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Network Working Group F. Adrangi Internet-Draft V. Lortz Expires:April 22,June 7, 2005 Intel F. Bari AT&T Wireless P. Eronen NokiaM. Watson Nortel October 22,December 7, 2004 Identity selection hints for Extensible Authentication Protocol (EAP)draft-adrangi-eap-network-discovery-05draft-adrangi-eap-network-discovery-06 Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. 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 become aware will be disclosed, in accordance with RFC 3668. 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 onApril 22,June 7, 2005. Copyright Notice Copyright (C) The Internet Society (2004). Abstract The Extensible Authentication Protocol (EAP) is defined in RFC 3748. This document defines a mechanism that allows an access network to provide identity selection hints to an EAP peer. The purpose is to Adrangi, et al. ExpiresApril 22,June 7, 2005 [Page 1] Internet-Draft Identity selection hints for EAPOctoberDecember 2004provide identity selection hints to an EAP client. The purpose is to helpassist theclientEAP peer in selectingthe mostan appropriateidentity and NAI decoration to use.Network Access Identifier (NAI). This is especially useful when the access network does not have a direct roaming relationship with theclient'speer's home network, so that a mediating network, such as a roaming consortium or broker, is used. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Implementation requirements . . . . . . . . . . . . . . . . .34 2.1 Packet format . . . . . . . . . . . . . . . . . . . . . . 4 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 4. Security considerations . . . . . . . . . . . . . . . . . . . 5 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .56 6. Appendix A (informative) - Delivery Options . . . . . . . . ..6 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1 Normative references . . . . . . . . . . . . . . . . . . ..9 7.2 Informative references . . . . . . . . . . . . . . . . . ..10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Intellectual Property and Copyright Statements . . . . . . . . . . 12 Adrangi, et al. ExpiresApril 22,June 7, 2005 [Page 2] Internet-Draft Identity selection hints for EAPOctoberDecember 2004 1. Introduction An EAP peer (hereafter, also referred to as the peer) can have several sets of credentials, and its home network may have roaming relationships with several mediating networks. As a result, the peer may be unclear about the appropriate Network Access Identity (NAI) to include in anEAP-Identity/Response.EAP-Response/Identity. The Extensible Authentication Protocol (EAP) is defined in [RFC3748]. This document defines a mechanism that allows the access network to provide identity selection hints,and more specificallyincluding information about its roaming relationships, to an EAP peer. This information is sent to the peer in anEAP Identity/RequestEAP-Request/Identity message by appending it after the displayable message and a NUL character. Exactly how the identity hint information is used by the peer depends largely on the peer's local policy and configuration, and is outside the scope of this document. In many roaming situations, an access network can have several roaming relationships, either with several home networks, or with mediating networks such as roaming consortiums and brokers, or both. One possible application for this mechanism is to help in selecting what kind of NAI decoration [rfc2486bis] must be applied to allow proper routing of AAA messages to the home AAA server. If there are several possible mediating networks, the peer can choose which one to use. However, exactly how the selection is made is beyond the scope of this document. See [netsel-problem] for more detailed discussion about this problem space. Section 2 describes the required behavior of implementations of this specification, as well as the packet format for structuring and presenting identity hint information to an EAP peer. The appendixin section 6A describes the delivery options that can be implemented by an access network to deliver identity hint information to an EAP peer. 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]. NAI Network Address Identifier [rfc2486bis]. Adrangi, et al. Expires June 7, 2005 [Page 3] Internet-Draft Identity selection hints for EAP December 2004 Decorated NAI An NAI with additional information for influencing AAA routing. Please refer to section 2.7 of [rfc2486bis] for its construction. NAI Realm Realm portion of an NAI [rfc2486bis]. 2. Implementation requirements An EAP peer implementing this specification MUST be able to receive an identity hint in an initialEAP Identity/Request,EAP-Request/Identity, or in a subsequentEAP Identity/Request. Adrangi, et al. Expires April 22, 2005 [Page 3] Internet-Draft Identity selection hints for EAP October 2004EAP-Request/Identity. The EAP authenticator MAY send an identity hint to the peer in the initialEAP Identity/Request.EAP-Request/Identity. If the identity hint is not sent initially (such as when the authenticator does not support this specification), then if the EAP server receives anEAP Identity/ResponseEAP-Response/Identity with an unacceptable NAI Realm, EAP servers implementing this specification SHOULD reply with anEAP Identity/RequestEAP-Request/Identity containing an identity hint. If after the EAP server sends anEAP Identity/RequestEAP-Request/Identity containing an identity hint, the peer responds with anEAP Identity/ResponseEAP-Response/Identity containing an unacceptable NAI Realm, then the EAP server MAY respond immediately with an EAP Failure packet, or it MAY first send an EAP-Notification providinginformation onthe reason for the failure. As noted in [RFC3748], Section 3.1, the minimum EAP MTU size is 1020 octets. EAP does not support fragmentationfor Identity/Requestof EAP-Request/Identity messages, so that thesizemaximum length of the identity hint information is limited by the link MTU.The exact limit depends on the lower layer in question, but it is at least 1020 octets.2.1 Packet format The Identity hint information is placed after the displayable string and a NUL character in theEAP Identity Request.EAP-Request/Identity. The following ABNF [RFC2234] definesa "NAIRealms"an NAIRealms attribute for presenting the identity hint information. The attribute's value consists of a set of realm names separated by a semicolon. identity-request-data = [ displayable-string ] "%0x00" [%x00 "NAIRealms=" realm-listNetwork-Info ] displayable-string =*OCTET*CHAR Network-Info = "NAIRealms=" realm-list Network-Info =/ 1*OCTET ",NAIRealms=" realm-list Network-Info =/ "NAIRealms=" realm-list "," 1*OCTET Network-Info =/ 1*OCTET ",NAIRealms=" realm-list "," 1*OCTET Adrangi, et al. Expires June 7, 2005 [Page 4] Internet-Draft Identity selection hints for EAP December 2004 realm-list = realm / ( realm-list ";" realm ) The "OCTET"rule isand "CHAR" rules are defined in [RFC2234] and the "realm" rule is defined in [rfc2486bis]. A sample hex dump of anEAP Identity RequestEAP-Request/Identity packet is shown below. 01 ; Code: Request 00 ; Identifier: 0 00 43 ; Length: 67 octets 01 ; Type: Identity 48 65 6c 6c 6f 21 00 4e ;"Hello\0NAIRealms=example.com;mnc014."Hello!\0NAIRealms=example.com;mnc014. 41 49 52 65 61 6c 6d 73 ; mcc310.3gppnetwork.org" 3d 69 73 70 2e 65 78 61 6d 70 6c 65 2e 63 6f 6d 3b 6d 6e 63 30 31 34 2e 6d 63 63 33 31 30 2e 33Adrangi, et al. Expires April 22, 2005 [Page 4] Internet-Draft Identity selection hints for EAP October 200467 70 70 6e 65 74 77 6f 72 6b 2e 6f 72 67Some existing systems are known to use EAP Identity/Request messagesThe Network-Info can contain NAIRealms list in addition tosendproprietaryinformation to the peer. Thisinformation. The proprietary informationis considered tocan bepart of the displayable-string inplaced before or after NAIRealms list. To extract NAIRealms list, an implementation either finds theABNF shown above. In other words,"NAIRealms=" immediately after the NULcharacter followed byor seeks forward to find ",NAIRealms" somewhere in theNAIRealms list MUST be placedstring. The realms data ends either at first "," or at theend.end of the string, whichever comes first. 3. IANA Considerations This document does not define any new namespaces to be managed by IANA, and does not require any assignments in existing namespaces. 4. Security considerations Identity hint information is delivered inside anEAP Identity RequestEAP-Request/Identity before theuser authenticates to the network,authentication conversation begins, andbefore the network is authenticated to the user. This informationtherefore can be modified by an attacker.Therefore, itThe NAIRealms attribute therefore MUST beconsidered an unauthenticated hint.treated as a hint by the peer Unauthenticated hints may result in peers inadvertently revealingother oradditionalidentities than they intended to, leading to a privacy vulnerability. Note that in EAP, the identityidentities, compromising privacy. Since thepeer wants to useEAP-Response/Identity is sent ingeneral carried in a cleartext message, so this is only a variation of an existing vulnerability. Method-specific identity protection is one oftheways thatclear, this vulnerability already exists. This vulnerability can beaddressed.addressed via method-specific identity exchanges. Similarly, in a situation where the peer has multiple identities to Adrangi, et al. Expires June 7, 2005 [Page 5] Internet-Draft Identity selection hints for EAP December 2004 choose from, anunauthenticated hintattacker canlead touse asituation where an attacker convincesforged hint to convince the peer to choose anidentifier that isidentity bound tothe weakesta weak EAP method.To guard against this vulnerability,Requiring the use ofasstrong EAP methodsas possible is recommended. Note that this vulnerability iscan protect against this. A similar issue already exists with respect toan existing vulnerability whereunprotected linklayers advertise network names (suchlayer advertisements such as 802.11SSIDs) without authenticating these advertisements either at all or only at the end of the authentication process. In caseSSIDs. Where the identity hintinformationis used to select a mediatingnetwork for NAI decoration, it should be noted that at leastnetwork, withsomeexisting EAPmethods,methods thereis nomay not be a way for the homenetworkAAA server to verify that the mediating networkused was actually the same one thatselected by the peerhad requested.was actually used. 5. Acknowledgements The authors would specially like to thank Jari Arkko and BernardAdrangi, et al. Expires April 22, 2005 [Page 5] Internet-Draft Identity selection hints for EAP October 2004Aboba for their help in scoping the problem, for reviewing the draft work in progress and for suggesting improvements to it. The authors would also like to acknowledge and thank Adrian Buckley, Blair Bullock, Jose Puthenkulam, Johanna Wild, Joe Salowey, Marco Spini, Simone Ruffino, Mark Grayson, Mark Watson, and Avi Lior for their support, feedback and guidance during the various stages of this work. 6. Appendix A (informative) - Delivery Options Although the delivery options are described in the context of IEEE 802.11 access networks, they are applicable to other access networks that use EAP [RFC3748] for authentication and use the NAI format [rfc2486bis] for identifying users. Also, the options assume that the AAA protocol in use is RADIUS [RFC2865]. Diameter [RFC3588] could also be used instead of RADIUS without introducing significant architectural differences. The main difference amongst the options is which entity in the access network creates theEAP Identity/ Request.EAP-Request/Identity. For example, the role of EAP server may be played by the EAP authenticator (where an initialEAP Request/IdentityEAP-Request/Identity is sent with an identity hint), or a RADIUS proxy/server (where the NAI Realm is used for forwarding). When an Identity hint is sent by a RADIUS proxy/server, a RADIUS State (24) attribute can be used to help the RADIUS proxy/server determine if an identity hint had previously been sent by it to the EAP peer. The RADIUS proxy/server acts only on the RADIUS UserName(1) attribute and does not have to parse the EAP-Message attribute. Option 1: InitialEAP Identity/RequestEAP-Request/Identity from access point Adrangi, et al. Expires June 7, 2005 [Page 6] Internet-Draft Identity selection hints for EAP December 2004 In typical IEEE 802.11 wireless LANs, the initialEAP Identity/RequestEAP-Request/Identity is sent by the access point (i.e., EAP authenticator). In the simplest case, the identity hint information is simply included in this request, as shown below.Adrangi, et al. Expires April 22, 2005 [Page 6] Internet-Draft Identity selection hints for EAP October 2004EAP Access Point local RADIUS home RADIUS Peer proxy/server server | 1. EAP | | | |Identity/RequestRequest/Identity | | | | (NAIRealms) | | | |<------------------| | | | 2. EAP | | | |Identity/Response |Response/Identity| | | |------------------>| | | | | 3. Access-Request | | | | (EAP | | | |Identity/Response) |Response/Identity)| | | |------------------->| | | | | 4.Access-Request | | | | (EAP | | | |Identity/Response)Response/Identity) | | | |------------------->| | | | | |<-------------------EAP conversation ----------------------->| Current access points do not support this mechanism, so other options may be preferable. This option can also require configuring the identity hint information in a potentially large number of access points, which may be problematic if the information changes often. Option 2: InitialEAP Identity/RequestEAP-Request/Identity from local RADIUS proxy/server This is similar to Option 1, but the initialEAP Identity RequestEAP-Request/Identity is created by the local RADIUS proxy/server instead of the access point. Once a peer associates with an access network AP using IEEE 802.11 procedures, the AP sends an EAP-Start message [RFC3579] within a RADIUS Access-Request. The access network RADIUS server can then send theEAP Identity/RequestEAP-Request/Identity containing the identity hint information. Adrangi, et al. ExpiresApril 22,June 7, 2005 [Page 7] Internet-Draft Identity selection hints for EAPOctoberDecember 2004 EAP Access Point local RADIUS home RADIUS Peer proxy/server server | | 1. Access-Request | | | | (EAP-Start) | | | |------------------->| | | | 2.Access-Challenge | | | | (EAP | | | |Identity/RequestRequest/Identity | | | | with NAIRealms) | | | |<-------------------| | | 3. EAP | | | |Identity/RequestRequest/Identity | | | | (NAIRealms) | | | |<------------------| | | | 4. EAP | | | |Identity/ResponseResponse/Identity | | | |------------------>| | | | | 5. Access-Request | | | | (EAP | | | |Identity/Response)Response/Identity) | | | |------------------->| | | | | 6. Access-Request | | | | (EAP | | | |Identity Response)Response/Identity) | | | |------------------->| | | | | |<------------------- EAP conversation ---------------------->| This option can work with current access points if they support the EAP-Start message. Option 3: SubsequentEAP-Identity/RequestEAP-Request/Identity from local RADIUS proxy/server In the third option, the access point sends the initialEAP Identity/RequestEAP-Request/Identity without any hint information. The peer then responds with anIdentity Response,EAP-Response/Identity, which is forwarded to the local RADIUS proxy/server. If the RADIUS proxy/server cannot route the message based on the identity provided by the peer, it sends a secondEAP Identity RequestEAP-Request/Identity containing the identity hint information. Adrangi, et al. ExpiresApril 22,June 7, 2005 [Page 8] Internet-Draft Identity selection hints for EAPOctoberDecember 2004 EAP Access Point local RADIUS home RADIUS Peer Proxy/Server server | | | | | 1. EAP | | | |Identity RequestRequest/Identity | | | | (w/o NAIRealms) | | | |<------------------| | | | 2. EAP | | | |Identity ResponseResponse/Identity | | | |------------------>| | | | | 3. Access-Request | | | | (EAP | | | |Identity Response)Response/Identity) | | | |------------------->| | | | 4.Access-Challenge | | | | (EAP | | | |Identity RequestRequest/Identity | | | | with NAIRealms) | | | |<-------------------| | | 5. EAP | | | |Identity RequestRequest/Identity | | | | (NAIRealms) | | | |<------------------| | | | 6. EAP | | | |Identity ResponseResponse/Identity | | | |------------------>| | | | | 7. Access-Request | | | | (EAP | | | |Identity Response)Response/Identity) | | | |------------------->| | | | | 8. Access-Request | | | | (EAP | | | |Identity Response)Response/Identity) | | | |------------------->| | | | | |<-------------------- EAP conversation --------------------->| This option does not require changes to existing NASes, so it may be preferable in many environments. 7. References 7.1 Normative references [rfc2486bis] Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The Network Access Identifier", Adrangi, et al. ExpiresApril 22,June 7, 2005 [Page 9] Internet-Draft Identity selection hints for EAPOctoberDecember 2004 draft-arkko-roamops-rfc2486bis-02 (work in progress), July 2004. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. 7.2 Informative references [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial In User Service) Support For Extensible Authentication Protocol (EAP)", RFC 3579, September 2003. [netsel-problem] Arkko, J. and B. Aboba, "Network Discovery and Selection Problem", draft-ietf-eap-netsel-problem-01 (work in progress), July 2004. [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J. Arkko, "Diameter Base Protocol", RFC 3588, September 2003. [RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. Authors' Addresses Farid Adrangi Intel Corporation 2111 N.E. 25th Avenue Hillsboro, OR 97124 USA Phone: +1 503-712-1791 EMail: farid.adrangi@intel.com Adrangi, et al. ExpiresApril 22,June 7, 2005 [Page 10] Internet-Draft Identity selection hints for EAPOctoberDecember 2004 Victor Lortz Intel Corporation 2111 N.E. 25th Avenue Hillsboro, OR 97124 USA Phone: +1 503-264-3253 EMail: victor.lortz@intel.com Farooq Bari AT&T Wireless 7277 164th Avenue N.E. Redmond, WA 98052 USA Phone: +1 425-580-5526 EMail: farooq.bari@attws.com Pasi Eronen Nokia Research Center P.O. Box 407 FIN-00045 Nokia Group Finland EMail: pasi.eronen@nokia.comMark Watson Nortel Networks 2221 Lakeside Blvd Richardson, TX 75082 USA EMail: mwatson@nortel.comAdrangi, et al. ExpiresApril 22,June 7, 2005 [Page 11] Internet-Draft Identity selection hints for EAPOctoberDecember 2004 Intellectual Property Statement 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. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Adrangi, et al. ExpiresApril 22,June 7, 2005 [Page 12] ----