Network Working Group F. Adrangi Internet-Draft V. Lortz Expires: April 22, 2005 Intel F. Bari AT&T Wireless P. Eronen Nokia M. Watson Nortel October 22, 2004 Identity selection hints for Extensible Authentication Protocol (EAP) draft-adrangi-eap-network-discovery-05 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 on April 22, 2005. Copyright Notice Copyright (C) The Internet Society (2004). Abstract This document defines a mechanism that allows an access network to Adrangi, et al. Expires April 22, 2005 [Page 1] Internet-Draft Identity selection hints for EAP October 2004 provide identity selection hints to an EAP client. The purpose is to help the client in selecting the most appropriate identity and NAI decoration to use. This is especially useful when the access network does not have a direct roaming relationship with the client'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 . . . . . . . . . . . . . . . . . 3 2.1 Packet format . . . . . . . . . . . . . . . . . . . . . . 4 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 4. Security considerations . . . . . . . . . . . . . . . . . . . 5 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 6. Appendix (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. Expires April 22, 2005 [Page 2] Internet-Draft Identity selection hints for EAP October 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 an EAP-Identity/Response. This document defines a mechanism that allows the access network to provide identity selection hints, and more specifically information about its roaming relationships, to an EAP peer. This information is sent to the peer in an EAP Identity/Request 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 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 appendix in section 6 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]. 2. Implementation requirements An EAP peer implementing this specification MUST be able to receive an identity hint in an initial EAP Identity/Request, or in a subsequent EAP Identity/Request. Adrangi, et al. Expires April 22, 2005 [Page 3] Internet-Draft Identity selection hints for EAP October 2004 The EAP authenticator MAY send an identity hint to the peer in the initial EAP Identity/Request. If the identity hint is not sent initially (such as when the authenticator does not support this specification), then if the EAP server receives an EAP Identity/Response with an unacceptable NAI Realm, EAP servers implementing this specification SHOULD reply with an EAP Identity/Request containing an identity hint. If after the EAP server sends an EAP Identity/Request containing an identity hint, the peer responds with an EAP Identity/Response 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 providing information on the reason for the failure. EAP does not support fragmentation for Identity/Request messages, so the size of 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 the EAP Identity Request. The following ABNF [RFC2234] defines a "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 ] [ %x00 "NAIRealms=" realm-list ] displayable-string = *OCTET realm-list = realm / ( realm-list ";" realm ) The "OCTET" rule is defined in [RFC2234] and the "realm" rule is defined in [rfc2486bis]. A sample hex dump of an EAP Identity Request 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. 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 33 Adrangi, et al. Expires April 22, 2005 [Page 4] Internet-Draft Identity selection hints for EAP October 2004 67 70 70 6e 65 74 77 6f 72 6b 2e 6f 72 67 Some existing systems are known to use EAP Identity/Request messages to send proprietary information to the peer. This proprietary information is considered to be part of the displayable-string in the ABNF shown above. In other words, the NUL character followed by the NAIRealms list MUST be placed at the end. 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 an EAP Identity Request before the user authenticates to the network, and before the network is authenticated to the user. This information can be modified by an attacker. Therefore, it MUST be considered an unauthenticated hint. Unauthenticated hints may result in peers inadvertently revealing other or additional identities than they intended to, leading to a privacy vulnerability. Note that in EAP, the identity the peer wants to use is in general carried in a cleartext message, so this is only a variation of an existing vulnerability. Method-specific identity protection is one of the ways that this vulnerability can be addressed. Similarly, in a situation where the peer has multiple identities to choose from, an unauthenticated hint can lead to a situation where an attacker convinces the peer to choose an identifier that is bound to the weakest EAP method. To guard against this vulnerability, the use of as strong EAP methods as possible is recommended. Note that this vulnerability is similar to an existing vulnerability where link layers advertise network names (such as 802.11 SSIDs) without authenticating these advertisements either at all or only at the end of the authentication process. In case the identity hint information is used to select a mediating network for NAI decoration, it should be noted that at least with some EAP methods, there is no way for the home network AAA server to verify that the mediating network used was actually the same one that the peer had requested. 5. Acknowledgements The authors would specially like to thank Jari Arkko and Bernard Adrangi, et al. Expires April 22, 2005 [Page 5] Internet-Draft Identity selection hints for EAP October 2004 Aboba 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, and Avi Lior for their support, feedback and guidance during the various stages of this work. 6. Appendix (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 the EAP Identity/ Request. For example, the role of EAP server may be played by the EAP authenticator (where an initial EAP 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: Initial EAP Identity/Request from access point In typical IEEE 802.11 wireless LANs, the initial EAP Identity/Request 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 2004 EAP Access Point local RADIUS home RADIUS Peer proxy/server server | 1. EAP | | | | Identity/Request | | | | (NAIRealms) | | | |<------------------| | | | 2. EAP | | | | Identity/Response | | | |------------------>| | | | | 3. Access-Request | | | | (EAP | | | | Identity/Response) | | | |------------------->| | | | | 4.Access-Request | | | | (EAP | | | | Identity/Response) | | | |------------------->| | | | | |<-------------------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: Initial EAP Identity/Request from local RADIUS proxy/server This is similar to Option 1, but the initial EAP Identity Request 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 the EAP Identity/Request containing the identity hint information. Adrangi, et al. Expires April 22, 2005 [Page 7] Internet-Draft Identity selection hints for EAP October 2004 EAP Access Point local RADIUS home RADIUS Peer proxy/server server | | 1. Access-Request | | | | (EAP-Start) | | | |------------------->| | | | 2.Access-Challenge | | | | (EAP | | | | Identity/Request | | | | with NAIRealms) | | | |<-------------------| | | 3. EAP | | | | Identity/Request | | | | (NAIRealms) | | | |<------------------| | | | 4. EAP | | | | Identity/Response | | | |------------------>| | | | | 5. Access-Request | | | | (EAP | | | | Identity/Response) | | | |------------------->| | | | | 6. Access-Request | | | | (EAP | | | | Identity Response) | | | |------------------->| | | | | |<------------------- EAP conversation ---------------------->| This option can work with current access points if they support the EAP-Start message. Option 3: Subsequent EAP-Identity/Request from local RADIUS proxy/server In the third option, the access point sends the initial EAP Identity/Request without any hint information. The peer then responds with an Identity Response, 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 second EAP Identity Request containing the identity hint information. Adrangi, et al. Expires April 22, 2005 [Page 8] Internet-Draft Identity selection hints for EAP October 2004 EAP Access Point local RADIUS home RADIUS Peer Proxy/Server server | | | | | 1. EAP | | | | Identity Request | | | | (w/o NAIRealms) | | | |<------------------| | | | 2. EAP | | | | Identity Response | | | |------------------>| | | | | 3. Access-Request | | | | (EAP | | | | Identity Response) | | | |------------------->| | | | 4.Access-Challenge | | | | (EAP | | | | Identity Request | | | | with NAIRealms) | | | |<-------------------| | | 5. EAP | | | | Identity Request | | | | (NAIRealms) | | | |<------------------| | | | 6. EAP | | | | Identity Response | | | |------------------>| | | | | 7. Access-Request | | | | (EAP | | | | Identity Response) | | | |------------------->| | | | | 8. Access-Request | | | | (EAP | | | | Identity Response) | | | |------------------->| | | | | |<-------------------- 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. Expires April 22, 2005 [Page 9] Internet-Draft Identity selection hints for EAP October 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. Expires April 22, 2005 [Page 10] Internet-Draft Identity selection hints for EAP October 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.com Mark Watson Nortel Networks 2221 Lakeside Blvd Richardson, TX 75082 USA EMail: mwatson@nortel.com Adrangi, et al. Expires April 22, 2005 [Page 11] Internet-Draft Identity selection hints for EAP October 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. 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Disclaimer of Validity 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 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. Copyright Statement Copyright (C) The Internet Society (2004). 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. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Adrangi, et al. Expires April 22, 2005 [Page 12]