Network Working Group F. Adrangi Internet-Draft Intel Expires: June 29, 2005 A. Lior Bridgewater Systems J. Korhonen Teliasonera J. Loughney Nokia December 29, 2004 Chargeable User Identity draft-ietf-radext-chargeable-user-id-01 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 June 29, 2005. Copyright Notice Copyright (C) The Internet Society (2004). Abstract This document describes a new RADIUS attribute, Chargeable-User-Identity. This attribute can be used by a home Adrangi, et al. Expires June 29, 2005 [Page 1] Internet-Draft Chargeable User Identity December 2004 network to identify a user for the purpose of roaming transactions that occur outside of the home network. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 2. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 Chargeable-User-Identity (CUI) Attribute . . . . . . . . . 5 3. Attribute Table . . . . . . . . . . . . . . . . . . . . . . . 7 4. Diameter RADIUS Interoperability . . . . . . . . . . . . . . . 7 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 5.1 CUI RADIUS Attribute . . . . . . . . . . . . . . . . . . . 7 5.2 Error-Cause Attribute . . . . . . . . . . . . . . . . . . 7 6. Security considerations . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 8.1 Normative references . . . . . . . . . . . . . . . . . . . 8 8.2 Informative references . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 Intellectual Property and Copyright Statements . . . . . . . . . . 11 Adrangi, et al. Expires June 29, 2005 [Page 2] Internet-Draft Chargeable User Identity December 2004 1. Introduction Some authentication methods, including EAP-PEAP, EAP-TTLS, EAP-SIM and EAP-AKA, can hide the true identity of the user from RADIUS servers outside of the user's home network. In these methods, the User-Name(1) attribute contains an anonymous identity (e.g., @example.com) sufficient to route the RADIUS packets to the home network but otherwise insufficient to identify the user. While this mechanism is good practice in some circumstances, there are problems if local and intermediate networks require a user identity in order to enforce usage policies. For example, local or intermediate networks may limit the number of simultaneous sessions for specific users; they may require a chargeable-user-identity in order to demonstrate willingness to pay or otherwise limit the potential for fraud. This implies that an authenticated and unique identity provided by the home network should be able to be conveyed to all parties involved in the roaming transaction for correlating the authentication and accounting packets. Providing a unique identity, called the Chargeable-User-Identity (CUI) to intermediaries, is necessary to fulfill certain business needs. This should not undermine the anonymity of the user. The mechanism provided by this draft allows the home operator to meet these business requirements by providing a temporary identity representing the subscriber and at the same time protecting the anonymity of the subscriber. 1.1 Motivation Several organizations, including WISPr, GSMA, 3GPP, Wi-Fi Alliance, IRAP, have been studying mechanisms to provide roaming services, using RADIUS. A mechanism for providing the current deployments with the capacity to deploy, bill and oversee WPA networks against fraud. The CUI attribute has been designed to close operational loopholes in RADIUS specifications that have impacted roaming solutions negatively, especially when tunneled protocols with multiple identities, such as PEAP or TTLS, are used. Use of the CUI is geared to multi-identity EAP authentications which are, for the most part, recent deployments. A chargeable identity reflecting the user profile authenticated by the home network is needed in such roaming scenarios. The CUI support by RADIUS infrastructure is driven by the business requirements between roaming entities. Therefore whether a RADIUS Adrangi, et al. Expires June 29, 2005 [Page 3] Internet-Draft Chargeable User Identity December 2004 server/proxy or client accepts or rejects the presence or lack of presence of the CUI attribute is a matter of business policy. Some other mechanisms have been proposed in place of the CUI attribute. These mechanisms are insufficient or cause other problems. It has been suggested that standard RADIUS Class(25) or User-Name(1) attributes could be used to indicate the Chargeable-User-Identity. However, in a complex global roaming environment where there could be one or more intermediaries between the NAS and the home RADIUS server, the use of aforementioned attributes could lead to problems as described below. - On use of RADIUS Class(25) attribute: [RFC2865] states: "This Attribute is available to be sent by the server to the client in an Access-Accept and SHOULD be sent unmodified by the client to the accounting server as part of the Accounting-Request packet if accounting is supported. The client MUST NOT interpret the attribute locally." So RADIUS clients or intermediaries MUST NOT interpret the Class(25) attribute, which precludes determining whether it contains a CUI. Additionally, there could be multiple class attributes in a RADIUS packet with unspecified ordering, which makes it hard to the entities outside home network to determine which one contains the CUI. - On use of RADIUS User-Name(1) attribute: The home network could use User-Name(1) in the Access-Accept message to convey the CUI to intermediaries and the NAS. However, as the Access-Accept packet is routed to the NAS, the User-Name(1) attribute could be (completely) rewritten by an intermediary and therefore the NAS or other intermediaries along the way will not have access to the CUI. Furthermore, the NAS may use the original value of the User-Name(1) attribute (the one sent in the Access-Request packet) in the Accounting-Request packets to ensure the billing follows the same path as authentication packets. The CUI attribute provides a solution to the above problem and avoids overloading the use of current RADIUS attributes (e.g., User-Name(1) re-write). The CUI is the correct standards-based approach to fixing the problems which have arisen with multiple-identity RADIUS authorization and accounting methods. It does not solve all related problems, but does provide networks the ability to bill and oversee WPA networks against fraud. When the home network assigns a value to the CUI, it asserts that this value represents a user in the home network. The assertion should be temporary. Long enough to be useful for the external applications and not too long such that it can be used to identify the user. Adrangi, et al. Expires June 29, 2005 [Page 4] Internet-Draft Chargeable User Identity December 2004 1.2 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 [RFC2119]. 3GPP - Third Generation Partnership Program AAA - Authentication, Authorization and Accounting CUI - Chargeable-User-Identity GSMA - GSM Association IRAP - International Roaming Access Protocols Program NAS - Network Access Server PEAP - Protected Extensible Authentication Protocol TTLS - Tunneled Transport Layer Security WISPr - Wireless ISP Roaming WPA - Wi-Fi Protected Access 2. Operation This document assumes that the RADIUS protocol operates as specified in [RFC2865], [RFC2866], dynamic authorization as specified in [RFC3576], and the Diameter protocol as specified in [RFC3588]. 2.1 Chargeable-User-Identity (CUI) Attribute This attribute serves as an alias to the user's real identity. It is provided by the home network as a suplemental or alternative information to User-Name(1). RADIUS clients (proxy or NAS) outside the home network MUST NOT modify the CUI attribute. In accordance to business policies, the RADIUS server (a RADIUS proxy, home RADIUS server) may include the CUI attribute in the Access-Accept message destined to a roaming partner. If an Access-Accept message without the CUI attribute was received by a RADIUS client (NAS or Proxy) that requires the presence of the CUI attribute, then the Access-Accept message MAY be treated as an Access-Reject message based on local policies. If the CUI was included in the Access-Accept message, RADIUS client (Proxy or NAS) that supports the CUI attribute MUST ensure that the CUI attribute appears in the RADIUS Accounting-Request (Start, Interim, and Stop). RADIUS client (Proxy or NAS) that does not support the CUI attribute MAY ignore this attribute or MAY treat the Access-Accept as Access-Reject. Adrangi, et al. Expires June 29, 2005 [Page 5] Internet-Draft Chargeable User Identity December 2004 If RADIUS client (Proxy or NAS) requires the presence of the CUI attribute in the Access-Accept, it MUST indicate its requirement by including this attribute with a nul character for its data field (hereafter, it is also referred to as a nul CUI) in the Access-Request message. If a home RADIUS server that supports the CUI attribute receives an Access-Request containing a nul CUI, it MUST include the CUI attribute in the Access-Accept. Otherwise, if the Access-Request does not contain a null CUI, the home RADIUS server MUST NOT include the CUI attribute in the Access-Accept. A RADIUS server (a RADIUS proxy or the home RADIUS server) that requires the presence of the CUI in the Accounting-Response messages (Start, Stop, Interims) MAY respond with an Access-Reject message if it receives an Access-Request messsage from a RADIUS client, or proxy chain that does not support the CUI attribute. The Access-Reject message MUST include Error-Cause attribute [RFC3576] with value (to-be-defined) (decimal), "CUI-Support-Required". If the NAS supports CUI attribute then the CUI attribute MAY also be used as one of the identity attribute in Disconnect Message and Change of Authorization messages defined by [RFC3576]. Determination of NAS support for the CUI is outside the scope of this document. A summary of the RADIUS CUI Attribute is given below. 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | String... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type: TBD for Chargeable-User-Identity. Length: >= 3 String: The string identifies the CUI of the end-user and is of type UTF8String. This string value is a reference to a particular user. The format and the interpretation of the string value , and the binding lifetime of the reference to the user is determined based on business agreements. For example, the lifetime can be set to one billing period. In cases where the attribute is used to indicate the NAS support for the CUI, the string value contains a nul character. Adrangi, et al. Expires June 29, 2005 [Page 6] Internet-Draft Chargeable User Identity December 2004 3. Attribute Table The following table provides a guide to which attribute(s) may be found in which kinds of packets, and in what quantity. Request Accept Reject Challenge Accounting # Attribute Request 0-1 0-1 0 0 0-1 TBD Chargeable-User-identity 0 0 0-1 0 0 101 Error-Cause [Note 1] If the Access-Accept contains CUI then the NAS MUST include the CUI in Accounting Requests (Start, Interim and Stop) packets. [Note 2] The Error-Cause attribute is defined in [RFC3576]. Change of Authorization and Disconnect-Request Request ACK NAK # Attribute 0-1 0 0 TBD Chargeable-User-Identity [Note 3] Where CUI attribute is included in Disconnect-Request or CoA-Request messages, it is used for session identification purposes only. This attribute MUST NOT be used for purposes other than identification (e.g. within CoA-Request messages to request authorization changes). 4. Diameter RADIUS Interoperability In deployments with both RADIUS and Diameter interworking, a translation agent will be deployed and operate in accordance to the NASREQ specification. 5. IANA Considerations 5.1 CUI RADIUS Attribute This document uses the RADIUS [RFC2865] namespace, see "http://www.iana.org/assignments/radius-types". This document instructs IANA to assign a new RADIUS attribute number for the CUI attribute. CUI TBA 5.2 Error-Cause Attribute This document instructs IANA to assign a new Error-Cause attribute [RFC3576], Adrangi, et al. Expires June 29, 2005 [Page 7] Internet-Draft Chargeable User Identity December 2004 "CUI-Support-Required" TBA 6. Security considerations The CUI attribute must be protected against Man-in-the-Middle attacks. The CUI appears in Access-Accept and Accounting-Requests packets and is protected by the mechanisms that are defined for RADIUS [RFC2865] and [RFC2866]. Therefore there are no additional security considerations beyond those already identified in [RFC2865] and [RFC2866]. Message-Authenticator(80) and Event-Timestamp(55) can be used to further protect against Man-in-the-middle attacks. It is strongly recommended that the CUI form used is such that the real user identity is not revealed. Furthermore, where a reference is used to a real user identity, the binding lifetime of that reference to the real user be kept as short as possible. 7. Acknowledgements The authors would like to thank Jari Arkko, Bernard Aboba, David Nelson, Barney Wolff, Blair Bullock, Sami Ala-Luukko, Lothar Reith, David Mariblanca, Eugene Chang, Greg Weber, and Mark Grayson, for their feedback and guidance. 8. References 8.1 Normative references [RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [rfc2486bis] Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The Network Access Identifier", draft-arkko-roamops-rfc2486bis-02 (work in progress), July 2004. Adrangi, et al. Expires June 29, 2005 [Page 8] Internet-Draft Chargeable User Identity December 2004 8.2 Informative references [RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B. Aboba, "Dynamic Authorization Extensions to Remote Authentication Dial In User Service (RADIUS)", RFC 3576, July 2003. [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J. Arkko, "Diameter Base Protocol", RFC 3588, September 2003. 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 Avi Lior Bridgewater Systems Corporation 303 Terry Fox Drive Ottawa, Ontario K2K 3J1 Canada Phone: +1 613-591-9104 EMail: avi@bridgewatersystems.com Jouni Korhonen Teliasonera Corporation P.O.Box 970 FIN-00051, Sonera Finland Phone: +358405344455 EMail: jouni.korhonen@teliasonera.com Adrangi, et al. Expires June 29, 2005 [Page 9] Internet-Draft Chargeable User Identity December 2004 John Loughney Nokia Itamerenkatu 11-13 FIN-00180, Helsinki Finland Phone: +358504836342 EMail: john.loughney@nokia.com Adrangi, et al. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Adrangi, et al. Expires June 29, 2005 [Page 11]