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
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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
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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
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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
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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.
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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.
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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.
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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],
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"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.
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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
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John Loughney
Nokia
Itamerenkatu 11-13
FIN-00180, Helsinki
Finland
Phone: +358504836342
EMail: john.loughney@nokia.com
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