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authorAndreas Steffen <andreas.steffen@strongswan.org>2010-09-20 20:03:20 +0200
committerAndreas Steffen <andreas.steffen@strongswan.org>2010-09-20 20:03:20 +0200
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treed1e2afbe2305ecadcd2c86cb8f3e51a385e25efb /doc/standards/draft-eronen-ipsec-ikev2-eap-auth-05.txt
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-
-
-
-Network Working Group P. Eronen
-Internet-Draft Nokia
-Expires: December 28, 2006 H. Tschofenig
- Siemens
- June 26, 2006
-
-
- Extension for EAP Authentication in IKEv2
- draft-eronen-ipsec-ikev2-eap-auth-05.txt
-
-Status of this Memo
-
- By submitting this Internet-Draft, each author represents that any
- applicable patent or other IPR claims of which he or she is aware
- have been or will be disclosed, and any of which he or she becomes
- aware will be disclosed, in accordance with Section 6 of BCP 79.
-
- Internet-Drafts are working documents of the Internet Engineering
- Task Force (IETF), its areas, and its working groups. Note that
- other groups may also distribute working documents as Internet-
- Drafts.
-
- Internet-Drafts are draft documents valid for a maximum of six months
- and may be updated, replaced, or obsoleted by other documents at any
- time. It is inappropriate to use Internet-Drafts as reference
- material or to cite them other than as "work in progress."
-
- The list of current Internet-Drafts can be accessed at
- http://www.ietf.org/ietf/1id-abstracts.txt.
-
- The list of Internet-Draft Shadow Directories can be accessed at
- http://www.ietf.org/shadow.html.
-
- This Internet-Draft will expire on December 28, 2006.
-
-Copyright Notice
-
- Copyright (C) The Internet Society (2006).
-
-Abstract
-
- IKEv2 specifies that EAP authentication must be used together with
- public key signature based responder authentication. 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
-
-
-
-Eronen & Tschofenig Expires December 28, 2006 [Page 1]
-
-Internet-Draft Extension for EAP in IKEv2 June 2006
-
-
- responder authentication for IKEv2 based on other methods than public
- key signatures.
-
-
-1. Introduction
-
- The Extensible Authentication Protocol (EAP), defined in [4], is an
- authentication framework which 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 [13],
- IEEE 802 wired switches [9], and IEEE 802.11 wireless access points
- [11].
-
- 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 which may implement some or
- all authentication methods.
-
- IKEv2 [3] is a component of IPsec used for performing mutual
- authentication and establishing and maintaining security associations
- for IPsec ESP and 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
- 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 also these EAP methods
-
-
-
-Eronen & Tschofenig Expires December 28, 2006 [Page 2]
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-
-
- must be used together with public key signature based responder
- authentication.
-
- In some environments, requiring the deployment of PKI for just this
- purpose can be counterproductive. Deploying new infrastructure can
- be expensive, and it may weaken security by creating new
- vulnerabilities. Mutually authenticating EAP methods alone can
- provide a sufficient level of security in many circumstances, and
- indeed, IEEE 802.11i uses EAP without any PKI for authenticating the
- 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.
-
-1.1. Terminology
-
- 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 [2].
-
-
-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). As an example it is possible to use GSS-API support within
- EAP [6] to support Kerberos based authentication which effectively
- replaces the need for KINK [14].
-
- +------+-----+ +------------+
- O | IKEv2 | | IKEv2 |
- /|\ | Initiator |<---////////////////////--->| Responder |
- / \ +------------+ IKEv2 +------------+
- User | EAP Peer | Exchange | EAP Server |
- +------------+ +------------+
-
- Figure 1: EAP and IKEv2 endpoints are co-located
-
-
-
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-
- 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
- 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 [4] or RADIUS [5]. See Section 5 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 (type TBD-BY-IANA) in message 3. The SPI size field is set
-
-
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-
- to zero, and there is no additional data associated with this
- notification.
-
- If the responder supports this notification, 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, it ignores the notification payload, and includes the
- AUTH payload in message 4. In this case the initiator can, based on
- its local policy, choose to either ignore the AUTH payload, or verify
- it and any associated certificates as usual.
-
- 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.
-
- 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] }
-
-
-
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-
- The NAT detection and Configuration payloads are shown for
- informative purposes only; they do not change how EAP authentication
- works.
-
-
-4. IANA considerations
-
- This document defines a new IKEv2 Notification Payload type,
- EAP_ONLY_AUTHENTICATION, described in Section 3. This payload must
- be assigned a new type number from the "status types" range.
-
- This document does not define any new namespaces to be managed by
- IANA.
-
-
-5. Security Considerations
-
- Security considerations applicable to all EAP methods are discussed
- in [1]. The EAP Key Management Framework [7] deals with issues that
- arise when EAP is used as a part of a larger system.
-
-5.1. 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.
-
-5.2. 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 terminates 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
- [7] 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
-
-
-
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-
- to the IKEv2 gateway over a connection authenticated using, e.g.,
- IPsec or TLS.
-
- Some EAP methods do not have any concept of pass-through
- authenticator (e.g., 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 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 [16].
-
- 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 [4] and [7] for more discussion.
-
-5.3. 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 WLANs, 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.
-
-5.4. User identity confidentiality
-
- IKEv2 provides confidentiality for the initiator identity against
-
-
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- 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 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 initiator is
- required then EAP methods that offer this functionality have to be
- used (see [1], Section 7.3).
-
-
-6. Acknowledgments
-
- This document borrows some text from [1], [3], and [4]. We would
- also like to thank Hugo Krawczyk for interesting discussions about
- this topic.
-
-
-7. References
-
-7.1. Normative References
-
- [1] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
- Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748,
- June 2004.
-
- [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
- Levels", RFC 2119, March 1997.
-
- [3] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306,
- December 2005.
-
- [4] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
- Authentication Protocol (EAP) Application", RFC 4072,
- August 2005.
-
-
-
-
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-7.2. Informative References
-
- [5] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial
- In User Service) Support For Extensible Authentication Protocol
- (EAP)", RFC 3579, September 2003.
-
- [6] Aboba, B. and D. Simon, "EAP GSS Authentication Protocol",
- draft-aboba-pppext-eapgss-12 (work in progress), April 2002.
-
- [7] Aboba, B., "Extensible Authentication Protocol (EAP) Key
- Management Framework", draft-ietf-eap-keying-13 (work in
- progress), May 2006.
-
- [8] Forsberg, D., "Protocol for Carrying Authentication for Network
- Access (PANA)", draft-ietf-pana-pana-11 (work in progress),
- March 2006.
-
- [9] Institute of Electrical and Electronics Engineers, "Local and
- Metropolitan Area Networks: Port-Based Network Access Control",
- IEEE Standard 802.1X-2001, 2001.
-
- [10] 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 802.11-1999, 1999.
-
- [11] 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.
-
- [12] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote
- Authentication Dial In User Service (RADIUS)", RFC 2865,
- June 2000.
-
- [13] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
- RFC 1661, July 1994.
-
- [14] Sakane, S., Kamada, K., Thomas, M., and J. Vilhuber,
- "Kerberized Internet Negotiation of Keys (KINK)", RFC 4430,
- March 2006.
-
- [15] Tschofenig, H., "EAP IKEv2 Method",
-
-
-
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- draft-tschofenig-eap-ikev2-11 (work in progress), June 2006.
-
- [16] Arkko, J. and P. Eronen, "Authenticated Service Information for
- the Extensible Authentication Protocol (EAP)",
- draft-arkko-eap-service-identity-auth-04 (work in progress),
- October 2005.
-
-
-Appendix A. Alternative Approaches
-
- In this section we list alternatives which have been considered
- during the work on this document. Finally, 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.
-
- The initiator could signal the responder (using a NOTIFY payload)
- that it did not verify the first AUTH payload.
-
-A.2. Unauthenticated PKs in AUTH payload (message 4)
-
- The first 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.
-
- If using RSA, the overhead of signature verification is quite small
- (compared to g^xy calculation).
-
-A.3. Use EAP derived session keys for IKEv2
-
- It has been proposed that when using an EAP methods that provides
- mutual authentication and key agreement, the IKEv2 Diffie-Hellman
-
-
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- exchange could also be omitted. This would mean that the sessions
- keys for IPsec SAs established later would rely only on EAP-provided
- keys.
-
- 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.
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-Authors' Addresses
-
- Pasi Eronen
- Nokia Research Center
- P.O. Box 407
- FIN-00045 Nokia Group
- Finland
-
- Email: pasi.eronen@nokia.com
-
-
- Hannes Tschofenig
- Siemens
- Otto-Hahn-Ring 6
- Munich, Bayern 81739
- Germany
-
- Email: Hannes.Tschofenig@siemens.com
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-Intellectual Property Statement
-
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-Copyright Statement
-
- Copyright (C) The Internet Society (2006). This document is subject
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-
-
-Acknowledgment
-
- Funding for the RFC Editor function is currently provided by the
- Internet Society.
-
-
-
-
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-
-