Independent Submission                                            Y. Nir
Request for Comments: 6023                                   Check Point
Category: Experimental                                     H. Tschofenig
ISSN: 2070-1721                                                      NSN
                                                                H. Deng
                                                           China Mobile
                                                               R. Singh
                                                                  Cisco
                                                           October 2010


                      A Childless Initiation of
the Internet Key Exchange Version 2 (IKEv2) Security Association (SA)

Abstract

  This document describes an extension to the Internet Key Exchange
  version 2 (IKEv2) protocol that allows an IKEv2 Security Association
  (SA) to be created and authenticated without generating a Child SA.

Status of This Memo

  This document is not an Internet Standards Track specification; it is
  published for examination, experimental implementation, and
  evaluation.

  This document defines an Experimental Protocol for the Internet
  community.  This is a contribution to the RFC Series, independently
  of any other RFC stream.  The RFC Editor has chosen to publish this
  document at its discretion and makes no statement about its value for
  implementation or deployment.  Documents approved for publication by
  the RFC Editor are not a candidate for any level of 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 obtained at
  http://www.rfc-editor.org/info/rfc6023.














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Copyright Notice

  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
  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.

1.  Introduction

  IKEv2, as specified in [RFC5996], requires that the IKE_AUTH exchange
  try to create a Child SA along with the IKEv2 SA.  This requirement
  is sometimes inconvenient or superfluous, as some implementations
  need to use IKEv2 for authentication only, while others would like to
  set up the IKEv2 SA before there is any actual traffic to protect.
  The extension described in this document allows the creation of an
  IKEv2 SA without also attempting to create a Child SA.  The terms
  IKEv2, IKEv2 SA, and Child SA and the various IKEv2 exchanges are
  defined in [RFC5996]

  An IKEv2 SA without any Child SA is not a fruitless endeavor.  Even
  without Child SAs, an IKEv2 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",
  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
  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 IKEv2 SA needs to be maintained.

  o  An IKEv2 SA may be needed between peers even when there is not
     IPsec traffic.  Such IKEv2 peers use liveness checks, and report
     to the administrator the status of the "VPN links".

  o  IKEv2 may be used on some physically secure links, where
     authentication is necessary but traffic protection is not.  An
     example of this is the Passive Optical Network (PON) links as
     described in [3GPP.33.820].

  o  Childless IKEv2 can be used for [RFC5106] where we use IKEv2 as a
     method for user authentication.

  o  A node receiving IPsec traffic with an unrecognized Security
     Parameter Index (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 IKEv2 SA so as to be able
     to send the notification in a protected INFORMATIONAL exchange.

  o  A future extension may have IKEv2 SAs used for generating keying
     material for applications, without ever requiring Child SAs.  This
     is similar to what [RFC5705] is doing in Transport Layer Security
     (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 IKEv2 peer might see the deletion of
  the Child SA as a reason to delete the IKEv2 SA.









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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.

4.  CHILDLESS_IKEV2_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    ! Childless Notify Message Type !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  o  Protocol ID (1 octet) MUST be 1, as this message is related to an
     IKEv2 SA.

  o  SPI Size (1 octet) MUST be zero, in conformance with section 3.10
     of [RFC5996].

  o  Childless Notify Message Type (2 octets) - MUST be 16418, the
     value assigned for CHILDLESS_IKEV2_SUPPORTED.






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5.  Modified IKE_AUTH Exchange

  For brevity, only the Extensible Authentication Protocol (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 [RFC5996].

   first request       --> IDi,
                           [N(INITIAL_CONTACT)],
                           [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+],
                           [IDr],
                           [CP(CFG_REQUEST)],
                           [V+][N+]

   first response      <-- IDr, [CERT+], AUTH,
                           EAP,
                           [V+][N+]

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

   last request        --> AUTH

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

  Note what is missing:

  o  The optional notifications: IPCOMP_SUPPORTED, USE_TRANSPORT_MODE,
     ESP_TFC_PADDING_NOT_SUPPORTED, and NON_FIRST_FRAGMENTS_ALSO.

  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 [RFC5996].

  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



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  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 has assigned a notify message type from the "IKEv2 Notify
  Message Types" registry with the name "CHILDLESS_IKEV2_SUPPORTED" and
  the value "16418".

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.

  [RFC5996]       Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
                  "Internet Key Exchange Protocol Version 2 (IKEv2)",
                  RFC 5996, September 2010.

8.2.  Informative References

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

  [RFC5106]       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.

  [RFC5705]       Rescorla, E., "Keying Material Exporters for
                  Transport Layer Security (TLS)", RFC 5705,
                  March 2010.

  [SecureBeacon]  Sheffer, Y. and Y. Nir, "Secure Beacon: Securely
                  Detecting a Trusted Network", 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: [email protected]


  Hannes Tschofenig
  Nokia Siemens Networks
  Linnoitustie 6
  Espoo  02600
  Finland

  Phone: +358 (50) 4871445
  EMail: [email protected]
  URI:   http://www.tschofenig.priv.at


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

  EMail: [email protected]


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

  Phone: +91 80 4103 3563
  EMail: [email protected]











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