One document matched: draft-adrangi-radius-chargeable-user-identity-00.txt
Network Working Group Farid Adrangi
INTERNET DRAFT Intel Corporation
Category: Informational (or standards?) Avi Lior
Expires: Feb 7, 2005 Bridgewater Systems
Jouni Korhonen
Teliasonera
Sept 7, 2004
Chargeable User Identity
draft-adrangi-radius-chargeable-user-identity-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
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Abstract
This document describes a new RADIUS attribute used by a home RADIUS
to indicate Chargeable User Identity to all parties involved in the
roaming transaction outside the home network.
Table of Contents
1. Introduction...................................................2
1.1 Requirements language..........................................3
2. Operation.......................................................3
2.1 Chargeable User Identity Attribute.............................3
3. Diameter RADIUS Interoperability................................5
4. IANA Considerations.............................................6
5. Security Considerations.........................................6
6. Acknowledgements................................................6
7. References......................................................6
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AuthorsÆ Addresses.................................................7
1. Introduction
In certain authentication methods such as, EAP-PEAP or EAP-TTLS,
EAP-SIM, and EAP-AKA, the true identity of the subscriber can be
hidden from the RADIUS AAA servers outside the subscriberÆs home
network. In these methods the User-Name(1) attribute contains an
anonymous identity (e.g., anonymous@example.com) sufficient to
route the RADIUS packets to the home network but otherwise
insufficient to identify the subscriber. While this mechanism is
good practice there are situations where this creates problems:
- In certain roaming situations intermediaries and visited
network require to be able to correlate an authentication session
with a user identity known to the userÆs home network for fraud
detection and revenue assurance. For example, a broker may
require to implement a policy where by only one session is allowed
per user entity, or third party billing brokers may require to
match accounting records to a user identity.
- NAS may require to match the user session and accounting
records to a user identity known to the userÆs home network for
future use û for example, charging dispute.
This basically implies that a unique identity known by the home
network needs to be conveyed to all parties involved in the
roaming transaction.
Providing a unique identity to intermediaries is therefore a
requirement to fulfill certain business needs. This fulfillment
need not undermine the need to protect the anonymity of the user.
The mechanism provided by this draft allows the home operator to
meet these business requirements by providing a temporal identity
representing the subscriber and at the same time protecting the
anonymity of the subscriber.
Standard RADIUS Class(25) or User-Name(1) attributes could be used
to indicate the CUI. However, in a complex global roaming
environment where there could be one or more intermediary between
the NAS and the home RADIUS server, the use of aforementioned
attributes could lead to problems as described below.
O RADIUS Class (25) is intended to be opaque to entities
outside the home network. It is known and interpreted by the
home RADIUS server. This combined with the fact that there
could be multiple class attributes or it could contain other
data than a chargeable identity, would make it impossible for
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the entities outside the home network to identify which class
attributes contains a chargeable identity.
O Use of RADIUS UserName(1) would be a problem, because it
could be rewritten by the intermediaries. Furthermore,
subsequent accounting request may fail to route through the
intermediary exchanges due to the lack of decoration knowledge
by the home network.
The Chargeable User Identity (CUI) attribute provides a solution
to the above problem and avoids overloading the use of current
RADIUS attributes (e.g., UserName(1) re-write). 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 to such that it can be used to identify the user.
1.1 Requirements language
In this document, several words are used to signify the
requirements of the specification. These words are often
capitalized. 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. Operation
This document assumes that the RADIUS protocol operates as
specified in [1, 2] and that the Diameter protocol operates as
specified in[RFC 3588, NASREQ].
2.1 Chargeable User Identity Attribute
This attribute serves as an alias to the userÆs identity. It is
assigned by the home RADIUS server and MAY be sent in Access-
Accept message. The NAS or the access network AAA server MUST
include this attribute in the Accounting Requests (Start,
Interim, and Stop) messages if it was included in the Access
Accept message. Entities (e.g., NASes, proxies) outside the home
network MUST NOT modify the Chargeable User Identity attribute.
If the RADIUS server includes this attribute in an Access-Accept
message it MAY also use this attribute as one of the identity
attributes in a Disconnect Message and Change of Authorization
message defined by [4].
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A summary of the RADIUS Chargeable User Identity 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...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Name
Chargeable User Identity
Type
To be assigned by IANA
Length
>= 6
String
The string field is four or more octets. This non-NULL
terminated string consists of two colon separated parts. The
first part determines the Chargeable-User-Identity type and
the second part is the actual Chargeable-User-Identity
value. The Chargeable-User-Identity type is coded as two
octet string. The Chargeable-User-Identity value must be at
least one octet.
The following User-Identity Alias types have been defined:
00 û reserved
01 û IMSI
The is in international IMSI format according to the
ITU-T E.212 numbering plan as defined in [8] and
[9]).
02 û NAI
The identifier is in the form of a Network Access
Identifier as defined in [5].
03 û E.164 number
The identifier is in international E.164 format
(e.g. MSISDN, according to the ITU-T E.164
numbering plan as defined in [6] and [7]).
04 û SIP URL
The identifier is in the form of a SIP URI as defined
(as defined in [10]).
05 û Opaque string
Opague string is a value that is assigned to the user
by the home network in an unspecified format. where
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the home network asserts that this value represents a
particular user û itÆs a handle to the user.
The length of time for which the Chargeable User Identity is
valid is unspecified by this specification and typically
would be long enough to serve some business needs and short
enough such that it minimizes the chance of revealing the
true identity of the user (either directly or indirectly).
Below are examples of User Identity Alias strings with NAI
and E.164 Charging Types:
ö02:charging-id@realm.orgö
ö03:+4689761234ö
ö05:charging-idö
Ideally, the real user identity should not be revealed
through this attribute. However, the operators will have
the final word on the used charging type and its identifier.
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 0-1 0 0 0-1 TBD Chargeable User ID
[Note 1] If the Access Accept contains Chargeable-User-Identity then
the NAS MUST include the Chargeable-User-Identity in Accounting
Requests (Start, Interim and Stop) packets.
Change of Authorization and Disconnect-Request
Request ACK NAK # Attribute
0-1 0 0 TBD Chargeable User
[Note 2] Where Chargeable-User-Identity attribute is included in
Disconnect-Request or CoA-Request messages, they are used for
identification purposes only. This attribute MUST NOT be used for
purposes other than identification (e.g. within CoA-Request messages
to request authorization changes).
3. Diameter RADIUS Interoperability
In deployments where both RADIUS clients talking with Diameter
Servers or Diameter Client talking with RADIUS server then a
translation agent will be deployed and operate in accordance to
the NASREQ specification. A counterpart Diameter AVP with a
similar content to Chargeable-User-Identity is Diameter Credit-
Control ApplicationÆs Subscription-ID AVP [11].
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4. IANA Considerations
This document requires the assignment of a new RADIUS attribute
number for the Chargeable User Identity attribute.
5. Security Considerations
The Chargeable-User-Identity attribute must be protected against
Man-in-the-Middle attacks. The Chargeable-User-Identity appears
in Access-Accept and Accounting Requests packets and is protected
by the mechanisms that are defined for RADIUS [1] and [2].
Therefore there are no additional security considerations beyond
those already identified in [1] and [2].
Message-Authenticator (80) and Event-Timestamp can be used to
further protect against Man-in-the-middle attacks.
In this document we require that entities outside the home network
not modify the value of this attribute yet there are no provisions
for protecting against or detecting that a RADIUS Proxy has
modified the attribute.
6. Acknowledgements
The authors would like to thank Jari Arkko (of Ericsson), Bernard
Aboba (of Microsoft), Blair Bullock (of iPass), Sami Ala-luukko
(of Teliasonera), Eugene Chang (of Funk), and Mark Grayson (of
Cisco) for their feedback and guidance.
7. References
[1] Rigney, C., Rubens, A., Simpson, W. and S. Willens, "Remote
Authentication Dial In User Server (RADIUS)", RFC 2865, June
2000.
[2] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
[3] Rigney, C., Willats, W., Calhoun, P., "RADIUS Extensions",
RFC 2869, June 2000.
[4] Chiba, M., Dommety, G., Eklud, M., Mitton, D., Aboba, B.,
öDynamic Authorization Extensions to Remote Authentication
Dial In User Service (RADIUS)ö, RFC 3576, July 2003.
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[5] Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The Network
Access Identifier", draft-arkko-roamops-rfc2486bis-02 (work in
progress), July 2004.
[6] Recommendation E.164/I.331 (05/97): The International Public
Telecommunication Numbering Plan. 1997.
[7] Complement to ITU-T Recommendation E.164 (05/1997):"List of
ITU-T Recommendation E.164 assigned country codes", June 2000.
[8] Recommendation E.212 (11/98): The international
identification plan for mobile terminals and mobile users.
1998.
[9] Complement to ITU-T Recommendation E.212 (11/1997):" List of
mobile country or geographical area codes ", February 1999.
[10] M. Handley, H. Schulzrinne, E. Schooler, J. Rosenberg,
G. Camarillo, A. Johnston, J. Peterson, R. Sparks
"SIP: Session Initiation Protocol", RFC 3261. June 2002.
[11] Hakala, H., Mattila, L., Koskinen, J.-P., Stura M., and
Loughney J., "Diameter Credit-Control Application", draft-
ietf-aaa-diameter-cc-06.txt (work in progress), September
2004.
AuthorsÆ Addresses
Farid Adrangi
Intel Corporation
2111 N.E. 25th Avenue
Hillsboro OR
USA
Phone: 503-712-1791
Email: farid.adrangi@intel.com
Avi Lior
Bridgewater Systems Corporation
303 Terry Fox Drive
Suite 100
Ottawa, Ontario K2K 3J1
Canada
Phone: 613-591-9104 ;x 6417
Email: avi@bridgewatersystems.com
Jouni Korhonen
Teliasonera Corporation
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Phone: +358405344455
Email: jouni.korhonen@teliasonera.com
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