RFC6023

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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".

References

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.

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.

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]