GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc5998

Internet Engineering Task Force (IETF) P. Eronen Request for Comments: 5998 Independent Updates: 5996 H. Tschofenig Category: Standards Track Nokia Siemens Networks ISSN: 2070-1721 Y. Sheffer

                                                           Independent
                                                        September 2010
         An Extension for EAP-Only Authentication in IKEv2

Abstract

 IKEv2 specifies that Extensible Authentication Protocol (EAP)
 authentication must be used together with responder authentication
 based on public key signatures.  This is necessary with old EAP
 methods that provide only unilateral authentication using, e.g., one-
 time passwords or token cards.
 This document specifies how EAP methods that provide mutual
 authentication and key agreement can be used to provide extensible
 responder authentication for IKEv2 based on methods other than public
 key signatures.

Status of This Memo

 This is an Internet Standards Track document.
 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).  Further information on
 Internet Standards is available in 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/rfc5998.

Eronen, et al. Standards Track [Page 1] RFC 5998 Extension for EAP in IKEv2 September 2010

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 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.

1. Introduction

 The Extensible Authentication Protocol (EAP), defined in [RFC3748],
 is an authentication framework that supports multiple authentication
 mechanisms.  Today, EAP has been implemented at end hosts and routers
 that connect via switched circuits or dial-up lines using PPP
 [RFC1661], IEEE 802 wired switches [IEEE8021X], and IEEE 802.11
 wireless access points [IEEE80211i].
 One of the advantages of the EAP architecture is its flexibility.
 EAP is used to select a specific authentication mechanism, typically
 after the authenticator requests more information in order to
 determine the specific authentication method to be used.  Rather than
 requiring the authenticator (e.g., wireless LAN access point) to be
 updated to support each new authentication method, EAP permits the
 use of a backend authentication server that may implement some or all
 authentication methods.

Eronen, et al. Standards Track [Page 2] RFC 5998 Extension for EAP in IKEv2 September 2010

 IKEv2 ([RFC4306] and [RFC5996]) is a component of IPsec used for
 performing mutual authentication and establishing and maintaining
 Security Associations (SAs) for IPsec ESP and Authentication Header
 (AH).  In addition to supporting authentication using public key
 signatures and shared secrets, IKEv2 also supports EAP
 authentication.
 IKEv2 provides EAP authentication since it was recognized that public
 key signatures and shared secrets are not flexible enough to meet the
 requirements of many deployment scenarios.  By using EAP, IKEv2 can
 leverage existing authentication infrastructure and credential
 databases, since EAP allows users to choose a method suitable for
 existing credentials, and also makes separation of the IKEv2
 responder (VPN gateway) from the EAP authentication endpoint (backend
 Authentication, Authorization, and Accounting (AAA) server) easier.
 Some older EAP methods are designed for unilateral authentication
 only (that is, EAP peer to EAP server).  These methods are used in
 conjunction with IKEv2 public-key-based authentication of the
 responder to the initiator.  It is expected that this approach is
 especially useful for "road warrior" VPN gateways that use, for
 instance, one-time passwords or token cards to authenticate the
 clients.
 However, most newer EAP methods, such as those typically used with
 IEEE 802.11i wireless LANs, provide mutual authentication and key
 agreement.  Currently, IKEv2 specifies that these EAP methods must
 also be used together with responder authentication based on public
 key signatures.
 In order for the public key signature authentication of the gateway
 to be effective, a deployment of Public Key Infrastructure (PKI) is
 required, which has to include management of trust anchors on all
 supplicants.  In many environments, this is not realistic, and the
 security of the gateway public key is the same as the security of a
 self-signed certificate.  Mutually authenticating EAP methods alone
 can provide a sufficient level of security in many circumstances, and
 in fact, in some deployments, IEEE 802.11i uses EAP without any PKI
 for authenticating the Wireless Local Area Network (WLAN) access
 points.
 This document specifies how EAP methods that offer mutual
 authentication and key agreement can be used to provide responder
 authentication in IKEv2 completely based on EAP.

Eronen, et al. Standards Track [Page 3] RFC 5998 Extension for EAP in IKEv2 September 2010

1.1. Terminology

 All notation in this protocol extension is taken from [RFC4306].
 Numbered messages refer to the IKEv2 message sequence when using EAP.
 Thus:
 o  Message 1 is the request message of IKE_SA_INIT.
 o  Message 2 is the response message of IKE_SA_INIT.
 o  Message 3 is the first request of IKE_AUTH.
 o  Message 4 is the first response of IKE_AUTH.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].

2. Scenarios

 In this section, we describe two scenarios for extensible
 authentication within IKEv2.  These scenarios are intended to be
 illustrative examples rather than specifying how things should be
 done.
 Figure 1 shows a configuration where the EAP and the IKEv2 endpoints
 are co-located.  Authenticating the IKEv2 responder using both EAP
 and public key signatures is redundant.  Offering EAP-based
 authentication has the advantage that multiple different
 authentication and key exchange protocols are available with EAP with
 different security properties (such as strong password-based
 protocols, protocols offering user identity confidentiality, and many
 more).
        +------+-----+                            +------------+
   O    |   IKEv2    |                            |   IKEv2    |
  /|\   | Initiator  |<---////////////////////--->| Responder  |
  / \   +------------+          IKEv2             +------------+
  User  |  EAP Peer  |          Exchange          | EAP Server |
        +------------+                            +------------+
           Figure 1: EAP and IKEv2 Endpoints Are Co-Located
 Figure 2 shows a typical corporate network access scenario.  The
 initiator (client) interacts with the responder (VPN gateway) in the
 corporate network.  The EAP exchange within IKE runs between the

Eronen, et al. Standards Track [Page 4] RFC 5998 Extension for EAP in IKEv2 September 2010

 client and the home AAA server.  As a result of a successful EAP
 authentication protocol run, session keys are established and sent
 from the AAA server to the VPN gateway, and then used to authenticate
 the IKEv2 SA with AUTH payloads.
 The protocol used between the VPN gateway and AAA server could be,
 for instance, Diameter [RFC4072] or RADIUS [RFC3579].  See Section 6
 for related security considerations.
                              +-------------------------------+
                              |       Corporate network       |
                              |                               |
                         +-----------+            +--------+  |
                         |   IKEv2   |     AAA    |  Home  |  |
   IKEv2      +////----->+ Responder +<---------->+  AAA   |  |
   Exchange   /          | (VPN GW)  |  (RADIUS/  | Server |  |
              /          +-----------+  Diameter) +--------+  |
              /               |        carrying EAP           |
              |               |                               |
              |               +-------------------------------+
              v
       +------+-----+
   o   |   IKEv2    |
  /|\  | Initiator  |
  / \  | VPN client |
 User  +------------+
                  Figure 2: Corporate Network Access

3. Solution

 IKEv2 specifies that when the EAP method establishes a shared secret
 key, that key is used by both the initiator and responder to generate
 an AUTH payload (thus authenticating the IKEv2 SA set up by messages
 1 and 2).
 When used together with public key responder authentication, the
 responder is, in effect, authenticated using two different methods:
 the public key signature AUTH payload in message 4, and the EAP-based
 AUTH payload later.
 If the initiator does not wish to use public-key-based responder
 authentication, it includes an EAP_ONLY_AUTHENTICATION notification
 payload (16417) in message 3.  The Protocol ID and Security Parameter
 Index (SPI) size fields are set to zero, and there is no additional
 data associated with this notification.

Eronen, et al. Standards Track [Page 5] RFC 5998 Extension for EAP in IKEv2 September 2010

 If the responder supports this notification and chooses to use it, it
 omits the public-key-based AUTH payload and CERT payloads from
 message 4.
 If the responder does not support the EAP_ONLY_AUTHENTICATION
 notification or does not wish to use it, it ignores the notification
 payload, and includes the AUTH payload in message 4.  In this case,
 the initiator MUST verify that payload and any associated
 certificates, as per [RFC4306].
 When receiving message 4, the initiator MUST verify that the proposed
 EAP method is allowed by this specification, and MUST abort the
 protocol immediately otherwise.
 Both the initiator and responder MUST verify that the EAP method
 actually used provided mutual authentication and established a shared
 secret key.  The AUTH payloads sent after EAP Success MUST use the
 EAP-generated key, and MUST NOT use SK_pi or SK_pr (see Section 2.15
 of [RFC5996]).

Eronen, et al. Standards Track [Page 6] RFC 5998 Extension for EAP in IKEv2 September 2010

 An IKEv2 message exchange with this modification is shown below:
    Initiator                   Responder
   -----------                 -----------
    HDR, SAi1, KEi, Ni,
         [N(NAT_DETECTION_SOURCE_IP),
          N(NAT_DETECTION_DESTINATION_IP)]  -->
                          <--   HDR, SAr1, KEr, Nr, [CERTREQ],
                                     [N(NAT_DETECTION_SOURCE_IP),
                                      N(NAT_DETECTION_DESTINATION_IP)]
    HDR, SK { IDi, [IDr], SAi2, TSi, TSr,
              N(EAP_ONLY_AUTHENTICATION),
              [CP(CFG_REQUEST)] }  -->
                          <--   HDR, SK { IDr, EAP(Request) }
    HDR, SK { EAP(Response) }  -->
                          <--   HDR, SK { EAP(Request) }
    HDR, SK { EAP(Response) }  -->
                          <--   HDR, SK { EAP(Success) }
    HDR, SK { AUTH }  -->
                          <--   HDR, SK { AUTH, SAr2, TSi, TSr,
                                          [CP(CFG_REPLY] }
 Note: all notation in the above protocol sequence and elsewhere in
 this specification is as defined in [RFC4306], and see in particular
 Sec. 1.2 of [RFC4306] for payload types.
 The NAT detection and Configuration payloads are shown for
 informative purposes only; they do not change how EAP authentication
 works.
 An IKE SA that was set up with this extension can be resumed using
 the mechanism described in [RFC5723].  However, session resumption
 does not change the authentication method.  Therefore, during the
 IKE_AUTH exchange of the resumed session, this extension MUST NOT be
 sent by the initiator.

Eronen, et al. Standards Track [Page 7] RFC 5998 Extension for EAP in IKEv2 September 2010

4. Safe EAP Methods

 EAP methods to be used with this extension MUST have the following
 properties:
 1.  The method provides mutual authentication of the peers.
 2.  The method is key-generating.
 3.  The method is resistant to dictionary attacks.
 The authors believe that the following EAP methods are secure when
 used with the current extension.  The list is not inclusive, and
 there are likely other safe methods that have not been listed here.
 +-------------------------------+-------------------+---------------+
 | Method Name                   | Allows Channel    | Reference     |
 |                               | Binding?          |               |
 +-------------------------------+-------------------+---------------+
 | EAP-SIM                       | No                | [RFC4186]     |
 | EAP-AKA                       | Yes               | [RFC4187]     |
 | EAP-AKA'                      | Yes               | [RFC5448]     |
 | EAP-GPSK                      | Yes               | [RFC5433]     |
 | EAP-pwd                       | No                | [RFC5931]     |
 | EAP-EKE                       | Yes               | [EMU-EAP-EKE] |
 | EAP-PAX                       | Yes               | [RFC4746]     |
 | EAP-SAKE                      | No                | [RFC4763]     |
 | EAP-SRP                       | No                | [EAP-SRP]     |
 | EAP-POTP (mutual              | Yes               | [RFC4793]     |
 | authentication variant)       |                   |               |
 | EAP-TLS                       | No                | [RFC5216]     |
 | EAP-FAST                      | No                | [RFC4851]     |
 | EAP-TTLS                      | No                | [RFC5281]     |
 +-------------------------------+-------------------+---------------+
 The "Allows channel binding?" column denotes protocols where
 protected identity information may be sent between the EAP endpoints.
 This third, optional property of the method provides protection
 against certain types of attacks (see Section 6.2 for an
 explanation), and therefore in some scenarios, methods that allow for
 channel binding are to be preferred.  It is noted that at the time of
 writing, even when such capabilities are provided, they are not fully
 specified in an interoperable manner.  In particular, no RFC
 specifies what identities should be sent under the protection of the
 channel binding mechanism, or what policy is to be used to correlate
 identities at the different layers.

Eronen, et al. Standards Track [Page 8] RFC 5998 Extension for EAP in IKEv2 September 2010

5. IANA Considerations

 This document defines a new IKEv2 Notification Payload type,
 EAP_ONLY_AUTHENTICATION, described in Section 3.  This payload has
 been assigned the type number 16417 from the "Status Types" range.

6. Security Considerations

 Security considerations applicable to all EAP methods are discussed
 in [RFC3748].  The EAP Key Management Framework [RFC5247] deals with
 issues that arise when EAP is used as a part of a larger system.

6.1. Authentication of IKEv2 SA

 It is important to note that the IKEv2 SA is not authenticated by
 just running an EAP conversation: the crucial step is the AUTH
 payload based on the EAP-generated key.  Thus, EAP methods that do
 not provide mutual authentication or establish a shared secret key
 MUST NOT be used with the modifications presented in this document.

6.2. Authentication with Separated IKEv2 Responder / EAP Server

 As described in Section 2, the EAP conversation can terminate either
 at the IKEv2 responder or at a backend AAA server.
 If the EAP method is terminated at the IKEv2 responder, then no key
 transport via the AAA infrastructure is required.  Pre-shared secret
 and public-key-based authentication offered by IKEv2 is then replaced
 by a wider range of authentication and key exchange methods.
 However, typically EAP will be used with a backend AAA server.  See
 [RFC5247] for a more complete discussion of the related security
 issues; here we provide only a short summary.
 When a backend server is used, there are actually two authentication
 exchanges: the EAP method between the client and the AAA server, and
 another authentication between the AAA server and IKEv2 gateway.  The
 AAA server authenticates the client using the selected EAP method,
 and they establish a session key.  The AAA server then sends this key
 to the IKEv2 gateway over a connection authenticated using, e.g.,
 IPsec or Transport Layer Security (TLS).
 Some EAP methods do not have any concept of pass-through
 authenticator (e.g., Network Access Server (NAS) or IKEv2 gateway)
 identity, and these two authentications remain quite independent of
 each other.  That is, after the client has verified the AUTH payload
 sent by the IKEv2 gateway, it knows that it is talking to SOME
 gateway trusted by the home AAA server, but not which one.  The

Eronen, et al. Standards Track [Page 9] RFC 5998 Extension for EAP in IKEv2 September 2010

 situation is somewhat similar if a single cryptographic hardware
 accelerator, containing a single private key, would be shared between
 multiple IKEv2 gateways (perhaps in some kind of cluster
 configuration).  In particular, if one of the gateways is
 compromised, it can impersonate any of the other gateways towards the
 user (until the compromise is discovered and access rights revoked).
 In some environments it is not desirable to trust the IKEv2 gateways
 this much (also known as the "Lying NAS Problem").  EAP methods that
 provide what is called "connection binding" or "channel binding"
 transport some identity or identities of the gateway (or WLAN access
 point / NAS) inside the EAP method.  Then the AAA server can check
 that it is indeed sending the key to the gateway expected by the
 client.  A potential solution is described in [EAP-SERVICE], see also
 [EMU-AAAPAY].
 In some deployment configurations, AAA proxies may be present between
 the IKEv2 gateway and the backend AAA server.  These AAA proxies MUST
 be trusted for secure operation, and therefore SHOULD be avoided when
 possible; see Section 2.3.4 of [RFC4072] and Section 4.3.7 of
 [RFC3579] for more discussion.

6.3. Protection of EAP Payloads

 Although the EAP payloads are encrypted and integrity protected with
 SK_e/SK_a, this does not provide any protection against active
 attackers.  Until the AUTH payload has been received and verified, a
 man-in-the-middle can change the KEi/KEr payloads and eavesdrop or
 modify the EAP payloads.
 In IEEE 802.11i wireless LANs, the EAP payloads are neither encrypted
 nor integrity protected (by the link layer), so EAP methods are
 typically designed to take that into account.
 In particular, EAP methods that are vulnerable to dictionary attacks
 when used in WLANs are still vulnerable (to active attackers) when
 run inside IKEv2.
 The rules in Section 4 are designed to avoid this potential
 vulnerability.

Eronen, et al. Standards Track [Page 10] RFC 5998 Extension for EAP in IKEv2 September 2010

6.4. Identities and Authenticated Identities

 When using this protocol, each of the peers sends two identity
 values:
 1.  An identity contained in the IKE ID payload.
 2.  An identity transferred within the specific EAP method's
     messages.
 (IKEv2 omits the EAP Identity request/response pair, see Section 3.16
 of [RFC5996].)  The first identity value can be used by the recipient
 to route AAA messages and/or to select authentication and EAP types.
 But it is only the second identity that is directly authenticated by
 the EAP method.  The reader is referred to Section 2.16 of [RFC5996]
 regarding the need to base IPsec policy decisions on the
 authenticated identity.  In the context of the extension described
 here, this guidance on IPsec policy applies both to the
 authentication of the client by the gateway and vice versa.

6.5. User Identity Confidentiality

 IKEv2 provides confidentiality for the initiator identity against
 passive eavesdroppers, but not against active attackers.  The
 initiator announces its identity first (in message 3), before the
 responder has been authenticated.  The usage of EAP in IKEv2 does not
 change this situation, since the ID payload in message 3 is used
 instead of the EAP Identity Request/Response exchange.  This is
 somewhat unfortunate since when EAP is used with public key
 authentication of the responder, it would be possible to provide
 active user identity confidentiality for the initiator.
 IKEv2 protects the responder's identity even against active attacks.
 This property cannot be provided when using EAP.  If public key
 responder authentication is used in addition to EAP, the responder
 reveals its identity before authenticating the initiator.  If only
 EAP is used (as proposed in this document), the situation depends on
 the EAP method used (in some EAP methods, the server reveals its
 identity first).
 Hence, if active user identity confidentiality for the responder is
 required then EAP methods that offer this functionality have to be
 used (see [RFC3748], Section 7.3).

Eronen, et al. Standards Track [Page 11] RFC 5998 Extension for EAP in IKEv2 September 2010

7. Acknowledgments

 This document borrows some text from [RFC3748], [RFC4306], and
 [RFC4072].  We would also like to thank Hugo Krawczyk for interesting
 discussions about this topic, Dan Harkins, and David Harrington for
 their comments.

8. References

8.1. Normative References

 [RFC2119]      Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3748]      Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and
                H. Levkowetz, "Extensible Authentication Protocol
                (EAP)", RFC 3748, June 2004.
 [RFC4306]      Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
                RFC 4306, December 2005.
 [RFC5723]      Sheffer, Y. and H. Tschofenig, "Internet Key Exchange
                Protocol Version 2 (IKEv2) Session Resumption",
                RFC 5723, January 2010.
 [RFC5996]      Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
                "Internet Key Exchange Protocol Version 2 (IKEv2)",
                RFC 5996, September 2010.

8.2. Informative References

 [EAP-SERVICE]  Arkko, J. and P. Eronen, "Authenticated Service
                Information for the Extensible Authentication Protocol
                (EAP)", Work in Progress, October 2005.
 [EAP-SRP]      Carlson, J., Aboba, B., and H. Haverinen, "EAP SRP-
                SHA1 Authentication Protocol", Work in Progress,
                July 2001.
 [EMU-AAAPAY]   Clancy, C., Lior, A., Zorn, G., and K. Hoeper, "EAP
                Method Support for Transporting AAA Payloads", Work
                in Progress, May 2010.
 [EMU-EAP-EKE]  Sheffer, Y., Zorn, G., Tschofenig, H., and S. Fluhrer,
                "An EAP Authentication Method Based on the EKE
                Protocol", Work in Progress, August 2010.

Eronen, et al. Standards Track [Page 12] RFC 5998 Extension for EAP in IKEv2 September 2010

 [IEEE80211i]   Institute of Electrical and Electronics Engineers,
                "IEEE Standard for Information technology -
                Telecommunications and information exchange between
                systems - Local and metropolitan area networks -
                Specific requirements - Part 11: Wireless Medium
                Access Control (MAC) and Physical Layer (PHY)
                specifications: Amendment 6: Medium Access Control
                (MAC) Security Enhancements", IEEE Standard 802.11i-
                2004, July 2004.
 [IEEE8021X]    Institute of Electrical and Electronics Engineers,
                "Local and Metropolitan Area Networks: Port-Based
                Network Access Control", IEEE Standard 802.1X-2001,
                2001.
 [RFC1661]      Simpson, W., "The Point-to-Point Protocol (PPP)",
                STD 51, RFC 1661, July 1994.
 [RFC3579]      Aboba, B. and P. Calhoun, "RADIUS (Remote
                Authentication Dial In User Service) Support For
                Extensible Authentication Protocol (EAP)", RFC 3579,
                September 2003.
 [RFC4072]      Eronen, P., Hiller, T., and G. Zorn, "Diameter
                Extensible Authentication Protocol (EAP) Application",
                RFC 4072, August 2005.
 [RFC4186]      Haverinen, H. and J. Salowey, "Extensible
                Authentication Protocol Method for Global System for
                Mobile Communications (GSM) Subscriber Identity
                Modules (EAP-SIM)", RFC 4186, January 2006.
 [RFC4187]      Arkko, J. and H. Haverinen, "Extensible Authentication
                Protocol Method for 3rd Generation Authentication and
                Key Agreement (EAP-AKA)", RFC 4187, January 2006.
 [RFC4746]      Clancy, T. and W. Arbaugh, "Extensible Authentication
                Protocol (EAP) Password Authenticated Exchange",
                RFC 4746, November 2006.
 [RFC4763]      Vanderveen, M. and H. Soliman, "Extensible
                Authentication Protocol Method for Shared-secret
                Authentication and Key Establishment (EAP-SAKE)",
                RFC 4763, November 2006.
 [RFC4793]      Nystroem, M., "The EAP Protected One-Time Password
                Protocol (EAP-POTP)", RFC 4793, February 2007.

Eronen, et al. Standards Track [Page 13] RFC 5998 Extension for EAP in IKEv2 September 2010

 [RFC4851]      Cam-Winget, N., McGrew, D., Salowey, J., and H. Zhou,
                "The Flexible Authentication via Secure Tunneling
                Extensible Authentication Protocol Method (EAP-FAST)",
                RFC 4851, May 2007.
 [RFC5216]      Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
                Authentication Protocol", RFC 5216, March 2008.
 [RFC5247]      Aboba, B., Simon, D., and P. Eronen, "Extensible
                Authentication Protocol (EAP) Key Management
                Framework", RFC 5247, August 2008.
 [RFC5281]      Funk, P. and S. Blake-Wilson, "Extensible
                Authentication Protocol Tunneled Transport Layer
                Security Authenticated Protocol Version 0 (EAP-
                TTLSv0)", RFC 5281, August 2008.
 [RFC5433]      Clancy, T. and H. Tschofenig, "Extensible
                Authentication Protocol - Generalized Pre-Shared Key
                (EAP-GPSK) Method", RFC 5433, February 2009.
 [RFC5448]      Arkko, J., Lehtovirta, V., and P. Eronen, "Improved
                Extensible Authentication Protocol Method for 3rd
                Generation Authentication and Key Agreement (EAP-
                AKA')", RFC 5448, May 2009.
 [RFC5931]      Harkins, D. and G. Zorn, "Extensible Authentication
                Protocol (EAP) Authentication Using Only A Password",
                RFC 5931, August 2010.

Eronen, et al. Standards Track [Page 14] RFC 5998 Extension for EAP in IKEv2 September 2010

Appendix A. Alternative Approaches

 In this section, we list alternatives that have been considered
 during the work on this document.  We concluded that the solution
 presented in Section 3 seems to fit better into IKEv2.

A.1. Ignore AUTH Payload at the Initiator

 With this approach, the initiator simply ignores the AUTH payload in
 message 4 (but obviously must check the second AUTH payload later!).
 The main advantage of this approach is that no protocol modifications
 are required and no signature verification is required.  A
 significant disadvantage is that the EAP method to be used cannot be
 selected to take this behavior into account.
 The initiator could signal to the responder (using a notification
 payload) that it did not verify the first AUTH payload.

A.2. Unauthenticated Public Keys in AUTH Payload (Message 4)

 Another solution approach suggests the use of unauthenticated public
 keys in the public key signature AUTH payload (for message 4).
 That is, the initiator verifies the signature in the AUTH payload,
 but does not verify that the public key indeed belongs to the
 intended party (using certificates) -- since it doesn't have a PKI
 that would allow this.  This could be used with X.509 certificates
 (the initiator ignores all other fields of the certificate except the
 public key), or "Raw RSA Key" CERT payloads.
 This approach has the advantage that initiators that wish to perform
 certificate-based responder authentication (in addition to EAP) may
 do so, without requiring the responder to handle these cases
 separately.  A disadvantage here, again, is that the EAP method
 selection cannot take into account the incomplete validation of the
 responder's certificate.
 If using RSA, the overhead of signature verification is quite small,
 compared to the g^xy calculation required by the Diffie-Hellman
 exchange.

A.3. Using EAP Derived Session Keys for IKEv2

 It has been proposed that when using an EAP method that provides
 mutual authentication and key agreement, the IKEv2 Diffie-Hellman
 exchange could also be omitted.  This would mean that the session
 keys for IPsec SAs established later would rely only on EAP-provided
 keys.

Eronen, et al. Standards Track [Page 15] RFC 5998 Extension for EAP in IKEv2 September 2010

 It seems the only benefit of this approach is saving some computation
 time (g^xy calculation).  This approach requires designing a
 completely new protocol (which would not resemble IKEv2 anymore); we
 do not believe that it should be considered.  Nevertheless, we
 include it for completeness.

Authors' Addresses

 Pasi Eronen
 Independent
 EMail: pe@iki.fi
 Hannes Tschofenig
 Nokia Siemens Networks
 Linnoitustie 6
 Espoo  02600
 Finland
 Phone: +358 (50) 4871445
 EMail: Hannes.Tschofenig@gmx.net
 URI:   http://www.tschofenig.priv.at
 Yaron Sheffer
 Independent
 EMail: yaronf.ietf@gmail.com

Eronen, et al. Standards Track [Page 16]

/data/webs/external/dokuwiki/data/pages/rfc/rfc5998.txt · Last modified: 2010/09/17 23:49 (external edit)