Network Working Group
Internet Engineering Task Force (IETF)                            Y. Nir
Internet-Draft
Request for Comments: 6867                                   Check Point
Intended status:
Category: Experimental                                             Q. Wu
Expires: June 23, 2013
ISSN: 2070-1721                                                   Huawei
                                                       December 20, 2012
                                                            January 2013

          An IKEv2 Internet Key Exchange Protocol Version 2 (IKEv2)
       Extension for Supporting ERP
                        draft-nir-ipsecme-erx-11 to Support EAP Re-authentication Protocol (ERP)

Abstract

   This document updates the IKEv2 protocol, Internet Key Exchange Protocol version 2
   (IKEv2) described in RFC 5996.  This extension allows an IKE Security
   Association (SA) to be created and authenticated using the EAP Extensible
   Authentication Protocol (EAP) Re-authentication Protocol extension extension,
   as described in RFC 6696.

Status of this This Memo

   This Internet-Draft document is submitted in full conformance with the
   provisions of BCP 78 not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and BCP 79.

   Internet-Drafts are working documents
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list  It represents the consensus of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid 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 maximum candidate for any level of six months
   Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 23, 2013.
   http://www.rfc-editor.org/info/rfc6867.

Copyright Notice

   Copyright (c) 2012 2013 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.

1.  Introduction

   IKEv2, as specified in section 2.16 of [RFC5996], allows (Section 2.16)
   authentication of the initiator using an EAP method.  Using EAP
   significantly increases the count of round-trips round trips required to
   establish the IPsec SA, 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, authenticators while
   performing the full EAP method only once.  Subsequent authentications
   require fewer round-trips 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, 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 setting set up of new tunnels when
   previous tunnels have been torn down due to things like network
   outage, device suspension, or temporarily moving a temporary move out of range.  This is
   similar to the session resumption mechanism described in
   [RFC5723], except [RFC5723].
   One exception being that instead of a ticket stored by the client,
   the re-authentication MSK (rMSK - see section Master Session Key (rMSK) (see Section 4.6 of RFC 6696)
   [RFC6696]) is used as the session key stored on both the client and
   the AAA Authentication, Authorization, and Accounting (AAA) server.

1.1.  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, while 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, and 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 network, where a VPN is
      necessary
      necessary, and back again.  Both the VPN server and the 802.1x
      access point are authenticators that connect to the same
      Authentication, Authorization and Accounting (AAA) 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,
      but VPN.  However, this process is beyond the scope of
      this document.
      [SecureBeacon]  [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 ERX EAP Re-authentication Extension (ERX) requires an EAP
   payload in the first IKE_AUTH request.  This is a deviation from the
   rules in RFC 5996, [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 in section Section 5.3.1 of RFC 6696. [RFC6696].  The
   domain name included in "Domain Name" field
   contains the content of the Domain-Name TLV as specified in section Section
   5.3.1.1 of the same document.

   A supporting initiator that has unexpired keys for this domain will
   send the EAP_Initiate/Re-auth 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 initiator in an EAP
   payload within the first IKE_AUTH response.

   The initiator then sends an additional IKE_AUTH request, request that includes
   the AUTH payload payload, which has been calculated using the rMSK in the
   role of the MSK as described in sections Sections 2.15 and 2.16 of RFC
   5996. [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 RFC 5996. [RFC5996].

   The following figure is adapted from appendixes Appendixes C.1 and C.3 of RFC
   5996,
   [RFC5996], with most of the optional payloads removed.  Note that the
   EAP_Initiate/Re-auth
   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), 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 ID_RFC822_ADDR, and the data field
   MUST contain the same value as the KeyName-NAI TLV in the
   EAP_Initiate/Re-auth EAP-
   Initiate/Re-auth message.  See Section 3.2 for details.

3.1.  Clarification About about EAP Codes

   Section 3.16 of RFC 5996 [RFC5996] enumerates the EAP codes in EAP messages
   which
   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 or
   not.
   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) from RFC 6696, Section 5.3 of [RFC6696], in addition to
   the four codes enumerated in RFC 5996. [RFC5996].  This document is
   intentionally silent about other EAP codes that are neither not enumerated in RFC 5996 nor in that
   document.
   those documents.

3.2.  User Name  Username in the Protocol

   The authors, as well as participants of the HOKEY and IPsecME working
   groups
   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,
   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 RFC 6696 [RFC6696] describes the EAP-Initiate/Re-auth packet,
   which
   which, in the case of IKEv2 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, message and is returned from the AAA
   server in the AccessAccept message.

   The username part of the NAI Network Access Identifier (NAI) within the
   TLV is the EMSKName
   ([RFC5295]) [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 they are 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 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 user
      name.
      username.  Meaningful logs can still be issued by correlating VPN
      gateway IKE events with AAA servers access records.

   o  Sometimes users receive different authorizations based on groups
      to which they belong to. belong.  The AAA server can communicate such
      information to the VPN gateway, for example example, using the CLASS
      attribute
      ([RFC2865]) [RFC2865] in RADIUS and Diameter ([RFC3588]). [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]), (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. Diameter.

   In any case 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 RFC 5996: [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  SPI  Security Parameter Index (SPI) Size (1 octet) - MUST be zero, in
      conformance with section Section 3.10 of RFC 5996. [RFC5996].

   o  ERX Notify Message Type (2 octets) - MUST be xxxxx, 16427, the value
      assigned for ERX.  TBA by IANA.

   o  Domain Name (variable) - contains the domain name or realm, as
      these terms are used in RFC 6696, [RFC6696] and encoded as ASCII, as
      specified in [RFC4282].

5.  Operational Considerations

   This specification changes the behavior of IKE peers, both initiators
   and responders.  The behavior of back-end backend AAA servers is not changed
   by this specification, but they are required to support RFC 6696. [RFC6696].
   The same goes for the EAP client, if it's not integrated into the IKE
   Initiator
   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
   sections
   Sections 3, 4, and 5 of RFC 6696. [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
   (see Section 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, supplicant or VPN client, 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, 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.

7.  IANA Considerations

   IANA is requested to assign has assigned a notify message type from the status
   types range (16418-40959) 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.  References

9.1.  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: IKEv2", 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.

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
              Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

   [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 5273, 5723,
              January 2010.

   [SecureBeacon]

   [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", draft-sheffer-ipsecme-secure-beacon
              (work Work in progress), Progress, June 2009.

Authors' Addresses

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

   Email:

   EMail: ynir@checkpoint.com

   Qin Wu
   Huawei Technologies Co., Ltd.
   101 Software Avenue, Yuhua District
   Nanjing, JiangSu  210012
   China

   Email:

   EMail: sunseawq@huawei.com