. Thomson & Winterbottom Expires August 26, 2007 [Page 16] Internet-Draft Location Dependability February 2007 8. Code and Examples 8.1. Dependability Data Schema The following XML Schema [W3C.REC-xmlschema-1-20041028] defines the "dependability" element. This element is intended for use in a PIDF-LO within a "tuple". GEOPRIV PIDF-LO Dependability Elements This document defines dependability elements for PIDF-LO. Thomson & Winterbottom Expires August 26, 2007 [Page 17] Internet-Draft Location Dependability February 2007 8.2. PIDF-LO Transforms The transforms defined in this section select certain parts of a PIDF-LO document for signing. These transforms ensure that only one tuple is signed, with varying amounts of content. This allows location information to be composed with other tuples and for independent signatures on multiple tuples. The LIS MUST use one of these transforms to avoid the implication that only the tuple is signed (where in fact the entire document would be signed). The enveloped signature transform MUST also be used. These transforms can be implemented by substituting instances of transforms (identified by URNs) with the XPath transforms below. However, equivalent implementations using other means might provide better performance. Thomson & Winterbottom Expires August 26, 2007 [Page 18] Internet-Draft Location Dependability February 2007 8.2.1. PIDF-LO Tuple-only Transform The following XPath filter [RFC3275] selects the first "tuple" descendant of the signature element and all its contents. The "presence" element that is the immediate parent of the "tuple" is also selected. This transform is identified by the URN "urn:ietf:params:xml:ns:pidf:geopriv10:dsig#tuple". (count(ancestor-or-self::pidf:tuple[1] | here()/ancestor::pidf:tuple[1]) == 1) or (count(self::pidf:presence | here()/ancestor::pidf:presence[1]) = 1) or ((count(parent::pidf:presence | here()/ancestor::pidf:presence[1]) = 1) and (count(self::node() | parent::*/attribute::* | parent::*/namespace::*) + 1 == (count(self::node()) + count(parent::*/attribute::*) + count(parent::*/namespace::*)))) Thomson & Winterbottom Expires August 26, 2007 [Page 19] Internet-Draft Location Dependability February 2007 8.2.2. PIDF-LO Selective Transform Similar to the tuple-only transform, this transform selects a single "tuple" element and its parent "presence" element. In contrast, this transform only selects those elements listed in Section 3.2. This transform allows a Target to make adjustments to non-critical elements in the PIDF-LO after the signed PIDF-LO is received from the LIS. In particular, this allows the Target to set the content of the "usage-rules" element and other PIDF data, like contact information. This transform is identified by the URN "urn:ietf:params:xml:ns:pidf:geopriv10:dsig#selective". Thomson & Winterbottom Expires August 26, 2007 [Page 20] Internet-Draft Location Dependability February 2007 (count(self::pidf:presence | here()/ancestor::pidf:presence[1]) = 1) or ((count(ancestor-or-self::pidf:tuple[1] | here()/ancestor::pidf:tuple[1]) == 1) and (self::pidf:tuple or self::pidf:status or ancestor-or-self::pidf:timestamp or self::gp:geopriv or self::gp:usage-rules or ancestor-or-self::gp:method or ancestor-or-self::gp:location-info or ancestor-or-self::dep:dependability)) or ((count(self::node() | parent::*/attribute::* | parent::*/namespace::*) + 1 == (count(self::node()) + count(parent::*/attribute::*) + count(parent::*/namespace::*))) and parent::*[ (count(self::pidf:presence | here()/ancestor::pidf:presence[1]) = 1) or ((count(ancestor-or-self::pidf:tuple[1] | here()/ancestor::pidf:tuple[1]) == 1) and (self::pidf:tuple or self::pidf:status or self::gp:geopriv or self::gp:usage-rules)) ]) 8.3. Example The following PIDF-LO document has been signed using the selective transform. [[NOTE: A proper example, with a verifiable signature, will be created in a later version of this draft.]] Thomson & Winterbottom Expires August 26, 2007 [Page 21] Internet-Draft Location Dependability February 2007 -34.407 150.88001 34 no 2004-12-01T21:28:43+10:00 2007-02-16T16:25:24+11:00 2007-02-17T16:25:24+11:00 pres:user@example.com Thomson & Winterbottom Expires August 26, 2007 [Page 22] Internet-Draft Location Dependability February 2007 60NvZvtdTB+7UnlLp/H24p7h4bs= juS5RhJ884qoFR8flVXd/rbrSDVGn40CapgB7qeQiT+rr0NekEQ6BHhUA 8dT3+BCTBUQI0dBjlml9lwzENXvS83zRECjzXbMRTUtVZiPZG2pqKPnL2 YU3A9645UCjTXU+jgFumv7k78hieAGDzNci+PQ9KRmm//icT7JaYztgt4= MIICeDCCAeGgAwIBAgIEOd3+iDANBgkqhkiG9w0BAQQFADBbMQsw CQYDVQQGEwJJRTEPMA0GA1UECBMGRHVibGluMSUwIwYDVQQKExxC YWx0aW1vcmUgVGVjaG5vbG9naWVzLCBMdGQuMRQwEgYDVQQDEwtU ZXN0IFJTQSBDQTAeFw0wMDEwMDYxNjMyMDdaFw0wMTEwMDYxNjMy MDRaMF0xCzAJBgNVBAYTAklFMQ8wDQYDVQQIEwZEdWJsaW4xJTAj BgNVBAoTHEJhbHRpbW9yZSBUZWNobm9sb2dpZXMsIEx0ZC4xFjAU BgNVBAMTDU1lcmxpbiBIdWdoZXMwgZ8wDQYJKoZIhvcNAQEBBQAD gY0AMIGJAoGBALgorpKYDmjpq6tXz1Ex9wgF8bhZj47JkuI50ysa 79MNSSnF7SdjN2pGldXf5Gq7yZZnmqNtIzcva/v7ysIm4zO+xft2 yJHjBBpgCFJxXIiZEfooTu2+HE7mJxIvMR7buIjJ+hjgwaBM6hUG HXfKeL62QbL7OOJ060vKssoW2uuPAgMBAAGjRzBFMB4GA1UdEQQX MBWBE21lcmxpbkBiYWx0aW1vcmUuaWUwDgYDVR0PAQH/BAQDAgeA MBMGA1UdIwQMMAqACEngrZIVgu03MA0GCSqGSIb3DQEBBAUAA4GB AHJu4JVq/WnXK2oqqfLWqes5vHOtfX/ZhCjFyDMhzslI8am62gZe dwZ9IIZIwlNRMvEDQB2zds/eEBnIAQPl/yRLCLOfZnbA8PXrbFP5 igs3qQWScBUjZVjik748HU2sUVZOa90c0mJl2vJs/RwyLW7/uCAf C/I/k9xGr7fneoIW This note may be changed without affecting the signature. 2005-05-18T15:03:39.362+10:00 Thomson & Winterbottom Expires August 26, 2007 [Page 23] Internet-Draft Location Dependability February 2007 Once the signature has been checked, the following document is extracted. Only these elements have been included in the signature. Whitespace has been added to this example to improve readability. -34.407 150.88001 34 2007-02-16T16:25:24+11:00 2007-02-17T16:25:24+11:00 pres:user@example.com 2005-05-18T15:03:39.362+10:00 Thomson & Winterbottom Expires August 26, 2007 [Page 24] Internet-Draft Location Dependability February 2007 9. Location Reference Attribution Digital signatures are less useful when location is provided by reference. In this case, the location recipient acquires location information directly from the LIS. The location recipient is able to authenticate the LIS when it establishes a session to retrieve location information (and indeed, this authentication is necessary to protect against other forms of attack). This authentication process reveals to the location recipient the same information that would be included in a digital signature. Therefore, signing the result of a location deference is not necessary, unless the dereferencing entity intends to then pass the location object to another entity (note that this MUST be permitted by the usage rules). Similar constraints apply to a location object that is retrieved by reference as those that apply to a signed location object (that is, a by-value location object). The location object that is retrieved by reference needs to include the same identity information that would be included in a signed location object. Validity elements are less critical, since it can be assumed that the LIS does not provide location information unless it is current. The LIS MAY include validity elements to provide an indication of the limits of the objects validity. Thomson & Winterbottom Expires August 26, 2007 [Page 25] Internet-Draft Location Dependability February 2007 10. Security Considerations This entire document is about the security properties of location objects. 10.1. Signature Rules Three rules that relate to the treatment of signed information are described in [RFC3275]. These rules are _Only What is Signed is Secure_, _Only What is "Seen" Should be Signed_, and _"See" What is Signed_. These should apply when a location recipient evaluates and uses a location object. These especially apply when displaying location information to a user. Thomson & Winterbottom Expires August 26, 2007 [Page 26] Internet-Draft Location Dependability February 2007 11. IANA Considerations This section registers the dependability elements schema and related namespace URNs with IANA. 11.1. URN Sub-Namespace Registration for urn:ietf:params:xml:ns:pidf:geopriv10:dsig This section registers a new XML namespace, "urn:ietf:params:xml:ns:pidf:geopriv10:dsig", as per the guidelines in [RFC3688]. URI: urn:ietf:params:xml:ns:pidf:geopriv10:dsig Registrant Contact: IETF, GEOPRIV working group, (geopriv@ietf.org), Martin Thomson (martin.thomson@andrew.com). XML: BEGIN GEOPRIV Dependability Elements

Namespace for GEOPRIV Dependability Elements

urn:ietf:params:xml:ns:pidf:geopriv10:dsig

[[NOTE TO IANA/RFC-EDITOR: Please update RFC URL and replace XXXX with the RFC number for this specification.]]

See RFCXXXX.

END Note: Two fragment identifiers ("#tuple" and "#selective") are added to this URN to identify the two transforms defined in RFCXXXX. 11.2. XML Schema Registration This section registers an XML schema as per the guidelines in [RFC3688]. Thomson & Winterbottom Expires August 26, 2007 [Page 27] Internet-Draft Location Dependability February 2007 URI: urn:ietf:params:xml:schema:pidf:geopriv10:dsig Registrant Contact: IETF, GEOPRIV working group, (geopriv@ietf.org), Martin Thomson (martin.thomson@andrew.com). Schema: The XML for this schema can be found in Section 8.1 of this document, between "" and "" (inclusive). 11.3. URN Sub-Namespace Registration for urn:ietf:params:xml:ns:pidf:geopriv10:dsig:identity This section registers a new XML namespace, "urn:ietf:params:xml:ns:pidf:geopriv10:dsig:identity", as per the guidelines in [RFC3688]. URI: urn:ietf:params:xml:ns:pidf:geopriv10:dsig:identity Registrant Contact: IETF, GEOPRIV working group, (geopriv@ietf.org), Martin Thomson (martin.thomson@andrew.com). XML: BEGIN GEOPRIV Dependability Elements

Namespace for GEOPRIV Dependability Elements: Identity Identifiers

urn:ietf:params:xml:ns:pidf:geopriv10:dsig:identity

[[NOTE TO IANA/RFC-EDITOR: Please update RFC URL and replace XXXX with the RFC number for this specification.]]

See RFCXXXX.

END Note: Two fragment identifiers ("#uri" and "#x509") are added to this URN to identify the two types of identity defined in RFCXXXX. Thomson & Winterbottom Expires August 26, 2007 [Page 28] Internet-Draft Location Dependability February 2007 12. Acknowledgements The authors would like to acknowledge the contribution of the GEOPRIV WG; the L7 design team; Hannes Tschofenig and Henning Schulzrinne. Thomson & Winterbottom Expires August 26, 2007 [Page 29] Internet-Draft Location Dependability February 2007 13. References 13.1. Normative References [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [RFC3076] Boyer, J., "Canonical XML Version 1.0", RFC 3076, March 2001. [RFC3275] Eastlake, D., Reagle, J., and D. Solo, "(Extensible Markup Language) XML-Signature Syntax and Processing", RFC 3275, March 2002. [RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object Format", RFC 4119, December 2005. [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-00 (work in progress), January 2007. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [X509v3] ITU-T Recommendation, "Information Technology - Open Systems Interconnection - The Directory Authentication Framework", ISO/IEC 9594-8:1997, 1997. [W3C.REC-xmlschema-1-20041028] Beech, D., Thompson, H., Maloney, M., and N. Mendelsohn, "XML Schema Part 1: Structures Second Edition", World Wide Web Consortium Recommendation REC-xmlschema-1-20041028, October 2004, . 13.2. Informative References [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. [RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. Polk, "Geopriv Requirements", RFC 3693, February 2004. [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.1", RFC 4346, April 2006. Thomson & Winterbottom Expires August 26, 2007 [Page 30] Internet-Draft Location Dependability February 2007 Authors' Addresses Martin Thomson Andrew PO Box U40 Wollongong University Campus, NSW 2500 AU Phone: +61 2 4221 2915 Email: martin.thomson@andrew.com URI: http://www.andrew.com/ James Winterbottom Andrew PO Box U40 Wollongong University Campus, NSW 2500 AU Phone: +61 2 4221 2938 Email: james.winterbottom@andrew.com URI: http://www.andrew.com/ Thomson & Winterbottom Expires August 26, 2007 [Page 31] Internet-Draft Location Dependability February 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). 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. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Thomson & Winterbottom Expires August 26, 2007 [Page 32]