Network Working Group                                             Y. Nir
Internet-Draft                                               Check Point
Updates: 5996 (if approved)                                        Q. Wu
Intended status: Standards Track                                  Huawei
Expires: November 22, 2012                                  May 21, 2012

                 An IKEv2 Extension for Supporting ERP


   This document describes an extension to the IKEv2 protocol that
   allows an IKE Security Association (SA) to be created and
   authenticated using the EAP Re-authentication Protocol extension as
   described in RFC 5296bis.

   NOTE TO RFC EDITOR: Replace 5296bis in the previous paragraph with
   the RFC number assigned to draft-ietf-hokey-rfc5296bis (now in the
   RFC Editor queue)

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on November 22, 2012.

Copyright Notice

   Copyright (c) 2012 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
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

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   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
   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
   [RFC5296bis], 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

   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.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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
      NYC.  An employee using 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 it is more desirable to have the client initiate

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      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 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, but this process is beyond the scope of this
      document.  [SecureBeacon] is a now-abandoned attempt at this.

3.  Protocol Outline

   Supporting ERX requires an EAP payload in the first IKE_AUTH request.
   This is a deviation from the rules in RFC 5996, so support needs to
   be indicated through a Notify payload in the IKE_SA_INIT response.
   This Notify replaces the EAP-Initiate/Re-auth-Start message of ERX,
   and therefore contains the domain name, as specified in section of [RFC5296bis].

   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,
   and receives the rMSK and an EAP-Finish/Re-auth message.  It 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 sections 2.15 and 2.16 of
   [RFC5996].  The responder replies similarly, and the IKE_AUTH
   exchange is finished.

   The following figure is adapted from appendixes C.1 and C.3 of RFC
   5996, with most of the optional payloads removed.  Note that the
   EAP_Initiate/Re-auth message is added.

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    init request         --> SA, KE, Ni,

    init response       <-- SA, KE, Nr,

    first request       --> EAP(EAP_Initiate/Re-auth),
                            [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+],
                            SA, TSi, TSr,

    first response      <-- IDr, [CERT+], 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.  See Section 3.2 for details.

3.1.  Clarification About EAP Codes

   Section 3.16 of RFC 5996 enumerates the EAP codes in EAP messages
   which are carried in EAP payloads.  The enumeration goes only to 4.
   It is not clear whether that list is supposed to be exhaustive or

   To clarify, an implementation supporting this specification MUST
   accept and transmit EAP messages with at least the codes for Initiate
   and Finish (5 and 6), in addition to the four codes enumerated in RFC
   5996.  This document is intentionally silent about other EAP codes
   that are not enumerated in RFC 5996 or in this document.

3.2.  User Name 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.

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   This section addresses instances where this is not the case.

   Section 5.3.2 of [RFC5296bis] 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 NAI within the TLV is the EMSKName 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 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 user
      name.  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
      they belong to.  The AAA server can communicate such information
      to the VPN gateway, for example using the CLASS attribute in
      RADIUS and Diameter.  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 LDAP, 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

   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.

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4.  ERX_SUPPORTED Notification

   The Notify payload is as described in RFC 5996:

                            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 1, as this message is related to an
      IKE SA.
   o  SPI Size (1 octet) MUST be zero, in conformance with section 3.10
      of [RFC5996].
   o  ERX Notify Message Type (2 octets) - MUST be xxxxx, the value
      assigned for ERX.  TBA by IANA.
   o  Domain Name (variable) - contains the domain name or realm, as
      these terms are used in [RFC5296bis], and encoded as UTF-8.

5.  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

   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.

   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.

6.  IANA Considerations

   IANA is requested to assign a notify message type from the status

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   types range (16418-40959) of the "IKEv2 Notify Message Types"
   registry with name "ERX_SUPPORTED".

7.  Acknowledgements

   The authors would like to thank Yaron Sheffer for comments and
   suggested text that have contributed to this document.

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.

              Wu, W., Cao, Z., Zorn, G., Shi, Y., and B. He, "EAP
              Extensions for EAP Re-authentication Protocol (ERP)",
              draft-ietf-hokey-rfc5296bis-07 (work in progress),
              May 2012.

   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol: IKEv2", RFC 5996,
              September 2010.

8.2.  Informative References

              Sheffer, Y. and Y. Nir, "Secure Beacon: Securely Detecting
              a Trusted Network", draft-sheffer-ipsecme-secure-beacon
              (work in progress), June 2009.

Authors' Addresses

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


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


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