One document matched: draft-clancy-emu-chbind-03.txt

Differences from draft-clancy-emu-chbind-02.txt




Network Working Group                                          T. Clancy
Internet-Draft                                                       LTS
Intended status: Standards Track                               K. Hoeper
Expires: April 18, 2009                                             NIST
                                                        October 15, 2008


                Channel Binding Support for EAP Methods
                       draft-clancy-emu-chbind-03

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
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   This Internet-Draft will expire on April 18, 2009.

Abstract

   This document defines how to implement channel bindings for
   Extensible Authentication Protocol (EAP) methods to address the lying
   NAS problem.











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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3

   3.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  4

   4.  Channel Bindings . . . . . . . . . . . . . . . . . . . . . . .  5

   5.  Channel Binding Protocol . . . . . . . . . . . . . . . . . . .  7

   6.  System Requirements  . . . . . . . . . . . . . . . . . . . . .  8

   7.  Lower-Layer Bindings . . . . . . . . . . . . . . . . . . . . .  9
     7.1.  General Attributes . . . . . . . . . . . . . . . . . . . . 10
     7.2.  IEEE 802.11  . . . . . . . . . . . . . . . . . . . . . . . 10
     7.3.  IEEE 802.16  . . . . . . . . . . . . . . . . . . . . . . . 10
     7.4.  Wired 802.1X . . . . . . . . . . . . . . . . . . . . . . . 10
     7.5.  Point to Point Protocol (PPP)  . . . . . . . . . . . . . . 10
     7.6.  Internet Key Exchange v2 (IKEv2) . . . . . . . . . . . . . 10
     7.7.  3GPP2  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     7.8.  PANA . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
     8.1.  Trust Model  . . . . . . . . . . . . . . . . . . . . . . . 11
     8.2.  Consequences of Trust Violation  . . . . . . . . . . . . . 11

   9.  Operations and Management Considerations . . . . . . . . . . . 12
     9.1.  System Impact  . . . . . . . . . . . . . . . . . . . . . . 12
     9.2.  Cost-Benefit Analysis  . . . . . . . . . . . . . . . . . . 14

   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14

   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 14
     11.2. Informative References . . . . . . . . . . . . . . . . . . 14

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
   Intellectual Property and Copyright Statements . . . . . . . . . . 16











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1.  Introduction

   The so-called "lying NAS" problem is a well-documented problem with
   the current Extensible Authentication Protocol (EAP) architecture
   [RFC3748] when used in pass-through authenticator mode.  Here, a
   Network Access Server (NAS), or pass-through authenticator, may
   represent one set of information (e.g. network identity,
   capabilities, configuration, etc) to the backend Authentication,
   Authorization, and Accounting (AAA) infrastructure, while
   representing contrary information to EAP clients.  Another
   possibility is that the same false information could be provided to
   both the EAP client and EAP server by the NAS.

   A concrete example of this may be an IEEE 802.11 access point with a
   security association to a particular AAA server.  While there may be
   some identity tied to that security association, there's no reason
   the access point needs to advertise a consistent identity to clients.
   In fact, it may include whatever information in its beacons (e.g.
   different SSID or security properties) it desires.  This could lead
   to situations where, for example, a client joins one network that is
   masquerading as another.

   Another current limitation of EAP is its minimal ability to perform
   authorization.  Currently EAP servers can only make authorization
   decisions about network access based on information they know about
   peers.  If the same EAP server controls access to multiple networks,
   it has little information about the NAS to which the peer is
   connecting, and does not know what information the NAS may be
   claiming about the network to the peer.  A mechanism is needed that
   allows the EAP server to apply more detailed policies to
   authorization.

   This document defines and implements EAP channel bindings to solve
   these two problems, using a process in which the EAP client provides
   information about the characteristics of the service provided by the
   authenticator to the AAA server protected within the EAP method,
   allowing the server to verify the authenticator is providing
   information to the peer consisent with the defined network policy,
   and that the peer is authorized to access the network in the manner
   described by the NAS.  "AAA Payloads" defined in
   [I-D.clancy-emu-aaapay] proposes a mechanism to carry this
   information.


2.  Terminology

   In this document, several words are used to signify the requirements
   of the specification.  These words are often capitalized.  The key



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   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].


3.  Problem Statement

   In a [RFC4017] and [RFC4962]-compliant EAP authentication, the EAP
   client and EAP server mutually authenticate each other, and derive
   keying material.  However, when operating in pass-through mode, the
   EAP server can be far removed from the authenticator.  A malicious or
   compromised authenticator may represent incorrect information about
   the network to the client in an effort to affect its operation in
   some way.  Additionally, while an authenticator may not be
   compromised, other compromised elements in the network could provide
   false information to the authenticator that it could simply be
   relaying to EAP clients.  Our goal is to ensure that the
   authenticator is providing correct information to the EAP client
   during the initial network discovery, selection, and authentication.

   There are two different types of networks to consider: enterprise
   networks and service provider networks.  In enterprise networks, we
   assume a single administrative domain, making it feasible for an EAP
   server to have information about all the authenticators in the
   network.  In service provider networks, global knowledge is
   infeasible due to indirection via roaming.  When a client is outside
   its home administrative domain, the goal is to ensure that the level
   of service received by the client is consistent with the contractual
   agreement between the two service providers.

   The following are a couple example attacks possible by presenting
   false network information to clients.

   o  Enterprise Network: A corporate network may have multiple virtual
      LANs (VLANs) running throughout their campus network, and have
      IEEE 802.11 access points connected to each VLAN.  Assume one VLAN
      connects users to the firewalled corporate network, while the
      other connects users to a public guest network.  The corporate
      network is assumed to be free of adversarial elements, while the
      guest network is assumed to possibly have malicious elements.
      Access Points on both VLANs are serviced by the same EAP server,
      but broadcast different SSIDs to differentiate.  A compromised
      access point connected to the guest network could advertise the
      SSID of the corporate network in an effort to lure clients to
      connect to a network with a false sense of security regarding
      their traffic.





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   o  Service Provider Network: An EAP-enabled mobile phone provider
      operating along a geo-political boundary could boost their cell
      towers' transmission power and advertise the network identity of
      the neighboring country's indigenous provider.  This would cause
      unknowing handsets to associate with an unintended operator, and
      consequently be subject to high roaming fees without realizing
      they had roamed off their home provider's network.

   To address these problems, a mechanism is required to validate
   unauthenticated information advertised by EAP authenticators.


4.  Channel Bindings

   EAP channel bindings seek to authenticate previously unauthenticated
   information provided by the authenticator to the EAP peer, by
   allowing the client and server to compare their perception of network
   properties in a secure channel.

   It should be noted that the definition of EAP channel bindings
   differs somewhat from channel bindings documented in [RFC5056], which
   seek to securely bind together the end points of a multi-layer
   protocol, allowing lower layers to protect data from higher layers.
   Unlike [RFC5056], EAP channel bindings do not ensure the binding
   different layers of a session but rather the information advertised
   to EAP client by an authenticator acting as pass-through device
   during an EAP session.

   There are two main approaches to EAP channel bindings:

   o  After keys have been derived during an EAP authentication, the
      peer and server can, in an integrity-protected channel, exchange
      plaintext information about the network with each other, and
      verify consistency and correctness.

   o  Network information can be uniquely encoded into an opaque blob
      that can be included directly in to the derivation of the EAP
      session keys.

   Both approaches have advantages and disadvantages.  Advantages of
   exchanging plaintext information include:

   o  It allows for policy-based comparisons of network properties,
      rather than requiring precise matches for every field.  This
      allows for a policy-defined consistency, rather than bitwise
      equality.  This allows network operators to define which
      properties are important and even verifiable in their network.




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   o  EAP methods that support extensible, integrity-protected channels
      can easily include support for exchanging this network
      information.  Direct inclusion into the key derivation would
      require revisions to existing EAP methods or a wrapper EAP method.

   o  Given it doesn't affect the key derivation, exact use of the
      results can be subject to policy, to facilitate debugging,
      incremental deployment, and backward compatibility.  Additionally,
      consisent information canonicalization and formatting for the key
      derivation approach would likely cause significant deployment
      problems.

   The following are advantages of directly including channel binding
   information in the key derivation:

   o  EAP methods not supporting extensible, integrity-protected
      channels could still be supported, either by revising their key
      derivation, revising EAP, or wrapping them in a universal method
      that supports channel binding.

   o  It can guarantee proper channel information, since subsequent
      communication would be impossible if differences in channel
      information yielded different session keys on the EAP client and
      server.

   The scope of EAP channel bindings differs somewhat depending on the
   type of deployment in which they are being used.  In enterprise
   networks, they can be used to authenticate very specific properties
   of the authenticator (e.g.  MAC address, supported link types and
   data rates, etc), while in service provider networks they can
   generally only authenticate broader information about a roaming
   partner's network (e.g. network name, roaming information, link
   security requirements, etc).  The reason for the difference has to do
   with the amount of information you expect your home EAP server to
   know about the authenticator and/or network to which the peer is
   connected.  In roaming cases, the home server is likely to only know
   information contained in their roaming agreements.

   With any multi-hop AAA infrastructure, many of the specific NAS
   properties are obscured by the AAA proxy that's decrypting,
   reframing, and retransmitting the underlying AAA messages.
   Consequently, information such as the NAS IP address may not be known
   to the EAP server.  This affects the ability of the EAP server to
   verify specific NAS properties.  However, often verification of the
   MAC or IP address of the NAS is not useful for improving the overall
   security posture of a network.  More often it is useful to make
   policy decisions about service being offered to peers.  For example,
   in an IEEE 802.11 network, the EAP server may wish to ensure that



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   clients connecting to the corporate intranet are using secure link-
   layer encryption, while link-layer security requirements for clients
   connecting to the guest network could be less stringent.  These types
   of policy decisions can be made without knowing or being able to
   verify the IP address of the NAS through which the peer is
   connecting.

   Also, a peer's expectations of a network may also differ.  In a
   mobile phone network, peers generally don't care what the name of the
   network is, as long as they can make their phone call and are charged
   the expected amount for the call.  However, in an enterprise network
   a peer may be more concerned with specifics of where their network
   traffic is being routed.

   Any deployment of channel bindings should take into consideration
   both what information the EAP server is likely to know, and also what
   type of network information the peer would want and need
   authenticated.


5.  Channel Binding Protocol

   This section defines a protocol for verifying channel binding
   information during an EAP authentication.  The protocol uses the
   approach where plaintext data is exchanged, since it allows channel
   bindings to be used more flexibly in varied deployment models.

                                         ---
     --------        -------------      /   \      ----------
    |EAP peer|<---->|Authenticator|<-->( AAA )<-->|EAP Server|
     --------        -------------      \   /      ----------
        .       i1         .             ---           . |   ______
        .<-----------------.                           . |  (______)
        .                  .             i2            . \--|      |
        .                  .-------------------------->.    |Policy|
        .                      i1                      .    |  DB  |
        .--------------------------------------------->.    (______)
        .        isConsistant(i1, i2, Policy)          .
        .<---------------------------------------------.

                   Figure 1: Overview of Channel Binding

   Channel bindings are always provided between two communication
   endpoints, here the EAP client and server, who communicate through an
   authenticator in pass-trough mode.  During network advertisement,
   selection, and authentication, the authenticator presents
   unauthenticated information, labeled i1 for convenience, about the
   network to the peer.  As there is no established trust relationship



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   between the peer and authenticator, there is no way for the peer to
   validate this information.

   Additionally, during the transaction the authenticator presents a
   number of information properties about itself to the AAA
   infrastructure which may or may not be valid.  We label this
   information i2.

   Our goal is to transport i1 from the peer to the server, and allow
   the server to verify the consisitency of i1 from the peer and i2 from
   the authenticator against the information stored in its local policy
   database.

   By doing this, we allow the EAP server the opportunity to make
   informed decisions about authorization.  The EAP server can
   authenticate the authenticator via the AAA security association, and
   using this channel bindings mechanism it can now authorize the
   circumstances under which a peer connects to the authenticator.

   This information, i1, could include an authenticator identifier and
   the identity of the network it represents, in addition to advertised
   network information such as offered services and roaming information.
   To prevent attacks by rogue authenticators, the EAP server must be
   able to verify that i1 either matches its knowledge of the network
   (enterprise model) or is consistent with the contractual agreement
   between itself and the roaming partner network to which the client is
   connected (service provider model).  Additionally, it should verify
   that this information is consistent with i2.

   The protocol defined in this document is a single round trip between
   the EAP peer and server, and formats data elements as Diameter AVPs.
   We provide requirements for a transport protocol.


6.  System Requirements

   The channel binding protocol defined in this document must be
   transported after keying material has been derived between the EAP
   peer and server, and before the peer would suffer adverse affects
   from joining an adversarial network.  To satisfy this requirement, it
   should occur either during the EAP method execution or during the EAP
   lower layer's secure association protocol.

   The transport protocol for carrying channel binding information MUST
   support end-to-end (i.e. between the EAP peer and server) message
   integrity protection to prevent the adversarial NAS or AAA device
   from manipulating the transported data.  The transport protocol
   SHOULD provide confidentiality.  The motivation for this that the



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   channel bindings could contain private information, including peer
   identities, which SHOULD be protected.

   If transporting data directly within an EAP method, it MUST be able
   to carry integrity protected data from the EAP peer to server.  EAP
   methods SHOULD provide a mechanism to carry protected data from
   server to peer.  EAP methods MUST export channel binding data to the
   AAA subsystem on the EAP server.  EAP methods MUST be able to import
   channel binding data from the lower layer on the EAP peer.

   The AAA subsystem MUST be able to process channel binding data
   returned from the EAP method.  It must be possible to pass the
   channel binding data in AAA attributes to proxy AAA if a proxy AAA
   will need to evaluate the data.

   One way to transport the single round-trip exchange is as a series of
   Diameter AVPs formatted and encapsulated in EAP methods per
   [I-D.clancy-emu-aaapay].  For each lower layer, this document defines
   the parameters of interest, and the appropriate Diameter AVPs for
   transporting them.  Additionally, guidance on how to perform
   consistency checks on those values will be provided.

   In order to minimize data formatting inconsistencies, parameters
   useful for channel binding MUST be allocated from the standard RADIUS
   space.  Two AVPs are considered equivalent for the purpose of channel
   binding if they have the same AVP Code, Vendor-Specific Bit, AVP
   Length, Vendor-ID (if Vendor-Specific Bit is set), and data.


7.  Lower-Layer Bindings

   This section discusses AVPs of some EAP-employing lower layer link
   protocols that seem appropriate for providing channel bindings.  The
   discussion is limited to protocols that establish fresh authentic
   keying material because such keying material is necessary to protect
   the integrity of all AVPs that are exchanged as part of the channel
   binding.  For each protocol, a variety of network information that
   can be encapsulated in AVPs is of interest for server and peer to
   ensure channel binding.  The respective appropriate AVPs depend on
   the lower layer protocol as well as on the network type (i.e.
   enterprise network or service provider network) of an application.

   For each EAP lower layer, a variety of AAA properties may be of
   interest to the server.  These values may already be known by the
   server, or may be transported to the server via an existing RADIUS or
   Diameter connection.

   As part of the channel binding protocol, the EAP peer sends



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   encapsulated AVPs to the server.  The server then validates the
   received information by comparing it to information stored in a local
   database.  If the received information is unsatisfactory given some
   validation policy, the server SHOULD respond by halting the EAP
   authentication and returning an EAP-Failure.

   If validation is successful, the server SHOULD send a message
   indicating the success to the client.  In addition, the server MAY
   respond back to the EAP peer with information encapsulated in AVPs
   that can be of use to the peer, and information the peer may not have
   any way of otherwise knowing.

7.1.  General Attributes

   This section lists AVPs useful to all link-layers.

   The server MAY send the Cost-Information AVP from the Diameter
   Credit-Control Application [RFC4006] to the peer indicating how much
   peers will be billed for service.

7.2.  IEEE 802.11

   The client SHOULD transmit to the server the following fields,
   encapsulated within the appropriate Diameter AVPs:

      Called-Station-Id (containing BSSID and SSID)
      Mobility-Domain-Id [I-D.aboba-radext-wlan]
      Mesh-Key-Distributor-Domain-Id [I-D.aboba-radext-wlan]
      Network-Id-Name [I-D.aboba-radext-wlan]

   [TODO: Need a way to transport the RSN-IE.]

7.3.  IEEE 802.16

   TBD

7.4.  Wired 802.1X

   TBD

7.5.  Point to Point Protocol (PPP)

   TBD

7.6.  Internet Key Exchange v2 (IKEv2)

   TBD




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7.7.  3GPP2

   TBD

7.8.  PANA

   TBD


8.  Security Considerations

8.1.  Trust Model

   We consider a trust model in which the peer and server trust each
   other.  This is not unreasonable, considering they already have a
   trust relationship.  In this trust model, client and authentication
   server are honest while the authenticator is maliciously sending
   false information to client and/or server.  The following are the
   trust relationships:

   o  The server trusts that the channel binding information received
      from the client is the information that the client received from
      the authenticator.
   o  The client trusts the channel binding result received from the
      server.
   o  The server trusts the information contained within its local
      database.

   In order to establish the first two trust relationships during an EAP
   execution, an EAP method MUST provide the following:

   o  mutual authentication between client and server
   o  derivation of keying material including a key for integrity
      protection of channel binding messages
   o  sending i1 from client to server over an integrity-protected
      channel
   o  sending the result and optionally i2 from server to client over an
      integrity-protected channel

8.2.  Consequences of Trust Violation

   If any of the trust relationships listed in Section 7.1 are violated,
   channel binding cannot be provided.  In other words, if mutual
   authentication with key establishment as part of the EAP method as
   well as protected database access are not provided, then achieving
   channel binding is not feasible.

   Dishonest peers can only manipulate the first message i1 of the



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   channel binding protocol.  In this scenario, a peer sends i1' to the
   server.  If i1' is invalid, the channel binding validation will fail
   and the server will abort the EAP authentication.  On the other hand
   if i1' passes the validation, either the original i1 was wrong and
   i1' corrected the problem or both i1 and i1' constitute valid
   information.  All cases do not seem to be of any benefit to a peer
   and do no pose a security risk.

   Dishonest servers can send EAP-Failure messages and abort the EAP
   authentication even if the received i1 is valid.  However, servers
   can always abort any EAP session independent of whether channel
   binding is offered or not.  On the other hand, dishonest servers can
   claim a successful validation even for an invalid i1.  This can be
   seen as collaboration of authenticator and server.  Channel binding
   can neither prevent nor detect such attacks.  In general such attacks
   cannot be prevented by cryptographic means and should be addressed
   using policies making servers liable for their provided information
   and services.

   Additional network entities (such as proxies) might be on the
   communication path between peer and server and may attempt to
   manipulate the channel binding protocol.  If these entities do not
   possess the keying material used for integrity protection of the
   channel binding messages, the same threat analysis applies as for the
   dishonest authenticators.  Hence, such entities can neither
   manipulate single channel binding messages nor the outcome.  On the
   other hand, entities with access to the keying material must be
   treated like a server in a threat analysis.  Hence such entities are
   able to manipulate the channel binding protocol without being
   detected.  However, the required knowledge of keying material is
   unlikely since channel binding is executed before the EAP method is
   completed, and thus before keying material is typically transported
   to other entities.


9.  Operations and Management Considerations

   This section analyzes the impact of channel bindings on existing
   deployments of EAP.

9.1.  System Impact

   As with any extension to existing protocols, there will be an impact
   on existing systems.  Typically the goal is to develop an extension
   that minimizes the impact on both development and deployment of the
   new system, subject to the system requirements.  In this section we
   discuss the impact on existing devices that currently utilize EAP,
   assuming the channel binding information is transported within the



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   EAP method execution.

   The EAP peer will need an API between the EAP lower layer and the EAP
   method that exposes the necessary information from the NAS to be
   validated to the EAP peer, which can then feed that information into
   the EAP methods for transport.  For example, an IEEE 802.11 system
   would need to make available the various information elements that
   require validation to the EAP peer which would properly format them
   and pass them to the EAP method.  Additionally, the EAP peer will
   require updated EAP methods that support transporting channel binding
   information.  While most method documents are written modularly to
   allow incorporating arbirary protected information, implementations
   of those methods would need to be revised to support these
   extensions.  Driver updates are also required so methods can access
   the required information.

   No changes to the pass-through authenticator would be required.

   The EAP server would need an API between the database storing NAS
   information and the individual EAP server.  The EAP methods need to
   be able to export received channel binding information to the EAP
   server so it can be validated.

   Additionally, an interface is necessary for populating the EAP server
   database with the appropriate parameters.  In the enterprise case,
   when a NAS is provisioned, information about what it should be
   advertising to peers needs to be entered into the database.  In the
   service provider case, there should be a mechanism for entering
   contractual information about roaming partners.

   To ease operator burdent it is highly recommended that there be a
   mechanism for automatically populating the EAP server policy
   database.  Channel bindings could be enabled to allow peers to
   transmit the NAS information to the EAP server, but the policy could
   be configured to allow all connections.  The obtained information
   could be used to auto-generate policy information for the database,
   assuming there are no adversarial elements in the network during the
   auto-population phase.

   Channel binding validation can also be implemented incrementally.  An
   initial database may be empty, and all channel bindings are
   automatically approved.  Operators can then incrementally add
   parameters to the database regarding specific authenticators or
   groups of authenticators that must be validated.  Additionally, a
   network could also self-form this database by putting the network
   into a "learning" mode, and could then recognize inconsistencies in
   the future.




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9.2.  Cost-Benefit Analysis

   [TBD]


10.  IANA Considerations

   This document contains no IANA considerations.


11.  References

11.1.  Normative References

   [I-D.aboba-radext-wlan]
              Aboba, B., Malinen, J., Congdon, P., and J. Salowey,
              "RADIUS Attributes for IEEE 802 Networks",
              draft-aboba-radext-wlan-08 (work in progress), June 2008.

   [I-D.ietf-dime-rfc3588bis]
              Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
              "Diameter Base Protocol", draft-ietf-dime-rfc3588bis-12
              (work in progress), September 2008.

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

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, "Extensible Authentication Protocol (EAP)",
              RFC 3748, June 2004.

11.2.  Informative References

   [I-D.clancy-emu-aaapay]
              Clancy, T., "EAP Method Support for Transporting AAA
              Payloads", Internet Draft draft-clancy-emu-aaapay-01,
              July 2008.

   [RFC4006]  Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and J.
              Loughney, "Diameter Credit-Control Application", RFC 4006,
              August 2005.

   [RFC4017]  Stanley, D., Walker, J., and B. Aboba, "Extensible
              Authentication Protocol (EAP) Method Requirements for
              Wireless LANs", RFC 4017, March 2005.

   [RFC4962]  Housley, R. and B. Aboba, "Guidance for Authentication,
              Authorization, and Accounting (AAA) Key Management",



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              BCP 132, RFC 4962, July 2007.

   [RFC5056]  Williams, N., "On the Use of Channel Bindings to Secure
              Channels", RFC 5056, November 2007.

   [RFC5247]  Aboba, B., Simon, D., and P. Eronen, "Extensible
              Authentication Protocol (EAP) Key Management Framework",
              RFC 5247, August 2008.

   [HC07]     Hoeper, K. and L. Chen, "Where EAP Security Claims Fail",
              ICST QShine, August 2007.


Authors' Addresses

   T. Charles Clancy
   Laboratory for Telecommunications Sciences
   US Department of Defense
   College Park, MD
   USA

   Email: clancy@ltsnet.net


   Katrin Hoeper
   National Institute of Standards and Technology
   100 Bureau Drive, mail stop 8930
   Gaithersburg, MD  20878
   USA

   Email: khoeper@nist.gov




















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