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Extensible Authentication Protocol                              J. Arkko
Working Group                                                   Ericsson
Internet-Draft                                                 P. Eronen
Expires: April 27, 2006                                            Nokia
                                                        October 24, 2005


  Authenticated Service Information for the Extensible Authentication
                             Protocol (EAP)
                draft-arkko-eap-service-identity-auth-04

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   This Internet-Draft will expire on April 27, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   EAP is typically used in an arrangement where the actual service
   (such as a wireless LAN access point) is separated from the
   authentication server.  However, EAP itself does not have a concept
   of a service identity or its parameters, and thus the client usually
   does not authenticate any information about the service itself, even
   when a mutually authenticating EAP method is used.  This document



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   specifies a backward compatible extension to popular EAP methods for
   authenticating service related information, such as the identity and
   type of the offered service.  A common parameter name space is
   created in order to ensure that the same kinds of identifiers can be
   authenticated independent of the choice of the EAP authentication
   method, retaining the EAP media independence principle.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
           1.1.  Authenticated Service Information  . . . . . . . . .  3
   2.  Design Considerations  . . . . . . . . . . . . . . . . . . . .  6
           2.1.  Media Independence . . . . . . . . . . . . . . . . .  6
           2.2.  Verifying Party  . . . . . . . . . . . . . . . . . .  8
           2.3.  Communication within EAP vs. within AAA  . . . . . .  9
   3.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . . 10
   4.  Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 12
           4.1.  Format . . . . . . . . . . . . . . . . . . . . . . . 12
           4.2.  General Parameters . . . . . . . . . . . . . . . . . 13
                   4.2.1.  Service Type Parameter . . . . . . . . . . 13
                   4.2.2.  Service Provider Parameter . . . . . . . . 14
                   4.2.3.  Country Code Parameter . . . . . . . . . . 14
           4.3.  Parameters for IEEE 802.11 wireless LANs . . . . . . 14
                   4.3.1.  SSID Parameter . . . . . . . . . . . . . . 14
                   4.3.2.  BSSID Parameter  . . . . . . . . . . . . . 14
           4.4.  Parameters for IEEE 802.16 Networks  . . . . . . . . 14
           4.5.  Parameters for IKEv2 . . . . . . . . . . . . . . . . 14
                   4.5.1.  Responder Address Parameter  . . . . . . . 15
                   4.5.2.  IDr Parameter  . . . . . . . . . . . . . . 15
   5.  EAP Method Extensions  . . . . . . . . . . . . . . . . . . . . 15
           5.1.  EAP-TLS  . . . . . . . . . . . . . . . . . . . . . . 15
           5.2.  PEAPv2 . . . . . . . . . . . . . . . . . . . . . . . 17
           5.3.  EAP-AKA  . . . . . . . . . . . . . . . . . . . . . . 17
           5.4.  EAP-SIM  . . . . . . . . . . . . . . . . . . . . . . 20
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 21
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
           7.1.  Allocations Requested in This Document . . . . . . . 21
           7.2.  Future Allocation Policy . . . . . . . . . . . . . . 22
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
           8.1.  Normative References . . . . . . . . . . . . . . . . 23
           8.2.  Informative References . . . . . . . . . . . . . . . 23
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
   Intellectual Property and Copyright Statements . . . . . . . . . . 26






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1.  Introduction

   EAP is typically used in an arrangement where the actual service
   (such as a wireless LAN access point) is separated from the
   authentication server.  However, EAP itself does not have a concept
   of a service identity or its parameters, and thus the client usually
   does not authenticate any information about the service itself, even
   when a mutually authenticating EAP method is used.

   However, if a method supports channel bindings as specified in RFC
   3748 [4] it becomes possible to ensure that the client, the node
   providing the service, and the authentication server all have the
   same information about this information.  This does not, by itself,
   ensure that the information is correct, just that everyone has the
   same information; a service node might be providing a service that
   this particular node should not be providing.  A method that supports
   authenticated service information ensures in addition that the
   authentication server knows this information to be correct.

   This document specifies a backwards compatible extension to popular
   EAP methods for supporting both channel bindings and authenticated
   service information.  It does so in a media-independent manner,
   making it possible to run the same EAP mechanisms across different
   media, and introducing new information elements without affecting
   interoperability.

   This extension is intended for the verification of service
   information.  It is not intended as a means for communicating
   information about parameters that EAP clients would not otherwise be
   aware of based on their communication with the node providing the
   service.

   This rest of the document is organized as follows.  In Section 1.1 we
   discuss the need for authenticated service information in more
   detail.  Section 2 discusses the design considerations and
   alternatives for solutions in this space.  Section 3 gives an
   overview of how our protocol operates and Section 4 describes the
   kind of information that can be verified.  We have provided only an
   initial list of parameters for IEEE 802.11 and IKEv2, but additional
   parameters can be defined through IANA.  Section 5 describes the
   extensions necessary for certain popular EAP methods.  Support for
   other EAP methods can be added in other specifications.

1.1.  Authenticated Service Information

   EAP is run for the purposes of providing granting access to a
   service, such as network access.  The nodes providing such services
   (called authenticators in EAP) typically have an identifier or



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   identifiers, and offer a specific type of a service with an
   associated set of parameters.  Collectively, this identifier, type
   and parameter information is called service information.

   In the Extensible Authentication Protocol (EAP) framework, different
   authentication methods can provide varying security properties.  One
   such property is called "channel bindings", which is described in RFC
   3748 [4] as follows:

      "The communication within an EAP method of integrity-protected
      channel properties such as endpoint identifiers which can be
      compared to values communicated via out of band mechanisms (such
      as via a AAA or lower layer protocol)."

   The document continues by describing the security implications of not
   being able to verify service information:

      "It is possible for a compromised or poorly implemented EAP
      authenticator to communicate incorrect information to the EAP peer
      and/or server.  This may enable an authenticator to impersonate
      another authenticator or communicate incorrect information via
      out-of-band mechanisms (such as via a AAA or lower layer
      protocol).

      Where EAP is used in pass-through mode, the EAP peer typically
      does not verify the identity of the pass-through authenticator, it
      only verifies that the pass-through authenticator is trusted by
      the EAP server.  This creates a potential security vulnerability.

      Section 4.3.7 of [11] describes how an EAP pass-through
      authenticator acting as a AAA client can be detected if it
      attempts to impersonate another authenticator (such by sending
      incorrect NAS-Identifier [9], NAS-IP-Address [9] or NAS-IPv6-
      Address [10] attributes via the AAA protocol).  However, it is
      possible for a pass-through authenticator acting as a AAA client
      to provide correct information to the AAA server while
      communicating misleading information to the EAP peer via a lower
      layer protocol.

      For example, it is possible for a compromised authenticator to
      utilize another authenticator's Called-Station-Id or NAS-
      Identifier in communicating with the EAP peer via a lower layer
      protocol, or for a pass-through authenticator acting as a AAA
      client to provide an incorrect peer Calling-Station-Id [9] [12] to
      the AAA server via the AAA protocol.

      In order to address this vulnerability, EAP methods may support a
      protected exchange of channel properties such as endpoint



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      identifiers, including (but not limited to): Called-Station-Id [9]
      [12], Calling-Station-Id [9] [12], NAS-Identifier [9], NAS-IP-
      Address [9], and NAS-IPv6-Address [10].

      Using such a protected exchange, it is possible to match the
      channel properties provided by the authenticator via out-of-band
      mechanisms against those exchanged within the EAP method.  Where
      discrepancies are found, these SHOULD be logged; additional
      actions MAY also be taken, such as denying access."

   Unfortunately, such verification is currently not possible in popular
   network scenarios.  For instance, in IEEE 802.11 networks a rogue
   operator can actually advertise the same identity (BSSID or SSID) as
   the local operator; the parameters advertised by the access point
   information are not authenticated end-to-end to the home network.
   There is no support is in the commonly used EAP methods for
   authentication of service information, and there are no alternative
   verification means in the IEEE 802 lower layer.  For instance, rogue
   access points can present a different identity to the client and to
   the home network.  Or a rogue IKEv2 gateway can claim to be a 802.11
   access point to its clients, but still appear as an IKEv2 gateway
   towards the authentication server.

   There are cases where the lower layer does provide its own means of
   authenticating the service information.  For instance, in IKE2, EAP
   is used together with certificate-based authentication of the
   responder.  However, this document may be useful with proposed IKEv2
   extensions like [15] that remove the need to deploy a PKI.  Also,
   even a lower layer that performs some kind of authentication for its
   service information may be unable to do so in all cases, such as
   distinguishing between different services offered by the nodes
   belonging to a group of nodes certified in the same manner.

   This situation is further complicated by the fact that services do
   not necessarily have just a single identifier, but several different
   identifiers of different types.  For instance, an IEEE 802.11 access
   point could be identified by a BSSID, an IPv4 address (e.g., NAS-IP-
   Address), or a domain name (e.g., NAS-Identifier).  Other
   identifiers, such as SSID, do not necessarily identify a single
   access point, but may be more interesting to the client (if you
   consider the "service" to be wireless LAN network access in some
   hotspot, rather than a single physical box).

   Ongoing development in the network access technology is opening up
   vulnerabilities that go beyond simple identifiers.  For instance,
   protocol mechanisms are being developed to indicate the "cost" of
   access, such as whether the access is free or for a charge.  Without
   a secure way to agree about the cost among the parties, fraudulent



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   local networks can get customers via an attractive offer and
   subsequently charge them for usage with less attractive conditions.
   Prevention of such attacks is of high interest, as without technical
   measures they are expected to occur due to the economic incentives.

   It is important to make a distinction between channel bindings and
   authenticating information related to the the pass-through
   authenticator.  Channel bindings only ensure that the same
   information is available to the EAP peer and the AAA server.  This
   alone does not prevent an authenticator from impersonating another
   authenticator if the AAA server blindly accepts any information
   received from the authenticator.  To provide authentication, the AAA
   server has to verify that the information actually corresponds to the
   entity the AAA-Key is sent to.


2.  Design Considerations

   The following considerations deserve some discussion:

   o  Retaining media independence in EAP

   o  Choosing the party (or parties) to perform the verification

   o  Communication within EAP vs. within AAA protocols

   These are discussed in following subsections.

2.1.  Media Independence

   An EAP-based channel binding solution can fail to retain EAP's
   independence from media in three ways.  First, an EAP method might
   support channel bindings only for some media, or make the addition of
   parameters for new media types hard.  This would make it harder for
   users to switch to new media.

   Second, if channel bindings are provided only by some EAP methods,
   the choice of authentication methods and credentials would be limited
   in an environment that requires channel binding support [13].

   Third, the EAP layer or EAP methods might have to interpret or
   understand the channel binding parameter information in some manner.
   This would result in a need to update EAP peer and server
   implementations when new media or new parameters on an existing media
   are developed.

   This draft avoids these problems by (1) defining the channel binding
   support simultaneously to the most popular EAP methods, (2) providing



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   a common parameter name space across these methods in order to ensure
   that the same kind of information can be authenticated independent of
   the choice of the EAP method, and (3) treating the channel binding
   information as opaque data at the EAP layer and within EAP methods.

   Note that while the parameters are represented as opaque data at the
   EAP layer, it is still necessary to specify the parameters in a
   publicly avaible, stable specification for interoperability.  This is
   why this document defines both the EAP transport and the actual
   parameters.

   Figures 1 and 2 illustrate how information is expected to be conveyed
   to upper layers where authorization decisions can be made.


         Peer         Pass-through Authenticator   Authentication
                            (optional)                 Server

    +-----------+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+
    |           |   |                           |   |           |
    |  Control  |   |          Control          |   |  Control  |
    |application|   |        application        |   |application|
    |           |   |                           |   |           |
    +-------+   +   +----------+     +----------+   +   +-------+
    |       |   |   |          |     |          |   |   |       |
    | EAP   |   |   |   EAP    |     |   EAP    |   |   | EAP   |
    | layer |   |   |  layer   |     |  layer   |   |   | layer |
    |       |   |   |          |     |          |   |   |       |
    +-------+---+   +----------+--+--+----------+   +---+-------+
    |           |   |             |             |   |           |
    |Lower layer|   |  Lower layer|  AAA/IP     |   |  AAA/IP   |
    |           |   |             |             |   |           |
    +-----+-----+   +-------+-----+-----+-------+   +-----+-----+
          !                 !           !                 !
          !                 !           !                 !
          +-------->--------+           +--------->-------+


                   Figure 1: Architecture












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     +----------------------------------------------------+
     |                                                    |
     |                Control application                 |
     |                                                    |
     |                                                    |
     |                                                    |
     |     Lower /|\                  /|\ Opaque channel  |
     |     layer  |                    |  binding data    |
     | information|                    |  to/from EAP     |
     |            |                    |  layer           |
     |           \|/                  \|/                 |
     +-------------------------+--------------------------+
     |                         |                          |
     |                         |                          |
     |                         |                          |
     |     Lower layer    <----+---->    EAP layer        |
     |                         |                          |
     |                         |                          |
     |                         |                          |
     |                         |                          |
     |                         |                          |
     |                         |                          |
     +-------------------------+--------------------------+

          Figure 2: Flow of information to and from EAP

2.2.  Verifying Party

   The main idea of channel bindings is to be able to verify information
   from two sources, such as comparing what the EAP authenticator has
   told the peer and the server.  Different designs could implement this
   check at different nodes: at the peer, the server, or both.

   Assuming a secure exchange of opaque data through EAP, both the peer
   and the server can have the same information available to them,
   including what the authenticator has communicated over AAA to the
   server and what it has told the peer over the lower layer.  (Note
   that there are vulnerabilities in both AAA and lower layer protocols;
   what matters, however, is that both ends see the same information.
   Assuming the EAP method is secure, this can be arranged.)

   However, the server may be in a better position to have an
   understanding of what roaming contracts exist, what authenticators
   are expected to exist and what services they should be offering.
   Similarly, fraud detection and policy rules are easier to arrange at
   a central site than in clients.  Finally, server-side verification is
   the model already adopted in PEAPv2 [7], it makes the introduction of
   a general channel binding model easier for this method.



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   As a result, it seems reasonable to assume a model where the server
   is in charge of the verification process.

2.3.  Communication within EAP vs. within AAA

   As discussed in [16], the communication of the verified parameters
   can occur in two ways:

   Within EAP

      Here the set of verified parameters is communicated end-to-end
      within EAP as an opaque string.

   Within AAA and Lower Layer

      Here the set of verified parameters is communicated from the
      authenticator (a) to the peer via the lower layer protocol and (b)
      to the server via the AAA protocol.  In order to prevent
      fraudulent claims about the parameters, the AAA protocol
      calculates AAA-Key based on the parameters, and communicates only
      this key (not the current MSK) to the authenticator.  As a result,
      the peer and the authenticator can not complete their network
      attachment process if there's a mismatch in the set of parameters.

   The overall result of both approaches is the same, but there are
   subtle security differences: One difference is that in the EAP
   approach we need to trust the endpoints to actually perform the
   check, whereas the key-based check is implicit and "non-skippable" in
   the latter approach; if the parameters mismatch the keys simply do
   not work.

   Another difference is in the timing of the check; in conventional AAA
   protocols the user is considered authenticated when the RADIUS
   Access-Accept or equivalent message is sent.  This ensures that the
   AAA server is aware of the result of the access request.  But in the
   AAA-based approach a mismatch in the parameters is learned after
   this, and may be hard to report in a secure way.  For instance, the
   authenticator could claim that a session was started, even if in
   reality the secure association protocol failed due to a mismatch.

   There is also a difference in terms of deployment implications.  The
   EAP-based approach means that EAP implementations and methods have be
   updated.  Existing credentials can continue to be used, however, and
   it is expected that the opaque data approach makes it possible to add
   new media and new parameters without additional code changes in EAP.

   There are no EAP updates in the AAA-based approach, but it is still
   necessary to add support for the new parameter communication means



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   and AAA-Key calculation to peers, authenticators, and servers.  The
   main difference to the EAP-based approach is that authenticators need
   to be changed.

   Because of the above considerations, this draft employs the EAP-based
   approach.


3.  Protocol Overview

   The basic idea in this extension is that the EAP peer sends the EAP
   server a statement that it going to accept service from an access
   device associated with particular set of identifiers and other
   information.

   In order to protect this statement, an EAP method needs to be able to
   pass data from the EAP peer to the EAP server, and be able to protect
   this exchange using keys known only them and not the access device.
   The Transient EAP Keys (TEKs) can be used for this purpose, as these
   keys are only known to the EAP endpoints and not communicated to the
   access device.

   After receiving this information, the EAP server can compare the
   information provided from the EAP peer to the information it has
   received directly from the access device.  If the information does
   not match, the access device has provided different information to
   the peer and to the AAA protocol.  This is disallowed, and the
   authentication SHOULD be terminated and the discrepancy MUST be
   logged.

   In order to provide a generic solution where any EAP method can be
   used on a given lower layer, the same format is used for the
   exchanged information.  This format consists of Tag-Length-Value
   triplets with IANA managed tag space.

   The parameter information is sent along the other messages in an EAP
   method.  The exact message sequences depend on the used EAP method,
   but Figure 1 shows a typical sequence.

       Peer                  Authenticator                  Server
          |                          |                          |
          | 802.11 attachment        |                          |
          |<------------------------>|                          |
          |                          |                          |
     +----------------------+        |                          |
     | Information received |        |                          |
     | at this point is     |        |                          |
     | not authenticated    |        |                          |



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     +----------------------+        |                          |
          |                          |                          |
          |   EAP Identity Request   |                          |
          |<-------------------------|                          |
          |                          |                          |
          |  EAP Identity Response   |                          |
          |------------------------->|                          |
          |                          | RADIUS Access-Request    |
          |                          |------------------------->|
          |                          |                          |
          |                          |       +----------------------+
          |                          |       | Server authenticates |
          |                          |       | the RADIUS request   |
          |                          |       +----------------------+
          |                          |                          |
          |                          | RADIUS Access-Challenge  |
          |       EAP TLS Start      |<-------------------------|
          |<-------------------------|                          |
          |                          |                          |
     +-----------------------+       |                          |
     | Peer sends the        |       |                          |
     | authenticator's info  |       |                          |
     | to the server in EAP  |       |                          |
     +-----------------------+       |                          |
          |                          |                          |
          | EAP TLS C-Hello + id.    |                          |
          |------------------------->|                          |
          |                          |  RADIUS Access-Request   |
          |                          |------------------------->|
          |                          |                          |
          |                          |       +-------------------------+
          |                          |       | Server can now verify   |
          |                          |       | that the information    |
          |                          |       | is what was expected    |
          |                          |       +-------------------------+
          |                          |                          |
          |                          | RADIUS Access-Challenge  |
          | EAP TLS S-Hello     .    |<-------------------------|
          |<-------------------------|                          |
          |                          |                          |
     +-------------------------+     |                          |
     | Peer learns here that   |     |                          |
     | the information was     |     |                          |
     | verified (EAP continues)|     |                          |
     +-------------------------+     |                          |
          |                          |                          |
          |                          |                          |
          |     EAP TLS Finished     |                          |



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          |------------------------->|  RADIUS Access-Request   |
          |                          |------------------------->|
          |                          |                          |
          |                          | RADIUS Access-Challenge  |
          |     EAP TLS Finished     |<-------------------------|
          |<-------------------------|                          |
          |                          |                          |
          |                          |                          |
          |         EAP TLS          |                          |
          |------------------------->|  RADIUS Access-Request   |
          |                          |------------------------->|
          |                          |                          |
          |                          | RADIUS Access-Accept +   |
          |                          |        AAA-Key           |
          |     EAP Success          |<-------------------------|
          |<-------------------------|                          |
          |                          |                          |
     +-----------------------------+
     | Authentication is completed |
     | when the authenticator      |
     | proves it knows the AAA-Key |
     +-----------------------------+


   Zero or more parameters are sent from the peer to the server.  Each
   parameter is of the format explained in the next section.


4.  Parameters

4.1.  Format

   Nodes supporting this extension pass parameters in the following
   format:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Res  |     Parameter Identifier      |        Length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                          Value                                .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The meaning of the fields is described as follows:



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   Res

      A 4-bit field reserved for future use.  The value MUST be
      initialized to zero by the sender, and MUST be ignored by the
      receiver.

   Parameter Identifier

      A 16-bit field that specifies what parameter is being
      communicated.

   Length

      A 12-bit field that indicates the length of the Value field, in
      bytes.

   Value

      The actual parameter value.  The interpretation of this value
      depends on the Parameter Identifier field.  Integers are
      represented as four bytes in all cases, whereas addresses and
      strings are represented in as many octets as they are long.

   The EAP or the EAP method layer SHOULD NOT attempt to interpret the
   information beyond this format.  In other words, the Parameter
   Identifier and Value fields are interpreted as opaque data in order
   to ensure EAP media independence.  EAP implementations SHOULD pass
   the information to higher layers that are in charge of authorization
   decisions, such as AAA server authorization logic.

   The encapsulation of this sequence of parameters is EAP method
   dependent.

4.2.  General Parameters

   These parameters are for any type of nodes and lower layers.  The
   Service Type parameter MUST be supported by all nodes conforming to
   this specification, and MUST be the first parameter in all messages
   containing a sequence of parameters defined here.

4.2.1.  Service Type Parameter

   The Parameter Identifier for this parameter is 0, and the Value is a
   32-bit integer, represented in network byte order.  The following
   values have been currently defined:






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      0  IEEE 802.11

      1  IEEE 802.16

      2  IKEv2

   The receiver SHOULD fail the authentication if the Value field is
   either not recognized by it or is not the same one for which it
   thinks access is being provided.

4.2.2.  Service Provider Parameter

   The Parameter Identifier for this parameter is 1, and the Value is an
   UTF-8 encoded string describing the human readable name of the
   service provider.  As EAP is used primarily for network access, this
   is typically the name of the access network provider.

4.2.3.  Country Code Parameter

   The Parameter Identifier for this parameter is 2, and the Value is an
   ASCII string of at most 3 characters, conforming to the ISO 3166 [8]
   country code.

4.3.  Parameters for IEEE 802.11 wireless LANs

   All the following parameters MUST be supported when IEEE 802.11 is
   accepted as a Service Type.

4.3.1.  SSID Parameter

   The Parameter Identifier for this parameter is 3, and the Value is an
   octet string containing the Service Set Identifier (SSID).

4.3.2.  BSSID Parameter

   The Parameter Identifier for this parameter is 4, and the Value is a
   6-octet string containing the BSSID.

4.4.  Parameters for IEEE 802.16 Networks

   No parameters have yet been defined for the IEEE 802.16 networks.

4.5.  Parameters for IKEv2

   All the following parameters MUST be supported when IKEv2 is accepted
   as the Service Type.





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4.5.1.  Responder Address Parameter

   The Parameter Identifier for this parameter is 14, and the Value is
   the IP address of the node who acted as the responder for this IKEv2
   EAP exchange.  The Value is either 4 or 16 bytes depending on whether
   IPv4 or IPv6 is used.

4.5.2.  IDr Parameter

   The Parameter Identifier for this parameter is 16, and the Value is
   an octet string containing the IKEv2 responder identity payload
   (IDr).


5.  EAP Method Extensions

   This section describes an initial set of extensions to some current
   EAP methods so that they can be transport the parameter information.

   The extensions are optional and backwards compatible, so that, where
   allowed by policy, EAP peers without these extensions can still
   contact EAP servers with these extensions and vice versa.  The
   default policy SHOULD be that such usage is allowed.

5.1.  EAP-TLS

   A TLS extension [3] is added to the EAP TLS [2] client_hello/
   server_hello messages.  The extension type of the extension is EAP
   Service Information and it has the number < To Be Assigned By IANA >.
   The extension contains a sequence of parameters, followed by each
   other.

   The extension sent in the server_hello message SHOULD contain zero
   parameters, and is only used to confirm that the server supports this
   specification.  As discussed in RFC 3546, when these extensions
   appear in a client hello message, they are ignored by old server
   implementations.  The lack of this extension in the authenticator's
   server hello response SHOULD be taken as an indication that the
   authenticator does not support the mechanisms defined in this
   document.  The authenticator MUST NOT use this extension unless the
   client provided the same extension in its own hello message, as per
   RFC 3546 the client is required to terminate the TLS session
   otherwise.

   The client_hello/server_hello messages are included in MACs in the
   TLS Finished messages, which ensures that modifications will be
   detected.




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   The following sequence illustrates the operation of the EAP TLS
   protocol with this extension:

        Peer                                               Authenticator
          |                                                          |
          |                   PPP EAP-Request/                       |
          |                   EAP-Type=EAP-TLS                       |
          |                   (TLS Start)                            |
          |<---------------------------------------------------------|
          |                                                          |
          |                  PPP EAP-Response/                       |
          |                  EAP-Type=EAP-TLS                        |
          |              (TLS client_hello + extension)              |
          |--------------------------------------------------------->|
          |                                                          |
          |                   PPP EAP-Request/                       |
          |                   EAP-Type=EAP-TLS                       |
          |             (TLS server_hello + extension,               |
          |                   TLS certificate,                       |
          |               [TLS server_key_exchange,]                 |
          |               [TLS certificate_request,]                 |
          |                 TLS server_hello_done)                   |
          |<---------------------------------------------------------|
          |                                                          |
          |                   PPP EAP-Response/                      |
          |                   EAP-Type=EAP-TLS                       |
          |                   (TLS certificate,                      |
          |                TLS client_key_exchange,                  |
          |                [TLS certificate_verify,]                 |
          |                 TLS change_cipher_spec,                  |
          |                    TLS finished)                         |
          |--------------------------------------------------------->|
          |                                                          |
          |                   PPP EAP-Request/                       |
          |                   EAP-Type=EAP-TLS                       |
          |                (TLS change_cipher_spec,                  |
          |                    TLS finished)                         |
          |<---------------------------------------------------------|
          |                                                          |
          |                   PPP EAP-Response/                      |
          |                   EAP-Type=EAP-TLS                       |
          |--------------------------------------------------------->|
          |                                                          |
          |                   PPP EAP-Success                        |
          |<---------------------------------------------------------|
          |                                                          |





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   This works the same way when resuming session.  Note that the
   parameters can change from the initial authentication.

5.2.  PEAPv2

   In PEAPv2 [7], the Connection-Binding TLV is used to carry parameter
   objects.  One Connection-Binding TLV for this purpose is exchanged in
   each direction, containing all the parameters that need to be
   exchanged.  The Connection-Binding TLV carries a set of PEAPv2 TLVs.
   The transport of parameters for the purposes of this document takes
   place through the PEAPv2 Service Information Parameter TLV defined in
   the following:

       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|         TLV Type          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Parameter...                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields of this TLV are as follows:

      M

         0 - Optional TLV.

      R

         Reserved, set to zero (0).

      TLV Type

         < To Be Assigned By IANA >

      Length

         Length of the TLV.

      Parameter...

         The parameter in the format described in Section 4.1.

5.3.  EAP-AKA

   For EAP-AKA, a new attribute AT_SERVICEID is added to the EAP-
   Request/AKA/Challenge message.




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   The format of the AT_SERVICEID attribute is shown below:


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | AT_SERVICEID  | Length        | Actual data length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                        Parameters...                          .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields of this attribute are as follows:

      AT_SERVICEID

         < To Be Assigned By IANA >

      Length

         Length of the attribute.

      Actual data length

         This field specifies the length of the following field in
         bytes, because the length of the parameter must be a multiple
         of 4 bytes, the sender pads the data with zero bytes when
         necessary.

      Parameters...

         The parameters in the format described in Section 4.1.

   The following sequence illustrates the operation of the EAP-AKA
   protocol with this extension:














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     Peer                                                Authenticator
       |                      EAP-Request/Identity             |
       |<------------------------------------------------------|
       |                                                       |
       | EAP-Response/Identity                                 |
       | (Includes user's NAI)                                 |
       |------------------------------------------------------>|
       |                                                       |
       |                            +------------------------------+
       |                            | Server runs UMTS algorithms, |
       |                            | generates RAND and AUTN.     |
       |                            +------------------------------+
       |                                                       |
       |                         EAP-Request/AKA-Challenge     |
       |           (AT_RAND, AT_AUTN, AT_MAC, AT_SERVICEID)    |
       |<------------------------------------------------------|
       |                                                       |
   +-------------------------------------+                     |
   | Peer runs UMTS algorithms on USIM,  |                     |
   | verifies AUTN and MAC, derives RES  |                     |
   | and session key                     |                     |
   +-------------------------------------+                     |
       |                                                       |
       | EAP-Response/AKA-Challenge                            |
       | (AT_RES, AT_MAC, AT_SERVICEID)                        |
       |------------------------------------------------------>|
       |                                                       |
       |                          +--------------------------------+
       |                          | Server checks the given RES,   |
       |                          | and MAC and finds them correct.|
       |                          +--------------------------------+
       |                                                       |
       |                                          EAP-Success  |
       |<------------------------------------------------------|

   The AT_SERVICEID attribute from the server to the peer is empty, and
   is only used for capability detection.  A peer MUST NOT send a
   AT_SERVICEID attribute if no such attribute was seen from the server
   previously.  In this case, the peer MAY disconnect if its policy
   requires the channel binding support.

   Note that the AT_SERVICEID attribute is used also in the EAP-Request/
   AKA/AKA-Reauthentication message, and that the set of parameters
   exchanged in this case may differ from those agreed upon earlier in
   the initial authentication.

   The use of the AT_SERVICEID attribute is backward compatible, because
   existing implementations ignore unknown parameters.



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5.4.  EAP-SIM

   For EAP-SIM, a new attribute AT_SERVICEID is added to the EAP-
   Request/SIM/Challenge message.  The format of the AT_SERVICEID
   attribute is as shown for EAP-AKA.

   The following sequence illustrates the operation of the EAP-SIM
   protocol with this extension:

        Peer                                               Authenticator
          |                                                          |
          |                               EAP-Request/Identity       |
          |<---------------------------------------------------------|
          |                                                          |
          | EAP-Response/Identity                                    |
          |--------------------------------------------------------->|
          |                                                          |
          |                        EAP-Request/SIM/Start             |
          |                        (AT_VERSION_LIST)                 |
          |<---------------------------------------------------------|
          |                                                          |
          | EAP-Response/SIM/Start                                   |
          | (AT_NONCE_MT, AT_SELECTED_VERSION)                       |
          |--------------------------------------------------------->|
          |                                                          |
          |               EAP-Request/SIM/Challenge                  |
          |               (AT_RAND, AT_MAC, AT_SERVICEID)            |
          |<---------------------------------------------------------|
          |                                                          |
      +-------------------------------------+                        |
      | Peer runs GSM algorithms,           |                        |
      | verifies AT_MAC and derives         |                        |
      | session keys                        |                        |
      +-------------------------------------+                        |
          |                                                          |
          | EAP-Response/SIM/Challenge                               |
          | (AT_MAC, AT_SERVICEID)                                   |
          |--------------------------------------------------------->|
          |                                                          |
          |                                                          |
          |                                             EAP-Success  |
          |<---------------------------------------------------------|
          |                                                          |

   As with EAP-AKA, the AT_SERVICEID attribute must be passed also in
   the EAP-Request/SIM/SIM-Reauthentication message.  Similarly, the
   AT_SERVICEID attribute from the server to the client is empty and
   only used for capability detection.



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6.  Security Considerations

   The implications of being unable to verify service information have
   been described in Section 7.15 of RFC 3748 [4].  These include
   vulnerabilities related to compromised access points or fraudulent
   service providers.  When properly used, the mechanism provided in
   this document removes these vulnerabilities.  The mechanism is
   generic and not tied to any specific EAP method or use of EAP over a
   specific link layer, and as such can be expected to be more easily
   deployed as alternative suggestions such as those described in PEAPv2
   [7] or EAP FAST [14].

   Authenticating the service information may complicate operation in
   some deployment scenarios, since it requires that the AAA server is
   able to authenticate the expected kinds of information.  For
   instance, RADIUS is often deployed in situations where the only
   authenticated information related to the RADIUS client is the IP
   address; other information may be present in the Access-Request
   message (such as BSSID/SSID in the Called-Station-Id attribute), but
   this is simply claimed information not authenticated information.
   Where such information is not available, some vulnerabilities still
   remain.

   In the deployment phase, it is possible that clients and servers do
   not get support for the mechanism described in this document at the
   same time.  It is a policy decision to accept an EAP exchange from a
   party that does not support this mechanism.  This decision is
   protected from a bidding down attack by a man-in-the-middle, because
   EAP methods have integrity protection for the exchanged messages.
   Therefore, the removal or modification of the parameter block would
   be detected.


7.  IANA Considerations

7.1.  Allocations Requested in This Document

   This document requests an IANA allocation of TLS Extension type [3]
   for EAP Service Identity (see Section 5.1).

   This document requests an IANA allocation of a PEAPv2 [7] TLV type
   number for the Service Identity Parameter TLV (see Section 5.2).

   This document requests an IANA allocation for the attribute type
   number AT_SERVICEID in the [6] and [5] protocols (see Section 5.3 and
   Section 5.4).  The same value should be allocated for both protocols.





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7.2.  Future Allocation Policy

   New Parameter Identifier values can be defined through Specification
   Required [1].  The following values have been currently allocated:

      0  Service Type

      1  Service Provider

      2  Country Code

      3  802.11/SSID

      4  802.11/BSSID

      6  IKEv2/Responder Address

      7  IKEv2/IDr

   Values 65000 through 65530 and for Experimental Use and can be used
   without allocation.  Values 65531 through 65535 are Reserved.

   New Service Type values can be defined through IETF Consensus [1].
   The following values have been currently allocated:

      0  IEEE 802.11

      1  IEEE 802.16

      2  IKEv2

   Values 429496700 through 4294967289 are for Experimental Use and can
   be used without allocation.  Values 4294967290 through 4294967295 are
   Reserved.

   Values in other enumerated parameters can be defined through First
   Come, First Served[1].  However, this extension is intended only for
   the verification of service information.  Its use for communicating
   other information not already known by the EAP client (such as for
   service discovery) is discouraged.  In all enumarated parameters,
   values 429496700 through 4294967289 are for Experimental Use and can
   be used without allocation.  Values 4294967290 through 4294967295 are
   Reserved.


8.  References





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8.1.  Normative References

   [1]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

   [2]  Aboba, B. and D. Simon, "PPP EAP TLS Authentication Protocol",
        RFC 2716, October 1999.

   [3]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and
        T. Wright, "Transport Layer Security (TLS) Extensions",
        RFC 3546, June 2003.

   [4]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
        Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748,
        June 2004.

   [5]  Haverinen, H. and J. Salowey, "EAP SIM Authentication",
        draft-haverinen-pppext-eap-sim-16 (work in progress),
        December 2004.

   [6]  Arkko, J. and H. Haverinen, "EAP AKA Authentication",
        draft-arkko-pppext-eap-aka-15 (work in progress), December 2004.

   [7]  Josefsson, S., Palekar, A., Simon, D., and G. Zorn, "Protected
        EAP Protocol (PEAP)", draft-josefsson-pppext-eap-tls-eap-10
        (work in progress), October 2004.

   [8]  International Organization for Standardization, "Codes for the
        representation of names of countries, 3rd edition", ISO Standard
        3166, August 1988.

8.2.  Informative References

   [9]   Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote
         Authentication Dial In User Service (RADIUS)", RFC 2865,
         June 2000.

   [10]  Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6",
         RFC 3162, August 2001.

   [11]  Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial
         In User Service) Support For Extensible Authentication Protocol
         (EAP)", RFC 3579, September 2003.

   [12]  Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese,
         "IEEE 802.1X Remote Authentication Dial In User Service
         (RADIUS) Usage Guidelines", RFC 3580, September 2003.




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   [13]  Stanley, D., Walker, J., and B. Aboba, "Extensible
         Authentication Protocol (EAP) Method Requirements for Wireless
         LANs", RFC 4017, March 2005.

   [14]  Cam-Winget, N., McGrew, D., and J. Salowey, "EAP Flexible
         Authentication via Secure Tunneling (EAP-FAST)",
         draft-cam-winget-eap-fast-01 (work in progress), October 2004.

   [15]  Eronen, P. and H. Tschofenig, "Extension for EAP Authentication
         in IKEv2", draft-eronen-ipsec-ikev2-eap-auth-03 (work in
         progress), April 2005.

   [16]  Yanagiya, M. and Y. Ohba, "AAA-Key Derivation with Lower-Layer
         Parameter Binding", draft-ohba-eap-aaakey-binding-01 (work in
         progress), July 2005.


Appendix A.  Acknowledgments

   The authors would like to thank Bernard Aboba, Yoshihiro Ohba, Mohan
   Parthasarathy, Hannes Tschofenig, Joe Salowey, Glen Zorn, and David
   Mariblanca for interesting discussions in this problem space.





























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Authors' Addresses

   Jari Arkko
   Ericsson
   FI-02420 Jorvas
   Finland

   Email: jari.arkko@ericsson.com


   Pasi Eronen
   Nokia Research Center
   P.O. Box 407
   FI-00045 Nokia Group
   Finland

   Email: pasi.eronen@nokia.com


































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