A Childless Initiation of the IKE SA
draft-nir-ike-nochild-01

Status of this Memo

This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work in progress.”

The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt.

The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html.

This Internet-Draft will expire on December 2, 2009.

Copyright Notice

Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document.

Abstract

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

Table of Contents

1.  Introduction
    1.1.  Conventions Used in This Document
2.  Usage Scenarios
3.  Protocol Outline
4.  VID Payload
5.  Modified IKE_AUTH Exchange
6.  Security Considerations
7.  IANA Considerations
8.  References
    8.1.  Normative References
    8.2.  Informative References
§  Author's Address

1.  Introduction

IKEv2, as specified in [RFC4306] (Kaufman, C., “Internet Key Exchange (IKEv2) Protocol,” December 2005.) requires that in an IKE_AUTH exchange, a child SA is created along with the IKE SA. This requirement is sometimes inconvenient, as some implementations need to use IKE for authentication only, while other implementations 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:

• Checking the liveness status of the peer via liveness checks.
• Quickly setting up child SAs without public key operations, and/or without user interaction.
• Authentication of the peer.

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] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

2.  Usage Scenarios

Several scenarios motivated this proposal:

• 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).
• Location aware security, as in [SecureBeacon] (Sheffer, Y. and Y. Nir, “Secure Beacon: Securely Detecting a Trusted Network,” January 2008.). 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.
• 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] (Rescorla, E., “Keying Material Exporters for Transport Layer Security (TLS),” March 2009.) 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 (VID Payload), within the IKE_INIT response.

A supporting initiator MAY send the modified IKE_AUTH request, described in Section 5 (Modified IKE_AUTH Exchange), if the VID payload was included in the IKE_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 IKE_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 (Modified IKE_AUTH Exchange).

4.  VID Payload

The VID payload is as described in [RFC4306] (Kaufman, C., “Internet Key Exchange (IKEv2) Protocol,” December 2005.) with the data as follows:

          73da4b423dd9f75563b15b9f918650fc

This value was obtained by hashing the string "Will do IKE_AUTH without child SA payloads"

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] (Eronen, P. and P. Hoffman, “IKEv2 Clarifications and Implementation Guidelines,” October 2006.).

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

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

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

 last request        --> AUTH

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

Note what is missing:

• The optional notifications: IPCOMP_SUPPORTED, USE_TRANSPORT_MODE, ESP_TFC_PADDING_NOT_SUPPORTED, and NON_FIRST_FRAGMENTS_ALSO.
• The SA payload.
• The traffic selector payloads.
• Any notification, extension payload or VendorID that has to do with child SA negotiation.

6.  Security Considerations

TBA

7.  IANA Considerations

There are no IANA considerations for this document.

8.  References

8.1. Normative References

8.2. Informative References

Author's Address