


Network Working Group                                       G. Zorn, Ed.
Internet-Draft                                               Network Zen
Intended status: Informational                                     Q. Wu
Expires: July 16, 2012                                         T. Taylor
                                                                  Huawei
                                                                  Y. Nir
                                                             Check Point
                                                               K. Hoeper
                                                                Motorola
                                                              S. Decugis
                                                           INSIDE Secure
                                                        January 13, 2012


              Handover Keying (HOKEY) Architecture Design
                    draft-ietf-hokey-arch-design-11

Abstract

   The Handover Keying (HOKEY) Working Group seeks to minimize handover
   delay due to authentication when a peer moves from one point of
   attachment to another.  Work has progressed on two different
   approaches to reduce handover delay: early authentication (so that
   authentication does not need to be performed during handover), and
   reuse of cryptographic material generated during an initial
   authentication to save time during re-authentication.  A basic
   assumption is that the mobile host or "peer" is initially
   authenticated using the Extensible Authentication Protocol (EAP),
   executed between the peer and an EAP server as defined in RFC 3748.

   This document defines the HOKEY architecture.  Specifically, it
   describes design objectives, the functional environment within which
   handover keying operates, the functions to be performed by the HOKEY
   architecture itself, and the assignment of those functions to
   architectural components.  It goes on to illustrate the operation of
   the architecture within various deployment scenarios that are
   described more fully in other documents produced by the HOKEY Working
   Group.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Design Goals . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  Reducing Signaling Overhead  . . . . . . . . . . . . . . .  7
       3.1.1.  Minimized Communications with Home Servers . . . . . .  7
       3.1.2.  Minimized User Interaction for Authentication  . . . .  7
     3.2.  Integrated Local Domain Name (LDN) Discovery . . . . . . .  7
     3.3.  Fault-tolerant re-authentication . . . . . . . . . . . . .  8
     3.4.  Improved Deployment Scalability  . . . . . . . . . . . . .  8
   4.  Required Functionality . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Authentication Subsystem Functional Overview . . . . . . .  8
     4.2.  Pre-Authentication Function (Direct or Indirect) . . . . .  9
     4.3.  EAP Re-authentication Function . . . . . . . . . . . . . .  9
     4.4.  EAP Authentication Function  . . . . . . . . . . . . . . . 10
     4.5.  Authenticated Anticipatory Keying (AAK) Function . . . . . 10
     4.6.  Management of EAP-Based Handover Keys  . . . . . . . . . . 10
   5.  Components of the HOKEY Architecture . . . . . . . . . . . . . 10
     5.1.  Functions of the Peer  . . . . . . . . . . . . . . . . . . 11
     5.2.  Functions of the Serving Authenticator . . . . . . . . . . 12
     5.3.  Functions of the Candidate Authenticator . . . . . . . . . 13
     5.4.  Functions of the EAP Server  . . . . . . . . . . . . . . . 13
     5.5.  Functions of the ER Server . . . . . . . . . . . . . . . . 14
   6.  Usage Scenarios  . . . . . . . . . . . . . . . . . . . . . . . 15
     6.1.  Simple Re-authentication . . . . . . . . . . . . . . . . . 15
     6.2.  Intra-domain Handover  . . . . . . . . . . . . . . . . . . 15
     6.3.  Inter-domain handover  . . . . . . . . . . . . . . . . . . 16
     6.4.  Inter-technology handover  . . . . . . . . . . . . . . . . 16
   7.  AAA Considerations . . . . . . . . . . . . . . . . . . . . . . 16
     7.1.  Authorization  . . . . . . . . . . . . . . . . . . . . . . 16
     7.2.  Transport Aspect . . . . . . . . . . . . . . . . . . . . . 17
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 17
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     11.2. Informative References . . . . . . . . . . . . . . . . . . 18
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19












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1.  Introduction

   The Extensible Authentication Protocol (EAP) [RFC3748] is an
   authentication framework that supports different types of
   authentication methods.  Originally designed for dial-up connections,
   EAP is now commonly used for authentication in in a variety of access
   networks.

   When a host (or "peer", the term used from this point onward) changes
   its point of attachment to the network, it must be re-authenticated.
   If a full EAP authentication must be repeated, several message round-
   trips between the peer and the home EAP server may be involved.  The
   resulting delay will result in degradation or in the worst case loss
   of any service session in progress if communication is suspended
   while re-authentication is carried out.  The delay is worse if the
   new point of attachment is in a visited network rather than the
   peer's home network, because of the extra procedural steps involved
   as well as because of the probable increase in round-trip time.

   RFC 5169 [RFC5169] describes this problem more fully and establishes
   design goals for solutions to reduce re-authentication delay for
   transfers within a single administrative domain.  It also suggests a
   number of ways to achieve a solution:

   o  specification of a method-independent, efficient, re-
      authentication protocol based upon EAP;

   o  reuse of keying material from the initial EAP authentication;

   o  deployment of re-authentication servers local to the peer to
      reduce round-trip delay; and

   o  specification of the additional protocol needed to allow the EAP
      server to pass authentication information to the local re-
      authentication servers.

   RFC 5295 [RFC5295] tackles the problem of reuse of keying material by
   specifying how to derive a hierarchy of cryptographically independent
   purpose-specific keys from the results of the original EAP
   authentication, while Wu, et al.  [I-D.ietf-hokey-rfc5296bis]
   specifies a method-independent re-authentication protocol (ERP)
   applicable to two specific deployment scenarios:

   o  where the peer's home EAP server also performs re-authentication;
      and

   o  where a local re-authentication server exists but is collocated
      with a AAA proxy within the domain.



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   Other work provides further pieces of the solution or insight into
   the problem.  For the purpose of this memo, RFC 5749 [RFC5749]
   provides an abstract mechanism for distribution of keying material
   from the EAP server to re-authentication servers.  RFC 5836 [RFC5836]
   contrasts the EAP re-authentication (ER) strategy provided by ERP
   with an alternative strategy called "early authentication".  RFC 5836
   defines EAP early authentication as the use of EAP by a mobile peer
   to establish authenticated keying material on a target attachment
   point prior to its arrival.  Hence, the goal of EAP early
   authentication is to complete all EAP-related communications,
   including AAA signaling, in preparation for the handover, before the
   mobile device actually moves.  Early authentication includes direct
   and indirect pre-authentication as well as Authenticated Anticipatory
   Keying (AAK).  All three early authentication mechanisms provide
   means to securely establish authenticated keying material on a
   Candidate Access Point (CAP) while still being connected to the
   Serving Access Point (SAP) but vary in their respective system
   assumptions and communication paths.  In particular, direct pre-
   authentication assumes that clients are capable of discovering
   candidate access points and all communications are routed through the
   serving access point.  On the other hand, indirect pre-authentication
   assumes an existing relationship between SAP and CAP, whereas the
   discovery and selection of Candidate Access Points is outside the
   scope of AAK.  Furthermore, both direct and indirect pre-
   authentication require a full EAP execution to occur before the
   handover of the peer takes place, while AAK (like ERP
   [I-D.ietf-hokey-rfc5296bis]) uses keys derived from the initial EAP
   authentication.

   Both EAP re-authentication and early authentication enable faster
   inter-authenticator handovers.  However, it is currently unclear how
   the necessary handover infrastructure can be deployed and integrated
   into existing EAP infrastructures.  In particular, previous work has
   not described how ER servers that act as endpoints in the re-
   authentication process should be integrated into local and home
   domain networks.  Furthermore, it is currently unspecified how EAP
   infrastructure can support the timely triggering of early
   authentications and aid with the selection of candidate access
   points.

   This document proposes a general HOKEY architecture and demonstrates
   how it can be adapted to different deployment scenarios.  To begin
   with, Section 3 recalls the design objectives for the HOKEY
   architecture.  Section 4 reviews the functions that must be supported
   within the architecture.  Section 5 describes the components of the
   HOKEY architecture.  Section 6 describes the different deployment
   scenarios that the HOKEY Working Group has addressed and the
   information flows that must occur within those scenarios, by



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   reference to the documents summarized above where possible and
   otherwise within this document itself.  Finally, Section 7 provides
   an analysis of how AAA protocols can be applied in the HOKEY
   architecture.


2.  Terminology

   This document contains no normative language, hence [RFC2119]
   language does not apply.

   This document reuses terms defined in Section 2.2 of Ohba, et al.
   [RFC5836] and Section 2 of Wu, et al.  [I-D.ietf-hokey-rfc5296bis].
   In addition, it defines the following:

   DSrRK
      Domain-Specific reauthentication Root Key.

   EAP Early Authentication
      The use of EAP by a mobile peer to establish authenticated keying
      material on a target attachment point prior to its arrival, see
      Ohba, et al.  [RFC5836].

   ER Key Management
      An instantiation of the mechanism described in Hoeper, et al.
      [RFC5749] for creating and delivering root keys from an EAP server
      to an ER server.

   EAP Re-authentication (ER)
      The use of keying material derived from an initial EAP
      authentication to enable single-roundtrip re-authentication of a
      mobile peer.  For a detailed description of the keying material
      see Section 4 of Wu, et al.  [I-D.ietf-hokey-rfc5296bis].

   ER Server
      A component of the HOKEY architecture that terminates the EAP re-
      authentication exchange with the peer.


3.  Design Goals

   This section investigates the design goals for the HOKEY
   architecture.  These include reducing the signaling overhead for re-
   authentication and early authentication, integrating local domain
   name discovery, enabling fault-tolerant re-authentication and
   improving deployment scalability.  These goals supplement those
   discussed in Section 4 of RFC 5169 [RFC5169].  Note that the
   identification and selection of Candidate Access Points is not a goal



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   of the architecture, since those operations are generally specific to
   the lower layer in use.

3.1.  Reducing Signaling Overhead

3.1.1.  Minimized Communications with Home Servers

   ERP [I-D.ietf-hokey-rfc5296bis] requires only one round trip;
   however, this roundtrip may require communication between a peer and
   its home ER and/or home AAA server in explicit bootstrapping and
   communication between local servers and home server in implicit
   bootstrapping even if the peer is currently attached to a visited
   (local) network.  As a result, even this one round trip may introduce
   long delays because the home ER and home AAA servers may be distant
   from the peer and the network to which it is attached.  To lower
   signaling overhead, communication with the home ER server and home
   AAA server should be minimized.  Ideally, a peer should only need to
   communicate with local servers and other local entities.

3.1.2.  Minimized User Interaction for Authentication

   When the peer is initially attached to the network or moves between
   heterogeneous networks, full EAP authentication between the peer and
   EAP server occurs and user interaction may be needed, e.g., a dialog
   to prompt the user for credentials.  To reduce latency, user
   interaction for authentication at each handover should be minimized.
   Ideally, user involvement should take place only during initial
   authentication and subsequent re-authentication should occur
   transparently.

3.2.  Integrated Local Domain Name (LDN) Discovery

   ERP bootstrapping must occur before (implicit) or during (explicit) a
   handover to transport the necessary keys to the local ER server
   involved.  Implicit bootstrapping is preferable because it does not
   require communication with the home ER server during handover, but it
   requires the peer to know the domain name of the ER server before the
   subsequent local ERP exchange happens in order to derive the
   necessary re-authentication keying material.  ERP
   [I-D.ietf-hokey-rfc5296bis] does not specify such a domain name
   discovery mechanism and suggests that the peer may learn the domain
   name through the EAP-Initiate/ Re-auth-Start message or via lower-
   layer announcements.  However, domain name discovery happens after
   the implicit bootstrapping completes, which may introduce extra
   latency.  To allow more efficient handovers, a HOKEY architecture
   should support an efficient domain name discovery mechanism (for
   example, see Zorn, Wu & Wang [RFC6440]) and allow its integration
   with ERP implicit bootstrapping.  Even in the case of explicit



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   bootstrapping, local domain name discovery should be optimized such
   that it does not require contacting the home AAA server, as is
   currently the case.

3.3.  Fault-tolerant re-authentication

   If all authentication services depend upon a remote server, a network
   partition can result in the denial of service to valid users.
   However, if for example an ER server exists in the local network,
   previously authenticated users can re-authenticate even though a link
   to the home or main authentication server doesn't exist.

3.4.  Improved Deployment Scalability

   To provide better deployment scalability, there should be no
   requirement for the co-location of entities proving handover keying
   services (e.g., ER servers) and AAA servers or proxies.  Separation
   of these entities may cause problems with routing, but allows greater
   flexibility in deployment and implementation.


4.  Required Functionality

4.1.  Authentication Subsystem Functional Overview

   The operation of the authentication subsystem provided by HOKEY also
   depends on the availability of a number of discovery functions:

   o  discovery of candidate access points, by the peer, by the serving
      attachment point, or by some other entity;

   o  discovery of the authentication services supported at a given
      candidate access point;

   o  discovery of the required server in the home domain when a
      candidate access point is not in the same domain as the serving
      attachment point, or no local server is available;

   o  peer discovery of the local domain name (LDN) when EAP re-
      authentication is used with a local server.

   It is assumed that these functions are provided by the environment
   within which the authentication subsystem operates, and are outside
   the scope of the authentication subsystem itself.  Local domain name
   discovery is a possible exception.

   The major functions comprising the authentication subsystem and their
   inter-dependencies are discussed in greater detail below.



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   o  When AAA is invoked to authorize network access, it uses one of
      two services offered by the authentication subsystem: full EAP
      authentication, or EAP re-authentication.  Note that although AAA
      may perform authentication directly in some cases, when EAP is
      utilized AAA functions only as a transport for EAP messages and
      the encryption keys (if any) resulting from successful EAP
      authentication.

   o  Pre-authentication triggers AAA network access authorization at
      each candidate access point, which in turn causes full EAP
      authentication to be invoked.

   o  EAP re-authentication invokes ER key management at the time of
      authentication to create and distribute keying material to ER
      servers.

   o  Authenticated anticipatory keying (AAK) relies on ER key
      management to establish keying material on ER/AAK servers, but
      uses an extension to ER key management to derive and establish
      keying material on candidate authenticators.  AAK uses an
      extension to EAP re-authentication to communicate with ER/AAK
      servers.

   EAP authentication, EAP re-authentication, and handover key
   distribution depend on the routing and secure transport service
   provided by AAA.  Discovery functions and the function of
   authentication and authorization of network entities (access points,
   ER servers) are not shown.  As stated above, these are external to
   the authentication subsystem.

4.2.  Pre-Authentication Function (Direct or Indirect)

   The pre-authentication function is responsible for discovery of
   candidate access points and completion of network access
   authentication and authorization at each candidate access point in
   advance of handover.  The operation of this function is described in
   general terms in Ohba, et al.  [RFC5836].  No document is yet
   available to describe the implementation of pre-authentication in
   terms of specific protocols; Pre-Authentication Support for PANA
   [RFC5873] could be part of the solution.

4.3.  EAP Re-authentication Function

   The EAP re-authentication function is responsible for authenticating
   the peer at a specific access point using keying material derived
   from a prior full EAP authentication.  RFC 5169 [RFC5169] provides
   the design objectives for an implementation of this function.  ERP
   [I-D.ietf-hokey-rfc5296bis] describes a protocol to implement EAP re-



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   authentication.

4.4.  EAP Authentication Function

   The EAP authentication function is responsible for authenticating the
   peer at a specific access point using a full EAP exchange.  Aboba, et
   al.  [RFC3748] defines the associated protocol, while Ohba, et al.
   [RFC5836] describe the use of EAP as part of pre-authentication.
   Note that the HOKEY Working Group has not specified the non-AAA
   protocol required to transport EAP frames over IP that is shown in
   Figures 3 and 5 of Ohba, et al.  [RFC5836], although PANA [RFC5873]
   is a candidate.

4.5.  Authenticated Anticipatory Keying (AAK) Function

   The authenticated anticipatory keying function is responsible for
   pre-placing keying material derived from an initial full EAP
   authentication on candidate access points.  The operation is carried
   out in two steps: ER key management (with trigger not currently
   specified) places root keys derived from initial EAP authentication
   onto an ER/AAK server associated with the peer.  When requested by
   the peer, the ER/AAK server derives and pushes predefined master
   session keys to one or more candidate access points.  The operation
   of the authenticated anticipatory keying function is described in
   very general terms in Ohba, et al.  [RFC5836].  A protocol
   specification exists (see Cao, et al.  [I-D.ietf-hokey-erp-aak]).

4.6.  Management of EAP-Based Handover Keys

   Handover key management consists of EAP method independent key
   derivation and distribution and comprises the following specific
   functions:

   o  handover key derivation; and

   o  handover key distribution.

   The derivation of handover keys is specified in Salowey, et al.
   [RFC5295], and AAA-based key distribution is specified in Hoeper,
   Nakhjiri & Ohba [RFC5749].


5.  Components of the HOKEY Architecture

   This section describes the components of the HOKEY architecture in
   terms of the functions they perform.  The components cooperate as
   described in this section to carry out the functions described in the
   previous section.  Section 6 describes the different deployment



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   scenarios that are possible using these functions.

   The components of the HOKEY architecture are as follows:

   o  the peer;

   o  the authenticator, which is a part of the serving access point and
      candidate access points;

   o  the EAP server; and

   o  the ER server, and

   o  the ER/AAK server , [I-D.ietf-hokey-erp-aak] either in the home
      domain or local to the authenticator.

5.1.  Functions of the Peer

   The peer participates in the functions described in Section 4 as
   shown in Table 1.

   +--------------------+----------------------------------------------+
   | Function           | Peer Role                                    |
   +--------------------+----------------------------------------------+
   | EAP authentication | Determines that full EAP authentication is   |
   |                    | needed based on context (e.g., initial       |
   |                    | authentication), prompting from the          |
   |                    | authenticator, or discovery that only EAP    |
   |                    | authentication is supported.  Participates   |
   |                    | in the EAP exchange with the EAP server.     |
   | -                  | -                                            |
   | Direct             | Discovers candidate access points.           |
   | pre-authentication | Initiates pre-authentication with each,      |
   |                    | followed by EAP authentication as above, but |
   |                    | using IP rather than L2 transport for the    |
   |                    | EAP frames.                                  |
   | -                  | -                                            |
   | Indirect           | Enters into a full EAP exchange when         |
   | pre-authentication | triggered, using either L2 or L3 transport   |
   |                    | for the frames.                              |
   | -                  | -                                            |
   | EAP                | Determines that EAP re-authentication is     |
   | re-authentication  | possible based on discovery or authenticator |
   |                    | prompting.  Participates in ERP exchange     |
   |                    | with ER server.                              |
   | -                  | -                                            |





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   | Authenticated      | Determines that AAK is possible based on     |
   | anticipatory       | discovery or serving authenticator           |
   | keying             | prompting.  Discovers candidate access       |
   |                    | points.  Participates in ERP/AAK exchange,   |
   |                    | requesting distribution of keying material   |
   |                    | to the candidate access points.              |
   | -                  | -                                            |
   | ER key management  | No role.                                     |
   +--------------------+----------------------------------------------+

                      Table 1: Functions of the Peer

5.2.  Functions of the Serving Authenticator

   The serving authenticator participates in the functions described in
   Section 4 as shown in Table 2.

   +--------------------+----------------------------------------------+
   | Function           | Serving Authenticator Role                   |
   +--------------------+----------------------------------------------+
   | EAP authentication | No role.                                     |
   | -                  | -                                            |
   | Direct             | No role.                                     |
   | pre-authentication |                                              |
   | -                  | -                                            |
   | Indirect           | Discovers candidate access points.           |
   | pre-authentication | Initiates an EAP exchange between the peer   |
   |                    | and the EAP server through each candidate    |
   |                    | authenticator.  Mediates between L2          |
   |                    | transport of EAP frames on the peer side and |
   |                    | a non-AAA protocol over IP toward the        |
   |                    | candidate access point.                      |
   | -                  | -                                            |
   | EAP                | No role.                                     |
   | re-authentication  |                                              |
   | -                  | -                                            |
   | Authenticated      | Mediates between L2 transport of AAK frames  |
   | anticipatory       | on the peer side and AAA transport toward    |
   | keying             | the ER/AAK server.                           |
   | -                  | -                                            |
   | ER key management  | No role.                                     |
   +--------------------+----------------------------------------------+

              Table 2: Functions of the Serving Authenticator







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5.3.  Functions of the Candidate Authenticator

   The candidate authenticator participates in the functions described
   in Section 4 as shown in Table 3.

   +--------------------+----------------------------------------------+
   | Function           | Candidate Authenticator Role                 |
   +--------------------+----------------------------------------------+
   | EAP authentication | Invokes AAA network access authentication    |
   |                    | and authorization upon handover/initial      |
   |                    | attachment.  Mediates between L2 transport   |
   |                    | of EAP frames on the peer link and AAA       |
   |                    | transport toward the EAP server.             |
   | -                  | -                                            |
   | Direct             | Invokes AAA network access authentication    |
   | pre-authentication | and authorization when the peer initiates    |
   |                    | authentication.  Mediates between non-AAA L3 |
   |                    | transport of EAP frames on the peer side and |
   |                    | AAA transport toward the EAP server.         |
   | -                  | -                                            |
   | Indirect           | Same as direct pre-authentication, except    |
   | pre-authentication | that it communicates with the serving        |
   |                    | authenticator rather than the peer.          |
   | -                  | -                                            |
   | EAP                | Invokes AAA network access authentication    |
   | re-authentication  | and authorization upon handover.  Discovers  |
   |                    | or is configured with the address of the ER  |
   |                    | server.  Mediates between L2 transport of a  |
   |                    | ERP frames on the peer side and AAA          |
   |                    | transport toward the ER server.              |
   | -                  | -                                            |
   | Authenticated      | Receives and saves pMSK.                     |
   | anticipatory       |                                              |
   | keying             |                                              |
   | -                  | -                                            |
   | ER key management  | No role.                                     |
   +--------------------+----------------------------------------------+

             Table 3: Functions of the Candidate Authenticator

5.4.  Functions of the EAP Server

   The EAP server participates in the functions described in Section 4
   as shown in Table 4.







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   +--------------------+----------------------------------------------+
   | Function           | EAP Server Role                              |
   +--------------------+----------------------------------------------+
   | EAP authentication | Terminates EAP signaling between it and the  |
   |                    | peer via the candidate authenticator.        |
   |                    | Determines whether network access            |
   |                    | authentication succeeds or fails.  Provides  |
   |                    | MSK to authenticator (via AAA).              |
   | -                  | -                                            |
   | Direct             | As for EAP authentication.                   |
   | pre-authentication |                                              |
   | -                  | -                                            |
   | Indirect           | As for EAP authentication.                   |
   | pre-authentication |                                              |
   | -                  | -                                            |
   | EAP                | Provides rRK or DSrRK to the ER server (via  |
   | re-authentication  | AAA).                                        |
   | -                  | -                                            |
   | Authenticated      | As for EAP re-authentication.                |
   | anticipatory       |                                              |
   | keying             |                                              |
   | -                  | -                                            |
   | ER key management  | Creates rRK or DSrRK and distributes it to   |
   |                    | ER server requesting the information.        |
   +--------------------+----------------------------------------------+

                   Table 4: Functions of the EAP Server

5.5.  Functions of the ER Server

   The ER server participates in the functions described in Section 4 as
   shown in Table 5.



















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   +--------------------+----------------------------------------------+
   | Function           | ER Server Role                               |
   +--------------------+----------------------------------------------+
   | EAP authentication | No role.                                     |
   | -                  | -                                            |
   | Direct             | No role.                                     |
   | pre-authentication |                                              |
   | -                  | -                                            |
   | Indirect           | No role.                                     |
   | pre-authentication |                                              |
   | -                  | -                                            |
   | EAP                | Acquires rRK or DSrRK as applicable when     |
   | re-authentication  | necessary.  Terminates ERP signaling between |
   |                    | it and the peer via the candidate            |
   |                    | authenticator.  Determines whether network   |
   |                    | access authentication succeeds or fails.     |
   |                    | Provides MSK to authenticator.               |
   | -                  | -                                            |
   | Authenticated      | And acquires rRK or DSrRK as applicable when |
   | anticipatory       | necessary.  Derives pMSKs and passes them to |
   | keying             | the candidate access points.                 |
   | -                  | -                                            |
   | ER key management  | Receives and saves rRK or DSrRK as           |
   |                    | applicable.                                  |
   +--------------------+----------------------------------------------+

                    Table 5: Functions of the ER Server


6.  Usage Scenarios

   Depending upon whether it involves a change in a domain or access
   technology, we have the following the usage scenarios.

6.1.  Simple Re-authentication

   The peer remains stationary and re-authenticates to the original
   access point.  Note that in this case, the SAP takes the role of the
   CAP in the discussion above.

6.2.  Intra-domain Handover

   The peer moves between two authenticators in the same domain.  In
   this scenario, the peer communicates with the ER server via the ER
   authenticator within the same network.






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6.3.  Inter-domain handover

   The peer moves between two different domains.  In this scenario, the
   peer communicates with more than one ER server via one or two
   different ER authenticators.  One ER server is located in the current
   network as the peer, one is located in the previous network from
   which the peer moves.  Another ER server is located in the home
   network to which the peer belongs.

6.4.  Inter-technology handover

   The peer moves between two heterogeneous networks.  In this scenario,
   the peer needs to support at least two access technologies.  The
   coverage of two access technologies usually is overlapped during
   handover.  In this case, only authentication corresponding to intra-
   domain handover is required, i.e., the peer can communicate with the
   same local ER server to complete authentication and obtain keying
   materials corresponding to the peer.


7.  AAA Considerations

   This section provides an analysis of how the AAA protocol can be
   applied in the hokey architecture in accordance with the
   Authentication Subsystem Functional Overview (see Section 4.1)

7.1.  Authorization

   Authorization is a major issue in deployments.  Wherever the peer
   moves around, the home AAA server provides authorization for the peer
   during its handover.  However, it is unnecessary to couple
   authorization with authentication at every handover, since
   authorization is only needed when the peer is initially attached to
   the network or moves between two different AAA domains.  The EAP key
   management document [RFC5247] discusses several vulnerabilities that
   are common to handover mechanisms.  One important issue arises from
   the way the authorization decisions which might be handled at the AAA
   server during network access authentication.  For example, if AAA
   proxies are involved, they may also influence in the authorization
   decision.  Furthermore, the reasons for choosing a particular
   decision are not communicated to the AAA clients.  In fact, the AAA
   client only knows the final authorization result.  Another issue
   regards session management.  In some circumstances when the peer
   moves from one authenticator to another, the peer may be
   authenticated by the different authenticator during a period of time
   and the authenticator to which the peer is currently attached needs
   to create a new AAA user session, however the AAA server should not
   view these handoffs as different sessions.  Otherwise this may affect



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   user experience and also cause accounting or logging issues.  For
   example, session ID creation, in most cases, is done by each
   authenticator to which the peer attaches.  In this sense, the new
   authenticator acting as AAA client needs to create a new AAA user
   session from scratch which forces its corresponding AAA Server to
   terminate the existing user session with previous authenticator and
   setup a new user session with the new authenticator.  This may
   complicate the set up and maintenance of the AAA user session.

7.2.  Transport Aspect

   The existing AAA protocols can be used to carry EAP messages and ERP
   messages between the AAA server and AAA clients.  AAA transport of
   ERP messages is specified in Hoeper, Nakhjiri & Ohba [RFC5749] and
   Bournelle, et al.  [I-D.ietf-dime-erp].  AAA transport of EAP
   messages is specified in [RFC4072].  Key transport also can be
   performed through a AAA protocol.  Zorn, Wu & Cakulev
   [I-D.ietf-dime-local-keytran] specifies a set of Attribute-Value
   Pairs (AVPs) providing native Diameter support of cryptographic key
   delivery.


8.  IANA Considerations

   This document does not require any actions by IANA.


9.  Security Considerations

   This note does not introduce any new security vulnerabilities.


10.  Acknowledgments

   The authors would like to thank Mark Jones, Zhen Cao, Semyon
   Mizikovsky, Stephen Farrell, Ondrej Sury, Richard Barnes, Jari Arkko
   and Lionel Morand for their reviews and comments.


11.  References

11.1.  Normative References

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

   [RFC5836]  Ohba, Y., Wu, Q., and G. Zorn, "Extensible Authentication



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              Protocol (EAP) Early Authentication Problem Statement",
              RFC 5836, April 2010.

   [I-D.ietf-hokey-rfc5296bis]
              Wu, W., Cao, Z., Zorn, G., Shi, Y., and B. He, "EAP
              Extensions for EAP Re-authentication Protocol (ERP)",
              draft-ietf-hokey-rfc5296bis-06 (work in progress),
              November 2011.

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

11.2.  Informative References

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

   [RFC5295]  Salowey, J., Dondeti, L., Narayanan, V., and M. Nakhjiri,
              "Specification for the Derivation of Root Keys from an
              Extended Master Session Key (EMSK)", RFC 5295,
              August 2008.

   [RFC5749]  Hoeper, K., Nakhjiri, M., and Y. Ohba, "Distribution of
              EAP-Based Keys for Handover and Re-Authentication",
              RFC 5749, March 2010.

   [RFC5873]  Ohba, Y. and A. Yegin, "Pre-Authentication Support for the
              Protocol for Carrying Authentication for Network Access
              (PANA)", RFC 5873, May 2010.

   [RFC6440]  Zorn, G., Wu, Q., and Y. Wang, "The EAP Re-authentication
              Protocol (ERP) Local Domain Name DHCPv6 Option", RFC 6440,
              December 2011.

   [I-D.ietf-hokey-erp-aak]
              Cao, Z., Deng, H., Wang, Y., Wu, Q., and G. Zorn, "EAP Re-
              authentication Protocol Extensions for Authenticated
              Anticipatory Keying (ERP/AAK)",
              draft-ietf-hokey-erp-aak-06 (work in progress),
              October 2011.

   [I-D.ietf-dime-erp]
              Bournelle, J., Morand, L., Decugis, S., Wu, W., and G.
              Zorn, "Diameter support for EAP Re-authentication Protocol
              (ERP)", draft-ietf-dime-erp-07 (work in progress),
              September 2011.




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   [I-D.ietf-dime-local-keytran]
              Zorn, G., Wu, W., and V. Cakulev, "Diameter Attribute-
              Value Pairs for Cryptographic Key Transport",
              draft-ietf-dime-local-keytran-14 (work in progress),
              August 2011.

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

   [RFC4072]  Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
              Authentication Protocol (EAP) Application", RFC 4072,
              August 2005.


Authors' Addresses

   Glen Zorn (editor)
   Network Zen
   227/358 Thanon Sanphawut
   Bang Na, Bangkok  10260
   Thailand

   Phone: +66 (0) 87-0404617
   Email: glenzorn@gmail.com


   Qin Wu
   Huawei Technologies Co.,Ltd
   Site B, Floor 12F, Huihong Mansion, No.91 Baixia Rd.
   Nanjing, JiangSu  210001
   China

   Phone: +86-25-84565892
   Email: bill.wu@huawei.com


   Tom Taylor
   Huawei Technologies Co., Ltd
   Ottawa, Ontario
   Canada

   Email: tom111.taylor@bell.net








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   Yoav Nir
   Check Point
   5 Hasolelim st.
   Tel Aviv  67897
   Israel

   Email: ynir@checkpoint.com


   Katrin Hoeper
   Motorola, Inc.
   1301 E. Algonquin Road
   Schaumburg, IL  60196
   USA

   Email: khoeper@motorola.com


   Sebastien Decugis
   INSIDE Secure
   41 Parc Club du Golf
   Aix-en-Provence  13856
   France

   Phone: +33 (0)4 42 39 63 00
   Email: sdecugis@freediameter.net

























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