Network Working Group                                             Y. Nir
Internet-Draft                                               Check Point
Intended status: Standards Track                                   Q. Wu
Expires: May 22, 2012                                             Huawei
                                                       November 19, 2011


                 An IKEv2 Extension for Supporting ERP
                        draft-nir-ipsecme-erx-02

Abstract

   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 5296 and its bis document.

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 May 22, 2012.

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   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.



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1.  Introduction

   IKEv2, as specified in [RFC5996], allows authentication of the
   initiator using an EAP method.  This is described in section 2.16.
   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 descripted 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
   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.

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

   Several scenarios motivated this proposal:
   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-2-site VPN), this is not
      efficient, and 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 VPN is
      necessary and back again.  Both the VPN server and the 802.1x



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      access point are authenticators that connect to the same AAA
      servers.  So it makes sense to make the transition smooth, without
      requiring user interaction.  [SecureBeacon] is an attempt to allow
      detecting whether the client should connect using VPN or not.


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
   5.3.1.1 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.  If forwards
   that 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 or
   [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 replaces the IDi payload.


















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    init request         --> SA, KE, Ni,

    init response       <-- SA, KE, Nr,
                            N[ERX_SUPPORTED]

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

    first response      <-- IDr, [CERT+], AUTH,
                            EAP(EAP-Finish/Re-auth),
                            [V+][N+]

    last request        --> AUTH

    last response       <-- AUTH,
                            [CP(CFG_REPLY)],
                            SA, TSi, TSr,
                            [V+][N+]

3.1.  Clarification About EAP Codes

   Section 3.16 of [RFC5996] 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
   not.

   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).

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.

   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



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   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 ID 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.  Logging can still be done 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
      DIAMETER.

   In any case authorization is a major issue in deployments, if the
   peer's home EAP server does not also perform the re-authentication.


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                        !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   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].


5.  Security Considerations

   TBA


6.  IANA Considerations

   IANA is requested to assign a notify message type from the status
   types range (16418-40959) of the "IKEv2 Notify Message Types"
   registry with name "ERX_SUPPORTED".


7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5296bis]
              Wu, W., Cao, Z., Zorn, G., Shi, Y., and B. He, "EAP
              Extensions for EAP Re-authentication Protocol (ERP)",
              draft-ietf-hokey-rfc5296bis-06 (work in progress),
              May 2011.

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

7.2.  Informative References

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






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Authors' Addresses

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

   Email: ynir@checkpoint.com


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

   Email: Sunseawq@huawei.com

































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