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Versions: 00 01 02 03 04 05 06 RFC 4851

Network Working Group                                      N. Cam-Winget
Internet-Draft                                                 D. McGrew
Expires: April 22, 2006                                       J. Salowey
                                                                 H. Zhou
                                                           Cisco Systems
                                                        October 19, 2005


      The Flexible Authentication via Secure Tunneling Extensible
               Authentication Protocol Method (EAP-FAST)
                    draft-cam-winget-eap-fast-03.txt

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Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document defines the Extensible Authentication Protocol (EAP)
   based Flexible Authentication via Secure Tunneling (EAP-FAST)
   protocol.  EAP-FAST is an EAP method that enables secure
   communication between a peer and a server by using the Transport
   Layer Security (TLS) to establish a mutually authenticated tunnel.



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   Within the tunnel, Type-Length-Value (TLV) objects are used to convey
   authentication related data between the peer and the EAP server.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1   Specification Requirements . . . . . . . . . . . . . . . .  5
     1.2   Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  5
     2.1   Architectural Model  . . . . . . . . . . . . . . . . . . .  6
     2.2   Protocol Layering Model  . . . . . . . . . . . . . . . . .  7
   3.  EAP-FAST Protocol  . . . . . . . . . . . . . . . . . . . . . .  7
     3.1   Version Negotiation  . . . . . . . . . . . . . . . . . . .  8
     3.2   EAP-FAST Authentication Phase 1: Tunnel Establishment  . .  9
       3.2.1   TLS Session Resume using Server State  . . . . . . . . 10
       3.2.2   TLS Session Resume Using a PAC . . . . . . . . . . . . 10
       3.2.3   Transition between Abbreviated and Full TLS
               Handshake  . . . . . . . . . . . . . . . . . . . . . . 11
     3.3   EAP-FAST Authentication Phase 2: Tunneled
           Authentication . . . . . . . . . . . . . . . . . . . . . . 12
       3.3.1   EAP Sequences  . . . . . . . . . . . . . . . . . . . . 12
       3.3.2   Protected Termination and Acknowledged Result
               Indication . . . . . . . . . . . . . . . . . . . . . . 13
     3.4   Error Handling . . . . . . . . . . . . . . . . . . . . . . 14
       3.4.1   TLS Layer Errors . . . . . . . . . . . . . . . . . . . 14
       3.4.2   Phase 2 Errors . . . . . . . . . . . . . . . . . . . . 14
     3.5   Fragmentation  . . . . . . . . . . . . . . . . . . . . . . 15
   4.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . . 16
     4.1   EAP-FAST Message Format  . . . . . . . . . . . . . . . . . 16
       4.1.1   Authority ID Data  . . . . . . . . . . . . . . . . . . 18
     4.2   EAP-FAST TLV Format and Support  . . . . . . . . . . . . . 19
       4.2.1   General TLV Format . . . . . . . . . . . . . . . . . . 19
       4.2.2   Result TLV . . . . . . . . . . . . . . . . . . . . . . 20
       4.2.3   NAK TLV  . . . . . . . . . . . . . . . . . . . . . . . 21
       4.2.4   Error TLV  . . . . . . . . . . . . . . . . . . . . . . 23
       4.2.5   Vendor-Specific TLV  . . . . . . . . . . . . . . . . . 24
       4.2.6   EAP-Payload TLV  . . . . . . . . . . . . . . . . . . . 25
       4.2.7   Intermediate-Result TLV  . . . . . . . . . . . . . . . 26
       4.2.8   Crypto-Binding TLV . . . . . . . . . . . . . . . . . . 27
       4.2.9   Request-Action TLV . . . . . . . . . . . . . . . . . . 29
     4.3   Table of TLVs  . . . . . . . . . . . . . . . . . . . . . . 30
   5.  Cryptographic Calculations . . . . . . . . . . . . . . . . . . 31
     5.1   EAP-FAST Authentication Phase 1: Key Derivations . . . . . 31
     5.2   Intermediate Compound Key Derivations  . . . . . . . . . . 32
     5.3   Computing the Compound MAC . . . . . . . . . . . . . . . . 32
     5.4   EAP Master Session Key Generation  . . . . . . . . . . . . 33
     5.5   T-PRF  . . . . . . . . . . . . . . . . . . . . . . . . . . 33
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 34



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   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 34
     7.1   Mutual Authentication and Integrity Protection . . . . . . 35
     7.2   Method Negotiation . . . . . . . . . . . . . . . . . . . . 35
     7.3   Separation of the EAP Server and the Authenticator . . . . 36
     7.4   Separation of Phase 1 and Phase 2 Servers  . . . . . . . . 36
     7.5   Mitigation of Known Vulnerabilities and Protocol
           Deficiencies . . . . . . . . . . . . . . . . . . . . . . . 37
       7.5.1   User Identity Protection and Verification  . . . . . . 38
       7.5.2   Dictionary Attack Resistance . . . . . . . . . . . . . 39
       7.5.3   Protection against MitM Attacks  . . . . . . . . . . . 39
       7.5.4   PAC Validation with User Credentials . . . . . . . . . 40
     7.6   Protecting against Forged Clear Text EAP Packets . . . . . 41
     7.7   Implementation . . . . . . . . . . . . . . . . . . . . . . 42
     7.8   Server Certificate Validation  . . . . . . . . . . . . . . 42
     7.9   Security Claims  . . . . . . . . . . . . . . . . . . . . . 42
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 43
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 43
     9.1   Normative References . . . . . . . . . . . . . . . . . . . 43
     9.2   Informative References . . . . . . . . . . . . . . . . . . 44
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 44
   A.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
     A.1   Successful Authentication  . . . . . . . . . . . . . . . . 45
     A.2   Failed Authentication  . . . . . . . . . . . . . . . . . . 46
     A.3   Full TLS Handshake using Certificate-based Cipher Suite  . 48
     A.4   Client authentication during Phase 1 with identity
           privacy  . . . . . . . . . . . . . . . . . . . . . . . . . 49
     A.5   Fragmentation and Reassembly . . . . . . . . . . . . . . . 51
     A.6   Sequence of EAP Methods  . . . . . . . . . . . . . . . . . 53
     A.7   Failed Crypto-binding  . . . . . . . . . . . . . . . . . . 55
     A.8   Stateless Session Resume Using Authorization PAC . . . . . 57
     A.9   Sequence of EAP Method with Vendor-Specific TLV
           Exchange . . . . . . . . . . . . . . . . . . . . . . . . . 58
   B.  Test Vectors . . . . . . . . . . . . . . . . . . . . . . . . . 60
     B.1   Key Derivation . . . . . . . . . . . . . . . . . . . . . . 60
     B.2   Crypto-Binding MIC . . . . . . . . . . . . . . . . . . . . 62
       Intellectual Property and Copyright Statements . . . . . . . . 63















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1.  Introduction

   The need to provide user friendly and easily deployable network
   access solutions has heightened the need for strong mutual
   authentication protocols that internally use weak user credentials.
   This document defines the base protocol which consists of
   establishing a Transport Layer Security (TLS) tunnel as defined in
   [RFC2246] and then exchanging data in the form of type, length, value
   objects (TLV) to perform further authentication.  [I-D.cam-winget-
   eap-fast-provisioning] defines extensions to provision an additional
   credential called a protected access credential (PAC) to optimize the
   EAP-FAST exchange.  In addition to regular TLS ciphersuites and
   handshakes, EAP-FAST supports using a PAC with the TLS extension
   defined in [I-D.salowey-tls-ticket] in order to support fast re-
   establishment of the secure tunnel without having to maintain per-
   session state on the server as described in Section 3.2.2.

   EAP-FAST's design motivations included:

   o  Mutual Authentication: an EAP Server must be able to verify the
      identity and authenticity of the peer, and the peer must be able
      to verify the authenticity of the EAP server.

   o  Immunity to passive dictionary attacks: as many authentication
      protocols require the password to be explicitly provided (either
      in the clear or hashed) by the peer to the EAP server; at minimum,
      the communication of the weak credential (e.g. password) must be
      immune from eavesdropping.

   o  Immunity to man-in-the-middle (MitM) attacks: in establishing a
      mutually authenticated protected tunnel, the protocol must prevent
      adversaries from successfully interjecting information into the
      conversation between the peer and the EAP server.

   o  Flexibility to enable support for most password authentication
      interfaces: as many different password interfaces (e.g.  MSCHAP,
      LDAP, OTP, etc) exist to authenticate a peer, the protocol must
      provide this support seamlessly.

   o  Efficiency: specifically when using wireless media, peers will be
      limited in computational and power resources.  The protocol must
      enable the network access communication to be computationally
      lightweight.

   With these motivational goals defined, further secondary design
   criteria are imposed:





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   o  Flexibility to extend the communications inside the tunnel: with
      the growing complexity in network infrastructures the need to gain
      authentication, authorization and accounting is also evolving.
      For instance, there may be instances in which multiple (already
      existent) authentication protocols are required to achieve mutual
      authentication.  Similarly, different protected conversations may
      be required to achieve the proper authorization once a peer has
      successfully authenticated.

   o  Minimize the authentication server's per user authentication state
      requirements: with large deployments, it is typical to have many
      servers acting as the authentication servers for many peers.  It
      is also highly desirable for a peer to use the same shared secret
      to secure a tunnel much the same way it uses the username and
      password to gain access to the network.  The protocol must
      facilitate the use of a single strong shared secret by the peer
      while enabling the servers to minimize the per user and device
      state it must cache and manage.

1.1  Specification Requirements

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

1.2  Terminology

   Much of the terminology in this document comes from [RFC3748].
   Additional terms are defined below:

   Protected Access Credential (PAC)

      Credentials distributed to a peer for future optimized network
      authentication.  The PAC consists of at most three components: a
      shared secret, an opaque element and optionally other information.
      The shared secret part contains the pre-shared key between the
      peer and the authentication server.  The opaque part is provided
      to the peer and is presented to the authentication server when the
      peer wishes to obtain access to network resources.  Finally, a PAC
      may optionally include other information that may be useful to the
      peer.  The opaque part of the PAC is the same type of data as the
      ticket in [I-D.salowey-tls-ticket].

2.  Protocol Overview

   EAP-FAST is an authentication protocol similar to EAP-TLS [RFC2716]
   that enables mutual authentication and cryptographic context
   establishment by using the TLS handshake protocol.  EAP-FAST allows



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   for the established TLS tunnel to be used for further authentication
   exchanges.  EAP-FAST makes use of TLVs to carry out the inner
   authentication exchanges.  The tunnel is then used to protect weaker
   inner authentication methods, which may be based on passwords, and to
   communicate the results of the authentication.

   EAP-FAST makes use of the TLS enhancements in [I-D.salowey-tls-
   ticket] to enable an optimized TLS tunnel session resume while
   minimizing server state.  In EAP-FAST the key and ticket used to
   establish the tunnel may be provisioned through mechanisms that do
   not involve the TLS handshake.  It is RECOMMENDED that
   implementations support the capability to distribute the ticket and
   secret key within the EAP-FAST tunnel as specified in [I-D.cam-
   winget-eap-fast-provisioning].  The pre-shared secret used in EAP-
   FAST is referred to as the protected access credential key (or PAC-
   Key); the PAC-Key is used to mutually authenticate the peer and the
   server when securing a tunnel.  The ticket is referred to as the
   protected access credential opaque data (or PAC-Opaque).

   The EAP-FAST conversation is used to establish or resume an existing
   session to typically establish network connectivity between a peer
   and the network.  Upon successful execution of EAP-FAST both EAP Peer
   and EAP Server derive strong session keys which can then communicated
   to the network access server (NAS).

2.1  Architectural Model

   The network architectural model for EAP-FAST usage is shown below:


    +----------+      +----------+      +----------+      +----------+
    |          |      |          |      |          |      |  Inner   |
    |   Peer   |<---->|  Authen- |<---->| EAP-FAST |<---->|  Method  |
    |          |      |  ticator |      |  server  |      |  server  |
    |          |      |          |      |          |      |          |
    +----------+      +----------+      +----------+      +----------+


   The entities depicted above are logical entities and may or may not
   correspond to separate network components.  For example, the EAP-
   FAST server and Inner Method server might be a single entity; the
   authenticator and EAP-FAST server might be a single entity; or, the
   functions of the authenticator, EAP-FAST server and Inner Method
   server might be combined into a single physical device.  For example,
   typical 802.11 deployments place the Authenticator in an access point
   (AP) while a Radius Server may provide the EAP-FAST and Inner Method
   server components.  The above diagram illustrates the division of
   labor among entities in a general manner and shows how a distributed



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   system might be constructed; however, actual systems might be
   realized more simply.  The security considerations Section 7.4
   provides an additional discussion of the implications of separating
   EAP-FAST server from the inner method server.

2.2  Protocol Layering Model

   EAP-FAST packets are encapsulated within EAP, and EAP in turn,
   requires a carrier protocol for transport.  EAP-FAST packets
   encapsulate TLS, which is then used to encapsulate user
   authentication information.  Thus, EAP-FAST messaging can be
   described using a layered model, where each layer encapsulates the
   layer beneath it.  The following diagram clarifies the relationship
   between protocols:


    +---------------------------------------------------------------+
    |       Inner EAP Method     |     Other TLV information        |
    |---------------------------------------------------------------|
    |                 TLV Encapsulation (TLVs)                      |
    |---------------------------------------------------------------|
    |                         TLS                                   |
    |---------------------------------------------------------------|
    |                       EAP-FAST                                |
    |---------------------------------------------------------------|
    |                         EAP                                   |
    |---------------------------------------------------------------|
    |        Carrier Protocol (EAPOL, RADIUS, Diameter, etc.)       |
    +---------------------------------------------------------------+


   The TLV layer is a payload with standard Type-Length-Value (TLV)
   Objects defined in Section 4.2.  The TLV objects are used to carry
   arbitrary parameters between an EAP peer and an EAP server.  All
   conversations in the EAP-FAST protected tunnel must be encapsulated
   in a TLV layer.

   Methods for encapsulating EAP within carrier protocols are already
   defined.  For example, IEEE 802.1x EAPOL may be used to transport EAP
   between the peer and the authenticator; RADIUS or Diameter are used
   to transport EAP between the authenticator and the EAP-FAST server.

3.  EAP-FAST Protocol

   EAP-FAST authentication occurs in two phases.  For the first phase
   EAP-FAST employs the TLS handshake to invoke an authenticated key
   agreement exchange to establish a protected tunnel.  Once the tunnel
   is established phase 2 begins in which the peer and server can engage



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   in further conversations to establish the required authentication and
   authorization policies.  The operation of the protocol including
   phase 1 and phase 2 are the topic of this section.  The format of
   EAP-FAST messages is given in Section 4 and the cryptographic
   calculations are given in Section 5.

3.1  Version Negotiation

   EAP-FAST packets contain a three bit version field, following the TLS
   Flags field, which enables EAP-FAST implementations to be backward
   compatible with previous versions of the protocol.  This
   specification documents the EAP-FAST version 1 protocol;
   implementations of this specification MUST use a version field set to
   1.

   Version negotiation proceeds as follows:

      In the first EAP-Request sent with EAP type=EAP-FAST, the EAP
      server must set the version field to the highest supported version
      number.

      If the EAP peer supports this version of the protocol, it MUST
      respond with an EAP-Response of EAP type=EAP-FAST, and the version
      number proposed by the EAP-FAST server.

      If the EAP-FAST peer does not support this version, it responds
      with an EAP-Response of EAP type=EAP-FAST and the highest
      supported version number.

      If the EAP-FAST server does not support the version number
      proposed by the EAP-FAST peer, it terminates the conversation.
      Otherwise the EAP-FAST conversation continues.

   The version negotiation procedure guarantees that the EAP-FAST peer
   and server will agree to the latest version supported by both
   parties.  If version negotiation fails, then use of EAP-FAST will not
   be possible, and another mutually acceptable EAP method will need to
   be negotiated if authentication is to proceed.

   The EAP-FAST version is not protected by TLS; and hence can be
   modified in transit.  In order to detect modification of EAP-FAST
   version and specifically downgrade of an EAP-FAST version negotiated,
   the peers MUST exchange information on the EAP-FAST version number
   received during version negotiation using the Crypto-Binding TLV
   described in Section 3.3.2.  The receiver of the Crypto-Binding TLV
   MUST verify that the version in the Crypto-Binding TLV matches the
   version sent in the EAP-FAST version negotiation.




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3.2  EAP-FAST Authentication Phase 1: Tunnel Establishment

   EAP-FAST is based on TLS handshake [RFC2246] to establish an
   authenticated and protected tunnel.  The TLS version offered by the
   peer and server MUST be TLS v1.0 or later.  This version of the EAP-
   FAST implementation MUST support the following TLS ciphersuites:

      TLS_RSA_WITH_RC4_128_SHA
      TLS_RSA_WITH_AES_128_CBC_SHA [RFC3268]
      TLS_DHE_RSA_WITH_AES_128_CBC_SHA [RFC3268]

   Other ciphersuites MAY be supported.  It is RECOMMENDED that
   anonymous ciphersuites such as TLS_DH_anon_WITH_AES_128_CBC_SHA only
   be used in the context of the provisioning described in [I-D.cam-
   winget-eap-fast-provisioning].  During the EAP-FAST Phase 1
   conversation the EAP-FAST endpoints MAY negotiate TLS compression.

   The EAP server initiates the EAP-FAST conversation with an EAP
   request containing an EAP-FAST/Start packet.  This packet includes a
   set Start (S) bit, the EAP-FAST version as specified in Section 3.1,
   and an authority identity.  The TLS payload in the initial packet is
   empty.  The authority identity (A-ID) is used to provide the peer a
   hint of the server's identity which may be useful in helping the peer
   select the appropriate credential to use.  Assuming that the peer
   supports EAP-FAST the conversation continues with the peer sending an
   EAP-Response packet with EAP type of EAP-FAST with the start (s) bit
   clear and the version as specified in Section 3.1.  This message
   encapsulates one or more TLS records containing the TLS handshake
   messages.  If the EAP-FAST version negotiation is successful then the
   EAP-FAST conversation continues until the EAP server and EAP peer are
   ready to enter phase 2.  When the full TLS handshake is performed,
   then the first payload of EAP-FAST Phase 2 MAY be sent along with
   finished handshake message to reduce the number of round trips.

   After the TLS session is established, another EAP exchange may occur
   within the tunnel to authenticate the EAP peer.  EAP-FAST
   implementations MUST support client authentication during tunnel
   establishment using the specified TLS ciphersuites specified in
   Section 3.2.  EAP-FAST implementations MUST also support the
   immediate re-negotiation of a TLS session to initiate a new handshake
   message exchange under the protection of the current ciphersuite.
   This allows support for protection of the peer's identity.  Note that
   the EAP peer does not need to authenticate as part of the TLS
   exchange, but can alternatively be authenticate through additional
   EAP exchanges carried out in phase 2.

   The EAP-FAST tunnel protects peer identity information from
   disclosure outside the tunnel.  Implementations that wish to provide



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   identity privacy for the peer identity must carefully consider what
   information is disclosed outside the tunnel.

   The following sections describe resuming a TLS session based on
   server side or client side state.

3.2.1  TLS Session Resume using Server State

   EAP-FAST session resumption is achieved in the same manner TLS
   achieves session resume.  To support session resumption, the server
   and peer must minimally cache the Session ID, master secret and
   ciphersuite.  The peer attempts to resume a session by including a
   valid Session ID from a previous handshake in its ClientHello
   message.  If the server finds a match for the Session ID and is
   willing to establish a new connection using the specified session
   state, the server will respond with the same session ID and proceed
   with the EAP-FAST Authentication Phase 1 tunnel establishment based
   on a TLS abbreviated handshake.  After a successful conclusion of the
   EAP-FAST Authentication Phase 1 conversation, the conversation then
   continues on to phase 2.

3.2.2  TLS Session Resume Using a PAC

   EAP-FAST supports the resumption of sessions based on client side
   state using techniques described in [I-D.salowey-tls-ticket].  This
   version of EAP-FAST does not support the provisioning of a ticket
   through the use of the SessionTicket handshake message.  Instead it
   supports the provisioning of a ticket called a Protected Access
   Credential (PAC) as described in [I-D.cam-winget-eap-fast-
   provisioning].  Since the PAC mentioned here is used for establishing
   the TLS Tunnel, it is more specifically referred to as the Tunnel
   PAC.  The Tunnel PAC is a security credential provided by the EAP
   server to a peer and comprised of:

   1.  PAC-Key: this is a 32-octet key used by the peer to establish the
       EAP-FAST Phase 1 tunnel.  This key is used to derive the TLS
       premaster secret as described in Section 5.1.  The PAC-Key is
       randomly generated by the EAP Server to produce a strong entropy
       32-octet key.  The PAC-Key is a secret and MUST be treated
       accordingly.  For example a PAC-Key MUST be delivered in a secure
       channel and stored securely.

   2.  PAC-Opaque: this is a variable length field that is sent to the
       EAP Server during the EAP-FAST Phase 1 tunnel establishment.  The
       PAC-Opaque can only be interpreted by the EAP Server to recover
       the required information for the server to validate the peer's
       identity and authentication.  For example, the PAC-Opaque may
       include the PAC-Key and the PAC's peer identity.  The PAC-Opaque



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       format and contents are specific to the PAC issuing server.  The
       PAC-Opaque is a public credential and MAY be presented in the
       clear, so an attacker MUST NOT be able to gain useful information
       from the PAC-Opaque itself.

   3.  PAC-Info: this is a variable length field used to provide at
       minimum, the authority identity of PAC issuer.  Other useful but
       not mandatory information, such as the PAC-Key lifetime, may also
       be conveyed by the EAP Server to the peer during PAC provisioning
       or refreshment.

   The use of the PAC is based on the SessionTicket extension defined in
   [I-D.salowey-tls-ticket].  The EAP Server initiates the TLS
   conversation as in the previous section.  Upon receiving the A-ID
   from the server the Peer checks to see if it has an existing valid
   PAC-Key and PAC-Opaque for the server.  If it does then it obtains
   the PAC-Opaque and puts it in the SessionTicket extension in the
   ClientHello.  It is RECOMMENDED in EAP-FAST that the peer include an
   empty session ID in a ClientHello containing a PAC-Opaque.  EAP-FAST
   does not currently support the SessionTicket Handshake message so an
   empty SessionTicket extension MUST NOT be included in the
   ClientHello.  If the PAC-Opaque included in SessionTicket extension
   is valid and EAP server permits the abbreviated TLS handshake, it
   will select the ciphersuite allowed to be used from information
   within the PAC and finish with the abbreviated TLS handshake.  If the
   server receives a Session ID and a PAC-Opaque in the SessionTicket
   extension in a ClientHello it should place the same Session ID in the
   ServerHello if it is resuming a session based on the PAC-Opaque.  The
   conversation then proceeds as described in [I-D.salowey-tls-ticket]
   until the handshake completes or a fatal error occurs.  After the
   abbreviated handshake completes the peer and server are ready to
   enter phase 2.  Note that when a PAC is used the TLS master secret is
   calculated from the PAC-Key, client random and server random as
   described in Section 5.1.


3.2.3  Transition between Abbreviated and Full TLS Handshake

   If session resumption based on server side or client side state fails
   the server can gracefully fall back to a full TLS handshake.  If the
   ServerHello received by the peer contains a empty Session ID or a
   Session ID that is different than in the ClientHello the server may
   be falling back to a full handshake.  The peer can distinguish
   Server's intent of negotiating full or abbreviated TLS handshake by
   checking the next TLS handshake messages in the server response to
   ClientHello.  If ChangeCipherSpec follows the ServerHello in response
   to the ClientHello, then the Server has accepted the session
   resumption and intends to negotiate the abbreviated handshake.



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   Otherwise, the Server intends to negotiate the full TLS handshake.  A
   peer can request for a new PAC to be provisioned after the full TLS
   handshake and mutual authentication of the peer and the server.  In
   order to facilitate the fall back to a full handshake the peer SHOULD
   include ciphersuites that allow for a full handshake and possibly PAC
   provisioning so the server can select one of this in case session
   resumption fails.  An example of the transition is shown in
   Appendix A.

3.3  EAP-FAST Authentication Phase 2: Tunneled Authentication

   The second portion of the EAP-FAST Authentication occurs immediately
   after successful completion of phase 1.  Phase 2 occurs even if both
   peer and authenticator are authenticated in the phase 1 TLS
   negotiation.  Phase 2 MUST NOT occur if the Phase 1 TLS handshake
   fails.  Phase 2 consists of a series of requests and responses formed
   of TLV objects defined in Section 4.2.  Phase 2 MUST always end with
   a protected termination exchange described in Section 3.3.2.  The TLV
   exchange may include the execution of zero or more EAP methods within
   the protected tunnel as described in Section 3.3.1.  A server MAY
   proceed directly to the protected termination exchange if it does not
   wish to request further authentication from the peer.  However, the
   peer and server must not assume that either will skip inner EAP
   methods or other TLV exchanges.  The peer may have roamed to a
   network which requires conformance with a different authentication
   policy or the peer may request the server take additional action
   through the use of the Request-Action TLV.

3.3.1  EAP Sequences

   EAP [RFC3748] prohibits use of multiple authentication methods within
   a single EAP conversation in order to limit vulnerabilities to man-
   in-the-middle attacks.  EAP-FAST addresses man-in-the-middle attacks
   through support for cryptographic protection of the inner EAP
   exchange and cryptographic binding of the inner authentication method
   to the protected tunnel.  EAP methods are executed serially in a
   sequence.  This version of EAP-FAST does not support initiating
   multiple EAP methods simultaneously in parallel.  The methods need
   not be distinct.  For example, EAP-TLS could be run twice as an inner
   method, initially with machine credentials followed by user
   credentials.

   EAP method messages are carried within EAP-Payload TLVs defined in
   Section 4.2.6.  Upon method completion of a method a server MUST send
   an Intermediate-Result TLV indicating the result.  The peer MUST
   respond to the Intermediate-Result TLV indicating its result.  If the
   result indicates success the Intermediate-Result TLV MUST be
   accompanied by a Crypto-Binding TLV.  The Crypto-Binding TLV is



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   further discussed in Section 4.2.8 and Section 5.3.  The
   Intermediate-Result TLVs can be included with other TLVs such as EAP-
   Payload TLVs starting a new EAP conversation or with the Result TLV
   used in the protected termination exchange.

   If both peer and server indicate success then the method is
   considered to have completed.  If either indicates failure then the
   method is considered to have failed.  The result of failure of a EAP
   method does not always imply a failure of the overall authentication.
   If one authentication method fails the server may attempt to
   authenticate the peer with a different method.

3.3.2  Protected Termination and Acknowledged Result Indication

   A successful EAP-FAST phase 2 conversation MUST always end in a
   successful Result TLV exchange.  An EAP-FAST server may initiate the
   Result TLV exchange without initiating any EAP conversation in EAP-
   FAST Phase 2.  After the final Result TLV exchange the TLS tunnel is
   terminated and a clear text EAP-Success or EAP-Failure is sent by the
   server.  The format of the Result TLV is described in Section 4.2.2.

   A server initiates a successful protected termination exchange by
   sending a Result TLV indicating success.  The server may send the
   Result TLV along with an Intermediate-Result TLV and a Crypto-Binding
   TLV.  If the peer requires nothing more from the server it will
   respond with a Result TLV indicating success accompanied by an
   Intermediate-Result TLV and Crypto-Binding TLV if necessary.  The
   server then tears down the tunnel and sends a clear text EAP-Success.

   If the peer receives a Result TLV indicating success from the server,
   but its authentication policies are not satisfied (for example it
   requires a particular authentication mechanism be run or it wants to
   request a PAC) it may request further action from the server using
   the Request-Action TLV.  The Request-Action TLV is sent along with
   the Result TLV indicating what EAP Success/Failure result peer would
   expect if the requested action is not granted.  The value of the
   Request-Action TLV indicates what the peer would like to do next.
   The format and values for the Request-Action TLV are defined in
   Section 4.2.9.

   Upon receiving the Request-Action TLV the server may process the
   request or ignore it, based on its policy.  If the server ignores the
   request, it proceeds with termination of the tunnel and send the
   clear text EAP Success or Failure message based on the value of the
   peer's result TLV.  If server honors and processes the request, it
   continues with the requested action.  The conversation completes with
   a Result TLV exchange.  The Result TLV may be included with the TLV
   that completes the requested action.



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   Error handling for phase 2 is discussed in Section 3.4.2.

3.4  Error Handling

   EAP-FAST uses the following error handling rules summarized below:

   1.  Errors in TLS layer are communicated via TLS alert messages in
       all phases of EAP-FAST.
   2.  The Intermediate-Result TLVs indicate success or failure
       indications of the individual EAP methods in EAP-FAST Phase 2.
       Errors within the EAP conversation in Phase 2 are expected to be
       handled by individual EAP methods.
   3.  Violations of the TLV rules are handled using Result TLVs
       together with Error TLVs.
   4.  Tunnel compromised errors (errors caused by Crypto-Binding failed
       or missing) are handled using Result TLVs and Error TLVs.

3.4.1  TLS Layer Errors

   If the EAP-FAST server detects an error at any point in the TLS
   Handshake or the TLS layer, the server SHOULD send an EAP-FAST
   request encapsulating a TLS record containing the appropriate TLS
   alert message rather than immediately terminating the conversation so
   as to allow the peer to inform the user of the cause of the failure
   and possibly allow for a restart of the conversation.  The peer MUST
   send an EAP-FAST response to an alert message.  The EAP-Response
   packet sent by the peer may encapsulate a TLS ClientHello handshake
   message, in which case the EAP-FAST server MAY allow the EAP-FAST
   conversation to be restarted, or it MAY contain an EAP-FAST response
   with a zero length message, in which case the server MUST terminate
   the conversation with an EAP-Failure packet.  It is up to the EAP-
   FAST server whether to allow restarts, and if so, how many times the
   conversation can be restarted.  An EAP-FAST Server implementing
   restart capability SHOULD impose a limit on the number of restarts,
   so as to protect against denial of service attacks.

   If the EAP-FAST peer detects an error at any point in the TLS layer,
   the EAP-FAST peer should send an EAP-FAST response encapsulating a
   TLS record containing the appropriate TLS alert message.  The server
   may restart the conversation by sending an EAP-FAST request packet
   encapsulating the TLS HelloRequest handshake message.  The peer may
   allow the EAP-FAST conversation to be restarted or it may terminate
   the conversation by sending an EAP-FAST response with an zero length
   message.

3.4.2  Phase 2 Errors

   Any time the peer or the server finds a fatal error outside of the



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   TLS layer during phase 2 TLV processing it MUST send a Result TLV of
   failure and an Error TLV with the appropriate error code.  For errors
   involving the processing the sequence of exchanges, such as a
   violation of TLV rules (e.g., multiple EAP-Payload TLVs) the error
   code is Unexpected_TLVs_Exchanged.  For errors involving a tunnel
   compromise the error-code is Tunnel_Compromise_Error.  Upon sending a
   Result TLV with a fatal Error TLV the sender terminates the TLS
   tunnel.

   If a server receives a Result TLV of failure with a fatal Error TLV
   it SHOULD send a clear text EAP-Failure.  If a peer receives a Result
   TLV of failure it MUST respond with a Result TLV indicating failure.
   If the server has sent a Result TLV of failure it ignores the peer
   response and it SHOULD send a clear text EAP-Failure.

3.5  Fragmentation

   A single TLS record may be up to 16384 octets in length, but a TLS
   message may span multiple TLS records, and a TLS certificate message
   may in principle be as long as 16MB.  This is larger than the maximum
   size for a message on most media types, therefore it is desirable to
   support fragmentation.  Note that in order to protect against
   reassembly lockup and denial of service attacks, it may be desirable
   for an implementation to set a maximum size for one such group of TLS
   messages.  Since a typical certificate chain is rarely longer than a
   few thousand octets, and no other field is likely to be anywhere near
   as long, a reasonable choice of maximum acceptable message length
   might be 64 KB.  This is still a fairly large message packet size so
   an EAP-FAST implementation MUST provide its own support for
   fragmentation and reassembly.

   Since EAP is an lock-step protocol, fragmentation support can be
   added in a simple manner.  In EAP, fragments that are lost or damaged
   in transit will be retransmitted, and since sequencing information is
   provided by the Identifier field in EAP, there is no need for a
   fragment offset field as is provided in IPv4.

   EAP-FAST fragmentation support is provided through addition of flag
   bits within the EAP-Response and EAP-Request packets, as well as a
   TLS Message Length field of four octets.  Flags include the Length
   included (L), More fragments (M), and EAP-FAST Start (S) bits.  The L
   flag is set to indicate the presence of the four octet TLS Message
   Length field, and MUST be set for the first fragment of a fragmented
   TLS message or set of messages.  The M flag is set on all but the
   last fragment.  The S flag is set only within the EAP-FAST start
   message sent from the EAP server to the peer.  The TLS Message Length
   field is four octets, and provides the total length of the TLS
   message or set of messages that is being fragmented; this simplifies



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   buffer allocation.

   When an EAP-FAST peer receives an EAP-Request packet with the M bit
   set, it MUST respond with an EAP-Response with EAP-Type of EAP-FAST
   and no data.  This serves as a fragment ACK.  The EAP server must
   wait until it receives the EAP-Response before sending another
   fragment.  In order to prevent errors in processing of fragments, the
   EAP server MUST increment the Identifier field for each fragment
   contained within an EAP-Request, and the peer must include this
   Identifier value in the fragment ACK contained within the EAP-
   Response.  Retransmitted fragments will contain the same Identifier
   value.

   Similarly, when the EAP-FAST server receives an EAP-Response with the
   M bit set, it must respond with an EAP-Request with EAP-Type of EAP-
   FAST and no data.  This serves as a fragment ACK.  The EAP peer MUST
   wait until it receives the EAP-Request before sending another
   fragment.  In order to prevent errors in the processing of fragments,
   the EAP server MUST increment the Identifier value for each fragment
   ACK contained within an EAP-Request, and the peer MUST include this
   Identifier value in the subsequent fragment contained within an EAP-
   Response.

4.  Message Formats

   The following sections describe the message formats used in EAP-FAST.
   The fields are transmitted from left to right in network byte order.

4.1  EAP-FAST Message Format

   A summary of the EAP-FAST Request/Response packet format 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |   Identifier  |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |   Flags | Ver |        Message Length         +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Message Length        |           Data...             +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+









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      Code

         1  Request
         2  Response

      Identifier

         The Identifier field is one octet and aids in matching
         responses with requests.  The Identifier field MUST be changed
         on each Request packet.  The Identifier field in the Response
         packet MUST match the Identifier field from the corresponding
         request.

      Length

         The Length field is two octets and indicates the length of the
         EAP packet including the Code, Identifier, Length, Type, Flags,
         Ver, Message Length and Data fields.  Octets outside the range
         of the Length field should be treated as Data Link Layer
         padding and should be ignored on reception.

      Type

         43 for EAP-FAST

      Flags

          0 1 2 3 4
         +-+-+-+-+-+
         |L M S R R|
         +-+-+-+-+-+

         L  Length included
         M  More fragments
         S  EAP-FAST start
         R  Reserved (must be zero)


            L bit (length included) is set to indicate the presence of
            the four octet Message Length field, and MUST be set for the
            first fragment of a fragmented TLS message or set of
            messages.  The M bit (more fragments) is set on all but the
            last fragment.  The S bit (EAP-FAST Start) is set in an EAP-
            FAST Start message.







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      Ver

         This field contains the version of the protocol.  This document
         describes version 1 (001 in binary) of EAP-FAST.

      Message Length

         The Message Length field is four octets, and is present only if
         the L bit is set.  This field provides the total length of the
         message that may be fragmented over the data fields of multiple
         packets.

      Data

         In the case of a EAP-FAST Start request (i.e. when the S bit is
         set) the Data field consists of the A-ID described in
         Section 4.1.1.  In other cases when the Data field is present
         it consists of an encapsulated TLS packet in TLS record format.
         An EAP-FAST packet with Flags and Version fields but with zero
         length data field to used to indicate EAP-FAST acknowledgement
         for either a fragmented message, a TLS Alert message or a TLS
         Finished message.

4.1.1  Authority ID Data

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Type (0x04)          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ID
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      Type

         0x04 for Authority ID

      Length

         The Length filed is two octets, which contains the length of
         the ID field in octets.

      ID

         Hint of the identity of the server.  It should be unique across
         the deployment.




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4.2  EAP-FAST TLV Format and Support

   The TLVs defined here are standard Type-Length-Value (TLV) objects.
   The TLV objects could be used to carry arbitrary parameters between
   EAP peer and EAP server within the protected TLS tunnel.

   The EAP peer may not necessarily implement all the TLVs supported by
   the EAP server.  To allow for interoperability, TLVs are designed to
   allow an EAP server to discover if a TLV is supported by the EAP
   peer, using the NAK TLV.  The mandatory bit in a TLV indicates
   whether support of the TLV is required.  If the peer or server does
   not support a TLV marked mandatory, then it MUST send a NAK TLV in
   the response, and all the other TLVs in the message MUST be ignored.
   If an EAP peer or server finds an unsupported TLV which is marked as
   optional, it can ignore the unsupported TLV.  It MUST NOT send an NAK
   TLV for a TLV that is not marked mandatory.

   Note that a peer or server may support a TLV with the mandatory bit
   set, but may not understand the contents.  The appropriate response
   to a supported TLV with content that is not understood is defined by
   the individual TLV specification.

   EAP implementations compliant with this specification MUST support
   TLV exchanges, as well as processing of mandatory/optional settings
   on the TLV.  Implementations conforming to this specification MUST
   support the following TLVs:

      Result TLV
      NAK TLV
      Error TLV
      EAP-Payload TLV
      Intermediate-Result TLV
      Crypto-Binding TLV
      Request-Action TLV

4.2.1  General TLV Format

   TLVs are defined as described below.  The fields are transmitted from
   left to right.

    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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Value...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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      M

         0  Optional TLV
         1  Mandatory TLV

      R

         Reserved, set to zero (0)

      TLV Type

         A 14-bit field, denoting the TLV type.  Allocated Types
         include:

         0  Reserved
         1  Reserved
         2  Reserved
         3  Result TLV
         4  NAK TLV
         5  Error TLV
         7  Vendor-Specific TLV
         9  EAP-Payload TLV
         10 Intermediate-Result TLV
         11 PAC TLV [I-D.cam-winget-eap-fast-provisioning]
         12 Crypto-Binding TLV
         18 Server-Trusted-Root TLV [I-D.cam-winget-eap-fast-
            provisioning]
         19 Request-Action TLV
         20 PKCS#7 TLV [I-D.cam-winget-eap-fast-provisioning]

      Length

         The length of the Value field in octets.

      Value

         The value of the TLV.

4.2.2  Result TLV

   The Result TLV provides support for acknowledged success and failure
   messages for protected termination within EAP-FAST.  If the Status
   field does not contain one of the known values, then the peer or EAP
   server MUST treat this as a fatal error of Unexpected_TLVs_Exchanged.
   The behavior of the Result TLV is further discussed in Section 3.3.2
   and Section 3.4.2.  An Result TLV indicating failure MUST NOT be
   accompanied by the following TLVs: NAK, EAP-Payload TLV, or Crypto-



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   Binding TLV.  Result TLV 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|         TLV Type          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Status            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      M

         Mandatory, set to one (1)

      R

         Reserved, set to zero (0)

      TLV Type

         3 for Result TLV

      Length

         2

      Status

         The Status field is two octets.  Values include:

         1  Success
         2  Failure


4.2.3  NAK TLV

   The NAK TLV allows a peer to detect TLVs that are not supported by
   the other peer.  An EAP-FAST packet can contain 0 or more NAK TLVs.
   A NAK TLV should not be accompanied by other TLVs.  A NAK TLV MUST
   NOT be sent in response to a message containing a Result TLV, instead
   a Result TLV of failure should be sent indicating failure and an
   Error TLV of Unexpected_TLVs_Exchanged.  The NAK TLV is defined as
   follows:







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    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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Vendor-Id                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            NAK-Type           |           TLVs....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      M

         Mandatory, set to one (1)

      R


         Reserved, set to zero (0)

      TLV Type

         4 for NAK TLV

      Length

         >=6

      Vendor-Id

         The Vendor-Id field is four octets, and contains the Vendor-Id
         of the TLV that was not supported.  The high-order octet is 0
         and the low-order 3 octets are the SMI Network Management
         Private Enterprise Code of the Vendor in network byte order.
         The Vendor-Id field MUST be zero for TLVs that are not Vendor-
         Specific TLVs.

      NAK-Type

         The NAK-Type field is two octets.  The field contains the Type
         of the TLV that was not supported.  A TLV of this Type MUST
         have been included in the previous packet.

      TLVs

         This field contains a list of TLVs, each of which MUST NOT have
         the mandatory bit set.  These optional TLVs are for future
         extensibility to communicate why the offending TLV was



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         determined to be unsupported.


4.2.4  Error TLV

   The Error TLV allows an EAP peer or server to indicate errors to the
   other party.  An EAP-FAST packet can contain 0 or more Error TLVs.
   The Error-Code field describes the type of error.  Error Codes 1-999
   represent successful outcomes (informative messages), 1000-1999
   represent warnings, and codes 2000-2999 represent fatal errors.  A
   fatal Error TLV MUST be accompanied by a Result TLV indicating
   failure and the conversation must be terminated as described in
   Section 3.4.2.  The Error TLV 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|         TLV Type          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Error-Code                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      M

         Mandatory, set to one (1)

      R

         Reserved, set to zero (0)

      TLV Type

         5 for Error TLV

      Length

         4

      Error-Code

         The Error-Code field is four octets.  Currently defined values
         for Error-Code include:







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            2001 Tunnel_Compromise_Error
            2002 Unexpected_TLVs_Exchanged

4.2.5  Vendor-Specific TLV

   The Vendor-Specific TLV is available to allow vendors to support
   their own extended attributes not suitable for general usage.  A
   Vendor-Specific TLV attribute can contain one or more TLVs, referred
   to as Vendor TLVs.  The TLV-type of a Vendor-TLV is defined by the
   vendor.  All the Vendor TLVs inside a single Vendor-Specific TLV
   belong to the same vendor.  The can be multiple Vendor-Specific TLVs
   from different vendors in the same message.

   Vendor TLVs may be optional or mandatory.  Vendor TLVs sent with
   Result TLVs MUST be marked as optional.

   The Vendor-Specific TLV 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|         TLV Type          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Vendor-Id                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Vendor TLVs....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      M

         0 or 1

      R

         Reserved, set to zero (0)

      TLV Type

         7 for Vendor Specific TLV

      Length

         >=4







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      Vendor-Id

         The Vendor-Id field is four octets, and contains the Vendor-Id
         of the TLV.  The high-order octet is 0 and the low-order 3
         octets are the SMI Network Management Private Enterprise Code
         of the Vendor in network byte order.

      Vendor TLVs

         This field is of indefinite length.  It contains vendor-
         specific TLVs, in a format defined by the vendor.

4.2.6  EAP-Payload TLV

   To allow piggybacking EAP request and response with other TLVs, the
   EAP-Payload TLV is defined, which includes an encapsulated EAP packet
   and a list of optional TLVs.  The optional TLVs are provided for
   future extensibility to provide hints about the current EAP
   authentication.  Only one EAP-Payload TLV is allowed in a message.
   The EAP-Payload TLV 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|         TLV Type          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          EAP packet...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             TLVs...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      M

         Mandatory, set to (1)

      R

         Reserved, set to zero (0)

      TLV Type

         9 for EAP-Payload TLV








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      Length

         >=0

      EAP packet

         This field contains a complete EAP packet, including the EAP
         header (Code, Identifier, Length, Type) fields.  The length of
         this field is determined by the Length field of the
         encapsulated EAP packet.

       TLVs

         This (optional) field contains a list of TLVs associated with
         the EAP packet field.  The TLVs MUST NOT have the mandatory bit
         set.  The total length of this field is equal to the Length
         field of the EAP-Payload TLV, minus the Length field in the EAP
         header of the EAP packet field.

4.2.7  Intermediate-Result TLV

   The Intermediate-Result TLV provides support for acknowledged
   intermediate Success and Failure messages between multiple inner EAP
   methods within EAP.  An Intermediate-Result TLV indicating success
   MUST be accompanied by a Crypto-Binding TLV.  The optional TLVs
   associated with this TLV are provided for future extensibility to
   provide hints about the current result.  The Intermediate-Result TLV
   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|         TLV Type          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Status            |        TLVs...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      M

         Mandatory, set to (1)

      R

         Reserved, set to zero (0)






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      TLV Type

         10 for Intermediate-Result TLV

      Length

         >=2

      Status

         The Status field is two octets.  Values include:

         1  Success
         2  Failure

      TLVs

         This (optional) field is of indeterminate length, and contains
         the TLVs associated with the Intermediate Result TLV.  The TLVs
         in this field MUST NOT have the mandatory bit set.

4.2.8  Crypto-Binding TLV

   The Crypto-Binding TLV is used to prove that both the peer and server
   participated in the tunnel establishment and sequence of
   authentications.  It also provides verification of the EAP-FAST
   version negotiated before TLS tunnel establishment, see Section 3.1.

   The Crypto-Binding TLV MUST be included with Intermediate-Result TLV
   to perform Cryptographic Binding after each successful EAP method in
   a sequence of EAP methods.  The Crypto-Binding TLV can be issued at
   other times as well.

   The Crypto-Binding TLV is valid only if the following checks pass:

   o  The Crypto-Binding TLV version is supported
   o  The MAC verifies correctly
   o  The received version in the Crypto-Binding TLV matches the version
      sent by the receiver during the EAP version negotiation
   o  The subtype is set to the correct value

   If any of the above checks fail then the TLV is invalid.  An invalid
   Crypto-Binding TLV is a fatal error and is handled as described in
   Section 3.4.2

   The Crypto-Binding TLV is defined as follows:





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    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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Reserved   |    Version    |  Received Ver.    | Sub-Type  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                             Nonce                             ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                          Compound MAC                         ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      M

         Mandatory, set to (1)

      R

         Reserved, set to zero (0)

      TLV Type

         12 for Crypto-Binding TLV

      Length

         56

      Reserved

         Reserved, set to zero (0)

      Version

         The Version field is a single octet, which is set to the
         version of Crypto-Binding TLV the EAP method is using.  For
         implementation compliant with this version of EAP-FAST, the
         version number MUST set to 1.








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      Received Version

         The Received Version field is a single octet and MUST be set to
         the EAP version number received during version negotiation.
         Note that this field only provides protection against downgrade
         attacks where a version of EAP requiring support for this TLV
         is required on both sides.

      Sub-Type

         The Sub-Type field is two octets.  Defined values are

         0  Binding Request
         1  Binding Response

      Nonce

         The Nonce field is 32 octets.  It contains a 256 bit nonce that
         is temporally unique, used for compound MAC key derivation at
         each end.  The nonce in a request MUST have its least
         significant bit set to 0 and the nonce in a response MUST have
         the same value as the request nonce except the least
         significant bit MUST be set to 1.

      Compound MAC

         The Compound MAC field is 20 octets.  This can be the Server
         MAC (B1_MAC) or the Client MAC (B2_MAC).  The computation of
         the MAC is described in Section 5.3

4.2.9  Request-Action TLV

   The Request-Action TLV MAY be sent by the peer along with a Result
   TLV in response to a server's successful Result TLV.  It allows the
   peer to request the EAP server to negotiate additional EAP methods or
   process TLVs specified in the response packet.  The server MAY ignore
   this TLV.

   The Request-Action TLV 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|         TLV Type          |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Action            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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      M

         Mandatory set to one (1)

      R

         Reserved, set to zero (0)

      TLV Type

         19 for Request-Action TLV

      Length

         2

      Action

         The Action field is two octets.  Values include:

         1  Process-TLV
         2  Negotiate-EAP


4.3  Table of TLVs

   The following table provides a guide to which TLVs may be found in
   which kinds of messages, and in what quantity.  The messages are as
   follows: Request is an EAP-FAST Request, Response is an EAP-FAST
   Response, Success is a message containing a successful Result TLV,
   and Failure is a message containing a failed Result TLV.

   Request  Response    Success   Failure   TLVs
   0-1      0-1         0-1       0-1       Intermediate-Result
   0-1      0-1         0         0         EAP-Payload
   0-1      0-1         1         1         Result
   0-1      0-1         0-1       0-1       Crypto-Binding
   0+       0+          0+        0+        Error
   0+       0+          0         0         NAK
   0+       0+          0+        0+        Vendor-Specific [NOTE1]
   0        0-1         0-1       0-1       Request-Action

   [Note1] Vendor TLVs (included in Vendor-Specific TLVs) sent with a
   Result TLV MUST be marked as optional.

   The following table defines the meaning of the table entries in the
   sections below:



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   0 This TLV MUST NOT be present in the message.

   0+ Zero or more instances of this TLV MAY be present in the message.

   0-1 Zero or one instance of this TLV MAY be present in the message.

   1 Exactly one instance of this TLV MUST be present in the message.

5.  Cryptographic Calculations

5.1  EAP-FAST Authentication Phase 1: Key Derivations

   The EAP-FAST Authentication tunnel key is calculated similarly to the
   TLS key calculation with an additional 40 octets (referred to, as the
   session_key_seed) generated.  The additional session_key_seed is used
   in the Session Key calculation in the EAP-FAST Tunneled
   Authentication conversation.

   To generate the key material required for EAP-FAST Authentication
   tunnel, the following construction from [RFC2246] is used:

      key_block = PRF(master_secret, "key expansion",
           server_random + client_random)

   where '+' denotes concatenation.

   The PRF function used to generate keying material is defined by
   [RFC2246].

   For example, if the EAP-FAST Authentication employs 128bit RC4 and
   SHA1, the key_block is 112 bytes long and is partitioned as follows:

      client_write_MAC_secret[20]
      server_write_MAC_secret[20]
      client_write_key[16]
      server_write_key[16]
      client_write_IV[0]
      server_write_IV[0]
      session_key_seed[40]

   The session_key_seed is used by the EAP-FAST Authentication Phase 2
   conversation to both cryptographically bind the inner method(s) to
   the tunnel as well as generate the resulting EAP-FAST session keys.
   The other quantities are used as they are defined in [RFC2246].







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   The master_secret is generated as specified in TLS unless a PAC is
   used to establish the TLS tunnel.  When a PAC is used to establish
   the TLS tunnel, the master_secret is calculated from the specified
   client_random, server_random and PAC-Key as follows:

      master_secret = T-PRF(PAC-Key, "PAC to master secret label hash",
           server_random + client_random, 48)

   where T-PRF is described in Section 5.5.

5.2  Intermediate Compound Key Derivations

   The session_key_seed derived as part of EAP-FAST phase 2 is used in
   EAP-FAST phase 2 to generate an Intermediate Compound Key (IMCK) used
   to verify the integrity of the TLS tunnel after each successful inner
   authentication and in the generation of Master Session Key (MSK) and
   Extended Master Session Key (EMSK) defined in [RFC3748].  Note that
   the IMCK must be recalculated after each successful inner EAP method.

   The first step in these calculations is the generation of the base
   compound key, IMCK[n] from the session_key_seed and any session keys
   derived from the successful execution of n inner EAP methods.  The
   inner EAP method(s) may provide Master Session Keys, MSK1..MSKn,
   corresponding to inner methods 1 through n.  The MSK is truncated at
   32 bytes if it is longer than 32 bytes or padded to a length of 32
   bytes with zeros if it is less than 32 bytes.  If the ith inner
   method does not generate an MSK, then MSKi is set to zero (e.g.  MSKi
   = 32 octets of 0x00s).  If an inner method fails then it is not
   included in this calculation.  The derivations of S-IMSK is as
   follow:

      S-IMCK[0] = session_key_seed
      For j = 1 to n-1 do
           IMCK[j] = T-PRF(S-IMCK[j-1], "Inner Methods Compound Keys",
                MSK[j], 60)
           S-IMCK[j] = first 40 octets of IMCK[j]
           CMK[j] = last 20 octets of IMCK[j]

   where T-PRF is described in Section 5.5.


5.3  Computing the Compound MAC

   For authentication methods that generate keying material, further
   protection against man-in-the-middle attacks is provided through
   cryptographically binding keying material established by both EAP-
   FAST Phase 1 and EAP-FAST Phase 2 conversations.  After each
   successful inner EAP authentication, EAP MSKs are cryptographically



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   combined with key material from EAP-FAST phase 1 to generate a
   compound session key, CMK.  The CMK is used to calculate the Compound
   MAC as part of the Crypto-Binding TLV described in Section 4.2.8,
   which helps provide assurance that the same entities are involved all
   communications in EAP-FAST.

   The Compound MAC computation is as follows:

      CMK = CMK[j]
      Compound-MAC = HMAC-SHA1( CMK, Crypto-Binding TLV )

   where j is the number of the last successfully executed inner EAP
   method.

5.4  EAP Master Session Key Generation

   EAP-FAST Authentication assures the master session key (MSK) and
   Extended Master Session Key (EMSK) output from the EAP method are the
   result of all authentication conversations by generating an
   intermediate compound session key (IMCK).  The IMCK is mutually
   derived by the peer and the server as described in Section 5.2 by
   combining the MSKs from inner EAP methods with key material from EAP-
   FAST phase 1.  The resulting MSK and EMSK are generated as part of
   the IMCKn key hierarchy as follows:

      MSK  = T-PRF(S-IMCK[j], "Session Key Generating Function", 64)
      EMSK = T-PRF(S-IMCK[j],
           "Extended Session Key Generating Function", 64)

   where j is the number of the last successfully executed inner EAP
   method.

   The EMSK is typically only known to the EAP-FAST peer and server and
   is not provided to a third party.  The derivation of additional keys
   and transportation of these keys to third party is outside the scope
   of this document.

   If no EAP methods have been negotiated inside the tunnel or no EAP
   methods have been successfully completed inside the tunnel, the MSK
   and EMSK will be generated directly from the session_key_seed meaning
   S-IMCK = session_key_seed.

5.5  T-PRF








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   EAP-FAST employs the following PRF prototype and definition:

      T-PRF = F(key, label, seed, outputlength)

   Where label is intended to be a unique label for each different use
   of the T-PRF. outputlength is a two octet value that is represented
   in big endian order.  Also note that the seed value may be optional
   and may be omitted as in the case of the MSK derivation described in
   Section 5.4.

   To generate the desired outputlength octet length of key material,
   the T-PRF is calculated as follows:

      S = label + 0x00 + seed
      T-PRF output = T1 + T2 + T3 + T4 + ... + Tn
      T1 = HMAC-SHA1 (key, S + outputlength + 0x01)
      T2 = HMAC-SHA1 (key, T1 + S + outputlength + 0x02)
      T3 = HMAC-SHA1 (key, T2 + S + outputlength + 0x03)
      T4 = HMAC-SHA1 (key, T3 + S + outputlength + 0x04)

   Where '+' indicates concatenation and "\0" is a NULL character.  Each
   Ti generates 20-octets of keying material, the last Tn may be
   truncated to accommodate the desired length specified by
   outputlength.

6.  IANA Considerations

   This section provides guidance to the Internet Assigned Numbers
   Authority (IANA) regarding registration of values related to the EAP
   protocol, in accordance with BCP 26, [RFC2434].

   There is a name space in EAP-FAST that requires registration: TLV
   Types.  All these numbers may be assigned by Specification Required
   as defined in BCP 26.

   The various values under Vendor-Specific TLV are assigned by Private
   Use and do not need to be assigned by IANA.

7.  Security Considerations

   EAP-FAST is designed with a focus on wireless media, where the medium
   itself is inherent to eavesdropping.  Whereas in wired media, an
   attacker would have to gain physical access to the wired medium;
   wireless media enables anyone to capture information as it is
   transmitted over the air, enabling passive attacks.  Thus, physical
   security can not be assumed and security vulnerabilities are far
   greater.  The threat model used for the security evaluation of EAP-
   FAST is that defined in the EAP [RFC3748].



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7.1  Mutual Authentication and Integrity Protection

   EAP-FAST as a whole, provides message and integrity protection by
   establishing a secure tunnel for protecting the authentication
   method(s).  The confidentiality and integrity protection is that
   defined by TLS [RFC 2246] and provides the same security strengths
   afforded by TLS employing a strong entropy shared master secret.

   When EAP-FAST is invoked for enabling network access, mutual
   authentication is first achieved by proof of a mutually shared unique
   PAC-Key during the tunnel establishment and optional inner method
   authentication.  Further, the Crypto-Binding TLV is enforced to be
   run after any EAP method that supports (mutual) authentication
   ensuring that it was the same peer and EAP server that communicated
   in all transpired methods (including tunnel establishment).

   The Result TLV is protected and conveys the true Success or Failure
   of EAP-FAST and should be used as the indicator of its success or
   failure respectively.  However, as EAP must terminate with a clear
   text EAP Success or Failure, a peer will also receive a clear text
   EAP success or failure.  The received clear text EAP success or
   failure must match that received in the Result TLV; the peer SHOULD
   silently discard those clear text EAP success or failure messages
   that do not coincide with the status sent in the protected Result
   TLV.

7.2  Method Negotiation

   As is true for any negotiated EAP protocol, NAK packets used to
   suggest an alternate authentication method are sent unprotected and
   as such, are subject to spoofing.  During EAP method negotiation, NAK
   packets may be interjected as active attacks to negotiate down to a
   weaker form of authentication, such as EAP-MD5 (which only provides
   one way authentication and does not derive a key).  Since a
   subsequent protected EAP conversation can take place within the TLS
   session, selection of EAP-FAST as an authentication method does not
   limit the potential secondary authentication methods.  As a result,
   the only legitimate reason for a peer to NAK EAP-FAST as an
   authentication method is that it does not support it.  Where the
   additional security of EAP-FAST is required, the server shall best
   determine how to respond to a NAK as this is beyond the scope of this
   specification.

   Inner method negotiation is protected by the mutually authenticated
   TLS tunnel established in EAP-FAST and immune to attacks.  An
   attacker cannot readily determine the EAP method used, except perhaps
   by traffic analysis.




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7.3  Separation of the EAP Server and the Authenticator

   When EAP-FAST is successfully invoked to gain network access, the EAP
   endpoints will mutually authenticate, and derive a session key for
   subsequent use in link layer security.  Since it is presumed that the
   peer and EAP client reside on the same machine, it is necessary for
   the EAP client module to pass the session key to the link layer
   encryption module.

   As EAP-FAST is defined to achieve mutual authentication between a
   peer and AS, it will not achieve direct authentication to the
   Authenticator (which is true for most if not all currently specified
   EAP methods).

   It is implied that there is an established trust between
   Authenticator and AS before the AS securely distributes the session
   keys to the authenticator.  Using the transitive property and the
   authenticator to AS trust assumption, if the AS trusts the
   authenticator and distributes the session key to the authenticator,
   and the peer has successfully gained authorization by mutually
   deriving fresh session keys, the peer may then presume trust with the
   authenticator who can prove it has those session keys.  Note however,
   that this presumed trust does not authenticate the authenticator to
   the peer, it merely proves that the AS has a trust relationship with
   said authenticator.  Further, it is presumed that a secure mechanism
   is used by the AS to distribute the session key to the authenticator.

   In the case of the AS and the home AAA server logical model, similar
   security properties hold as that between the AS and authenticator.
   Though in general, it is highly recommended that the AAA server be
   reside on the same host as the AS.  In both cases, the presumed trust
   between authenticator and AS as well as AS and AAA server as well as
   the security in the transport (such as IPsec) and key delivery (such
   as NIST approved key wrapping) mechanisms for these links are outside
   the scope of the EAP-FAST specification.  Without these presumed
   trusts and secure transport mechanisms, security vulnerabilities will
   exist.

7.4  Separation of Phase 1 and Phase 2 Servers

   Separation of the EAP-FAST Phase 1 from the Phase 2 conversation is
   not recommended.  Without a trust relationship and proper protection
   (such as IPsec) for RADIUS, by allowing a the Phase 1 conversation to
   be terminated at a different (proxy) AS (AS1) than the Phase 2
   conversation (terminated at AS2), vulnerabilities are introduced
   since clear text transmission between AS1 and AS2 ensue.  Some
   vulnerabilities include:




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   o  Loss of identity protection
   o  Offline dictionary attacks
   o  Lack of policy enforcement

   In order to find the proper EAP-FAST destination, the peer SHOULD
   place a Network Access Identifier (NAI) conforming to [RFC2486] in
   the clear-text Identity Response.

   There may be cases where a natural trust relationship exists between
   the (foreign) authentication server and final EAP server, such as on
   a campus or between two offices within the same company, where there
   is no danger in revealing the identity of the station to the
   authentication server.  In these cases, using a proxy solution
   without end to end protection of EAP-FAST MAY be used.  The EAP-FAST
   encrypting/decrypting gateway SHOULD provide support for IPsec
   protection of RADIUS in order to provide confidentiality for the
   portion of the conversation between the gateway and the EAP server,
   as described in [RFC3162].

7.5  Mitigation of Known Vulnerabilities and Protocol Deficiencies

   EAP-FAST addresses the known deficiencies and weaknesses in the EAP
   method.  By employing a shared secret between the peer and server to
   establish a secured tunnel, EAP-FAST enables:

   o  Per packet confidentiality and integrity protection
   o  User identity protection
   o  Better support for notification messages
   o  Protected EAP inner method negotiation
   o  Sequencing of EAP methods
   o  Strong mutually derived master session keys
   o  Acknowledged success/failure indication
   o  Faster re-authentications through session resumption
   o  Mitigation of dictionary attacks
   o  Mitigation of man-in-the-middle attacks
   o  Mitigation of some denial of service attacks

   It should be noted that EAP-FAST as in many other authentication
   protocols, a denial of service attack can be easily mounted by
   adversaries imposing as either peer or AS and failing to present the
   proper credential.  This is an inherent problem in most
   authentication or key agreement protocols and is so noted for EAP-
   FAST as well.

   EAP-FAST protection addresses a number of weaknesses present in LEAP,
   PEAPv1, EAP-TTLS and the inner EAP methods used in the EAP- FAST
   Authentication Phase 2 conversation.  These weaknesses have been
   described in draft-puthenkulam-eap-binding-03.txt.



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   EAP-FAST was designed with a focus on protected authentication
   methods that typically rely on weak credentials, such as password
   based secrets.  To that extent, the EAP-FAST Authentication mitigates
   several vulnerabilities such as dictionary attacks by protecting the
   weak credential based authentication method.  The protection is based
   on strong cryptographic algorithms in TLS to provide message
   confidentiality and integrity respectively.  The keys derived for the
   protection relies on strong random challenges provided by both peer
   and AS as well as a shared secret with strong entropy (minimally 32
   octets).  It is recommended that peers provide strong random number
   generators that can satisfy the criteria as that described by NIST
   Special Publication 800-22b (e.g.  NIST SP800-22b).  The AS acting as
   the PAC distributor must generate unique and randomly generated 32
   octet keys for each peer.

7.5.1  User Identity Protection and Verification

   As EAP-FAST employs TLS to establish a secure tunnel, the initial
   Identity request/response may be omitted as it must be transmitted in
   the clear and thus subject to snooping and forgery.  It may be
   omitted also in deployments where it is known that all users are
   required to authenticate with EAP-FAST.  Alternately, an anonymous
   identity may be used in the Identity response.

   If the initial Identity request/response has been tampered with, the
   AS may be unable to verify the peer's identity.  For example, the
   peer's user name may not be valid or may not be within a realm
   handled by the AS.  Rather than attempting to proxy the
   authentication to the server within the correct realm, the AS should
   terminate the conversation.

   The EAP-FAST peer can present the server with multiple identities.
   This includes the claim of identity within the initial EAP- Response/
   Identity (MyID) packet, which is typically used to route the EAP
   conversation to the appropriate home back end AS.  There may also be
   subsequent EAP-Response/Identity packets sent by the peer once the
   secure tunnel has been established.

   The PAC-Opaque field conveyed by the peer to the AS contains the
   peer's identity that should be validated with at least one identity
   presented in the EAP-FAST Authentication Phase 2 conversation.  This
   ensures that the PAC-Key is employed by the intended peer.  Though
   EAP-FAST implementations should not attempt to compare the EAP-FAST
   Authentication Phase 1 Identity disclosed in the EAP Identity
   response packet with those Identities claimed in Phase 2; the AS
   should match the identity disclosed in the PAC-Opaque field with at
   least one identity disclosed in EAP-FAST Authentication Phase 2.




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   Note that since TLS client certificates are sent in the clear, if
   identity protection is required, then it is possible for the TLS
   authentication to be re-negotiated after the first server
   authentication.  Alternatively, if identity protection is required,
   then it is possible to perform certificate authentication using an
   EAP method (for example: EAP-TLS) within the TLS session in EAP-FAST
   Phase 2.

   To accomplish TLS restart, the server will typically not request a
   certificate in the server_hello, then after the server_finished
   message is sent, and before EAP-FAST Phase 2, the server MAY send a
   TLS hello_request.  This allows the client to perform client
   authentication by sending a client_hello if it wants to, or send a
   no_renegotiation alert to the server indicating that it wants to
   continue with EAP-FAST Phase 2 instead.  Assuming that the client
   permits renegotiation by sending a client_hello, then the server will
   respond with server_hello, a certificate and certificate_request
   messages.  The client replies with certificate, client_key_exchange
   and certificate_verify messages.  Since this re-negotiation occurs
   within the encrypted TLS channel, it does not reveal client
   certificate details.}

7.5.2  Dictionary Attack Resistance

   EAP-FAST was designed with a focus on protected authentication
   methods that typically rely on weak credentials, such as password
   based secrets.  To that extent, by establishing a mutually
   authenticated protected tunnel, EAP-FAST mitigates dictionary attacks
   by protecting the weak credential based authentication method.  The
   protection is based on strong cryptographic algorithms such as RC4
   and HMAC-SHA1 to provide message confidentiality and integrity
   respectively.  The keys derived for the protection relies on strong
   random challenges provided by both peer and AS as well as a strong
   entropy (minimally 32 octet) shared secret.  The AS acting as the PAC
   distributor MUST generate unique and randomly generated 32 octet keys
   for each peer.

7.5.3  Protection against MitM Attacks

   The recommended solution is to always deploy authentication methods
   with protection of EAP-FAST.  If a deployment chooses to allow an EAP
   method protected by EAP-FAST without protection of EAP-FAST at the
   same time, then this opens up a possibility of a Compound
   Authentication Binding man-in-the-middle attack [MITM].

   A man-in-the-middle can spoof the client to authenticate to it
   instead of the real EAP server; and forward the authentication to the
   real server over a protected tunnel.  Since the attacker has access



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   to the keys derived from the tunnel, it can gain access to the
   network.  EAP-FAST prevents this attack in two ways:

   1.  An adversary must have the corresponding peer's PAC-Key to
       mutually authenticate during EAP-FAST Authentication Phase 1
       establishment of a secure tunnel; and
   2.  By using the keys generated by the inner authentication method in
       the crypto-binding exchange described in above protected
       termination section 6.5.

   Both compound MAC and compound session key approaches are used to
   prevent the aforementioned man-in-the-middle attack.  Both the peer
   and the EAP server MUST derive compound MAC and compound session keys
   using the procedure described in Section 6.7.  As a strong PAC-Key is
   used to establish mutual authentication in EAP-FAST Phase 1, this
   attack is also prevented if the inner authentication method does not
   generate keys.  Thus, most EAP authentication methods are protected
   from these MitM attacks when protected by EAP-FAST.

   To summarize, EAP-FAST Authentication mitigates most MitM attacks in
   the following ways:

   1.  Identity binding with PAC-Key: in presenting the PAC-Opaque field
       to the AS, a peer is presenting an authenticated credential.
       With the user identity serving as another validation point for
       the inner EAP authentication method, a MitM may not interject and
       impersonate itself as the peer unless it has recovered the PAC-
       Key as well as the PAC-Opaque field.  Thus, the PAC-Key binding
       to an Identity prevents an adversary from interjection regardless
       of whether the authentication method generates session keys.
   2.  Cryptographic binding of EAP-FAST Phase 1 and all methods within
       Phase 2: by cryptographically binding key material generated in
       all methods, peer and AS are assured that they were the sole
       participants of all transpired methods.

7.5.4  PAC Validation with User Credentials

   The PAC-Opaque field is consumed by the AS during a network access
   EAP-FAST invocation to both acquire and validate the authenticity of
   the PAC credential.  However, during the EAP-FAST Phase 1
   conversation it validates the peer based on the secret, PAC-Key and
   not on the identity.  Further, since the EAP-FAST Phase 1
   conversation occurs in clear text, it is feasible for an adversary to
   acquire a PAC-Opaque credential.

   While a PAC-Opaque credential can be easily acquired, the shared
   secret, PAC-Key is not discernible from the PAC-Opaque field.  Thus,
   an adversary must resort to a brute force attack to gain the PAC- Key



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   from PAC-Opaque information.

   Another feasible scenario due to the clear text transmission is the
   spoofing of the PAC-Opaque field.  While the PAC-Opaque is
   authenticated to mitigate forgery, a denial of service and potential
   user lockout (based on deployment configurations that may choose to
   lock a peer after a configurable number of failed attempts) is
   feasible.

   The final validation and binding of the PAC credential is the
   identity validation in the EAP-FAST Phase 2 conversation.  A
   compliant implementation of EAP-FAST MUST match the identity
   presented to the AS in the PAC-Opaque field with at minimum one of
   the identities provided in the EAP-FAST Phase 2 authentication
   method.  This validation provides another binding to ensure that the
   intended peer (based on identity) has successfully completed the EAP-
   FAST Phase 1 and proved identity in the Phase 2 conversations.  This
   validation helps mitigate the MitM attack as described in Section
   12.5.3.

7.6  Protecting against Forged Clear Text EAP Packets

   As described earlier, EAP Success and EAP Failure packets are in
   general sent in clear text and may be forged by an attacker without
   fear of detection.  Forged EAP Failure packets can be used to
   convince an EAP peer to disconnect.  Forged EAP Success packets may
   be used by any rogue to convince a peer to let itself access the
   network, even though the authenticator has not authenticated itself
   to the peer.

   By providing message confidentiality and integrity, EAP-FAST provides
   protection against these attacks.  Once the peer and AS initiate the
   EAP-FAST Authentication Phase 2, compliant EAP-FAST implementations
   must silently discard all clear text EAP messages unless both the
   EAP-FAST peer and server have indicated success or failure using a
   protected mechanism.  Protected mechanisms include TLS alert
   mechanism and the protected termination mechanism described in
   Section 6.5.

   The success/failure decisions sent by a protected mechanism indicate
   the final decision of the EAP-FAST authentication conversation.
   After a success/failure result has been indicated by a protected
   mechanism, the EAP-FAST peer can process unprotected EAP success and
   EAP failure message; however the peer must ignore any unprotected EAP
   success or failure messages where the result does not match the
   result of the protected mechanism.

   To abide by RFC 3748, the AS must send a clear text EAP Success or



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   EAP Failure packet to terminate the EAP conversation, so that no
   response is possible.  However, since EAP Success and EAP Failure
   packets are not retransmitted, if the final packet is lost, then
   authentication will fail.  As a result, where packet loss is expected
   to be non-negligible, unacknowledged success/failure indications lack
   robustness.

   While an EAP-FAST protected EAP Success or EAP Failure packet should
   not be a final packet in an EAP-FAST conversation, it may be feasible
   based on the conditions stated above and construed as an optimization
   savings of a full round-trip in low packet loss environments.

7.7  Implementation

   Both server and in particular, client implementations must provide a
   suitably strong PRNG to ensure good entropy challenges.  Suitable
   recommendations for PRNGs can be found in PKCS#5, PKCS#11 and
   criteria for suitable PRNGS are also defined by NIST Special
   Publication 800-22b.

7.8  Server Certificate Validation

   As part of the TLS negotiation, the server presents a certificate to
   the peer.  The peer MUST verify the validity of the EAP server
   certificate, and SHOULD also examine the EAP server name presented in
   the certificate, in order to determine whether the EAP server can be
   trusted.  Please note that in the case where the EAP authentication
   is remoted, the EAP server will not reside on the same machine as the
   authenticator, and therefore the name in the EAP server's certificate
   cannot be expected to match that of the intended destination.  In
   this case, a more appropriate test might be whether the EAP server's
   certificate is signed by a CA controlling the intended destination
   and whether the EAP server exists within a target sub-domain.

7.9  Security Claims

   This section provides needed security claim requirement for EAP
   [RFC3748].

   Auth. mechanism:         Tunneled authentication as well as pre-
                            shared key.
   Ciphersuite negotiation: Yes
   Mutual authentication:   Yes
   Integrity protection:    Yes,Only EAP Type Data field and inner EAP
                            methods contained in this field are
                            protected.





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   Replay protection:       Yes
   Confidentiality:         Yes
   Key derivation:          Yes
   Key strength:            TLS key strength, may be enhanced by binding
                            keys with inner methods
   Dictionary attack prot.: yes
   Fast reconnect:          yes
   Cryptographic binding:   yes
   Session independence:    yes
   Fragmentation:           yes
   Key Hierarchy:           yes
   Channel binding:         No, but TLVs could be defined for this.

8.  Acknowledgements

   The EAP-FAST design and protocol specification is based on the ideas
   and hard efforts of Pad Jakkahalli, Mark Krischer, Doug Smith, Ilan
   Frenkel, Glen Zorn and Jeremy Steiglitz of Cisco Systems, Inc.

   The TLV processing was inspired from work on PEAPv2 with Ashwin
   Palekar, Dan Smith and Simon Josefsson.  Helpful review comments were
   provided by Russ Housley and Jari Arkko.

9.  References

9.1  Normative References

   [I-D.cam-winget-eap-fast-provisioning]
              Cam-Winget, N., "Dynamic Provisioning using EAP-FAST",
              draft-cam-winget-eap-fast-provisioning-01 (work in
              progress), July 2005.

   [I-D.salowey-tls-ticket]
              Salowey, J., "Transport Layer Security Session Resumption
              without Server-Side State", draft-salowey-tls-ticket-04
              (work in progress), September 2005.

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

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC3268]  Chown, P., "Advanced Encryption Standard (AES)



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              Ciphersuites for Transport Layer Security (TLS)",
              RFC 3268, June 2002.

   [RFC3546]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
              and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 3546, June 2003.

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

9.2  Informative References

   [RFC2486]  Aboba, B. and M. Beadles, "The Network Access Identifier",
              RFC 2486, January 1999.

   [RFC2716]  Aboba, B. and D. Simon, "PPP EAP TLS Authentication
              Protocol", RFC 2716, October 1999.

   [RFC3162]  Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6",
              RFC 3162, August 2001.


Authors' Addresses

   Nancy Cam-Winget
   Cisco Systems
   3625 Cisco Way
   San Jose, CA  95134
   US

   Email: ncamwing@cisco.com


   David McGrew
   Cisco Systems
   San Jose, CA  95134
   US

   Email: mcgrew@cisco.com











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   Joseph Salowey
   Cisco Systems
   2901 3rd Ave
   Seattle, WA  98121
   US

   Email: jsalowey@cisco.com


   Hao Zhou
   Cisco Systems
   4125 Highlander Parkway
   Richfield, OH  44286
   US

   Email: hzhou@cisco.com

Appendix A.  Examples

A.1  Successful Authentication

   The following exchanges show a successful EAP-FAST authentication
   with optional PAC refreshment, the conversation will appear as
   follows:

       Authenticating Peer     Authenticator
       -------------------     -------------
                               <- EAP-Request/
                               Identity
       EAP-Response/
       Identity (MyID1) ->

                               <- EAP-Request/
                               EAP-Type=EAP-FAST, V=1
                               (EAP-FAST Start, S bit set, A-ID)

       EAP-Response/
       EAP-Type=EAP-FAST, V=1
       (TLS client_hello with
        PAC-Opaque in SessionTicket extension)->

                               <- EAP-Request/
                               EAP-Type=EAP-FAST, V=1
                               (TLS server_hello,
                               (TLS change_cipher_spec,
                                TLS finished)





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       EAP-Response/
       EAP-Type=EAP-FAST, V=1 ->
       (TLS change_cipher_spec,
        TLS finished)

       TLS channel established
       (messages sent within the TLS channel)

                              <- EAP Payload TLV, EAP-Request,
                               EAP-GTC, Challenge

       EAP Payload TLV, EAP-Response,
       EAP-GTC, Response with both
       user name and password) ->

       optional additional exchanges (new pin mode,
       password change etc.) ...

                               <- Intermediate-Result TLV (Success)
                               Crypto-Binding TLV (Request)


       Intermediate-Result TLV (Success)
       Crypto-Binding TLV(Response) ->

                                <- Result TLV (Success)
                                  (Optional PAC TLV)

       Result TLV (Success)
       (PAC TLV Acknowledgment) ->

       TLS channel torn down
       (messages sent in clear text)

                               <- EAP-Success


A.2  Failed Authentication

   The following exchanges show a failed EAP-FAST authentication due to
   wrong user credentials, the conversation will appear as follows:

       Authenticating Peer     Authenticator
       -------------------     -------------
                               <- EAP-Request/
                               Identity

       EAP-Response/



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       Identity (MyID1) ->


                               <- EAP-Request/
                               EAP-Type=EAP-FAST, V=1
                               (EAP-FAST Start, S bit set, A-ID)

       EAP-Response/
       EAP-Type=EAP-FAST, V=1
       (TLS client_hello with
        PAC-Opaque in SessionTicket extension)->

                               <- EAP-Request/
                               EAP-Type=EAP-FAST, V=1
                               (TLS server_hello,
                               (TLS change_cipher_spec,
                                TLS finished)

       EAP-Response/
       EAP-Type=EAP-FAST, V=1 ->
       (TLS change_cipher_spec,
        TLS finished)

       TLS channel established
       (messages sent within the TLS channel)

                              <- EAP Payload TLV, EAP-Request,
                               EAP-GTC, Challenge

       EAP Payload TLV, EAP-Response,
       EAP-GTC, Response with both
       user name and password) ->

                              <- EAP Payload TLV, EAP-Request,
                               EAP-GTC, error message

       EAP Payload TLV, EAP-Response,
       EAP-GTC, empty data packet to
       acknowledge unrecoverable error) ->

                               <- Result TLV (Failure)

       Result TLV (Failure) ->

       TLS channel torn down
       (messages sent in clear text)

                               <- EAP-Failure



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A.3  Full TLS Handshake using Certificate-based Cipher Suite

   In the case where an abbreviated TLS handshake is tried and failed
   and falls back to certificate based full TLS handshake occurs within
   EAP-FAST Phase 1, the conversation will appear as follows:

      Authenticating Peer    Authenticator
      -------------------    -------------
                             <- EAP-Request/Identity
      EAP-Response/
      Identity (MyID1) ->

      // Identity sent in the clear. May be a hint to help route
         the authentication request to EAP server, instead of the
         full user identity.

                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (EAP-FAST Start, S bit set, A-ID)
      EAP-Response/
      EAP-Type=EAP-FAST, V=1
      (TLS client_hello
      [PAC-Opaque extension])->

      // Peer sends PAC-Opaque of Tunnel PAC along with a list of
         ciphersuites supported. If Server rejects the PAC-
         Opaque, if falls through to the full TLS handshake

                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (TLS server_hello,
                               TLS certificate,
                              [TLS server_key_exchange,]
                              [TLS certificate_request,]
                               TLS server_hello_done)
      EAP-Response/
      EAP-Type=EAP-FAST, V=1
      ([TLS certificate,]
       TLS client_key_exchange,
      [TLS certificate_verify,]
       TLS change_cipher_spec,
       TLS finished) ->
                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (TLS change_cipher_spec,
                               TLS finished,
                               EAP-Payload-TLV[EAP-Request/
                               Identity])



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      // TLS channel established
         (messages sent within the TLS channel)

      // First EAP Payload TLV is piggybacked to the TLS Finished as
         Application Data and protected by the TLS tunnel

      EAP-Payload-TLV
      [EAP-Response/Identity (MyID2)]->

      // identity protected by TLS.

                               <- EAP-Payload-TLV
                               [EAP-Request/EAP-Type=X]

      EAP-Payload-TLV
      [EAP-Response/EAP-Type=X] ->

      // Method X exchanges followed by Protected Termination

                               <- Crypto-Binding TLV (Version=1,
                               EAP-FAST Version=1, Nonce,
                               CompoundMAC),
                               Result TLV (Success)

      Crypto-Binding TLV (Version=1,
      EAP-FAST Version=1, Nonce,
      CompoundMAC),
      Result-TLV (Success) ->

      // TLS channel torn down
      (messages sent in clear text)

                              <- EAP-Success

A.4  Client authentication during Phase 1 with identity privacy

   In the case where a certificate based TLS handshake occurs within
   EAP-FAST Phase 1, and client certificate authentication and identity
   privacy is desired, the conversation will appear as follows:

      Authenticating Peer     Authenticator
      -------------------     -------------
                             <- EAP-Request/Identity
      EAP-Response/
      Identity (MyID1) ->

      // Identity sent in the clear. May be a hint to help route
         the authentication request to EAP server, instead of the



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         full user identity.

                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (EAP-FAST Start, S bit set, A-ID)
      EAP-Response/
      EAP-Type=EAP-FAST, V=1
      (TLS client_hello)->
                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (TLS server_hello,
                               TLS certificate,
                              [TLS server_key_exchange,]
                              [TLS certificate_request,]
                               TLS server_hello_done)
      EAP-Response/
      EAP-Type=EAP-FAST, V=1
      (TLS client_key_exchange,
       TLS change_cipher_spec,
       TLS finished) ->
                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (TLS change_cipher_spec,
                               TLS finished,TLS Hello-Request)

      // TLS channel established
         (messages sent within the TLS channel)

      // TLS Hello-Request is piggybacked to the TLS Finished as
         Handshake Data and protected by the TLS tunnel

      TLS client_hello ->


                              <- TLS server_hello,
                               TLS certificate,
                               [TLS server_key_exchange,]
                               [TLS certificate_request,]
                               TLS server_hello_done
      [TLS certificate,]
       TLS client_key_exchange,
      [TLS certificate_verify,]
       TLS change_cipher_spec,
       TLS finished ->

                              <- TLS change_cipher_spec,
                                 TLS finished,
                                 Result TLV (Success)



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      Result-TLV (Success)) ->

      //TLS channel torn down
      (messages sent in clear text)

                              <- EAP-Success



A.5  Fragmentation and Reassembly

   In the case where EAP-FAST fragmentation is required, the
   conversation will appear as follows:

      Authenticating Peer     Authenticator
      -------------------     -------------
                              <- EAP-Request/
                              Identity
      EAP-Response/
      Identity (MyID) ->
                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (EAP-FAST Start, S bit set, A-ID)

      EAP-Response/
      EAP-Type=EAP-FAST, V=1
      (TLS client_hello)->
                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (TLS server_hello,
                               TLS certificate,
                              [TLS server_key_exchange,]
                              [TLS certificate_request,]
                               TLS server_hello_done)
                              (Fragment 1: L, M bits set)

      EAP-Response/
      EAP-Type=EAP-FAST, V=1 ->

                              <- EAP-Request/
                                 EAP-Type=EAP-FAST, V=1
                              (Fragment 2: M bit set)
      EAP-Response/
      EAP-Type=EAP-FAST, V=1 ->
                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (Fragment 3)
      EAP-Response/



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      EAP-Type=EAP-FAST, V=1
      ([TLS certificate,]
       TLS client_key_exchange,
      [TLS certificate_verify,]
       TLS change_cipher_spec,
       TLS finished)
       (Fragment 1: L, M bits set)->

                               <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
      EAP-Response/
      EAP-Type=EAP-FAST, V=1
      (Fragment 2)->
                             <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (TLS change_cipher_spec,
                               TLS finished,
                              [EAP-Payload-TLV[
                              EAP-Request/Identity]])

      // TLS channel established
         (messages sent within the TLS channel)

      // First EAP Payload TLV is piggybacked to the TLS Finished as
         Application Data and protected by the TLS tunnel

      EAP-Payload-TLV
      [EAP-Response/Identity (MyID2)]->

      // identity protected by TLS.

                               <- EAP-Payload-TLV
                               [EAP-Request/EAP-Type=X]

      EAP-Payload-TLV
      [EAP-Response/EAP-Type=X] ->

      // Method X exchanges followed by Protected Termination

                               <- Crypto-Binding TLV (Version=1,
                               EAP-FAST Version=1, Nonce,
                               CompoundMAC),
                               Result TLV (Success)

      Crypto-Binding TLV (Version=1,
      EAP-FAST Version=1, Nonce,
      CompoundMAC),
      Result-TLV (Success) ->



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      // TLS channel torn down
      (messages sent in clear text)

                              <- EAP-Success



A.6  Sequence of EAP Methods

   Where EAP-FAST is negotiated, with a sequence of EAP method X
   followed by method Y, the conversation will occur as follows:

      Authenticating Peer     Authenticator
      -------------------     -------------
                              <- EAP-Request/
                              Identity
      EAP-Response/
      Identity (MyID1) ->
                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (EAP-FAST Start, S bit set, A-ID)

      EAP-Response/
      EAP-Type=EAP-FAST, V=1
      (TLS client_hello)->
                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (TLS server_hello,
                               TLS certificate,
                              [TLS server_key_exchange,]
                              [TLS certificate_request,]
                               TLS server_hello_done)
      EAP-Response/
      EAP-Type=EAP-FAST, V=1
      ([TLS certificate,]
       TLS client_key_exchange,
      [TLS certificate_verify,]
       TLS change_cipher_spec,
       TLS finished) ->
                             <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (TLS change_cipher_spec,
                               TLS finished,
                              EAP-Payload-TLV[
                              EAP-Request/Identity])

      // TLS channel established
         (messages sent within the TLS channel)



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      // First EAP Payload TLV is piggybacked to the TLS Finished as
         Application Data and protected by the TLS tunnel

      EAP-Payload-TLV
      [EAP-Response/Identity] ->

                              <- EAP-Payload-TLV
                            [EAP-Request/EAP-Type=X]

      EAP-Payload-TLV
      [EAP-Response/EAP-Type=X] ->

             // Optional additional X Method exchanges...

                             <- EAP-Payload-TLV
                            [EAP-Request/EAP-Type=X]

      EAP-Payload-TLV
      [EAP-Response/EAP-Type=X]->

                              <- Intermediate Result TLV (Success),
                               Crypto-Binding TLV (Version=1
                               EAP-FAST Version=1, Nonce,
                               CompoundMAC),
                               EAP Payload TLV [EAP-Type=Y],

      // Next EAP conversation started after successful completion
         of previous method X. The Intermediate-Result and Crypto-
         Binding TLVs are sent in next packet to minimize round-
         trips.  In this example, identity request is not sent
         before negotiating EAP-Type=Y.

      // Compound MAC calculated using Keys generated from
         EAP methods X and the TLS tunnel.

      Intermediate Result TLV (Success),
      Crypto-Binding TLV (Version=1,
      EAP-FAST Version=1, Nonce,
      CompoundMAC),
      EAP-Payload-TLV [EAP-Type=Y] ->

             // Optional additional Y Method exchanges...

                             <- EAP Payload TLV [
                             EAP-Type=Y]

      EAP Payload TLV
      [EAP-Type=Y] ->



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                             <- Intermediate-Result-TLV (Success),
                               Crypto-Binding TLV (Version=1
                               EAP-FAST Version=1, Nonce,
                               CompoundMAC),
                               Result TLV (Success)

      Intermediate-Result-TLV (Success),
      Crypto-Binding TLV (Version=1,
      EAP-FAST Version=1, Nonce,
      CompoundMAC),
      Result-TLV (Success) ->

      // Compound MAC calculated using Keys generated from EAP
         methods X and Y and the TLS tunnel. Compound Keys
         generated using Keys generated from EAP methods X and Y;
         and the TLS tunnel.

      // TLS channel torn down (messages sent in clear text)

                              <- EAP-Success


A.7  Failed Crypto-binding

   The following exchanges show a failed crypto-binding validation.  The
   conversation will appear as follows:

   Authenticating Peer     Authenticator
   -------------------     -------------
                           <- EAP-Request/
                           Identity
   EAP-Response/
   Identity (MyID1) ->
                           <- EAP-Request/
                           EAP-Type=EAP-FAST, V=1
                           (EAP-FAST Start, S bit set, A-ID)

   EAP-Response/
   EAP-Type=EAP-FAST, V=1
   (TLS client_hello without
   PAC-Opaque extension)->
                           <- EAP-Request/
                           EAP-Type=EAP-FAST, V=1
                           (TLS Server Key Exchange
                            TLS Server Hello Done)
   EAP-Response/
   EAP-Type=EAP-FAST, V=1 ->
   (TLS Client Key Exchange



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    TLS change_cipher_spec,
    TLS finished)

                           <- EAP-Request/
                           EAP-Type=EAP-FAST, V=1
                           (TLS change_cipher_spec
                            TLS finished)
                            EAP-Payload-TLV[
                            EAP-Request/Identity])

      // TLS channel established
         (messages sent within the TLS channel)

      // First EAP Payload TLV is piggybacked to the TLS Finished as
         Application Data and protected by the TLS tunnel

   EAP-Payload TLV/
   EAP Identity Response ->

                          <-  EAP Payload TLV, EAP-Request,
                              (EAP-MSCHAPV2, Challenge)

   EAP Payload TLV, EAP-Response,
   (EAP-MSCHAPV2, Response) ->

                          <-  EAP Payload TLV, EAP-Request,
                              (EAP-MSCHAPV2, Success Request)

   EAP Payload TLV, EAP-Response,
   (EAP-MSCHAPV2, Success Response) ->

                            <- Crypto-Binding TLV (Version=1,
                               EAP-FAST Version=1, Nonce,
                               CompoundMAC),
                               Result TLV (Success)

      Result TLV (Failure)
      Error TLV with
      (Error Code = 2001) ->

   // TLS channel torn down
      (messages sent in clear text)

                           <- EAP-Failure







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A.8  Stateless Session Resume Using Authorization PAC

   The following exchanges show a successful server stateless EAP-FAST
   session resume using Tunnel PAC with User Authorization PAC.  The
   conversation will appear as follows:


   Authenticating Peer     Authenticator
   -------------------     -------------
                           <- EAP-Request/
                           Identity
   EAP-Response/
   Identity (MyID1) ->
                           <- EAP-Request/
                           EAP-Type=EAP-FAST, V=1
                           (EAP-FAST Start, S bit set, A-ID)

   EAP-Response/
   EAP-Type=EAP-FAST, V=1
   (TLS client_hello with
   PAC-Opaque extension)->
                           <- EAP-Request/
                           EAP-Type=EAP-FAST, V=1
                           (TLS server_hello,
                           (TLS change_cipher_spec,
                            TLS finished)
   EAP-Response/
   EAP-Type=EAP-FAST, V=1
   (TLS change_cipher_spec,
    TLS finished)
   (PAC-TLV with User Authorization
    PAC) ->

      // TLS channel established
         (messages sent within the TLS channel)

      // User Authorization PAC is piggybacked to the TLS Finished as
         Application Data and protected by the TLS tunnel

                           <- Result TLV (Success)

      // User Authorization PAC is valid and inner methods are bypassed


   Result TLV (Success) ->

   // TLS channel torn down
      (messages sent in clear text)



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                           <- EAP-Success



A.9  Sequence of EAP Method with Vendor-Specific TLV Exchange

   Where EAP-FAST is negotiated, with a sequence of EAP method followed
   by Vendor-Specific TLV exchange, the conversation will occur as
   follows:

      Authenticating Peer     Authenticator
      -------------------     -------------
                              <- EAP-Request/
                              Identity
      EAP-Response/
      Identity (MyID1) ->
                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (EAP-FAST Start, S bit set, A-ID)

      EAP-Response/
      EAP-Type=EAP-FAST, V=1
      (TLS client_hello)->
                              <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (TLS server_hello,
                               TLS certificate,
                       [TLS server_key_exchange,]
                       [TLS certificate_request,]
                           TLS server_hello_done)

      EAP-Response/
      EAP-Type=EAP-FAST, V=1
      ([TLS certificate,]
       TLS client_key_exchange,
      [TLS certificate_verify,]
       TLS change_cipher_spec,
       TLS finished) ->
                             <- EAP-Request/
                              EAP-Type=EAP-FAST, V=1
                              (TLS change_cipher_spec,
                               TLS finished,
                              EAP-Payload-TLV[
                              EAP-Request/Identity])

      // TLS channel established
         (messages sent within the TLS channel)




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      // First EAP Payload TLV is piggybacked to the TLS Finished as
         Application Data and protected by the TLS tunnel

      EAP-Payload-TLV
      [EAP-Response/Identity] ->

                            <- EAP-Payload-TLV
                            [EAP-Request/EAP-Type=X]

      EAP-Payload-TLV
      [EAP-Response/EAP-Type=X] ->

                             <- EAP-Payload-TLV
                            [EAP-Request/EAP-Type=X]

      EAP-Payload-TLV
      [EAP-Response/EAP-Type=X]->

                              <- Intermediate Result TLV (Success),
                               Crypto-Binding TLV (Version=1
                               EAP-FAST Version=1, Nonce,
                               CompoundMAC),
                               Vendor-Specific TLV,

      // Vendor Specific TLV exchange started after successful
         completion of previous method X. The Intermediate-Result
         and Crypto-Binding TLVs are sent with Vendor Specific TLV
         in next packet to minimize round-trips.

      // Compound MAC calculated using Keys generated from
         EAP methods X and the TLS tunnel.

      Intermediate Result TLV (Success),
      Crypto-Binding TLV (Version=1,
      EAP-FAST Version=1, Nonce,
      CompoundMAC),
      Vendor-Specific TLV ->

          // Optional additional Vendor-Specific TLV exchanges...

                             <- Vendor-Specific TLV

      Vendor Specific TLV ->
                             <- Result TLV (Success)

      Result-TLV (Success) ->

      // TLS channel torn down (messages sent in clear text)



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                              <- EAP-Success

Appendix B.  Test Vectors

B.1  Key Derivation

       PAC KEY:

       0B 97 39 0F 37 51 78 09 81 1E FD 9C 6E 65 94 2B
       63 2C E9 53 89 38 08 BA 36 0B 03 7C D1 85 E4 14

       Server_hello Random

       3F FB 11 C4 6C BF A5 7A 54 40 DA E8 22 D3 11 D3
       F7 6D E4 1D D9 33 E5 93 70 97 EB A9 B3 66 F4 2A

       Client_hello Random

       00 00 00 02 6A 66 43 2A 8D 14 43 2C EC 58 2D 2F
       C7 9C 33 64 BA 04 AD 3A 52 54 D6 A5 79 AD 1E 00



       Master_secret = T-PRF(PAC-Key,
                        "PAC to master secret label hash",
                             server_random + Client_random,
                             48)

       4A 1A 51 2C 01 60 BC 02 3C CF BC 83 3F 03 BC 64
       88 C1 31 2F 0B A9 A2 77 16 A8 D8 E8 BD C9 D2 29
       38 4B 7A 85 BE 16 4D 27 33 D5 24 79 87 B1 C5 A2


       Key_block  = PRF(Master_secret,
                   "key expansion",
                         server_random + Client_random)

       59 59 BE 8E 41 3A 77 74 8B B2 E5 D3 60 AC 4D 35
       DF FB C8 1E 9C 24 9C 8B 0E C3 1D 72 C8 84 9D 57
       48 51 2E 45 97 6C 88 70 BE 5F 01 D3 64 E7 4C BB
       11 24 E3 49 E2 3B CD EF 7A B3 05 39 5D 64 8A 44
       11 B6 69 88 34 2E 8E 29 D6 4B 7D 72 17 59 28 05
       AF F9 B7 FF 66 6D A1 96 8F 0B 5E 06 46 7A 44 84
       64 C1 C8 0C 96 44 09 98 FF 92 A8 B4 C6 42 28 71

       Session Key Seed

       D6 4B 7D 72 17 59 28 05 AF F9 B7 FF 66 6D A1 96



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       8F 0B 5E 06 46 7A 44 84 64 C1 C8 0C 96 44 09 98
       FF 92 A8 B4 C6 42 28 71

       IMCK = T-PRF(SKS,
                    "Inner Methods Compound Keys",
                    ISK,
                    60)

              Note: ISK is 32 bytes 0's.

       16 15 3C 3F 21 55 EF D9 7F 34 AE C8 1A 4E 66 80
       4C C3 76 F2 8A A9 6F 96 C2 54 5F 8C AB 65 02 E1
       18 40 7B 56 BE EA A7 C5 76 5D 8F 0B C5 07 C6 B9
       04 D0 69 56 72 8B 6B B8 15 EC 57 7B

       [SIMCK 1]
       16 15 3C 3F 21 55 EF D9 7F 34 AE C8 1A 4E 66 80
       4C C3 76 F2 8A A9 6F 96 C2 54 5F 8C AB 65 02 E1
       18 40 7B 56 BE EA A7 C5


       MSK = T-PRF(S-IMCKn,
                   "Session Key Generating Function",
                    64);



       4D 83 A9 BE 6F 8A 74 ED 6A 02 66 0A 63 4D 2C 33
       C2 DA 60 15 C6 37 04 51 90 38 63 DA 54 3E 14 B9
       27 99 18 1E 07 BF 0F 5A 5E 3C 32 93 80 8C 6C 49
       67 ED 24 FE 45 40 A0 59 5E 37 C2 E9 D0 5D 0A E3




















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B.2  Crypto-Binding MIC

       [Compound MAC Key 1]
       76 5D 8F 0B C5 07 C6 B9 04 D0 69 56 72 8B 6B B8
       15 EC 57 7B

       [Crypto-Binding TLV]
       80 0C 00 38 00 01 01 00 D8 6A 8C 68 3C 32 31 A8 56 63 B6 40 21 FE
       21 14 4E E7 54 20 79 2D 42 62 C9 BF 53 7F 54 FD AC 58 43 24 6E 30
       92 17 6D CF E6 E0 69 EB 33 61 6A CC 05 C5 5B B7

       [Server Nonce]
       D8 6A 8C 68 3C 32 31 A8 56 63 B6 40 21 FE 21 14
       4E E7 54 20 79 2D 42 62 C9 BF 53 7F 54 FD AC 58


       [Compound MAC]
       43 24 6E 30 92 17 6D CF E6 E0 69 EB 33 61 6A CC
       05 C5 5B B7
































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