Network Working Group                                             Y. Nir
Internet-Draft                                               Check Point
Intended status: Experimental                              H. Tschofenig
Expires: February 13, 2011                                           NSN
                                                                 H. Deng
                                                            China Mobile
                                                                R. Singh
                                                         August 12, 2010

                  A Childless Initiation of the IKE SA


   This document describes an extension to the IKEv2 protocol that
   allows an IKE SA to be created and authenticated without generating a
   Child SA.

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 February 13, 2011.

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   Copyright (c) 2010 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
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   ( in effect on the date of
   publication of this document.  Please review these documents
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   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 [IKEv2bis], requires that the IKE_AUTH
   exchange try to create a Child SA along with the IKE SA.  This
   requirement is sometimes inconvenient or superfluous, as some
   implementations need to use IKE for authentication only, while others
   would like to set up the IKE SA before there is any actual traffic to
   protect.  The extension described in this document allows the
   creation of an IKE SA without also attempting to create a Child SA.

   An IKE SA without any Child SA is not a fruitless endeavor.  Even
   without Child SAs, an IKE SA allows:
   o  Checking the liveness status of the peer via liveness checks.
   o  Quickly setting up Child SAs without public key operations, and
      without user interaction.
   o  Authentication of the peer.
   o  Detection of NAT boxes between two hosts on the Internet

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

   Several scenarios motivated this proposal:
   o  Interactive remote access VPN: the user tells the client to
      "connect", which may involve interactive authentication.  There is
      still no traffic, but some may come later.  Since there is no
      traffic, it is impossible for the gateway to know what selectors
      to use (how to narrow down the client's proposal).
   o  Location aware security, as in [SecureBeacon].  The user is
      roaming between trusted and untrusted networks.  While in an
      untrusted network, all traffic should be encrypted, but on the
      trusted network, only the IKE SA needs to be maintained.
   o  An IKE SA may be needed between peers even when there is not IPsec
      traffic.  Such IKE peers use liveness checks, and report to the
      administrator the status of the "VPN links".
   o  IKE may be used on some physically secure links, where
      authentication is necessary, but traffic protection is not.  An
      example of this in the PON links as described in [3GPP.33.820].

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   o  Childless IKE can be used for [EAP-IKEv2] where we use IKEv2 as a
      method for user authentication.
   o  A node receiving IPsec traffic with an unrecognized SPI should
      send an INVALID_SPI notification.  If this traffic comes from a
      peer, which it recognizes based on its IP address, then this node
      may set up an IKE SA so as to be able to send the notification in
      a protected IKE_INFORMATIONAL exchange.
   o  A future extension may have IKE SAs used for generating keying
      material for applications, without ever requiring Child SAs.  This
      is similar to what [extractors] is doing in TLS.

   In some of these cases it may be possible to create a dummy Child SA
   and then remove it, but this creates undesirable side effects and
   race conditions.  Moreover, the IKE peer might see the deletion of
   the Child SA as a reason to delete the IKE SA.

3.  Protocol Outline

   The decision of whether or not to support an IKE_AUTH exchange
   without the piggy-backed Child SA negotiation is ultimately up to the
   responder.  A supporting responder MUST include the Notify payload,
   described in Section 4, within the IKE_SA_INIT response.

   A supporting initiator MAY send the modified IKE_AUTH request,
   described in Section 5, if the Notification was included in the
   IKE_SA_INIT response.  The initiator MUST NOT send the modified
   IKE_AUTH request if the Notification was not present.

   A supporting responder that has advertised support by including the
   notification in the IKE_SA_INIT response MUST process a modified
   IKE_AUTH request, and MUST reply with a modified IKE_AUTH response.
   Such a responder MUST NOT reply with a modified IKE_AUTH response if
   the initiator did not send a modified IKE_AUTH request.

   A supporting responder that has been configured not to support this
   extension to the protocol MUST behave as the same as if it didn't
   support this extension.  It MUST NOT advertise the capability with a
   notification, and it SHOULD reply with an INVALID_SYNTAX Notify
   payload if the client sends an IKE_AUTH request that is modified as
   described in Section 5.


   The Notify payload is as described in [IKEv2bis]

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                            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    ! Childless Notify Message Type !

   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 [IKEv2bis].
   o  Childless Notify Message Type (2 octets) - MUST be xxxxx, the
      value assigned for CHILDLESS_IKE_SUPPORTED.  TBA by IANA.

5.  Modified IKE_AUTH Exchange

   For brevity, only the EAP version of an AUTH exchange will be
   presented here.  The non-EAP version is very similar.  The figures
   below are based on appendix C.3 of [IKEv2bis].

    first request       --> IDi,
                            [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+],

    first response      <-- IDr, [CERT+], AUTH,

                      / --> EAP
    repeat 1..N times |
                      \ <-- EAP

    last request        --> AUTH

    last response       <-- AUTH,

   Note what is missing:
   o  The optional notifications: IPCOMP_SUPPORTED, USE_TRANSPORT_MODE,

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   o  The SA payload.
   o  The traffic selector payloads.
   o  Any notification, extension payload or VendorID that has to do
      with Child SA negotiation.

6.  Security Considerations

   This protocol variation inherits all the security properties of
   regular IKEv2 as described in [IKEv2bis].

   The new notification carried in the initial exchange advertises the
   capability, and cannot be forged or added by an adversary without
   being detected, because the response to the initial exchange is
   authenticated with the AUTH payload of the IKE_AUTH exchange.
   Furthermore, both peers have to be configured to use this variation
   of the exchange in order for the responder to accept a childless
   proposal from the initiator.

7.  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 "CHILDLESS_IKE_SUPPORTED".

8.  References

8.1.  Normative References

              Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol: IKEv2",
              draft-ietf-ipsecme-ikev2bis-11 (work in progress),
              May 2010.

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

8.2.  Informative References

              3GPP, "Security of H(e)NB", 3GPP TR 33.820 8.0.0,
              March 2009.

              Tschofenig, H., Kroeselberg, D., Pashalidis, A., Ohba, Y.,

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              and F. Bersani, "The Extensible Authentication Protocol-
              Internet Key Exchange Protocol version 2 (EAP-IKEv2)
              Method", RFC 5106, February 2008.

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

              Rescorla, E., "Keying Material Exporters for Transport
              Layer Security (TLS)", draft-ietf-tls-extractor (work in
              progress), March 2009.

Authors' Addresses

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


   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600

   Phone: +358 (50) 4871445

   Hui Deng
   China Mobile
   53A,Xibianmennei Ave.
   Xuanwu District
   Beijing  100053


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   Rajeshwar Singh Jenwar
   Cisco Systems, Inc.
   O'Shaugnessy Road
   Bangalore, Karnataka  560025

   Phone: +91 80 4103 3563

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