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RFC 5836 - Extensible Authentication Protocol (EAP) Early Authen


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Internet Engineering Task Force (IETF)                           Y. Ohba
Request for Comments: 5836                                       Toshiba
Category: Informational                                       Q. Wu, Ed.
ISSN: 2070-1721                                                   Huawei
                                                            G. Zorn, Ed.
                                                             Network Zen
                                                              April 2010

                Extensible Authentication Protocol (EAP)
                 Early Authentication Problem Statement

Abstract

   Extensible Authentication Protocol (EAP) early authentication may be
   defined as the use of EAP by a mobile device to establish
   authenticated keying material on a target attachment point prior to
   its arrival.  This document discusses the EAP early authentication
   problem in detail.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5836.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
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   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................4
   3. Problem Statement ...............................................6
      3.1. Handover Preparation .......................................6
      3.2. Handover Execution .........................................6
           3.2.1. Examples ............................................7
      3.3. Solution Space .............................................7
           3.3.1. Context Transfer ....................................7
           3.3.2. Early Authentication ................................8
   4. System Overview .................................................8
   5. Topological Classification of Handover Scenarios ................9
   6. Models of Early Authentication .................................10
      6.1. EAP Pre-Authentication Usage Models .......................10
           6.1.1. The Direct Pre-Authentication Model ................11
           6.1.2. The Indirect Pre-Authentication Usage Model ........11
      6.2. The Authenticated Anticipatory Keying Usage Model .........13
   7. Architectural Considerations ...................................13
      7.1. Authenticator Discovery ...................................13
      7.2. Context Binding ...........................................14
   8. AAA Issues .....................................................14
   9. Security Considerations ........................................16
   10. Acknowledgments ...............................................17
   11. Contributors ..................................................17
   12. References ....................................................17
      12.1. Normative References .....................................17
      12.2. Informative References ...................................18

1.  Introduction

   When a mobile device, during an active communication session, moves
   from one access network to another and changes its attachment point,
   the session may be subjected to disruption of service due to the
   delay associated with the handover operation.  The performance
   requirements of a real-time application will vary based on the type
   of application and its characteristics such as delay and packet-loss
   tolerance.  For Voice over IP applications, ITU-T G.114 [ITU]
   recommends a steady-state end-to-end delay of 150 ms as the upper
   limit and rates 400 ms as generally unacceptable delay.  Similarly, a
   streaming application has tolerable packet-error rates ranging from
   0.1 to 0.00001 with a transfer delay of less than 300 ms.  Any help
   that an optimized handoff mechanism can provide toward meeting these
   objectives is useful.  The ultimate objective is to achieve seamless
   handover with low latency, even when handover is between different
   link technologies or between different Authentication, Authorization,
   and Accounting (AAA) realms.

   As a mobile device goes through a handover process, it is subjected
   to delay because of the rebinding of its association at or across
   several layers of the protocol stack and because of the additional
   round trips needed for a new EAP exchange.  Delays incurred within
   each protocol layer affect the ongoing multimedia application and
   data traffic within the client [WCM].

   The handover process often requires authentication and authorization
   for acquisition or modification of resources assigned to the mobile
   device.  In most cases, these authentications and authorizations
   require interaction with a central authority in a realm.  In some
   cases, the central authority may be distant from the mobile device.
   The delay introduced due to such an authentication and authorization
   procedure adds to the handover latency and consequently affects
   ongoing application sessions [MQ7].  The discussion in this document
   is focused on mitigating delay due to EAP authentication.

2.  Terminology

   AAA

      Authentication, Authorization, and Accounting (see below).  RADIUS
      [RFC2865] and Diameter [RFC3588] are examples of AAA protocols
      defined in the IETF.

   AAA realm
      The set of access networks within the scope of a specific AAA
      server.  Thus, if a mobile device moves from one attachment point
      to another within the same AAA realm, it continues to be served by
      the same AAA server.

   Accounting
      The act of collecting information on resource usage for the
      purpose of trend analysis, auditing, billing, or cost allocation
      [RFC2989].

   Attachment Point
      A device, such as a wireless access point, that serves as a
      gateway between access clients and a network.  In the context of
      this document, an attachment point must also support EAP
      authenticator functionality and may act as a AAA client.

   Authentication
      The act of verifying a claimed identity, in the form of a
      preexisting label from a mutually known name space, as the
      originator of a message (message authentication) or as the end-
      point of a channel (entity authentication) [RFC2989].

   Authenticator
      The end of the link initiating EAP authentication [RFC3748].

   Authorization
      The act of determining if a particular right, such as access to
      some resource, can be granted to the presenter of a particular
      credential [RFC2989].

   Candidate Access Network
      An access network that can potentially become the target access
      network for a mobile device.  Multiple access networks may be
      candidates simultaneously.

   Candidate Attachment Point (CAP)
      An attachment point that can potentially become the target
      attachment point for a mobile device.  Multiple attachment points
      may be candidates simultaneously.

   Candidate Authenticator (CA)
      The EAP authenticator on the CAP.

   EAP Server
      The entity that terminates the EAP authentication method with the
      peer [RFC3748].  EAP servers are often, but not necessarily,
      co-located with AAA servers, using a AAA protocol to communicate
      with remote pass-through authenticators.

   Inter-AAA-realm Handover (Inter-realm Handover)
      A handover across multiple AAA realms.

   Inter-Technology Handover
      A handover across different link-layer technologies.

   Intra-AAA-realm Handover (Intra-realm Handover)
      A handover within the same AAA realm.  Intra-AAA-realm handover
      includes a handover across different authenticators within the
      same AAA realm.

   Intra-Technology Handover
      A handover within the same link-layer technology.

   Master Session Key (MSK)
      Keying material that is derived between the EAP peer and server
      and exported by the EAP method [RFC3748].

   Peer
      The entity that responds to the authenticator and requires
      authentication [RFC3748].

   Serving Access Network
      An access network that is currently serving the mobile device.

   Serving Attachment Point (SAP)
      An attachment point that is currently serving the mobile device.

   Target Access Network
      An access network that has been selected to be the new serving
      access network for a mobile device.

   Target Attachment Point (TAP)
      An attachment point that has been selected to be the new SAP for a
      mobile device.

3.  Problem Statement

   The basic mechanism of handover is a two-step procedure involving

   o  handover preparation and

   o  handover execution

3.1.  Handover Preparation

   Handover preparation includes the discovery of candidate attachment
   points and selection of an appropriate target attachment point from
   the candidate set.  Handover preparation is outside the scope of this
   document.

3.2.  Handover Execution

   Handover execution consists of setting up Layer 2 (L2) and Layer 3
   (L3) connectivity with the TAP.  Currently, handover execution
   includes network access authentication and authorization performed
   directly with the target network; this may include full EAP
   authentication in the absence of any particular optimization for
   handover key management.  Following a successful EAP authentication,
   a secure association procedure is typically performed between the
   mobile device and the TAP to derive a new set of link-layer
   encryption keys from EAP keying material such as the MSK.  The
   handover latency introduced by full EAP authentication has proven to
   be higher than that which is acceptable for real-time application
   scenarios [MQ7]; hence, reduction in handover latency due to EAP is a
   necessary objective for such scenarios.

3.2.1.  Examples

3.2.1.1.  IEEE 802.11

   In IEEE 802.11 Wireless Local Area Networks (WLANs)
   [IEEE.802-11.2007] network access authentication and authorization
   involves performing a new IEEE 802.1X [IEEE.802-1X.2004] message
   exchange with the authenticator in the TAP to execute an EAP exchange
   with the authentication server [WPA].  There has been some
   optimization work undertaken by the IEEE, but these efforts have been
   scoped to IEEE link-layer technologies; for example, the work done in
   the IEEE 802.11f [IEEE.802-11F.2003] and 802.11r [IEEE.802-11R.2008]
   Task Groups applies only to intra-technology handovers.

3.2.1.2.  3GPP TS33.402

   The Third Generation Partnership Project (3GPP) Technical
   Specification 33.402 [TS33.402] defines the authentication and key
   management procedures performed during interworking between non-3GPP
   access networks and the Evolved Packet System (EPS).  Network access
   authentication and authorization happens after the L2 connection is
   established between the mobile device and a non-3GPP target access
   network, and involves an EAP exchange between the mobile device and
   the 3GPP AAA server via the non-3GPP target access network.  These
   procedures are not really independent of link technology, since they
   assume either that the authenticator lies in the EPS network or that
   separate authentications are performed in the access network and then
   in the EPS network.

3.3.  Solution Space

   As the examples in the preceding sections illustrate, a solution is
   needed to enable EAP early authentication for inter-AAA-realm
   handovers and inter-technology handovers.  A search for solutions at
   the IP level may offer the necessary technology independence.

   Optimized solutions for secure inter-authenticator handovers can be
   seen either as security context transfer (e.g., using the EAP
   Extensions for EAP Re-authentication Protocol (ERP)) [RFC5296], or as
   EAP early authentication.

3.3.1.  Context Transfer

   Security context transfer involves transfer of reusable key context
   to the TAP and can take two forms: horizontal and vertical.

   Horizontal security context transfer (e.g., from SAP to TAP) is not
   recommended because of the possibility that the compromise of one
   attachment point might lead to the compromise of another (the
   so-called domino effect, [RFC4962]).  Vertical context transfer is
   similar to the initial establishment of keying material on an
   attachment point in that the keys are sent from a trusted server to
   the TAP as a direct result of a successful authentication.  ERP
   specifies vertical context transfer using existing EAP keying
   material obtained from the home AAA server during the initial
   authentication.  A cryptographically independent re-authentication
   key is derived and transmitted to the TAP as a result of successful
   ERP authentication.  This reduces handover delay for intra-realm
   handovers by eliminating the need to run full EAP authentication with
   the home EAP server.

   However, in the case of inter-realm handover, either ERP is not
   applicable or an additional optimization mechanism is needed to
   establish a key on the TAP.

3.3.2.  Early Authentication

   In EAP early authentication, AAA-based authentication and
   authorization for a CAP is performed while ongoing data communication
   is in progress via the serving access network, the goal being to
   complete AAA signaling for EAP before the mobile device moves.  The
   applicability of EAP early authentication is limited to the scenarios
   where candidate authenticators can be discovered and an accurate
   prediction of movement can be easily made.  In addition, the
   effectiveness of EAP early authentication may be less significant for
   particular inter-technology-handover scenarios where simultaneous use
   of multiple technologies is not a major concern.

   There are also several AAA issues related to EAP early
   authentication, discussed in Section 8.

4.  System Overview

   Figure 1 shows the functional elements that are related to EAP early
   authentication.  These functional elements include a mobile device, a
   SAP, a CAP, and one or more AAA and EAP servers; for the sake of
   convenience, the AAA and EAP servers are represented as being
   co-located.  When the SAP and CAP belong to different AAA realms, the
   CAP may require a different set of user credentials than those used
   by the peer when authenticating to the SAP.  Alternatively, the CAP
   and the SAP may rely on the same AAA server, located in the home
   realm of the mobile device (MD).

         +------+      +-------+      +---------+      +---------+
         |  MD  |------|  SAP  |------|         |      |         |
         +------+      +-------+      |   IP    |      | EAP/AAA
            .                         |         |------|         |
            . Move                    | Network |      | Server  |
            v          +-------+      |         |      |         |
                       |  CAP  |------|         |      |         |
                       +-------+      +---------+      +---------+

          Figure 1: EAP Early Authentication Functional Elements

   A mobile device is attached to the serving access network.  Before
   the MD performs handover from the serving access network to a
   candidate access network, it performs EAP early authentication with a
   candidate authenticator via the serving access network.  The peer may
   perform EAP early authentication with one or more candidate
   authenticators.  It is assumed that each attachment point has an IP
   address.  It is assumed that there is at least one CAP in each
   candidate access network.  The serving and candidate access networks
   may use different link-layer technologies.

   Each authenticator is either a standalone authenticator or a pass-
   through authenticator [RFC3748].  When an authenticator acts as a
   standalone authenticator, it also has the functionality of an EAP
   server.  When an authenticator acts as a pass-through authenticator,
   it communicates with the EAP server, typically using a AAA transport
   protocol such as RADIUS [RFC2865] or Diameter [RFC3588].

   If the CAP uses an MSK [RFC5247] for generating lower-layer ciphering
   keys, EAP early authentication is used to proactively generate an MSK
   for the CAP.

5.  Topological Classification of Handover Scenarios

   The complexity of the authentication and authorization part of
   handover depends on whether it involves a change in EAP server.
   Consider first the case where the authenticators operate in pass-
   through mode, so that the EAP server is co-located with a AAA server.
   Then, there is a strict hierarchy of complexity, as follows:

   1.  inter-attachment-point handover with common AAA server: the CAP
       and SAP are different entities, but the AAA server is the same.
       There are two sub-cases here:

       (a)  the AAA server is common because both attachment points lie
            within the same network, or

       (b)  the AAA server is common because AAA entities in the serving
            and candidate networks proxy to a AAA server in the home
            realm.

   2.  inter-AAA-realm handover: the CAP and SAP are different entities,
       and the respective AAA servers also differ.  As a result,
       authentication in the candidate network requires a second set of
       user credentials.

   A third case is where one or both authenticators are co-located with
   an EAP server.  This has some of the characteristics of an inter-AAA-
   realm handover, but offers less flexibility for resolution of the
   early authentication problem.

   Orthogonally to this classification, one can distinguish intra-
   technology handover from inter-technology handover thinking of the
   link technologies involved.  In the inter-technology case, it is
   highly probable that the authenticators will differ.  The most likely
   cases are 1(b) or 2 in the above list.

6.  Models of Early Authentication

   As noted in Section 3, there are cases where early authentication is
   applicable while ERP does not work.  This section concentrates on
   providing some models around which we can build our analysis of the
   EAP early authentication problem.  Different usage models can be
   defined depending on whether

   o  the SAP is not involved in early authentication (direct pre-
      authentication usage model),

   o  the SAP interacts only with the CAP (indirect pre-authentication
      usage model), or

   o  the SAP interacts with the AAA server (the authenticated
      anticipatory keying usage model).

   It is assumed that the CAP and SAP are different entities.  It is
   further assumed in describing these models that there is no direct L2
   connectivity between the peer and the candidate attachment point.

6.1.  EAP Pre-Authentication Usage Models

   In the EAP pre-authentication model, the SAP does not interact with
   the AAA server directly.  Depending on how the SAP is involved in the
   pre-authentication signaling, the EAP pre-authentication usage model
   can be further categorized into the following two sub-models, direct
   and indirect.

6.1.1.  The Direct Pre-Authentication Model

   In this model, the SAP is not involved in the EAP exchange and only
   forwards the EAP pre-authentication traffic as it would any other
   data traffic.  The direct pre-authentication model is based on the
   assumption that the MD can discover candidate authenticators and
   establish direct IP communication with them.  It is applicable to any
   of the cases described in Section 5.

           Mobile          Candidate Attachment          AAA Server
           Device              Point(CAP)
       +-----------+    +-------------------------+    +------------+
       |           |    |        Candidate        |    |            |
       |   Peer    |    |      Authenticator      |    | EAP Server |
       |           |    |                         |    |            |
       +-----------+    +-------------------------+    +------------+
       | MD-CAP    |<-->| MD-CAP    | | CAP-AAA   |<-->| CAP-AAA    |
       | Signaling |    | Signaling | | Signaling |    | Signaling  |
       +-----------+    +-----------+ +-----------+    +------------+

              Figure 2: Direct Pre-Authentication Usage Model

   The direct pre-authentication signaling for the usage model is shown
   in Figure 3.

    Mobile             Serving             Candidate            AAA/EAP
    Device         Attachment Point      Authenticator          Server
                        (SAP)
      |                   |                    |                   |
      |                   |                    |                   |
      |     EAP over MD-CAP Signaling (L3)     |    EAP over AAA   |
      |<------------------+------------------->|<----------------->|
      |                   |                    |                   |
      |                   |                    |                   |

     Figure 3: Direct Pre-Authentication Signaling for the Usage Model

6.1.2.  The Indirect Pre-Authentication Usage Model

   The indirect pre-authentication usage model is illustrated in
   Figure 4.

    Mobile Device      Serving              Candidate          AAA
        (MD)       Attachment Point     Attachment Point      Server
                        (SAP)                 (CAP)
    +----------+                         +----------------+   +--------+
    |          |                         |                |   |        |
    | EAP Peer |                         |    Candidate   |   | EAP    |
    |          |                         |  Authenticator |   | Server |
    |          |                         |                |   |        |
    +----------+   +---------+-------+   +-------+--------+   +--------+
    |  MD-SAP  |<->| MD-SAP  |SAP-CAP|<->|SAP-CAP|CAP-AAA |<->|CAP-AAA |
    +----------+   +---------+-------+   +-------+--------+   +--------+

    {-----------------------------Signaling----------------------------}

             Figure 4: Indirect Pre-Authentication Usage Model

   In the indirect pre-authentication model, it is assumed that a trust
   relationship exists between the serving network (or serving AAA
   realm) and candidate network (or candidate AAA realm).  The SAP is
   involved in EAP pre-authentication signaling.  This pre-
   authentication model is needed if the peer cannot discover the
   candidate authenticators identity or if direct IP communication
   between the MD and CAP is not possible due to security or network
   topology issues.

   The role of the SAP in this pre-authentication model is to forward
   EAP pre-authentication signaling between the mobile device and CAP;
   the role of the CAP is to forward EAP pre-authentication signaling
   between the peer (via the SAP) and EAP server and receive the
   transported keying material.

   The pre-authentication signaling for this model is shown in Figure 5.

    Mobile             Serving              Candidate            AAA/EAP
    Device         Attachment Point     Attachment Point         Server
                        (SAP)                (CAP)
      |                   |                    |                   |
      |     EAP over      |       EAP over     |   EAP over AAA    |
      | MD-SAP Signaling  |  SAP-CAP Signaling |                   |
      |    (L2 or L3)     |        (L3)        |                   |
      |<----------------->|<------------------<|<----------------->|
      |                   |                    |                   |
      |                   |                    |                   |

    Figure 5: Indirect Pre-Authentication Signaling for the Usage Model

   In this model, the pre-authentication signaling path between a peer
   and a candidate authenticator consists of two segments: peer-to-SAP
   signaling (over L2 or L3) and SAP-to-CAP signaling over L3.

6.2.  The Authenticated Anticipatory Keying Usage Model

   In this model, it is assumed that there is no trust relationship
   between the SAP and the CAP, and the SAP is required to interact with
   the AAA server directly.  The authenticated anticipatory keying usage
   model is illustrated in Figure 6.

     Mobile            Serving               AAA Server      Candidate
     Device        Attachment Point                          Attachment
                        (SAP)                                Point (CAP)
   +---------+   +------------------+   +-----------------+  +--------+
   |         |   |                  |   |                 |  |        |
   |  Peer   |   |   Authenticator  |   |   EAP Server    |  |  AAA   |
   |         |   |                  |   |                 |  | Client |
   +---------+   +------------------+   +-----------------+  +--------+
   |  MD-SA  |<->|  MD-SAP |SAP-AAA |<->|SAP-AAA |CAP-AAA |<>|CAP-AAA |
   +---------+   +------------------+   +--------+--------+  +--------+
   {------------------------------Signaling---------------------------}

          Figure 6: Authenticated Anticipatory Keying Usage Model

   The SAP is involved in EAP authenticated anticipatory keying
   signaling.

   The role of the serving attachment point in this usage model is to
   communicate with the peer on one side and exchange authenticated
   anticipatory keying signaling with the EAP server on the other side.
   The role of the candidate authenticator is to receive the transported
   keying materials from the EAP server and to act as the serving
   attachment point after handover occurs.  The MD-SAP signaling is
   performed over L2 or L3; the SAP-AAA and AAA-CAP segments operate
   over L3.

7.  Architectural Considerations

   There are two architectural issues relating to early authentication:
   authenticator discovery and context binding.

7.1.  Authenticator Discovery

   In general, early authentication requires the identity of a candidate
   attachment point to be discovered by a peer, by a serving attachment
   point, or by some other entity prior to handover.  An attachment
   point discovery protocol is typically defined as a separate protocol

   from an early authentication protocol.  For example, the IEEE 802.21
   Information Service (IS) [IEEE.802-21] provides a link-layer-
   independent mechanism for obtaining neighboring network information
   by defining a set of Information Elements (IEs), where one of the IEs
   is defined to contain an IP address of an attachment point.  IEEE
   802.21 IS queries for such an IE may be used as a method for
   authenticator discovery.

   If IEEE 802.21 IS or a similar mechanism is used, authenticator
   discovery requires a database of information regarding the target
   network; the provisioning of a server with such a database is another
   issue.

7.2.  Context Binding

   When a candidate authenticator uses different EAP transport protocols
   for normal authentication and early authentication, a mechanism is
   needed to bind link-layer-independent context carried over early
   authentication signaling to the link-layer-specific context of the
   link to be established between the peer and the candidate
   authenticator.  The link-layer-independent context includes the
   identities of the peer and authenticator as well as the MSK.  The
   link-layer-specific context includes link-layer addresses of the peer
   and the candidate authenticator.  Such context binding can happen
   before or after the peer changes its point of attachment.

   There are at least two possible approaches to address the context
   binding issue.  The first approach is based on communicating the
   link-layer context as opaque data via early authentication signaling.
   The second approach is based on running EAP over the link layer of
   the candidate authenticator after the peer arrives at the
   authenticator, using short-term credentials generated via early
   authentication.  In this case, the short-term credentials are shared
   between the peer and the candidate authenticator.  In both
   approaches, context binding needs to be securely made between the
   peer and the candidate authenticator.  Also, the peer is not fully
   authorized by the candidate authenticator until the peer completes
   the link-layer-specific secure association procedure with the
   authenticator using link-layer signaling.

8.  AAA Issues

   Most of the AAA documents today do not distinguish between a normal
   authentication and an early authentication, and this creates a set of
   open issues:

   Early authentication authorization
      Users may not be allowed to have more than one logon session at
      the time.  This means that while such users actively engage in a
      session (as a result of a previously valid authentication), they
      will not be able to perform early authentication.  The AAA server
      currently has no way of distinguishing between a normal
      authentication request and an early authentication request.

   Early authentication lifetime
      Currently, AAA protocols define attributes carrying lifetime
      information for a normal authentication session.  Even when a user
      profile and the AAA server support early authentication, the
      lifetime for an early authentication session is typically valid
      only for a short amount of time because the peer has not completed
      its authentication at the target link layer.  It is currently not
      possible for a AAA server to indicate to the AAA client or a peer
      the lifetime of the early authenticated session unless AAA
      protocols are extended to carry early authentication session
      lifetime information.  In other words, it is not clear to the peer
      or the authenticator when the early authentication session will
      expire.

   Early authentication retries
      It is typically expected that, shortly following the early
      authentication process, the peer moves to the new point of
      attachment and converts the early authentication state to a normal
      authentication state (the procedure for which is not the topic of
      this particular subsection).  However, if the peer has not yet
      moved to the new location and realizes that the early
      authentication session is expiring, it may perform another early
      authentication.  Some limiting mechanism is needed to avoid an
      unlimited number of early authentication attempts.

   Completion of network attachment
      Once the peer has successfully attached to the new point of
      attachment, it needs to convert its authentication state from
      early authenticated to fully attached and authorized.  If the AAA
      server needs to differentiate between early authentication and
      normal authentication, there may need to be a mechanism within the
      AAA protocol to provide this indication to the AAA server.  This
      may be important from a billing perspective if the billing policy
      does not charge for an early authenticated peer until the peer is
      fully attached to the target authenticator.

   Session resumption
      In the case where the peer cycles between a network N1 with which
      it has fully authenticated and another network N2 and then back to
      N1, it should be possible to simply convert the fully

      authenticated state on N1 to an early authenticated state.  The
      problems around handling session lifetime and keying material
      caching need to be dealt with.

   Multiple candidate attachment points
      There may be situations where the peer needs to choose from a
      number of CAPs.  In such cases, it is desirable for the peer to
      perform early authentication with multiple candidate
      authenticators.  This amplifies the difficulties noted under the
      point "Early authentication authorization".

   Inter-AAA-realm handover support
      There may be situations where the peer moves out of the home AAA
      realm or across different visited AAA realms.  In such cases, the
      early authentication should be performed through the visited AAA
      realm with the AAA server in the home AAA realm.  It also requires
      AAA in the visited realm to acquire the identity information of
      the home AAA realms for routing the EAP early authentication
      traffic.  Knowledge of realm identities is required by both the
      peer and AAA to generate the early authentication key for mutual
      authentication between the peer and the visited AAA server.

   Inter-technology support
      Current specifications on early authentication mostly deal with
      homogeneous 802.11 networks.  AAA attributes such as Calling-
      Station-ID [RADEXT-WLAN] may need to be expanded to cover other
      access technologies.  Furthermore, inter-technology handovers may
      require a change of the peer identifier as part of the handover.
      Investigation on the best type of identifiers for peers that
      support multiple access technologies is required.

9.  Security Considerations

   This section specifically covers threats introduced to the EAP model
   by early authentication.  Security issues on general EAP and handover
   are described in other documents such as [RFC3748], [RFC4962],
   [RFC5169], and [RFC5247].

   Since early authentication, as described in this document, needs to
   work across multiple attachment points, any solution needs to
   consider the following security threats.

   First, a resource consumption denial-of-service attack is possible,
   where an attacker that is not on the same IP link as the legitimate
   peer or the candidate authenticator may send unprotected early
   authentication messages to the legitimate peer or the candidate
   authenticator.  As a result, the latter may spend computational and
   bandwidth resources on processing early authentication messages sent

   by the attacker.  This attack is possible in both the direct and
   indirect pre-authentication scenarios.  To mitigate this attack, the
   candidate network or authenticator may apply non-cryptographic packet
   filtering so that only early authentication messages received from a
   specific set of serving networks or authenticators are processed.  In
   addition, a simple solution for the peer side would be to let the
   peer always initiate EAP early authentication and not allow EAP early
   authentication initiation from an authenticator.

   Second, consideration for the channel binding problem described in
   [RFC5247] is needed as lack of channel binding may enable an
   authenticator to impersonate another authenticator or communicate
   incorrect information via out-of-band mechanisms (such as via a AAA
   or lower-layer protocol) [RFC3748].  It should be noted that it is
   relatively easier to launch such an impersonation attack for early
   authentication than normal authentication because an attacker does
   not need to be physically on the same link as the legitimate peer to
   send an early authentication trigger to the peer.

10.  Acknowledgments

   The editors would like to thank Preetida Vinayakray, Shubhranshu
   Singh, Ajay Rajkumar, Rafa Marin Lopez, Jong-Hyouk Lee, Maryna
   Komarova, Katrin Hoeper, Subir Das, Charles Clancy, Jari Arkko, and
   Bernard Aboba for their valuable input.

11.  Contributors

   The following people all contributed to this document: Alper E.
   Yegin, Tom Taylor, Srinivas Sreemanthula, Madjid Nakhjiri, Mahalingam
   Mani, and Ashutosh Dutta.

12.  References

12.1.  Normative References

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

   [RFC4962]  Housley, R. and B. Aboba, "Guidance for Authentication,
              Authorization, and Accounting (AAA) Key Management",
              BCP 132, RFC 4962, July 2007.

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

12.2.  Informative References

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W.  Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, June 2000.

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
              Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

   [RFC5169]  Clancy, T., Nakhjiri, M., Narayanan, V., and L.  Dondeti,
              "Handover Key Management and Re- Authentication Problem
              Statement", RFC 5169, March 2008.

   [RFC5296]  Narayanan, V. and L. Dondeti, "EAP Extensions for EAP
              Re-authentication Protocol (ERP)", RFC 5296, August 2008.

   [RADEXT-WLAN]
              Aboba, B., Malinen, J., Congdon, P., and J.  Salowey,
              "RADIUS Attributes for IEEE 802 Networks", Work
              in Progress, February 2010.

   [RFC2989]  Aboba, B., Calhoun, P., Glass, S., Hiller, T., McCann, P.,
              Shiino, H., Zorn, G., Dommety, G., C.Perkins, B.Patil,
              D.Mitton, S.Manning, M.Beadles, P.Walsh, X.Chen,
              S.Sivalingham, A.Hameed, M.Munson, S.Jacobs, B.Lim,
              B.Hirschman, R.Hsu, Y.Xu, E.Campell, S.Baba, and E.Jaques,
              "Criteria for Evaluating AAA Protocols for Network
              Access", RFC 2989, November 2000.

   [IEEE.802-1X.2004]
              Institute of Electrical and Electronics Engineers,
              "Port-Based Network Access Control", IEEE Standard 802.1X,
              2004.

   [IEEE.802-21]
              Institute of Electrical and Electronics Engineers,
              "Standard for Local and Metropolitan Area Networks: Media
              Independent Handover Services", IEEE Standard 802.21,
              2008.

   [IEEE.802-11.2007]
              Institute of Electrical and Electronics Engineers,
              "Information technology - Telecommunications and
              information exchange between systems - Local and
              metropolitan area networks - Specific requirements - Part
              11: Wireless LAN Medium Access Control (MAC) and Physical
              Layer (PHY) specifications", IEEE Standard 802.11, 2007.

   [IEEE.802-11R.2008]
              Institute of Electrical and Electronics Engineers,
              "Information technology - Telecommunications and
              information exchange between systems - Local and
              metropolitan area networks - Specific requirements - Part
              11: Wireless LAN Medium Access Control (MAC) and Physical
              Layer (PHY) specifications - Amendment 2: Fast BSS
              Transition", IEEE Standard 802.11R, 2008.

   [IEEE.802-11F.2003]
              Institute of Electrical and Electronics Engineers, "IEEE
              Trial-Use Recommended Practice for Multi-Vendor Access
              Point Interoperability via an Inter-Access Point Protocol
              Across Distribution Systems Supporting IEEE 802.11
              Operation", IEEE Recommendation 802.11F, 2003.

   [TS33.402] 3GPP, "System Architecture Evolution (SAE): Security
              aspects of non-3GPP accesses (Release 8)", 3GPP
              TS33.402 V8.3.1, 2009.

   [ITU]      ITU-T, "General Characteristics of International Telephone
              Connections and International Telephone Circuits: One-Way
              Transmission Time", ITU-T Recommendation G.114, 1998.

   [WPA]      The Wi-Fi Alliance, "WPA (Wi-Fi Protected Access)",
              Wi-Fi WPA v3.1, 2004.

   [MQ7]      Lopez, R., Dutta, A., Ohba, Y., Schulzrinne, H., and A.
              Skarmeta, "Network-layer Assisted Mechanism to Optimize
              Authentication Delay During Handoff in 802.11 Networks",
              The 4th Annual International Conference on Mobile and
              Ubiquitous Systems: Computing, Networking and
              Services (MOBIQUITOUS 2007), 2007.

   [WCM]      Dutta, A., Famorali, D., Das, S., Ohba, Y., and R. Lopez,
              "Media-independent pre-authentication supporting secure
              interdomain handover optimization", IEEE Wireless
              Communications Volume 15, Issue 2, April 2008.

Authors' Addresses

   Yoshihiro Ohba
   Toshiba Corporate Research and Development Center
   1 Komukai-Toshiba-cho
   Saiwai-ku, Kawasaki, Kanagawa,   212-8582
   Japan

   Phone: +81 44 549 2230
   EMail: yoshihiro.ohba@toshiba.co.jp

   Qin Wu (editor)
   Huawei Technologies Co., Ltd
   Huawei Nanjing R&D Center, Floor 1F, Software Avenue, No.101.,
   Yuhua District
   Nanjing, JiangSu  210012
   China

   Phone: +86 25 56622908
   EMail: sunseawq@huawei.com

   Glen Zorn (editor)
   Network Zen
   1463 East Republican Street
   Seattle, Washington  98112
   USA

   EMail: gwz@net-zen.net

 

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