MIP6 Working Group F. Dupont Internet-Draft CELAR Expires: September 1, 2007 J-M. Combes France Telecom DR&D February 28, 2007 Using IPsec between Mobile and Correspondent IPv6 Nodes draft-ietf-mip6-cn-ipsec-04.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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 September 1, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract Mobile IPv6 uses IPsec to protect signaling between the Mobile Node and the Home Agent. This document defines how IPsec can be used between the Mobile Node and Correspondent Nodes for Home Address Option validation (aka. triangular routing) and protection of mobility signaling for Route Optimization. The configuration details for IPsec and IKE are also provided. Dupont & Combes Expires September 1, 2007 [Page 1] Internet-Draft Using IPsec between MN and CN February 2007 1. Introduction Mobile IPv6 documents [RFC3775][RFC3776] [MIP6IKE2] specifies IPsec [RFC4301] for the protection of the signaling between the Mobile Node (MN) and its Home Agent (HA), and the return routability procedure between the Mobile Node and its Correspondent Nodes (CN) for Route Optimization. This document defines an alternative mechanism based on strong authentication and IPsec. This document specifies which IPsec configurations can be useful in a Mobile IPv6 context and how they can validate Home Address Options (enabling triangular routing) and protect mobility signaling (enabling Route Optimization). It gives detailed IKE [RFC2409][RFC4306] configuration guidelines for common cases. 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]. IKE terminology is copied from IKEv2 [RFC4306]. 2. Applicability The purpose of this document is not to replace the [RFC3775] return routability procedure by the use of IPsec/IKE. It is unrealistic to expect credentials to be available today for strong authentication between any pair of Internet nodes. The idea is to enable the use of the superior security provided by IPsec when it is already in use (i.e., comes at no extra cost), when obstacles (i.e., authentication) to its use no more stand in the way, or simply when it can be considered as highly desirable. This mechanism should only be turned on by explicit configuration between specific peers. It does not support automatic capability negociation at this time. 3. IPsec in a Mobile IPv6 context This document considers only suitable IPsec Security Associations, i.e., anything which does not fulfill the following requirements is out of scope: - IPsec Security Association pairs MUST be between the Mobile Node and one of its Correspondent Nodes. Dupont & Combes Expires September 1, 2007 [Page 2] Internet-Draft Using IPsec between MN and CN February 2007 - origin authentication, payload integrity and anti-replay services MUST be selected. - the Traffic Selectors MUST match exclusively the Home Address of the Mobile Node and an address of the Correspondent Node (the address used for communication between peers). - the transport mode MUST be used. - for Route Optimization, the Mobility Header "upper protocol" with at least Binding Update (BU, from the MN) and Binding Acknowledgment (BA, from the CN) message types MUST be accepted by the Traffic Selectors. The purpose of the first three requirements is to allow to use IPsec as a proof of origin. 4. Home Address Option validation This document amends the Mobile IPv6 [RFC3775] section 9.3.1 by adding a second way (other than Binding Cache Entry check) to provide Home Address Option validation. When a packet carrying a Home Address Option is protected by a suitable IPsec Security Association, the Home Address Option SHOULD be considered valid. A way to implement this is to mark the Home Address Option as "to be validated" when it is processed. When the upper protocol is reached, in order either: - an IPsec header was processed according to [RFC4301] section 5.2 with a suitable IPsec Security Association, or - a Binding Cache Entry check is successfully performed, or - the packet contains a Binding Update, or - the packet MUST be dropped. By just setting up an IPsec SA with the CN, the MN is able to send packets directly to the CN, i.e., triangular routing is enabled. The CN does the Home Address Option validation by successful IPsec processing of the packet. The Care-of Address in the source address field of the IPv6 header is not used by IPsec at all as the IPsec policy checks happen against the Home Address. The CN continues to send the packets via the home network until a Binding Update is processed. 5. Route Optimization A suitable IPsec Security Association can protect Binding Updates and Acknowledgments. In Binding Updates the new requirements are: Dupont & Combes Expires September 1, 2007 [Page 3] Internet-Draft Using IPsec between MN and CN February 2007 - Nonce Indices and Binding Authorization Data options SHOULD NOT be sent by the Mobile Node and MUST be ignored by the Correspondent Node. - when an Alternate Care-of Address option is present, the alternate Care-of Address MUST match the source address in the IP header or the Home Address itself. Any Binding Update which does not fulfill this requirement MUST be rejected. In Binding Acknowledgments the new requirement is: - Binding Authorization Data option SHOULD NOT be sent by the Correspondent Node and MUST be ignored by the Mobile Node. The use of the K (Key Management Mobility Capability) bit with Correspondent Nodes is not defined. This bit is always set to zero on sending a Binding Update or Binding Acknowledgment, and ignored on receipt. Note that a relatively long lifetime compatible with the IPsec policy (i.e., by default up to the IPsec Security Association lifetime) MAY be used with correspondent registrations, in contrast to the short lifetime required by standard RFC 3775 mechanisms. 6. IKE configurations This document considers only IKE where it is used for mobility purpose. Peer addresses (addresses IKE runs over) are the addresses seen at the transport or application layer, i.e., when the mobile node uses its Home Address as the source of an IKE message, the source address in the IP header can (should!) be a Care-of Address. IKE MUST be run over the Home Address for the Mobile Node side when the Home Address is usable. The case where the Home Address in unusable is the subject of Appendix A. The Home Address MAY be used in (phase 1) Mobile Node Identification payloads. But this does not work well with dynamic Home Addresses, so when it is acceptable by the Correspondent Node policy, name based Identification (i.e., of type ID_FQDN or ID_RFC822_ADDR, [RFC4306] section 3.5) payloads SHOULD be used by the Mobile Node. 7. Security considerations The Mobile IPv6 Route Optimization security design background document [RFC4225] describes the unauthorized creation of Binding Cache entries as the main avenue of attack. The authentication and authorization of the Mobile Node provided by IPsec/IKE is the best Dupont & Combes Expires September 1, 2007 [Page 4] Internet-Draft Using IPsec between MN and CN February 2007 possible defense against this threat. The mechanism of this document does not perform Care-of Address check (but see Section 9) so it does not provide a protection against a Mobile Node using a fake address in order to bomb a third party but: - the attacker has to be the Mobile Node itself, i.e., the IPsec/IKE peer, which is supposed to be the subject of a minimal level of trust. - the attack can be easily traced back to the Mobile Node. Note that these two arguments were used for the Home Agent case, protected by IPsec/IKE too. - the ingress filtering blocks topologically incorrect Care-of Addresses (because there are source addresses too), and when it is not enforced direct Denial of Services attacks using still/regular IPv6 are possible. In order to avoid granting extra privileges by a side effect, the application of this mechanism must not lead to allowing any new, previously unauthorized traffic to flow between the peers beyond mobility signaling with the Mobility Header (MH) protocol. The IPsec peer policy MAY also restrict IPsec Security Associations to the protection of Mobile IPv6 signaling, i.e., restrict the Traffic Selectors to MH with at least Binding Update and Binding Acknowledgment message types. 8. Acknowledgments The authors would like to thank many people for believing in IPsec as a right way to secure Mobile IPv6. Special thanks to Wassim Haddad and Claude Castelluccia for keeping our attention to special cases where Home Addresses are derived from public keys. 9. Possible enhancements A number of potential enhancements of this method are possible, including, for instance, various mechanisms for verification of Care-of Addresses or use of addresses bound to keys. [ROENC] describes many proposals for the general Route Optimization problem. [COOKIE] is an active Care-of Address test which may relax the "MUST NOT" against real alternate Care-of Addresses, and improve the trust in the Mobile Node not presenting a fake Care-of Address. When the Home Address is bound to a public key, for instance when the Home Address is a Cryptographically Generated Addresses [RFC3972], the strong authentication MAY be replaced by an address ownership Dupont & Combes Expires September 1, 2007 [Page 5] Internet-Draft Using IPsec between MN and CN February 2007 proof as described for instance in [IKECGA]. This property fulfills the need of the Route Optimization. Better Than Nothing Security [BTNS] at the opposite seems to be too weak so does not present today a clear interest in this context. 10. Changes from previous versions To be removed prior to publication as an RFC. Some names begin with a capital when it seems to be the usage, including in references. The security considerations were rewritten. Arguable stuff was moved to new section "possible enhancements". An applicability section was added. The IKE running over a Care-of Address was moved to an appendix as it is not at all the standard case. The Care-of Address test annex was moved to its own document [COOKIE]. Peer address clarification (thanks to Mohan Parthasarathy). Change SHOULD/MAY to MUST/MUST for Mobile Node peer address. 11. References 11.1. Normative References [MIP6IKE2] Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with IKEv2 and the revised IPsec Architecture", draft-ietf-mip6-ikev2-ipsec-08.txt (work in progress), December 2006. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP 14, March 1997. [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, November 1998. [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. Dupont & Combes Expires September 1, 2007 [Page 6] Internet-Draft Using IPsec between MN and CN February 2007 [RFC3776] Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to Protect Mobile IPv6 Signaling Between Mobile Nodes and Home Agents", RFC 3776, June 2004. [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. [RFC4306] Kaufman, C., Ed., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, December 2005. 11.2. Informative References [BTNS] Touch, J., Black, D., and Y. Wang, "Problem and Applicability Statement for Better Than Nothing Security (BTNS)", draft-ietf-btns-prob-and-applic-04.txt (work in progress), September 2006. [COOKIE] Dupont, F. and J-M. Combes, "Care-of Address Test for MIPv6 using a State Cookie", draft-dupont-mipv6-rrcookie-04.txt (work in progress), January 2007. [IKECGA] Laganier, J. and G. Montenegro, "Using IKE with IPv6 Cryptographically Generated Address", draft-laganier-ike-ipv6-cga-01.txt (work in progress), June 2003. [ORCHID] Nikander, P., Laganier, J., and F. Dupont, "An IPv6 Prefix for Overlay Routable Cryptographic Hash Identifiers (ORCHID)", draft-laganier-ipv6-khi-05.txt (work in progress), September 2006. [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, March 2005. [RFC4225] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E. Nordmark, "Mobile IP Version 6 Route Optimization Security Design Background", RFC 4225, December 2005. [ROENC] Vogt, C. and J. Arkko, "A Taxonomy and Analysis of Enhancements to Mobile IPv6 Route Optimization", draft-irtf-mobopts-ro-enhancements-08.txt (work in progress), May 2006. Appendix A. IKE running over a Care-of Address In special circumstances where the Home Address can be unusable, as Dupont & Combes Expires September 1, 2007 [Page 7] Internet-Draft Using IPsec between MN and CN February 2007 when the Home Address is ORCHID [ORCHID] based and not routable, IKE must be run over a Care-of Address but this has many known drawbacks: - a Care-of Address can not be used for authentication nor authorization. - Security Associations do not survive handoffs. - the establishment of transport mode IPsec Security Association using the Home Address as the Mobile Node Traffic Selector raises a policy / authorization issue as IKE runs over another address. Authors' Addresses Francis Dupont CELAR Email: Francis.Dupont@fdupont.fr Jean-Michel Combes France Telecom DR&D 38/40 rue du General Leclerc 92794 Issy-les-Moulineaux Cedex 9 France Fax: +33 1 45 29 65 19 Email: jeanmichel.combes@gmail.com Dupont & Combes Expires September 1, 2007 [Page 8] Internet-Draft Using IPsec between MN and CN February 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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