Network Working Group                                             Y. Nir
Internet-Draft                                               Check Point
Intended status: Standards Track                           H. Tschofenig
Expires: September 8, 2010                                           NSN
                                                                 H. Deng
                                                            China Mobile
                                                                R. Singh
                                                           March 7, 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

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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   than English.

1.  Introduction

   IKEv2, as specified in [RFC4306] 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.

   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].

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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].
   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 exchage without
   the piggy-backed Child SA negotiation is ultimately up to the
   reponsder.  A supporting resonder MUST include the VID 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 VID payload was included in the
   IKE_SA_INIT response.  The initiator MUST NOT send the modified
   IKE_AUTH request if the VID was not present.

   A supporting responder that advertised the VID payload in the

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   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
   VID payload, 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.

4.  VID Payload

   The VID payload is as described in [RFC4306] with a 16-octets data
   field as follows:


   This value was obtained by hashing the string "Will do IKE_AUTH
   without Child SA payloads" using the MD5 algorithms.  Note that this
   is only an explanation, and the actual content of the VID data MUST
   be the value above.

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 A.3 of [RFC4718].

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    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,
   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 [RFC4306].

   The new Vendor ID 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

   There are no IANA considerations for this document.

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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.

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

   [RFC4718]  Eronen, P. and P. Hoffman, "IKEv2 Clarifications and
              Implementation Guidelines", RFC 4718, October 2006.

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.,
              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


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   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600

   Phone: +358 (50) 4871445

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


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

   Phone: +91 80 4103 3563

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