RFC 6023

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

Okay bestie, this is RFC 6023 🎀. It's an Independent Submission, the category is Experimental, the ISSN is 2070-1721, and it's dated October 2010. The authors are Y. Nir (Check Point) 💜, H. Tschofenig (NSN) 🌸, H. Deng (China Mobile) 🧚, and R. Singh (Cisco) 🦋. The header doesn't list any RFC that this one obsoletes or updates.

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Abstract

This doc describes an extension to the Internet Key Exchange version 2 (IKEv2) protocol that lets an IKEv2 Security Association (SA) get created and authenticated without generating a Child SA. Main character energy 💅

Status of This Memo

Not an Internet Standards Track spec here 🙈. It's published for examination, experimental implementation, and evaluation.

This document defines an Experimental Protocol for the Internet community. It's a contribution to the RFC Series, independent of any other RFC stream. The RFC Editor picked to publish it at their discretion and makes no statement about its value for implementation or deployment. Documents the RFC Editor approves for publication are not a candidate for any level of Internet Standard; see Section 2 of RFC 5741.

Info about the current status of this doc, any errata, and how to give feedback is 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, because they describe your rights and restrictions with respect to this document 🫶

1. Introduction 🌈

So IKEv2, as specified in [RFC5996], says the IKE_AUTH exchange has to try to create a Child SA along with the IKEv2 SA. Honestly? That's sometimes inconvenient or just extra 🙄. Some implementations only need IKEv2 for authentication, and others want to set up the IKEv2 SA before there's any real traffic to protect. This extension lets you create an IKEv2 SA without also trying to create a Child SA ✨. The terms IKEv2, IKEv2 SA, Child SA, and the various IKEv2 exchanges are defined in [RFC5996].

An IKEv2 SA without any Child SA is not a wasted effort, bestie 💖. Even without Child SAs, an IKEv2 SA lets you do the following:

• Check the liveness status of the peer via liveness checks.
• Quickly set up Child SAs without public key operations and without user interaction.
• Authenticate the peer.
• Detect 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] 📖.

2. Usage Scenarios 🍓

Several scenarios motivated this proposal, and they're all very real:

• Interactive remote access VPN: the user tells the client to "connect", which may involve interactive authentication. There's still no traffic, but some may come later. Since there's no traffic, the gateway can't know which selectors to use (how to narrow down the client's proposal) 😭.
• Location-aware security, as in [SecureBeacon]. The user is roaming between trusted and untrusted networks. While on an untrusted network, all traffic should be encrypted, but on the trusted network, only the IKEv2 SA needs to be maintained 🔥.
• An IKEv2 SA may be needed between peers even when there isn't any IPsec traffic. Such IKEv2 peers use liveness checks and report the status of the "VPN links" to the administrator 👑.
• IKEv2 may be used on some physically secure links, where authentication is necessary but traffic protection isn't. An example is the Passive Optical Network (PON) links described in [3GPP.33.820] 🦋.
• Childless IKEv2 can be used for [RFC5106], where IKEv2 serves as a method for user authentication 🫶.
• 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 that it recognizes based on its IP address, then this node may set up an IKEv2 SA so it can send the notification in a protected INFORMATIONAL exchange 🙈.
• 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] does in Transport Layer Security (TLS) ✨.

In some of these cases, you could create a dummy Child SA and then remove it, but that causes undesirable side effects and race conditions 💀. Plus, the IKEv2 peer might see the deletion of the Child SA as a reason to delete the IKEv2 SA. Yikes 😭.

3. Protocol Outline 🧚

Whether to support an IKE_AUTH exchange without the piggy-backed Child SA negotiation is ultimately the responder's call 👑. 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 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 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

• Protocol ID (1 octet) MUST be 1, as this message is related to an IKEv2 SA.
• SPI Size (1 octet) MUST be zero, in conformance with section 3.10 of [RFC5996].
• Childless Notify Message Type (2 octets) MUST be 16418, the value assigned for CHILDLESS_IKEV2_SUPPORTED.

5. Modified IKE_AUTH Exchange 🎀

To keep it brief, only the Extensible Authentication Protocol (EAP) version of an AUTH exchange is 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+]

Now, the "what's missing" list 👀:

• 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 🔥

This is the serious part, so pay attention 🚨

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 an adversary can't forge or add it without being detected, because the response to the initial exchange is authenticated with the AUTH payload of the IKE_AUTH exchange. On top of that, both peers have to be configured to use this variation of the exchange 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.

Authors' Addresses 💌

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

EMail: ynir@checkpoint.com


Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo  02600
Finland

Phone: +358 (50) 4871445
EMail: Hannes.Tschofenig@gmx.net
URI:   http://www.tschofenig.priv.at


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

EMail: denghui02@gmail.com


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

Phone: +91 80 4103 3563
EMail: rsj@cisco.com