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Internet Engineering Task Force (IETF)                           Y. OhbaRequest for Comments: 5836                                       ToshibaCategory: Informational                                       Q. Wu, Ed.ISSN: 2070-1721                                                   Huawei                                                            G. Zorn, Ed.                                                             Network Zen                                                              April 2010Extensible Authentication Protocol (EAP)Early Authentication Problem StatementAbstract   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; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc5836.Ohba, et al.                  Informational                     [Page 1]

RFC 5836                 Early Authentication PS              April 2010Copyright Notice   Copyright (c) 2010 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.   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   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Ohba, et al.                  Informational                     [Page 2]

RFC 5836                 Early Authentication PS              April 2010Table of Contents1. Introduction ....................................................32. Terminology .....................................................43. Problem Statement ...............................................63.1. Handover Preparation .......................................63.2. Handover Execution .........................................63.2.1. Examples ............................................73.3. Solution Space .............................................73.3.1. Context Transfer ....................................73.3.2. Early Authentication ................................84. System Overview .................................................85. Topological Classification of Handover Scenarios ................96. Models of Early Authentication .................................106.1. EAP Pre-Authentication Usage Models .......................106.1.1. The Direct Pre-Authentication Model ................116.1.2. The Indirect Pre-Authentication Usage Model ........116.2. The Authenticated Anticipatory Keying Usage Model .........137. Architectural Considerations ...................................137.1. Authenticator Discovery ...................................137.2. Context Binding ...........................................148. AAA Issues .....................................................149. Security Considerations ........................................1610. Acknowledgments ...............................................1711. Contributors ..................................................1712. References ....................................................1712.1. Normative References .....................................1712.2. Informative References ...................................181.  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.Ohba, et al.                  Informational                     [Page 3]

RFC 5836                 Early Authentication PS              April 2010   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].Ohba, et al.                  Informational                     [Page 4]

RFC 5836                 Early Authentication PS              April 2010   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].Ohba, et al.                  Informational                     [Page 5]

RFC 5836                 Early Authentication PS              April 2010   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 execution3.1.  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.Ohba, et al.                  Informational                     [Page 6]

RFC 5836                 Early Authentication PS              April 20103.2.1.  Examples3.2.1.1.  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.Ohba, et al.                  Informational                     [Page 7]

RFC 5836                 Early Authentication PS              April 2010   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 inSection 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).Ohba, et al.                  Informational                     [Page 8]

RFC 5836                 Early Authentication PS              April 2010         +------+      +-------+      +---------+      +---------+         |  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, orOhba, et al.                  Informational                     [Page 9]

RFC 5836                 Early Authentication PS              April 2010       (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 inSection 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.Ohba, et al.                  Informational                    [Page 10]

RFC 5836                 Early Authentication PS              April 20106.1.1.  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 inSection 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 Model6.1.2.  The Indirect Pre-Authentication Usage Model   The indirect pre-authentication usage model is illustrated in   Figure 4.Ohba, et al.                  Informational                    [Page 11]

RFC 5836                 Early Authentication PS              April 2010    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 ModelOhba, et al.                  Informational                    [Page 12]

RFC 5836                 Early Authentication PS              April 2010   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 protocolOhba, et al.                  Informational                    [Page 13]

RFC 5836                 Early Authentication PS              April 2010   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:Ohba, et al.                  Informational                    [Page 14]

RFC 5836                 Early Authentication PS              April 2010   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 fullyOhba, et al.                  Informational                    [Page 15]

RFC 5836                 Early Authentication PS              April 2010      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 sentOhba, et al.                  Informational                    [Page 16]

RFC 5836                 Early Authentication PS              April 2010   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.  References12.1.  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.Ohba, et al.                  Informational                    [Page 17]

RFC 5836                 Early Authentication PS              April 201012.2.  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.Ohba, et al.                  Informational                    [Page 18]

RFC 5836                 Early Authentication PS              April 2010   [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.Ohba, et al.                  Informational                    [Page 19]

RFC 5836                 Early Authentication PS              April 2010Authors' 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.netOhba, et al.                  Informational                    [Page 20]