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Internet Engineering Task Force (IETF)                            Y. NirRequest for Comments: 6867                                   Check PointCategory: Experimental                                             Q. WuISSN: 2070-1721                                                   Huawei                                                            January 2013An Internet Key Exchange Protocol Version 2 (IKEv2)Extension to Support EAP Re-authentication Protocol (ERP)Abstract   This document updates the Internet Key Exchange Protocol version 2   (IKEv2) described inRFC 5996.  This extension allows an IKE Security   Association (SA) to be created and authenticated using the Extensible   Authentication Protocol (EAP) Re-authentication Protocol extension,   as described inRFC 6696.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for examination, experimental implementation, and   evaluation.   This document defines an Experimental Protocol for the Internet   community.  This document is a product of the Internet Engineering   Task Force (IETF).  It represents the consensus of the IETF   community.  It has received public review and has been approved for   publication by the Internet Engineering Steering Group (IESG).  Not   all documents approved by the IESG are a candidate for any level of   Internet Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6867.Nir & Wu                      Experimental                      [Page 1]

RFC 6867                       ERP for IKE                  January 2013Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.1.  Introduction   IKEv2, as specified in [RFC5996], allows (Section 2.16)   authentication of the initiator using an EAP method.  Using EAP   significantly increases the count of round trips required to   establish the IPsec SA and also may require user interaction.  This   makes it inconvenient to allow a single remote access client to   create multiple IPsec tunnels with multiple IPsec gateways that   belong to the same domain.   The EAP Re-authentication Protocol (ERP), as described in [RFC6696],   allows an EAP peer to authenticate to multiple authenticators while   performing the full EAP method only once.  Subsequent authentications   require fewer round trips and no user interaction.   Bringing these two technologies together allows a remote access IPsec   client to create multiple tunnels with different gateways that belong   to a single domain as well as using the keys from other contexts of   using EAP, such as network access within the same domain, to   transparently connect to VPN gateways within this domain.   Additionally, it allows for faster set up of new tunnels when   previous tunnels have been torn down due to things like network   outage, device suspension, or a temporary move out of range.  This is   similar to the session resumption mechanism described in [RFC5723].   One exception being that instead of a ticket stored by the client,   the re-authentication Master Session Key (rMSK) (seeSection 4.6 of   [RFC6696]) is used as the session key stored on both the client and   the Authentication, Authorization, and Accounting (AAA) server.Nir & Wu                      Experimental                      [Page 2]

RFC 6867                       ERP for IKE                  January 20131.1.  Conventions Used in This Document   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.  Usage Scenarios   This work is motivated by the following scenarios:   o  Multiple tunnels for a single remote access VPN client.  Suppose a      company has offices in New York City, Paris, and Shanghai.  For      historical reasons, the email server is located in the Paris      office, most of the servers hosting the company's intranet are      located in Shanghai, and the finance department servers are in New      York City.  An employee using a remote access VPN may need to      connect to servers from all three locations.  While it is possible      to connect to a single gateway, and have that gateway route the      requests to the other gateways (perhaps through site to site VPN),      this is not efficient; it is more desirable to have the client      initiate three different tunnels.  It is, however, not desirable      to have the user type in a password three times.   o  Roaming.  In these days of mobile phones and tablets, users often      move from the wireless LAN in their office, where access may be      granted through 802.1x, to a cellular network, where a VPN is      necessary, and back again.  Both the VPN server and the 802.1x      access point are authenticators that connect to the same AAA      servers.  So it makes sense to make the transition smooth, without      requiring user interaction.  The device still needs to detect      whether it is within the protected network, in which case it      should not use VPN.  However, this process is beyond the scope of      this document.  [SECBEAC] is a now-abandoned attempt at this.   o  Resumption.  If a device gets disconnected from an IKE peer, ERP      can be used to reconnect to the same gateway without user      intervention.3.  Protocol Outline   Supporting EAP Re-authentication Extension (ERX) requires an EAP   payload in the first IKE_AUTH request.  This is a deviation from the   rules in [RFC5996], so support needs to be indicated through a Notify   payload in the IKE_SA_INIT response.  This Notify serves the same   purpose as the EAP-Initiate/Re-auth-Start message of ERX, as   specified inSection 5.3.1 of [RFC6696].  The "Domain Name" field   contains the content of the Domain-Name TLV as specified inSection5.3.1.1 of the same document.Nir & Wu                      Experimental                      [Page 3]

RFC 6867                       ERP for IKE                  January 2013   A supporting initiator that has unexpired keys for this domain will   send the EAP-Initiate/Re-auth message in an EAP payload in the first   IKE_AUTH request.   The responder sends the EAP payload content to a backend AAA server.   If that server has a valid rMSK for that session, it sends those   along with an EAP-Finish/Re-auth message.  The responder then   forwards the EAP-Finish/Re-auth message to the initiator in an EAP   payload within the first IKE_AUTH response.   The initiator then sends an additional IKE_AUTH request that includes   the AUTH payload, which has been calculated using the rMSK in the   role of the MSK as described in Sections2.15 and2.16 of [RFC5996].   The responder replies similarly, and the IKE_AUTH exchange is   finished.   If the backend AAA server does not have valid keys for the Re-auth-   Start message, it sends back a normal EAP request, and no rMSK key.   EAP flow continues as in [RFC5996].   The following figure is adapted from Appendixes C.1 and C.3 of   [RFC5996], with most of the optional payloads removed.  Note that the   EAP-Initiate/Re-auth message is added.   IKE_SA_INIT Exchange:   | init request         --> SA, KE, Ni,   |   | init response       <-- SA, KE, Nr,   |                         N[ERX_SUPPORTED]   IKE_AUTH Exchanges:   | first request       --> EAP(EAP-Initiate/Re-auth),   |                         IDi,   |                         SA, TSi, TSr   |   | first response      <-- IDr, [CERT+], AUTH,   |                         EAP(EAP-Finish/Re-auth)   |   | last request        --> AUTH   |   | last response       <-- AUTH,   |                         SA, TSi, TSr   The IDi payload MUST have ID Type ID_RFC822_ADDR, and the data field   MUST contain the same value as the KeyName-NAI TLV in the EAP-   Initiate/Re-auth message.  SeeSection 3.2 for details.Nir & Wu                      Experimental                      [Page 4]

RFC 6867                       ERP for IKE                  January 20133.1.  Clarification about EAP CodesSection 3.16 of [RFC5996] enumerates the EAP codes in EAP messages   that are carried in EAP payloads.  The enumeration goes only to 4.   It is not clear whether or not that list is supposed to be   exhaustive.   To clarify, an implementation conforming to this specification MUST   accept and transmit EAP messages with at least the codes for Initiate   and Finish (5 and 6) fromSection 5.3 of [RFC6696], in addition to   the four codes enumerated in [RFC5996].  This document is   intentionally silent about other EAP codes that are not enumerated in   those documents.3.2.  Username in the Protocol   The authors, as well as participants of the HOKEY and IPsecME working   groups, believe that all use cases for this extension to IKE have a   single backend AAA server doing both the authentication and the re-   authentication.  The reasoning behind this is that IKE runs over the   Internet and would naturally connect to the user's home network.   This section addresses instances where this is not the case.Section 5.3.2 of [RFC6696] describes the EAP-Initiate/Re-auth packet,   which, in the case of IKEv2, is carried in the first IKE_AUTH   request.  This packet contains the KeyName-NAI TLV.  This TLV   contains the username used in authentication.  It is relayed to the   AAA server in the AccessRequest message and is returned from the AAA   server in the AccessAccept message.   The username part of the Network Access Identifier (NAI) within the   TLV is the EMSKName [RFC5295] encoded in hexadecimal digits.  The   domain part is the domain name of the home domain of the user.  The   username part is ephemeral in the sense that a new one is generated   for each full authentication.  This ephemeral value is not a good   basis for making policy decisions, and it is also a poor source of   user identification for the purposes of logging.   Instead, it is up to the implementation in the IPsec gateway to make   policy decisions based on other factors.  The following list is by no   means exhaustive:   o  In some cases, the home domain name may be enough to make policy      decisions.  If all users with a particular home domain get the      same authorization, then policy does not depend on the real      username.  Meaningful logs can still be issued by correlating VPN      gateway IKE events with AAA servers access records.Nir & Wu                      Experimental                      [Page 5]

RFC 6867                       ERP for IKE                  January 2013   o  Sometimes users receive different authorizations based on groups      to which they belong.  The AAA server can communicate such      information to the VPN gateway, for example, using the CLASS      attribute [RFC2865] in RADIUS and Diameter [RFC6733].  Logging      again depends on correlation with AAA servers.   o  AAA servers may support extensions that allow them to communicate      with their clients (in our case -- the VPN gateway) to push user      information.  For example, a certain product integrates a RADIUS      server with the Lightweight Directory Access Protocol (LDAP)      [RFC4511], so a client could query the server using LDAP and      receive the real record for this user.  Others may provide this      data through vendor-specific extensions to RADIUS or Diameter.   In any case, authorization is a major issue in deployments, if the   backend AAA server supporting the re-authentication is different from   the AAA server that had supported the original authentication.  It is   up to the re-authenticating AAA server to provide the necessary   information for authorization.  A conforming implementation of this   protocol MAY reject initiators for which it is unable to make policy   decisions because of these reasons.4.  ERX_SUPPORTED Notification   The Notify payload is as described in [RFC5996]:                            1                   2                   3        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       ! Next Payload  !C!  RESERVED   !         Payload Length        !       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       !  Protocol ID  !   SPI Size    !    ERX Notify Message Type    !       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       !                            Domain Name                        !       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   o  Protocol ID (1 octet) - MUST be zero, as this message is related      to an IKE SA.   o  Security Parameter Index (SPI) Size (1 octet) - MUST be zero, in      conformance withSection 3.10 of [RFC5996].   o  ERX Notify Message Type (2 octets) - MUST be 16427, the value      assigned for ERX.   o  Domain Name (variable) - contains the domain name or realm, as      these terms are used in [RFC6696] and encoded as ASCII, as      specified in [RFC4282].Nir & Wu                      Experimental                      [Page 6]

RFC 6867                       ERP for IKE                  January 20135.  Operational Considerations   This specification changes the behavior of IKE peers, both initiators   and responders.  The behavior of backend AAA servers is not changed   by this specification, but they are required to support [RFC6696].   The same goes for the EAP client, if it's not integrated into the IKE   initiator (for example, if the EAP client is an operating system   component).   This specification is silent about key storage and key lifetimes on   either the EAP client or the EAP server.  These issues are covered in   Sections3,4, and5 of [RFC6696].  The key lifetime may be   communicated from the AAA server to the EAP client via the Lifetime   attribute in the EAP-Finish/Re-auth message.  If the server does not   have a valid key, while the client does have one, regular EAP is used   (seeSection 3).  This should not happen if lifetimes are   communicated.  In such a case, the IKEv2 initiator / EAP client MAY   alert the user and MAY log the event.  Note that this does not   necessarily indicate an attack.  It could simply be a loss of state   on the AAA server.6.  Security Considerations   The protocol extension described in this document extends the   authentication from one EAP context, which may or may not be part of   IKEv2, to an IKEv2 context.  Successful completion of the protocol   proves to the authenticator, which in our case is a VPN gateway, that   the supplicant or VPN client has authenticated in some other EAP   context.   The protocol supplies the authenticator with the domain name with   which the supplicant has authenticated, but does not supply it with a   specific identity.  Instead, the gateway receives an EMSKName, which   is an ephemeral ID.  With this variant of the IKEv2 protocol, the   initiator never sends its real identity on the wire while the server   does.  This is different from the usual IKEv2 practice of the   initiator revealing its identity first.   If the domain name is sufficient to make access control decisions,   this is enough.  If not, then the gateway needs to find out either   the real name or authorization information for that particular user.   This may be done using the AAA protocol or by some other federation   protocol, which is out of scope for this specification.Nir & Wu                      Experimental                      [Page 7]

RFC 6867                       ERP for IKE                  January 20137.  IANA Considerations   IANA has assigned a notify message type of 16427 from the "IKEv2   Notify Message Types - Status Types" registry with the name   "ERX_SUPPORTED".8.  Acknowledgements   The authors would like to thank Yaron Sheffer for comments and   suggested text that have contributed to this document.   Thanks also to Juergen Schoenwaelder for his OPS-DIR review comments.9.  References9.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC4282]  Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The              Network Access Identifier",RFC 4282, December 2005.   [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.   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,              "Internet Key Exchange Protocol Version 2 (IKEv2)",RFC 5996, September 2010.   [RFC6696]  Cao, Z., He, B., Shi, Y., Wu, Q., and G. Zorn, "EAP              Extensions for the EAP Re-authentication Protocol (ERP)",RFC 6696, July 2012.9.2.  Informative References   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,              "Remote Authentication Dial In User Service (RADIUS)",RFC 2865, June 2000.   [RFC4511]  Sermersheim, J., "Lightweight Directory Access Protocol              (LDAP): The Protocol",RFC 4511, June 2006.   [RFC5723]  Sheffer, Y. and H. Tschofenig, "Internet Key Exchange              Protocol Version 2 (IKEv2) Session Resumption",RFC 5723,              January 2010.Nir & Wu                      Experimental                      [Page 8]

RFC 6867                       ERP for IKE                  January 2013   [RFC6733]  Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,              "Diameter Base Protocol",RFC 6733, October 2012.   [SECBEAC]  Sheffer, Y. and Y. Nir, "Secure Beacon: Securely Detecting              a Trusted Network", Work in Progress, June 2009.Authors' Addresses   Yoav Nir   Check Point Software Technologies Ltd.   5 Hasolelim st.   Tel Aviv  67897   Israel   EMail: ynir@checkpoint.com   Qin Wu   Huawei Technologies Co., Ltd.   101 Software Avenue, Yuhua District   Nanjing, JiangSu  210012   China   EMail: sunseawq@huawei.comNir & Wu                      Experimental                      [Page 9]