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Network Working Group                                          T. Hiller
INTERNET-DRAFT                                       Lucent Technologies
Category: Standards Track                                     A. Palekar
<draft-hiller-eap-tlv-00.txt>                      Microsoft Corporation
28 October 2002                                                  G. Zorn
                                                           Cisco Systems

   A Container Type for the Extensible Authentication Protocol (EAP)

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026.

Internet-Drafts are working documents of the Internet Engineering Task
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This memo is filed as <draft-hiller-eap-tlv-00.txt>,  and  expires April
28, 2003.

Copyright Notice

Copyright (C) The Internet Society (2002).  All Rights Reserved.


The Extensible Authentication Protocol (EAP), defined in RFC 2284,
provides for support of multiple authentication methods. While EAP was
originally created for use with PPP, it has since been adopted for use
with IEEE 802.1X "Network Port Authentication".

Since its deployment, a number of weaknesses in EAP have become
apparent.  These include the lack of protection for, and acknowledgement
of Success and Failure messages.

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This memo describes an approach that may be taken to solve these
problems and others by defining a new EAP type which includes as payload
standard Type-Length-Value (TLV) objects.

1.  Introduction

The Extensible Authentication Protocol (EAP), described in [RFC2284],
provides a standard mechanism for support of multiple authentication
methods.  Through the use of EAP, support for a number of authentication
schemes may be added, including smart cards, Kerberos, Public Key, One
Time Passwords, and others.

One of the goals of EAP is to enable development of new authentication
methods without requiring deployment of new code on the Network Access
Server (NAS). As a result, the NAS acts as a "passthrough", and need not
understand specific EAP methods.

Figure 1 describes the relationship between the EAP peer, NAS and
backend authentication server.  As described in the figure, the EAP
conversation "passes through" the NAS on its way between the client and
the backend authentication server.  While the authentication
conversation is between the EAP peer and backend authentication server,
the NAS and backend authentication server need to have established trust
for the conversation to proceed.

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   +-+-+-+-+-+               +-+-+-+-+-+
   | Link    |               | Link    |
   | Layer   |               | Layer   |
   | Cipher- |               | Cipher- |
   | Suite   |               | Suite   |
   |         |               |         |
   +-+-+-+-+-+               +-+-+-+-+-+
       ^                         ^
       |                         |
       |                         |
       |                         |
       V                         V
   +-+-+-+-+-+               +-+-+-+-+-+  Trust +-+-+-+-+-+
   |         |  EAP          |         |<======>|         |
   |         |  Conversation |         |        |         |
   | EAP     |<================================>|  EAP    |
   | Peer    |  (over PPP,   |   NAS   |        |  Server |
   |         |  802.11,etc.) |         |<=======|         |
   |         |               |         |  Keys  |         |
   |         |               |         |        |         |
   +-+-+-+-+-+               +-+-+-+-+-+        +-+-+-+-+-+
       ^                                            ^
       |                                            |
       | EAP API                                    | EAP API
       |                                            |
       V                                            V
   +-+-+-+-+-+                                  +-+-+-+-+-+
   |         |                                  |         |
   |         |                                  |         |
   |  EAP    |                                  |  EAP    |
   |  Method |                                  |  Method |
   |         |                                  |         |
   +-+-+-+-+-+                                  +-+-+-+-+-+

   Figure 1 - Relationship between EAP client, backend authentication
              server and NAS.

Using EAP-TLV, it is possible for various type of data to be passed
directly between the backend authentication server and the EAP peer, and
to provide functionality not included in RFC 2284 without defining a
multiplicity of new EAP Types.

[Editor's Note: In fact, I'm not sure why we couldn't just redefine the
whole of EAP in terms of this type...]

This memo is offered to the EAP WG for discussion and possible adoption
as a solution to issues #10, 26 and 40.

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2.  Requirements language

In this document, the key words "MAY", "MUST,  "MUST  NOT",  "OPTIONAL",
"RECOMMENDED",  "SHOULD",  and  "SHOULD  NOT",  are to be interpreted as
described in [RFC2119].

3.  The EAP Type-Length-Value (EAP-TLV) Type


      EAP-TLV is a "special case" Type, more akin to the Identity and
      Notification Types than the authentication Types such as
      MD5-Challenge [RFC2284].  EAP-TLV differs from the Identity and
      Notification Types, however, in that a Peer MAY respond to an EAP-
      TLV Request with a Nak Response.  This is allowed for backward
      compatability with implementations that do not support the EAP-TLV




      The Data field is variable length, and contains Type-Length-Value
      objects (TLVs).

3.1.  TLV Format

TLVs are defined as follows:

    0                   1                   2                   3
    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
   |M|R|             Type          |            Length             |
   |                              Value...


      0 - Non-mandatory TLV
      1 - Mandatory TLV


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      Reserved, set to zero (0)


      A 14-bit field, denoting the attribute type. Allocated AVP Types
      0 - Reserved
      1 - Reserved
      2 - Reserved
      3 - Acknowledged Result


      The length of the Value field in octets.


      The value of the object.

3.2.  Result TLV

   The Result TLV provides support for acknowledged Success and Failure
   messages within EAP. It is defined as follows:

    0                   1                   2                   3
    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
   |M|R|           Type            |            Length             |
   |             Status            |


      1 - Mandatory TLV


      Reserved, set to zero (0)

   AVP Type

      3 - Success/Failure



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      The status field is two octets. Values include:

      1 - Success
      2 - Failure

4.  Discussion

It's not hard to come up with other uses for the EAP-TLV Type.  For
example, it could be used in the negotiation of language and charset for
Notification messages; a MAC TLV might be defined to cryptographically
protect the message (and incidentally enable mutual authentication for
types that might not otherwise support it); a Response might contain an
IPv6 Binding Update and the corresponding protected Success message
include the address of a dynamically assigned home agent, etc.

5.  Normative references

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
          Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2246] Blunk, L., Vollbrecht, J., "PPP Extensible Authentication
          Protocol (EAP)", RFC 2284, March 1998.

Author's Addresses

Tom Hiller
Lucent Technologies
1960 Lucent Lane
Naperville, IL 60566

Phone: +1 630 979 7673
Email: tom.hiller@lucent.com

Ashwin Palekar
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

Phone: +1 425 882 8080
EMail: ashwinp@microsoft.com

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Glen Zorn
Cisco Systems
500 108th Avenue N.E.
Suite 500
Bellevue, Washington 98004

Phone: +1 425 344 8113
Fax:   +1 425 740 0168
EMail: gwz@cisco.com

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Expiration Date

This memo is filed as <draft-hiller-eap-tlv-00.txt>,  and  expires April
28, 2003.

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