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Versions: 00 01 02 03 04 05 06 RFC 4851

    Network Working Group                                  N. Cam-Winget
    Internet-Draft                                             D. McGrew
    Category: Informational                                   J. Salowey
    Expires: October 25, 2005                                    H. Zhou
                                                           Cisco Systems
                                                          April 25, 2005


        EAP Flexible Authentication via Secure Tunneling (EAP-FAST)
                    draft-cam-winget-eap-fast-02.txt

 Status of this Memo

    By submitting this Internet-Draft, each author represents that any
    applicable patent or other IPR claims of which he or she is aware
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 Copyright Notice

    Copyright (C) The Internet Society (2005).  All Rights Reserved.


 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 client and a server by using the Transport
    Layer Security (TLS) to establish a mutually authenticated tunnel.
    However, unlike current existing tunneled authentication protocols,
    EAP-FAST also enables the establishment of a mutually authenticated
    tunnel by means of symmetric cryptography.  Furthermore, within the
    secure tunnel, EAP encapsulated methods can ensue to either
    facilitate further provision of credentials, authentication or
    authorization policies by the server to the client.




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 Table of Contents

    1. Introduction..................................................3
       1.1 Specification Requirements................................4
       1.2 Terminology...............................................4
    2. Protocol Overview.............................................6
    3. Architectural Model...........................................7
    4. Protocol Layering Model.......................................7
    5. Protected Access Credential (PAC) for EAP-FAST Authentication.8
    6. EAP-FAST Authentication.......................................9
       6.1 EAP-FAST Authentication Phase 1: Tunnel Establishment.....9
       6.2 EAP-FAST Authentication Phase 1: Key Derivations.........11
       6.3 EAP-FAST Authentication Phase 2: Tunneled Authentication.12
       6.4 Protected EAP Conversation...............................12
       6.5 Protected Termination and Acknowledged Result Indication.13
       6.6 EAP-FAST Authentication Phase 2: Key Derivations.........14
       6.7 Cryptographic Binding: Computing the Compound MAC........15
       6.8 EAP-FAST Authentication: Session Key Generation..........16
       6.9 PAC Distribution and Refreshing..........................16
    7. Version Negotiation..........................................17
    8. Error Handling...............................................18
       8.1 Error Alerts.............................................19
    9. Session Resume...............................................19
    10. Fragmentation...............................................20
    11. EAP-FAST Detailed Description...............................22
       11.1 EAP-FAST Packet Format..................................22
       11.2 EAP-FAST TLV Format.....................................23
       11.3 TLV format..............................................24
       11.4 Result TLV..............................................25
       11.5 NAK TLV.................................................26
       11.6 Crypto-Binding TLV......................................27
       11.7 EAP-Payload TLV.........................................29
       11.8 Intermediate-Result TLV.................................30
       11.9 PAC TLV.................................................31
          11.9.1 Formats for PAC TLV attributes.....................32
          11.9.2 PAC-Key............................................32
          11.9.3 PAC-Opaque.........................................33
          11.9.4 PAC-Info...........................................34
          11.9.5 PAC-Acknowledgement TLV............................35
       11.10 TLS SessionTicket Extension............................36
    12. Security Considerations.....................................36
       12.1 Mutual Authentication and Integrity Protection..........37
       12.2 Method Negotiation......................................37
       12.3 Separation of the EAP Server and the Authenticator......38
       12.4 Separation of Phase 1 and Phase 2 Servers...............38
       12.5 Mitigation of Known Vulnerabilities and Protocol
            Deficiencies............................................39
          12.5.1 User Identity Protection and Verification..........40
          12.5.2 Dictionary Attack Resistance.......................41
          12.5.3 Protection against MitM Attacks....................41
          12.5.4 PAC Validation with User Credentials...............42
       12.6 PAC Storage Considerations..............................43
       12.7 Protecting against Forged Clear Text EAP Packets........44

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       12.8 Implementation..........................................44
       12.9 Security Claims.........................................45
    13. IANA Considerations.........................................45
    14. References..................................................45
       14.1 Normative...............................................45
       14.2 Informative.............................................46
    15. Acknowledgments.............................................47
    16. Authors' Addresses..........................................47
    17. Appendix A: Examples........................................48
       17.1 Successful Authentication...............................48
       17.2 Failed Authentication...................................49
    18. Appendix B: EAP-FAST PRF (T-PRF)............................51
    19. Appendix C: Test Vectors....................................51
       19.1 Key derivation..........................................51
       19.2 Crypto-Binding MIC:.....................................53
    20. Intellectual Property Statement.............................53
    21. Disclaimer of Validity......................................54
    22. Copyright Statement.........................................54
    23. Expiration Date.............................................54


 1. Introduction

    The need to provide user friendly and easily deployable network
    access solutions has heightened the need to enable strong mutual
    authentication protocols that internally use weak user credentials.
    While several such authentication protocols [PEAP] [EAP-TTLS] exist
    today, they are encumbered by the use of asymmetric cryptographic
    operations that often render such protocols prohibitive on very low
    end peer devices.

    Like [TLS-PSK], EAP-FAST employs symmetric cryptography to allay
    the PKI requirements of [PEAP] or [EAP-TTLS].  Additionally, EAP-
    FAST employs the TLS SessionTicket extension [TICKET] as a further
    optimization to minimize the state maintained by the server. EAP-
    FAST's design motivations included:

      * Mutual Authentication: an Authentication Server (AS) must verify
      the identity and authenticity of the peer, and the peer must
      verify the authenticity of an AS.

      * 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 AS; at minimum,  the
      communication of the weak credential (e.g. password) must be
      immune from eavesdropping.

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



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      * 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.

      * 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:

      * 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. This capability is
      similar to [PEAP].

      * Minimize the authentication server's per user authentication
      state requirements: with large deployments, it is typical to have
      many servers acting as the AS 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

    Some of the following terms are taken from RFC3748 [EAP]:

    EAP Server

       The entity that terminates the EAP authentication with the peer.
       In the case where there is no back end authentication server,
       this term refers to the authenticator. Where the authenticator
       operates in pass-through, it refers to the back end
       authentication server.




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    Authenticator

       The end of the link initiating EAP authentication. The term
       Authenticator is used in [IEEE-802.1x], and authenticator has
       the same meaning in this document.

    Peer

       The end of the link that responds to the authenticator. In
       [IEEE-802.1x], this end is known as the Supplicant.

    Supplicant

       The end of the link that responds to the authenticator in [IEEE-
       802.1x].  In this document, this end of the link is called the
       peer.

    Back end Authentication Server

       A back end authentication server is an entity that provides an
       authentication service to an authenticator.  When used, this
       server typically executes EAP methods for the authenticator.
       This terminology is also used in [IEEE-802.1x].

    Master Session Key (MSK)

       Keying material exported by an EAP method.

    Man in the Middle (MitM)

       An adversary that can successfully inject itself between a peer
       and EAP server. The MitM succeeds by impersonating itself as a
       valid peer, authenticator or authentication server.

    Message Authentication Code (MAC)

       A MAC is a function that takes a variable length input and a key
       to produce a fixed-length output to carry authentication and
       integrity protection of data.

    Message Integrity Check (MIC)

       A keyed hash function used for authentication and integrity
       protection of data.  This is usually called a Message
       Authentication Code (MAC), but IEEE 802 specifications (and this
       document) use the acronym MIC to avoid confusion with Medium
       Access Control.

    Protected Access Credential (PAC)

       Credentials distributed to users for future optimized network
       authentication, which always consists of a secret part and an


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       opaque part. The secret part is secret key material that can be
       used in future transactions.  The opaque part is presented when
       the client wishes to obtain access to network resources.  It
       aids the server in validating that the client possesses the
       secret part.

    Silently Discard

       This means the implementation discards the packet without
       further processing.  The implementation SHOULD provide the
       capability of logging the event, including the contents of the
       silently discarded packet, and SHOULD record the event in a
       statistics counter.

    Successful Authentication

       In the context of this document, "successful authentication" is
       an exchange of EAP messages, as a result of which the
       authenticator decides to allow access by the peer, and the peer
       decides to use this access. The authenticator's decision
       typically involves both authentication and authorization
       aspects; the peer may successfully authenticate to the
       authenticator but access may be denied by the authenticator due
       to policy reasons.

 2. Protocol Overview

    EAP-FAST is an extensible framework that enables mutual
    authentication by using a pre-shared secret to establish a
    protected tunnel.  Like [PEAP] [EAP-TTLS], the protocol is based on
    TLS; however, enhancements are made to TLS to enable EAP-FAST to
    initiate the tunnel establishment exchange using symmetric
    cryptography while minimizing server state. The tunnel is then used
    to protect weaker authentication methods, typically based on
    passwords.

    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 client and server when securing a
    tunnel.   Furthermore, the PAC-Key is refreshed and managed as part
    of the EAP-FAST protocol.  EAP-FAST allays server state by the use
    of a PAC-Opaque, which contains the PAC-Key encrypted by a strong
    key only known to the server and sent to the server with the TLS
    ClientHello SessionTicket extension [TICKET]. With the use of
    PAC-Opaque and SessionTicket extension, EAP-FAST alleviates the
    server's need to store per user PAC and state.

    The EAP-FAST conversation is used to establish or resume an
    existing session to typically establish network connectivity
    between a peer and the network.  A peer and AS achieve mutual
    authentication by invoking a symmetric authenticated key agreement
    to protect the communications that further authenticates and
    authorizes the client to use the network.  A successful result is a

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    mutual derivation of strong session keys which can then be
    provisioned (by the AS) to the network access server (NAS,
    typically these are the access points in 802.11 or 802.1x
    authenticators).

 3. 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,
    indeed, 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 system might be
    constructed; however, actual systems might be realized more simply.
    The security considerations (Section 12) provides an additional
    discussion of the implications of separating EAP-FAST from the
    inner method.

 4. 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:
    +---------------------------------------------------------------+
    |           |                                                   |
    | Lower     | TLV Encapsulation (TLVs)                          |
    | to        |---------------------------------------------------|
    | Upper     | TLS                                               |
    | Layer     |---------------------------------------------------|
    |           | EAP-FAST                                          |
    |           |---------------------------------------------------|
    |           | EAP                                               |
    |           |---------------------------------------------------|
    |           | Carrier Protocol (EAPOL, RADIUS, Diameter, etc.)  |
    +---------------------------------------------------------------+

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    The TLV layer is a payload with standard Type-Length-Value (TLV)
    objects. 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.
    When the user authentication protocol is itself EAP, the layering
    is as follows:


    +---------------------------------------------------------------+
    |           | Inner EAP Method                                  |
    |           |---------------------------------------------------|
    | Lower     | TLV Encapsulation (TLVs)                          |
    | to        |---------------------------------------------------|
    | Upper     | TLS                                               |
    | Layer     |---------------------------------------------------|
    |           | EAP-FAST                                          |
    |           |---------------------------------------------------|
    |           | EAP                                               |
    |           |---------------------------------------------------|
    |           | Carrier Protocol (EAPOL, RADIUS, Diameter, etc.)  |
    +---------------------------------------------------------------+

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


 5. Protected Access Credential (PAC) for EAP-FAST Authentication

    A pre-shared secret mutually and uniquely shared between the peer
    and AS is used to secure a tunnel during EAP-FAST Authentication.
    EAP-FAST uses a Protected Access Credential (PAC) to facilitate the
    use of a single shared secret by the peer and minimize the per user
    state management on the AS.  The PAC is a security credential
    provided by the AS 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 maps as the TLS pre-
         master-secret. The PAC-Key is randomly generated by the AS to
         produce a strong entropy 32-octet key.

       2. PAC-Opaque: this is a variable length field that is sent to
         the AS during the EAP-FAST Phase 1 tunnel establishment.  The
         PAC-Opaque can only be interpreted by the AS 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 format and contents are specific to the issuing PAC
         server.

       3. PAC-Info: this is a variable length field used to provide at
         minimum, the authority identity of PAC issuer.  Other useful

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         but not mandatory information, such as the PAC-Key lifetime,
         may also be conveyed by the AS to the peer during PAC
         provisioning or refreshment.

    As the focus of this draft is to define the EAP-FAST protected
    tunneling and authentication mechanism, it does not address
    provisioning.  That is, provisioning of the PAC may be achieved
    using the same mechanisms as the provisioning of any other
    credential such as certificates or username/password credential
    types.


 6. EAP-FAST Authentication

    To establish a new session, EAP-FAST employs the PAC to invoke an
    authenticated key agreement exchange to establish a protected
    tunnel.  Once the tunnel is established, the peer and AS can ensue
    in further conversations to establish the required authentication
    and authorization policies.  Part of the authorization policy is
    the generation of the Master Session Keys (MSKs).  Portions of the
    MSKs may be distributed to the NAS using the RADIUS MS-MPPE
    [RFC2548] attribute.  Finally, the server may also update the PAC
    as part of the EAP-FAST protocol conclusion.  This section
    describes the two phases of EAP-FAST Authentication: Phase 1, the
    tunnel establishment and Phase 2, the tunneled authentication.

 6.1 EAP-FAST Authentication Phase 1: Tunnel Establishment

    This conversation is similar to establishing a new EAP-TLS session
    except it uses new EAP type (EAP-FAST) and new TLS SessionTicket
    extension in TLS ClientHello. The SessionTicket extension is
    modeled after [RFC3546] and described in [TICKET].

    The initial conversation begins with the authenticator and the peer
    negotiating EAP.  The authenticator will typically send an EAP-
    Request/Identity packet to the peer, and the peer will respond with
    an EAP-Response/Identity packet to the authenticator, containing
    the username.  If the client desires to protect its identity, it
    may use an anonymous username.

    Once the initial Identity Request/Response exchange is completed,
    while the EAP conversation typically occurs between the
    authenticator and the peer, the authenticator may act as a pass-
    through device, with the EAP packets received from the peer being
    encapsulated for transmission to a back end authentication server.
    In the discussion that follows, the term "EAP server" or "server"
    is used to denote the ultimate endpoint conversing with the peer.

    Once having received the peer's Identity, and determined that EAP-
    FAST Authentication is to occur, the EAP server must respond with a
    EAP-FAST/Start packet, which is an EAP-Request packet with EAP-
    Type=EAP-FAST and the Start (S) bit set. The EAP-FAST/Start packet
    shall also include an authority identity (A-ID) TLV to better

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    inform the peer the server's identity.  Assuming that the peer
    supports EAP-FAST, the EAP-FAST conversation will then begin, with
    the peer sending an EAP-Response packet with EAP-Type=EAP-FAST.

    The data field of the EAP-Response packet contains an EAP-FAST
    encapsulated TLS ClientHello handshake message.

    The ClientHello message contains the peer's challenge (also called
    the client_random) and PAC-Opaque in TLS SessionTicket extension.
    As there may be different EAP-FAST servers a peer may encounter, a
    peer may be provisioned with unique PACs uniquely identified by the
    A-ID corresponding to the EAP-FAST server.  A peer may choose to
    cache the different PACs and determine based on the A-ID the
    corresponding PAC to employ.  While EAP-FAST is capable of
    supporting any ciphersuite, in this version, the ClientHello uses
    the TLS_RSA_WITH_RC4_128_SHA ciphersuite.  As EAP-FAST uses the PAC
    to establish the keys, the RSA key exchange is not executed, but
    the specification of RC4 and SHA signals the EAP server that the
    tunnel must be protected using 128bit RC4 for confidentiality and
    SHA1 for authenticity.

    The EAP server will then respond with an EAP-Request packet with
    EAP-Type=EAP-FAST. The data field of this packet will encapsulate
    three TLS records, ServerHello, ChangeCipherSpec and Finished
    messages.  The ServerHello will contain a server_random and
    ChangeCipherSpec. The TLS Finished message, sent immediately after
    the ChangeCipherSpec message, contains the first protected message
    with the negotiated algorithm, keys, and secrets.

    The server generates the master_secret prior to composing the EAP-
    FAST TLS ServerHello message to properly generate the TLS Finished
    message contents.  The server must compute the Tunnel Keys as
    described in Section 6.2 at this time to properly respond and
    generate its TLS Finished message.

    The peer in turn, must consume the ServerHello to extract the
    server_random before it can generate the master_secret and Tunnel
    Keys, as described in Section 6.2.

    After verifying the server Finished message, the peer responds back
    with two TLS records, a ChangeCipherSpec and the peer's TLS
    Finished message.  At this state, the client is ready to receive
    and transmit protected messages with the server.

    Upon verifying the peer's Finished message, the EAP server
    establishes the tunnel and is ready for the receiving and
    transmitting protected messages with the peer.  The messages are
    protected using the Tunnel Keys described in Section 6.2.






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 6.2 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.

    An EAP-FAST specific PRF function, T-PRF described in Appendix B
    (Section 18) is used to generate a fresh master_secret from the
    specified client_random, server_random and PAC-Key.

    The PRF function used to generate keying material is defined by
    [RFC 2246].

    Since a PAC may be used as a credential for other applications
    beyond EAP-FAST, the PAC-Key is further hashed using T-PRF to
    generate a fresh TLS master_secret.   Additionally, the hash of
    PAC-Key is required to stretch it to the required 48 octet
    master_secret:

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

    To generate the key material required for EAP-FAST Authentication,
    the following TLS construction is used:

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

    where '+' denotes concatenation.

    Since this version of EAP-FAST Authentication employs 128bit RC4
    and SHA1, the key_block is partitioned as follows:

           client_write_MAC_secret[hash_size=20]
           server_write_MAC_secret[hash_size=20]
           client_write_key[Key_material_length=16]
           server_write_key[key_material_length=16]
           client_write_IV[IV_size=0]
           server_write_IV[IV_size=0]
           session_key_seed[seed_size= 40]

    The client_write_MAC_secret and server_write_MAC_secret are the
    keys used by the client and server to authenticate subsequent
    messages respectively.  Similarly, the client_write_key and
    client_write_IV are used by the client to provide message
    confidentiality while the server uses the server_write_key and
    server_write_IV to achieve confidentiality.  The session_key_seed
    is later 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.


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 6.3 EAP-FAST Authentication Phase 2: Tunneled Authentication

    The second portion of the EAP-FAST Authentication conversation
    consists of at least one complete EAP conversation occurring within
    the TLS session negotiated in EAP-FAST Authentication Phase 1;
    ending with protected termination using the Result-TLV and Crypto-
    Binding TLV.  All EAP messages are encapsulated in the EAP Message
    TLV.

    EAP-FAST Phase 2 will occur only if establishment of a new TLS
    session in Phase 1 is successful or a TLS session is successfully
    resumed in Phase 1.

    Phase 2 must not occur if the EAP Peer or EAP Server fails
    authentication during Phase 1.  That is, if the tunnel
    establishment fails and a TLS alert is provided prior to a
    clear text EAP failure.

    Additionally, Phase 2 must not occur if a protected EAP-Failure has
    been sent by the EAP Server to the peer, terminating the
    conversation.  Since all packets sent within the EAP-FAST Phase 2
    conversation occur after TLS session establishment, they are
    protected using the negotiated TLS cipher suite. For example, if
    the cipher suite negotiated is TLS_RSA_WITH_RC4_128_SHA, all EAP-
    TLV packets of the conversation in Phase 2 including the EAP-TLV
    header are protected using 128bit RC4 and SHA1 as defined by the
    TLS protocol [RFC 2246].


 6.4 Protected EAP Conversation

    Phase 2 of the EAP-FAST Authentication conversation consists of at
    least one protected EAP authentication, typically using the peer's
    credentials (typically username and password).  This entire EAP
    conversation including the user identity and EAP type are protected
    from eavesdropping and modification by the tunnel encapsulation.  A
    hacker cannot readily determine the EAP method used (except perhaps
    by traffic analysis) nor can the hacker inject/modify packets to
    subvert the authentication.

    Phase 2 of the EAP-FAST conversation begins with the EAP server
    sending an EAP-Request/Identity packet to the peer, protected by
    the TLS ciphersuite negotiated in EAP-FAST Phase 1. The peer
    responds with an EAP-Response/Identity packet to the EAP server,
    containing the peer's userID.

    After the protected Identity exchange, the EAP server will send an
    EAP-Request with the supported EAP type, for example, EAP-Type=EAP-
    GTC.  EAP-FAST enables the use of any (EAP) method to ensue inside
    the tunnel, the EAP-GTC type is used in this specification as an
    example.



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    The EAP conversation within the TLS protected session may involve
    zero or more EAP authentication methods, including the TLV
    exchanges; and completes with protected termination shown in Section
    6.5.

    After any EAP method, the EAP-FAST server or peer may request the
    EAP-FAST peer or server respectively, to prove that it has
    participated in the sequence of authentications successfully
    completed until that point.  The server also concludes the EAP-FAST
    Phase 2 conversation by invoking a final Result TLV with a Crypto-
    Binding TLV. The Crypto-Binding TLV is sent in the protected TLS
    channel.  If the EAP-FAST server sends a valid Crypto-Binding TLV
    to the EAP-FAST peer, the peer MUST respond with a Crypto-Binding
    TLV in an EAP Response. If the Crypto-Binding TLV is invalid, it
    MUST be considered failed authentication by EAP-FAST peer and a
    Result TLV with a failure status should follow. If the peer does
    not respond with an EAP-FAST packet containing the Crypto-Binding
    TLV, it MUST be considered failed authentication by the EAP-FAST
    server. Once the EAP-FAST peer and EAP-FAST server considers them
    as failed authentications, they are the last packets inside the
    protected tunnel.

 6.5 Protected Termination and Acknowledged Result Indication

    The EAP-FAST server and EAP-FAST peer indicate success/failure of a
    conversation ensued inside the TLS tunnel. Either an Intermediate-
    Result TLV is used if further conversations will occur, or a final
    Result TLV if it is the concluding success/failure indication.  The
    inclusion of a Crypto-Binding TLV exchange is used to prove that
    both peers participated in the sequence of authentications
    (specifically the TLS session and inner authentication methods that
    generate keys).  The Crypto-Binding TLV exchange is only needed
    with a Success Result TLV to verify the integrity of the tunnel. If
    the inner EAP method fails, then no Crypto-Binding TLV exchange is
    needed.

    If the PAC needs to be updated, the Crypto-Binding TLV must precede
    the final Result TLV as the final Result TLV exchange may also
    include the distribution of the PAC in a PAC TLV. Following a
    successful Intermediate-Result TLV and Crypto-Binding TLV exchange,
    the Result TLV will be the next subsequent TLV exchange that also
    includes a PAC TLV to update the PAC.

    Both Intermediate and final Result TLVs are sent protected within
    the TLS channel. The EAP-FAST peer then replies with a
    corresponding Intermediate or final Result TLV inside protected
    channel.  The conversation concludes with a final Result TLV
    exchange followed by the EAP-FAST server sending a clear text EAP-
    Success/Failure indication.

    The only outcome which should be considered as a successful EAP-
    FAST Authentication is when the final Result TLV of Status=Success


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    and a valid concluding Crypto-Binding TLV, is answered by a final
    Result TLV of Status=Success and a valid Crypto-Binding-TLV.

    All other combinations of the (request, response) Result TLVs such
    as (Failure, Success), (Failure, Failure), (no Result TLV exchange,
    no Crypto-Binding TLVs or where the Crypto-Binding TLV validation
    is not successful) MUST be considered failed authentications, both
    by the EAP-FAST peer and EAP-FAST server. Once the EAP-FAST peer
    and EAP-FAST server considers them as failed authentications, they
    are the last packets inside the protected tunnel. These are
    considered failed authentications regardless of whether a clear text
    EAP Success or EAP Failure packet is subsequently sent.

    In support for session resumption, an EAP-FAST server may send the
    success indication and Crypto-Binding TLV, without initiating any
    EAP conversation in EAP-FAST Phase 2. The EAP-FAST peer is
    allowed to refuse to accept a success message from the EAP-FAST
    server since the peer's policy may require completion of certain
    authentication methods.  If session resume is invoked and the
    EAP-FAST server has sent Result-TLV with Status=Success; and the
    response from the EAP peer is Status=Failure, then the server MUST
    continue with the EAP-FAST Phase 2 authentication conversation.

 6.6 EAP-FAST Authentication Phase 2: Key Derivations

    Keying material resulting from all successful conversations ensued
    in both phases of EAP-FAST Authentication are used to both prove
    tunnel integrity and generate session keys.  A base compound key is
    the resulting key generated as follows:

    EAP-FAST session_key_seed(SKS) is a 40 octet value obtained from
    the EAP-FAST Authentication Phase 1 described in Section 6.2.

    The inner authentication method(s) provide session keys: ISK1..ISKn
    corresponding to inner methods 1 through n.  Only the MSKs from the
    inner methods are required. If the inner method (i) does not
    generate an ISK, then ISKi is set to zero (e.g. ISKi = 32 octets of
    0x00s). If the inner method generates keying material, EAP-FAST
    presumes that a minimum of 32 octets are provided.  Otherwise, the
    resulting ISK is padded with zeroes to generate a 32 octet value.
    Thus, the first 32 octets generated as the encryption keying
    material by the inner method is used and assigned as the ISK.  For
    example, if EAP-TLS [RFC 2716] is used as an inner method, the
    resulting first 32 bytes described as the "peer encryption key" in
    Section 3.5 of [RFC 2716] is assigned as the ISK.

    The algorithm uses the EAP-FAST T-PRF as described in Appendix B
    (Section 18) to generate the following:






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    S-IMCK[0] = SKS

    For j = 1 to n-1 do
    IMCK[j] = T-PRF(S-IMCK[j-1], "Inner Methods Compound Keys", ISK[j],
    60);
       Where S-IMCK[j] are the first 40 octets of IMCK[j]

    ICMK[j] may generate up to 60 octets of keying material.  The first
    40 octets are used as the key input to the succeeding ICMK[j+1]
    derivation and the latter 20 octets are used as the key, CMK[j],
    used to generate the intermediate Crypto-Binding Compound MAC
    value.


 6.7 Cryptographic Binding: Computing the Compound MAC

    For authentication methods that generate keying material, further
    protection against man-in-the-middle attacks are mitigated through
    the enforcement of cryptographically binding keying material
    established by both EAP-FAST Phase 1 and EAP-FAST Phase 2
    conversations.

    For a successful EAP-FAST Authentication, inner methods are
    cryptographically combined to generate a compound session key, CMK,
    used to generate an authentication tag referred to as a Compound
    MAC and transported in a Crypto-Binding TLV.  The Crypto-Binding
    TLV is used to assure that the same peers invoked all methods in
    EAP-FAST.

    EAP-FAST optionally enables the server or peer to invoke
    Intermediate-Result TLV request/response exchanges with Crypto-
    Binding TLVs to verify the integrity of the tunnel between methods
    inside the EAP-FAST Phase 2 conversation.

    Similarly, EAP-FAST enforces a mandatory inclusion of a Crypto-
    Binding TLV after a final method has completed.  In both instances,
    a Crypto-Binding TLV is included when either an Intermediate-Result
    TLV or a final Result TLV is used.  The Crypto-Binding TLV includes
    a 20 octet authentication tag that represents the HMAC-SHA1 hash of
    the entire Crypto-Binding TLV.  The Compound MAC field is zeroed
    out prior to the computation of the HMAC-SHA1 and subsequently
    populated with the resulting hash value.

    The requesting server shall provide a 32-octet random server_nonce
    with its last bit set to 0 and compute the Compound MAC field as
    follows:
    HMAC-SHA1( CMK, [Crypto-Binding TLV with Compound MAC field=
    zeroes])

    The responding peer shall respond with the same 32-octet
    server_nonce value provided by the requestor with its last bit set
    to 1 and computes the responding Compound MAC field as described
    above.

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 6.8 EAP-FAST Authentication: Session Key Generation

    EAP-FAST Authentication assures the master session keys are a
    result of all conversations ensued by generating a compound session
    key (IMCK).  The IMCK is mutually derived by the peer and server
    using the T-PRF; the IMCK calculation is defined in Section 6.6.
    The resulting master session key, MSK, is generated as part of the
    IMCKn key hierarchy. Where the S-IMCKn is used to generate the
    session keys as follows:

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

    The first version of EAP-FAST generates 64 octets to serve as the
    successful EAP-FAST authentication master session keys.
    Interpretation and assignment of these 64 octets of the master
    session key is specific to each link layer ciphersuite.

    EAP-FAST implementations MAY generate EMSK as follows:

    EMSK = T-PRF(S-IMCKn, "Extended Session Key Generating Function",
    64)

    The Extended Master Session Key (EMSK) is only known to the EAP-
    FAST peer and server and is not provided to a third party.



 6.9 PAC Distribution and Refreshing

    The server may distribute or refresh a peer's PAC after a
    successful EAP-FAST Authentication. A PAC TLV is created to
    facilitate the distribution and update.  A fresh PAC may be
    distributed after a successful Intermediate-Result TLV and Crypto-
    Binding TLV exchange.   A successful EAP-FAST authentication,
    including a successful Crypto-Binding exchange must ensue before an
    EAP-FAST server can distribute a fresh PAC.  A PAC TLV should not
    be accepted if it is not TLS tunnel-encapsulated.  The fresh PAC is
    encapsulated in a PAC TLV containing the PAC-Key, PAC-Opaque and
    PAC-Info TLVs.  The PAC-Key is the shared secret key the peer uses
    to mutually authenticate with the server and establish the tunnel.
    The PAC-Opaque contains data that is opaque to the recipient, the
    peer is not the intended consumer of PAC-Opaque and thus should not
    attempt to interpret it.  A peer that has been issued a PAC-Opaque
    by a server must store that data, and present it back to the server
    as is, in the TLS ClientHello SessionTicket extension [TICKET].
    PAC-Info provides the peer information about the PAC, at minimum,
    it provides the information about the authority identity issuing
    the PAC.





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    Once the EAP-FAST peer receives a PAC TLV, it needs to securely
    save the new PAC-Key, PAC-Opaque and optionally, the PAC-Info.
    Additionally, upon receipt of a new PAC, the peer must respond with
    a successful PAC-Acknowledgement TLV.  If the peer responds with a
    PAC-Acknowledgement failure, the EAP-FAST server may invoke another
    Result TLV failure resulting in a failed EAP-FAST authentication.

    The server may refresh a PAC only after a successful exchange of
    the concluding Intermediate-Result TLV and Crypto-Binding TLV.  The
    peer must use the new PAC-Key and PAC-Info in subsequent EAP-FAST
    Authentication sessions.

    N.B. In-band PAC refreshing is enforced by server policy.  The
    server, based on the PAC-Opaque information, may determine not to
    refresh a peer's PAC through the PAC TLV mechanism even if the PAC-
    Key has expired.


 7. 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.

    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 client, it terminates the conversation.

    The version negotiation procedure guarantees that the EAP-FAST
    client 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 a EAP-FAST version
    negotiated, the peers MUST exchange information on the EAP-FAST



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    version negotiated using the Crypto-Binding TLV.  The concluding
    Intermediate or final Result TLV comes with a mandatory Crypto-
    Binding TLV that includes the EAP-FAST version which MUST be
    consistent to that specified in the EAP-FAST Start message.

 8. Error Handling

    The EAP-FAST protocol uses TLS alert messages to communicate and
    handle error conditions in all phases of EAP-FAST. Errors during
    the tunnel establishment or protection in EAP-FAST Authentication
    are handled via TLS alert messages, while errors during the
    protected tunnel are expected to be handled by the individual EAP
    methods.  Intermediate-Result TLVs are also used as status
    indications of the individual EAP methods in EAP-FAST Phase 2.
    If the EAP-FAST server detects an error at any point in the TLS
    conversation, the EAP-FAST server should send an EAP-Request
    packet with EAP-Type=EAP-FAST, encapsulating a TLS record
    containing the appropriate TLS alert message.

    The EAP-FAST server should send a 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.  To ensure that the peer receives
    the TLS alert message, the EAP server must wait for the peer to
    reply with an EAP-Response packet before terminating the
    connection.

    The EAP-Response packet sent by the peer may encapsulate a TLS
    client_hello handshake message, in which case the EAP-FAST server
    MAY allow the EAP-FAST conversation to be restarted, or it MAY
    contain an EAP-Response packet with EAP-Type=EAP-FAST and Flags and
    Version fields without any additional data , in which case the EAP-
    FAST Server MUST send an EAP-Failure packet, and terminate the
    conversation.

    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 client detects an error at any point in the TLS
    conversation, the EAP-FAST client should send an EAP-Response
    packet with EAP-Type=EAP-FAST, encapsulating a TLS record
    containing the appropriate TLS alert message. The EAP-FAST server
    may restart the conversation by sending an EAP-Request packet
    encapsulating the TLS server_hello handshake message, in which case
    the EAP-FAST client may allow the EAP-FAST conversation to be
    restarted; or terminate the conversation.




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    If during the EAP-FAST Authentication Phase 1 session
    establishment, EAP-FAST servers cannot obtain or verify the PAC,
    the server should send an EAP-Request packet with EAP-Type=EAP-
    FAST, encapsulating a TLS record containing the appropriate TLS
    alert message, before terminating the conversation. The EAP-FAST
    peer should inform the use of the mismatching PAC and terminating
    the conversation.

 8.1 Error Alerts

    EAP-FAST uses TLS-Alert to handle errors in the EAP-TLS handshake.
    EAP-FAST employs the standard TLS error alerts described in TLS
    Protocol Specification [RFC 2246].  In addition, it reuses the
    following TLS alert to support EAP-FAST specific error conditions:

    bad certificate

      Server cannot find an acceptable PAC-Opaque in the ClientHello
      message.  This can be a result of either the peer not sending the
      PAC-Opaque or the PAC-Opaque provided cannot be decrypted by the
      server or expired. This message is always a fatal error.

    decrypt_error

      If PAC-Key doesn't match between the peer and server and either
      peer or server fails to validate Finished message, decrypt_error
      Alert should be used. This message is always a fatal error.


 9. Session Resume

    EAP-FAST offers a means to bypass further conversations such as
    inner EAP authentication methods when a peer has an established
    session identified by Session ID.   This enables a peer to
    optimally generate fresh master session keys without having to re-
    invoke the inner EAP authentication method in EAP-FAST
    Authentication Phase 2.  Applications that require user
    intervention for the inner authentication method (e.g. OTP) can
    benefit from this feature when service has been established but
    believes it must refresh its master session keys.

    EAP-FAST session resumption is achieved in the same manner TLS
    achieves session resume.  Session Resume is achieved by the peer
    responding with a known Session ID in its ClientHello record.  The
    EAP-FAST Authentication Phase 1 conversation proceeds in a similar
    fashion as described in Section 6 with the exception of the use of
    the PAC-Opaque in the ClientHello.   That is, a session resumption
    is distinguished by the client's indication of a valid (e.g. non-
    zero) SessionID and omission of the PAC-Opaque in its ClientHello
    message.   To support session resumption, the server must minimally
    cache the client's SessionID, master_secret and CipherSpec.   If
    the server finds a match for the SessionID and is willing to


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    establish a new connection using the specified session state, the
    server will respond with the same SessionID and proceed with the
    EAP-FAST Authentication Phase 1 tunnel establishment described in
    Section 6.1.  The key derivations used in the EAP-FAST
    Authentication Phase 1 employ the corresponding SessionID's
    master_secret in accordance to the TLS [RFC 2246] session
    resumption specification.

    After a successful conclusion of the EAP-FAST Authentication Phase
    1 conversation, the server then decides whether to honor session
    resumption based on the Session ID value.  It may reject and
    initiate the inner EAP authentication method to signal the start of
    a full EAP-FAST Authentication Phase 2 conversation.  The server
    may accept a session resumption based on the Session ID specified
    by the peer as well as the time elapsed since the previous
    authentication.

    The server may accept a session resumption and bypass the inner EAP
    authentication method by immediately requesting a final Result TLV
    without a Crypto-Binding TLV.  The concluding Result TLV exchange
    is the same as that described in Section 6.5.  The EAP-FAST master
    session keys are generated as described in Section 6.8, with the
    exception that S-IMCK[n] is SKS without going through the compound
    key derivation, as in this case no inner EAP method has run.

    Even if the session is successfully resumed, the peer and EAP-FAST
    server must not assume that either will skip inner EAP methods. The
    peer may have roamed to a network which may use the same EAP
    server, but may require conformance with a different authentication
    policy. After a session is successfully resumed, the EAP-Server may
    start a full Phase 2 of the EAP-FAST Authentication conversation.

 10. 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. The group of EAP-FAST
    messages sent in a single round may thus be larger than the PPP MTU
    size, the maximum RADIUS packet size of 4096 octets, or even the
    Multilink Maximum Received Reconstructed Unit (MRRU).  As described
    in [2], the multilink MRRU is negotiated via the Multilink MRRU LCP
    option, which includes an MRRU length field of two octets, and thus
    can support MRRUs as large as 64 KB.

    However, 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.



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    If this value is chosen, then fragmentation can be handled via the
    multilink PPP fragmentation mechanisms described in [RFC1990].
    While this is desirable, EAP methods are used in other applications
    such as [IEEE80211] and there may be cases in which multilink or
    the MRRU LCP option cannot be negotiated. As a result, an EAP-FAST
    implementation MUST provide its own support for fragmentation and
    reassembly.

    Since EAP is an ACK-NAK 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 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=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=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.







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 11. EAP-FAST Detailed Description

 11.1 EAP-FAST Packet Format

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


    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.

    Length

      The Length field is two octets and indicates the length of the
      EAP packet including the Code, Identifier, Length, Type, 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 - EAP-FAST

    Flags

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




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

      The L bit (length included) 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 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.
      This differentiates the EAP-FAST Start message from a fragment
      acknowledgement.

    Version

             0 1 2
            +-+-+-+
            |R|R|1|
            +-+-+-+

            R = Reserved (must be zero)

    TLS Message Length

      The TLS Message Length field is four octets, and is present only
      if the L bit is set.  This field provides the total length of the
      TLS message or set of messages that is being fragmented.

    TLS data

      The TLS data consists of the encapsulated packet in TLS record
      format. An EAP-FAST packet with Flags and Version fields but with
      empty data field to used to indicate EAP-FAST acknowledgement for
      either TLS Alert or TLS Finished.


 11.2 EAP-FAST TLV Format

    The EAP-FAST TLV is a payload with standard Type-Length-Value (TLV)
    objects similar to those defined by [PEAP]. The TLV objects could
    be used to carry arbitrary parameters between EAP peer and EAP
    server. Possible uses for TLV objects include: language and
    character set for Notification messages; cryptographic binding;
    IPv6 Binding Update.

    The EAP peer may not necessarily implement all the TLVs supported
    by the EAP server; and hence to allow for interoperability, the TLV
    method allows an EAP server to discover if a TLV is supported by
    the EAP peer, using the NAK TLV.





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    The mandatory bit in a TLV indicates that the peer must understand
    the TLV. A peer can determine that a TLV is unknown when it does
    not support the TLV; or when the TLV is corrupted. The mandatory
    bit does not indicate that the peer successfully applied the value
    of the TLV. The specification of a TLV could define additional
    conditions under which the TLV can be determined to be unknown.

    If an EAP peer finds an unknown TLV which is marked as mandatory;
    it must indicate a failure to the EAP server using the NAK TLV; and
    all the other TLVs in the message MUST be ignored.

    If an EAP peer finds an unknown TLV which is marked as optional;
    then it must ignore the TLV. The EAP peer is not required to inform
    the EAP server of unknown TLVs which are marked as optional. If the
    EAP peer finds that the packet has no TLVs, then it must send a
    response with EAP-TLV Response Packet. The Response packet may
    contain no TLVs.

    If an EAP server finds an unknown TLV which is marked as mandatory;
    the other TLVs in the message MUST be ignored. The EAP server can
    drop the connection or send an EAP-TLV request packet with NAK-TLV
    to the EAP client.

    An EAP-FAST TLV packet can be sequenced before or after any other
    EAP method. The packet does not have to contain any mandatory TLVs.

    Compliant EAP-FAST implementations must support the EAP-FAST TLV
    exchange, including processing of mandatory/optional settings on
    the TLV, the NAK TLV, the Crypto-Binding TLV, EAP Payload TLV, PAC
    TLV, Intermediate-Result TLV and the Result TLV.


 11.3 TLV format

    EAP-FAST TLVs are defined as follows:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |M|R|            TLV Type       |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              Value...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


     M

      0 - Non-mandatory TLV
      1 - Mandatory TLV





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     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 -   Reserved
            6 -   Reserved
            7 -   Reserved
            8 -   Reserved
            9 -   EAP-Payload TLV
            10 -  Intermediate-Result TLV
            11 -  PAC TLV
            12 -  Crypto-Binding TLV

    Length

      The length of the Value field in octets.

    Value

      The value of the TLV.


 11.4 Result TLV

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

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |M|R|         TLV Type          |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             Status            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    M

      1 - Mandatory TLV





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    R

      Reserved, set to zero (0)

    TLV Type

      3 - Result TLV

    Length

      2

    Status

      The status field is two octets. Values include:

      1 - Success
      2 - Failure

 11.5 NAK TLV

    The NAK TLV allows a peer to detect when TLVs that are not
    supported by the other peer. It is defined as follows:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |M|R|         TLV Type          |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Vendor-Id                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          NAK-Type             |          TLVs...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    M

      1 - Mandatory TLV

    R

      Reserved, set to zero (0)

    TLV Type

      4 - NAK TLV

    Length

      Variable





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    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.
      For Vendor-Specific TLVs, the Vendor-ID MUST be set to the SMI
      code.

     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 can be used in the
      future to communicate why the offending TLV was determined to be
      unsupported.


 11.6 Crypto-Binding TLV

    The Crypto-Binding TLV is used to prove that both peers
    participated in the sequence of authentications (specifically the
    TLS session and inner EAP methods that generate keys).

    Both the Binding Request and Binding Response use the same packet
    format; with the SubType field indicating whether it is a request
    or response.

    The Crypto-Binding TLV can be used to perform Cryptographic Binding
    after each EAP method in a sequence of EAP methods completes within
    the EAP-FAST Authentication Phase 2. The Crypto-Binding TLV MUST be
    used once during or before a Protected Termination along with a
    Result or Intermediate-Result TLV.

    This message format is used for the Binding Request and also the
    Binding Response. This uses TLV type CRYPTO-BINDING TLV. The format
    is as given below, with fields transmitted from left to right:











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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. |    SubType    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                           NONCE                               ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                         Compound MAC                          ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    M

      1 - Mandatory TLV

    R

      Reserved, set to zero (0)

    TLV Type

      12 - Crypto-Binding TLV.

    Length

      56

    Reserved

      The Reserved field is a single octet and must be set to all
      zeros.

    Version

      The Version field is a single octet, which is set to the version
      of Crypto Binding TLV.  For the crypto-binding TLV defined in
      this specification, it is set to 1.

    Received Version

      The Received Version field is a single octet and MUST be set to
      the EAP-FAST version number received during version negotiation.

    SubType

      The SubType field is 1 octet.
      0 - Binding Request
      1 - Binding Response

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    Nonce

      The Nonce field is 32 octets. It contains a 256 bit random number
      generated by the server on request.  The peer responds with the
      server nonce incremented by 1.

    Compound MAC

      The Compound MAC field is 20 octets. It contains an
      authentication tag for this TLV. It is calculated over entire
      Crypto-Binding TLV with Compound MAC field filled with zero.

 11.7 EAP-Payload TLV

    EAP-Payload TLV is used to encapsulate all the inner EAP messages.
    It is defined as follows:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |M|R|         TLV Type          |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          EAP Packet...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                             TLVs...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    M

      1 - Mandatory TLV

    R

      Reserved, set to zero (0)

    TLV Type

      9

    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.





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    TLVs...

      This (optional) field contains a list of TLVs associated with the
      EAP packet field.  The TLVs utilize the same format described
      Section 11.3, and 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.



 11.8 Intermediate-Result TLV

    The Intermediate-Result TLV provides support for acknowledged
    intermediate Success and Failure messages within EAP-FAST. EAP-FAST
    implementations MUST support this TLV; and this TLV cannot be
    responded to with a NAK TLV. It is defined as follows:


     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |M|R|         TLV Type          |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             Status            |        TLVs...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    M

      1 - Mandatory TLV

    R

      Reserved, set to zero (0)

    TLV Type

      10

    Length

      >=2

    Status

      The Status field is two octets.  Values include:

            1 - Success
            2 - Failure






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    TLVs

      This (optional) field is of indeterminate length, and contains
      the TLVs associated with the Intermediate-Result TLV, in the same
      format as described in Section 11.3.  The TLVs in this field MUST
      NOT have the mandatory bit set.


 11.9 PAC TLV

    The PAC TLV provides support for acknowledged refreshing from the
    server side within EAP-FAST.  A consistent PAC format will allow it
    to be used by multiple applications beyond EAP-FAST.  A general PAC
    TLV format 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             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        PAC Attributes...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    M

       0 - Non-mandatory TLV
       1 - Mandatory TLV


    R

       Reserved, set to zero (0)

    TLV Type

       11- PAC TLV:

    Length

       The length of the PAC Attributes field in octets.

    PAC Attributes

       A list of PAC attributes in the TLV format.

       A PAC attribute is comprised of three general PAC fields
       encapsulated in a common format.  The contents of these fields
       are described in succeeding sections.  The PAC TLV contains all
       of the required information to appropriately distribute the
       peer with a PAC.




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 11.9.1    Formats for PAC TLV attributes

    A common encapsulating format is used to convey the different
    fields that comprise a PAC attribute.  The common encapsulation 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Type               |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              Value...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Type

      The type field is two octets, denoting the attribute type.
      Allocated Types include:

           1 - PAC-Key
           2 - PAC-Opaque
           3 - CRED_LIFETIME
           4 - A-ID
           5 - I-ID
           6 - SERVER_PROTECTED_DATA
           7 - A-ID-Info
           8 - PAC-Acknowledgement
           9 - PAC-Info

    Length

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

    Value

      The value of the PAC Attribute.



 11.9.2    PAC-Key

    The PAC-Key is distributed as an attribute of type PAC-Key
    (Type=1).  The key is a randomly generated octet string.  The key
    is represented as an octet string whose length is determined by the
    length field.  The generator of this key is the issuer of the
    credential, identified by the A-ID.







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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Type               |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                              Key                              ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Type

      1 - PAC-Key

    Length

      The Length filed is two octets. For this version of EAP-FAST,
      PAC-Key is 32 octets.

    Key

      The Key field contains the PAC-Key.




 11.9.3    PAC-Opaque

    The PAC-Opaque section contains data that is opaque to the
    recipient, the peer is not the intended consumer of PAC-Opaque and
    thus should not attempt to interpret it.  A peer that has been
    issued a PAC-Opaque by a server MUST store that data, and present
    it back to the server as is, in the ClientHello SessionTicket
    extension field [TICKET]. If a client has opaque data issued to it
    by multiple servers, then it MUST store the data issued by each
    server separately.  This requirement allows the client to maintain
    and use each opaque data as an independent PAC pairing, with a
    PAC-Key mapping to a PAC-Opaque identified by the A-ID. As there
    is a one to one correspondence between PAC-Key and PAC-Opaque, a
    peer must determine the PAC-Key and corresponding PAC-Opaque based
    on the A-ID provided in the EAP-FAST/Start message and the A-ID
    provided in the PAC-Info when it was provisioned with a PAC-Opaque.
    Each client must not parse any PAC-Opaque data given to it.

    As the PAC-Opaque is server specific, its contents and definition
    are specific to the issuer of the PAC, e.g. the PAC server.

    The PAC-Opaque field is embedded as part of the PAC TLV when the
    server has determined that the PAC must be refreshed and sends a
    new PAC.




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    The PAC-Opaque field format is summarized 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Type               |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              Value ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    Type

      2 - PAC-Opaque

    Length

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

    Value

      The Value field contains the actual data for PAC-Opaque

    The PAC-Opaque field is also passed from the peer to the server
    during the EAP-FAST Authentication Phase 1 conversation to enable
    the server to validate and recreate the PAC-Key.  When it is passed
    from the peer, it is encapsulated as defined above in the
    ClientHello SessionTicket Extension [TICKET].

 11.9.4    PAC-Info

    PAC-Info is comprised of a set of PAC attributes.  At minimum, the
    A-ID TLV is required to convey the issuing identity to the peer.
    Other optional fields may be included in the PAC to provide more
    information to the peer. It is a container attribute for various
    types of information each of which is encoded in conformance to the
    PAC TLV field format as defined in Section 11.9.1.

     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               |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           Attributes...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Type

      9 - PAC-Info




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    Length

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

    Attributes

      The Attributes field contains a list of PAC Attributes.

    Each mandatory and optional field type is defined as follows:

    CRED_LIFETIME (type 3)

      This is a 4 octet quantity representing the expiration time of the
      credential in UNIX UTC time.  This is a mandatory field contained
      in the PAC-Opaque field to enable the server to validate the PAC.
      This field may also be optionally provided to the peer as part of
      PAC-Info.

    A-ID (type 4)

      Authority identifier is the name of the authority that issued the
      token.  The A-ID is intended to be unique across all issuing
      servers to avoid namespace collisions.  Server implementations
      should use measures to ensure the A-ID used is globally unique to
      avoid name collisions. The A-ID is used by the peer to determine
      which PAC to employ.  Similarly, the server uses the A-ID to both
      authenticate the PAC-Opaque and determine which master key was
      used to issue the PAC.  This field is mandatory and included in
      both the PAC-Opaque and as the first TLV comprising PAC-Info.

    I-ID (type 5)

      Initiator identifier is the peer identity associated with the
      credential. The server employs the I-ID in the EAP-FAST Phase 2
      conversation to validate that the same peer identity used to
      execute EAP-FAST Phase 1 is also used in at minimum one inner EAP
      method in EAP-FAST Phase 2.  This field is a mandatory field in
      PAC-Opaque and may optionally be included in the PAC-Info. If the
      AS is enforcing the I-ID validation on inner EAP method, then I-ID
      is mandatory in PAC-Info, to enable the client to also enforce a
      unique PAC for each unique user. If I-ID is missing from the PAC-
      Info, it is assumed that the PAC can be used for multiple users
      and client will not enforce the unique PAC per user policy.

    A-ID-Info (type 7)

      Authority Identifier Information is a mandatory TLV intended to
      provide a user-friendly name for the A-ID. It may contain the
      enterprise name and server name in a more human-readable format.
      This TLV serves as an aid to the peer to better inform the end-
      user about the A-ID.  This field is a mandatory field in the
      PAC-Info.

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 11.9.5    PAC-Acknowledgement TLV

    The PAC-Acknowledgement TLV is used to acknowledge the receipt of
    the PAC TLV by the peer. Peer sends this TLV in response to the PAC
    TLV to indicate the result of the retrieving and storing of the new
    PAC.

     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               |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Result             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Type

      8 - PAC-Acknowledgement

    Length

          2

    Result

      1 - Success
      2 - Failure


 11.10 TLS SessionTicket Extension

    EAP-FAST employs the TLS SessionTicket extension (as defined in
    [TICKET]) to enable the client to convey the opaque credential,
    PAC-Opaque, to the server for the server to restore its session
    state. The SessionTicket extension format follows the [RFC3546]
    syntax and is defined in [TICKET] and duplicated as follows:


    struct {
              opaque _ticket<0..2^16-1>
           } SessionTicket;

    The extension type number for the TLS SessionTicket extension used
    in EAP-FAST is 35.


 12. Security Considerations

    EAP-FAST is designed with a focus on wireless media, where the
    medium itself is inherent to eavesdropping.  Whereas in wired




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    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 RFC 3748 [EAP].

 12.1 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.  Further, the
    Result TLV is enforced to be run after any EAP method that supports
    (mutual) authentication ensuring that it was the same peer and AS
    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 may silently discard those clear text EAP success or failure
    messages that do not coincide with the status sent in the protected
    Result TLV.

 12.2 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.


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12.3 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.


 12.4 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:

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

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    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].


 12.5 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:

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

    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




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    mitigates several vulnerabilities such as 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 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.

 12.5.1    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 userID 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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 12.5.2    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.


 12.5.3    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 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.





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

    * 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,

    * 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.

 12.5.4    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 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.





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 12.6 PAC Storage Considerations

    The main premise behind EAP-FAST is to protect the authentication
    stream over the media link.  However, physical security is still an
    issue.  Some care should be taken to protect the PAC on both the
    peer and server.  The peer must store securely both the PAC-Key and
    PAC-Opaque, while the server must secure storage of its security
    association context used to consume the PAC-Opaque.  Additionally,
    if manual provisioning is employed, the transportation mechanism
    used to distribute the PAC must also be secured.

    Most of the attacks described here would require some level of
    effort to execute; conceivably greater than their value.  The main
    focus therefore, should be to ensure that proper protections are
    used on both the client and server.  There are a number of
    potential attacks which can be considered against secure key
    storage such as:

    * weak passphrases
      On the client side, keys are usually protected by a passphrase.
      On some environments, this passphrase may be associated with the
      user's password.  In either case, if an attacker can obtain the
      encrypted key for a range of users, he may be able to
      successfully attack a weak passphrase.  The tools are already in
      place today to allow an attacker to easily attack all Outlook or
      Outlook Express users in an enterprise environment.  Most viruses
      or worms of this sort attract attention to themselves by their
      action, but that need not be the case.  A simple, genuine
      appearing e-mail could surreptitiously access keys from known
      locations and e-mail them directly to the attacker, attracting
      little notice.

    * key finding attacks
      Key finding attacks are usually mentioned in reference to web
      servers, where the private SSL key may be stored securely, but at
      some point it must be decrypted and stored in system memory.  An
      attacker with access to system memory can actually find the key
      by identifying their mathematical properties.  To date, this
      attack appears to be purely theoretical and primarily acts to
      argue strongly for secure access controls on the server itself to
      prevent such unauthorized code from executing.

    * key duplication, key substitution, key modification
      Once keys are accessible to an attacker on either the client or
      server, they fall under three forms of attack: key duplication,
      key substitution and key modification.  The first option would be
      the most common, allowing the attacker to masquerade as the user
      in question.  The second option could have some use if an
      attacker could implement it on the server.




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    Another consideration is the use of secure mechanisms afforded by
    the particular device.  For instance, some laptops enable secure
    key storage through a special chip.  It would be worthwhile for
    implementations to explore the use of such a mechanism.

 12.7 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
    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.

 12.8 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.

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 12.9 Security Claims

    This section provides needed security claim requirement for
    RFC 3748 [EAP].

          Auth. mechanism:        Tunneled authentication as well as
                                  pre-shared key.
          Ciphersuite negotiation:Yes. See [RFC2246].
          Mutual authentication:  Yes. See Section 12.1.
          Integrity protection:   Yes. See Section 12.1. Only EAP Type
                                  Data field and inner EAP methods
                                  contained in this field are
                                  protected.
          Replay protection:      Yes. See [RFC2246].
          Confidentiality:        Yes. See [RFC2246].
          Key derivation:         Yes. See Section 6.6.
          Key strength:           TLS key strength, may be enhanced by
                                  binding keys with inner methods
          Dictionary attack prot.:Yes. See Section 12.5.2.
          Key hierarchy:          Yes. See Section 6.6.
          Fast reconnect:         Yes. See Section 9.
          Cryptographic binding:  Yes. See Section 6.7.
          Session independence:   Yes. See [RFC2716].
          Fragmentation:          Yes. See Section 10.
          Channel binding:        No.


 13. 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 namespace in EAP-FAST that requires registration: TLV
    Types. These numbers may be assigned by First Come First Served
    [RFC2434].


 14. References

 14.1 Normative

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

    [EAP]
           Blunk, L., et. al., "Extensible Authentication Protocol
           (EAP)", RFC 3748, June 2004.





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    [RFC3268]
           Chown, P., "Advanced Encryption Standard (AES) Ciphersuites
           for Transport Layer Security (TLS)", RFC 3268, June 2002.

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

    [RFC3546]
           Blake-Wilson, S., et al, "Transport Layer Security (TLS)
           Extensions", RFC 3546, June 2003.

    [TICKET]
           Salowey, J., et al, "TLS Session Resumption without
           Server-Side State", draft-salowey-tls-ticket-02.txt,
           February 2005



 14.2 Informative

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

    [RFC2279]
           Yergeau, F., "UTF-8, a transformation format of ISO 10646",
           RFC 2279, January 1998.

    [RFC2631]
           Rescorla, E., "Diffie-Hellman Key Agreement Method", RFC
           2631, January 1999.

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

    [SHARED KEYS IN TLS]
           Gutmann, P., "Use of Shared Keys in the TLS Protocol",
           draft-ietf-tls-sharedkeys-02.txt (expired), October 2003.

    [IKEv2]
           Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
           draft-ietf-ipsec-ikev2-17 (work in progress), September
           2004.

    [PEAP]
           Palekar, et. al., "Protected EAP Protocol (PEAP) Version 2",
           draft-josefsson-pppext-eap-tls-eap-10 (work in progress),
           October 2004



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    [RFC3526]
           Kivinen, T., "More Modular Exponential (MODP) DIffie-Hellman
           groups for Internet Key Exchange (IKE)", RFC 3526, May 2003

    [MITM]
           Puthenkulam, J., "The Compound Authentication Binding
           Problem", draft-puthenkulam-eap-binding-04 (expired),
           October 2003.

    [RFC2486BIS]
           Aboba, et. al., "The Network Access Identifier", draft-
           ietf-radext-rfc2486bis-05.txt (work in progress),
           February, 2005.

    [RFC2548]
           Zorn, G., "Microsoft Vendor-specific RADIUS Attributes", RFC
           2548, March 1999.

    [EAP-TTLS]
           Funk & Blake-Wilson, "EAP Tunneled TLS Authentication
           Protocol", draft-funk-eap-ttls-v0-00.txt (work in
           progress), February 2005

    [TLS-PSK]
           Eronen & Tschofenig, "Pre-Shared Key Ciphersuites for
           Transport Layer Security (TLS)", draft-ietf-tls-psk-07,
           March 2005



 15. Acknowledgments

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


 16. Authors' Addresses

    Nancy Cam-Winget
    Cisco Systems
    3625 Cisco Way
    San Jose, CA 95134
    US
    Phone: +1 408 853 0532
    E-mail: ncamwing@cisco.com







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    David McGrew
    Cisco Systems
    San Jose, CA 95134
    US
    E-mail: mcgrew@cisco.com

    Joseph Salowey
    Cisco Systems
    2901 3rd Ave
    Seattle, WA 98121
    US
    Phone: +1 206 256 3380
    E-mail: jsalowey@cisco.com

    Hao Zhou
    Cisco Systems
    4125 Highlander Parkway
    Richfield, OH 44286
    US
    Phone : +1 330 523 2132
    E-mail: hzhou@cisco.com

 17. Appendix A: Examples

 17.1 Successful Authentication

    The following exchanges show a successful EAP-FAST authentication
    with 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)->

                            <- 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(Version=0,SNonce,
                            CompoundMAC)


    Intermediate-Result TLV (Success)
    Crypto-Binding TLV(Version=0,
    CNonce, CompoundMAC) ->

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

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

    TLS channel torn down
    (messages sent in clear text)

                            <- EAP-Success

 17.2 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/
    Identity (MyID1) ->




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                            <- 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)->

                            <- 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

    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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 18. Appendix B: EAP-FAST PRF (T-PRF)

    EAP-FAST employs a simpler PRF than the TLS PRF where possible.
    For instance, when generating the master_secret, master session
    keys and cryptographic binding keys and computations, EAP-FAST
    employs the following PRF construction:

    PRF(key, label, seed) = HMAC-SHA1(key, label + "\0" + seed)

    Where '+' indicates concatenation and "\0" is a NULL character.
    Label is intended to be a unique label for each different use of
    the T-PRF.

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

    T-PRF (Key, S, OutputLength) = T1 + T2 + T3 + T4 + ...
          Where S = label + 0x00 + seed;  and

    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)

    OutputLength is a two octet value that is represented in big endian
    order.  The NULL character, 0x00 shall be present when a label
    string is provided.  Also note that the seed value may be optional
    and may be omitted as in the case of the MSK derivation described
    in Section 6.8.

    Where each Ti generates 20-octets of keying material, the last Tn
    may be truncated to accommodate the desired length specified by
    OutputLength.

 19. Appendix C: Test Vectors

 19.1 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


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    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
    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);





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    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



 19.2 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


 20. Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed
   to pertain to the implementation or use of the technology
   described in this document or the extent to which any license
   under such rights might or might not be available; nor does it
   represent that it has made any independent effort to identify any
   such rights.  Information on the procedures with respect to rights
   in RFC documents can be found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard. Please address the information to the IETF at
   ietf-ipr@ietf.org.



Cam-Winget, et al.      Expires - October 25, 2005            [Page 53]

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 21. Disclaimer of Validity

    This document and the information contained herein are provided on
    an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
    REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND
    THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
    THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR
    ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
    PARTICULAR PURPOSE.


 22. Copyright Statement

    Copyright (C) The Internet Society (2005).  This document is
    subject to the rights, licenses and restrictions contained in BCP
    78, and except as set forth therein, the authors retain all their
    rights.


 23. Expiration Date

    This memo is filed as <draft-cam-winget-eap-fast-02.txt>, and
    expires October 25, 2005.






























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