MIP6 Working Group F. Dupont Internet-Draft Point6 Expires: December 29, 2005 J-M. Combes France Telecom DR&D June 27, 2005 Using IPsec between Mobile and Correspondent IPv6 Nodes draft-ietf-mip6-cn-ipsec-01.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 December 29, 2005. Copyright Notice Copyright (C) The Internet Society (2005). 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, including home address option validation (aka. triangular routing), protection of mobility signaling for routing optimization and suitable configurations. Dupont & Combes Expires December 29, 2005 [Page 1] Internet-Draft Using IPsec between MN and CN June 2005 1. Introduction Mobile IPv6 documents [RFC3775][RFC3776] specifies IPsec [RFC2401] 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 routing optimization. But any stronger mechanism (i.e., more secure than the return routability procedure) MAY be used, including of course IPsec (cf. [RFC3775] Appendix 3 "New Authorization Methods"). 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 routing optimization). It gives detailed IKE [RFC2409][IKEv2] configuration guidelines for common cases. This document uses the "MUST", "SHOULD", "MAY", ..., key words according to [RFC2119]. IKE terminology is copied from IKEv2 [IKEv2]. 2. 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. - authentication, 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 routing optimization, the mobility header "upper protocol" with at least binding update (BU) and acknowledgment (BA) message type 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. 3. 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 Dupont & Combes Expires December 29, 2005 [Page 2] Internet-Draft Using IPsec between MN and CN June 2005 be considered as validated. 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 [RFC2401] section 5.2.1 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. Note this enables triangular routing from any unicast routable care-of address, i.e., half optimization without any mobility signaling. 4. Routing Optimization A suitable IPsec security association can protect binding updates and acknowledgments. In binding updates the new requirements are: - the H (home registration) and K (key management mobility capability) bits MUST be cleared. - 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 and is not checked using the state cookie mechanism [cookie], 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. - as ESP can only protect the payload, an alternate care-of address option MUST be used in conjunction with ESP (cf [RFC3775] section 11.7.1). In binding acknowledgments the new requirements are: - the K (key management mobility capability) bit MUST be cleared. - Binding authorization data option SHOULD NOT be sent by the correspondent node and MUST be ignored by the mobile node. - "long" lifetime compatible with the IPsec policy (i.e., by default up to the IPsec security association lifetime) MAY be granted. As explained in [bombing], ingress filtering either is not used and bombing attacks are possible without the "help" of any Mobile IPv6 mechanism, or is used and provides protection against fake care-of addresses from a rogue mobile node. So the only constraint is to accept real alternate care-of addresses only when they are successfully checked using the state cookie mechanism. This mechanism [cookie] MUST NOT be used when the new care-of address Dupont & Combes Expires December 29, 2005 [Page 3] Internet-Draft Using IPsec between MN and CN June 2005 is the home address, MUST be used when the alternate care-of address is a real one, i.e., is not the same than the source address in the IPv6 header nor the home address. It MAY be used in other cases but in general in the context of this document the mobile node is enough trusted to make this check not necessary or even not useful. 5. 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 layers, 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. In special circumstances where the home address can be unusable, 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. 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, [IKEv2] section 3.5) payloads SHOULD be used by the mobile node. 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 proof. In this case the public key MAY be transported by IKE from the mobile node to the correspondent node, for instance in a Certificate payload of type 11 ([IKEv2] section 3.6). Auxiliary parameters MAY be transported in an Identification payload of type ID_KEY_ID... The IKE peer policy MAY restrict IPsec security associations to the protection of Mobile IPv6 signaling, i.e., restrict the traffic selectors to the mobility header "upper protocol" with at least binding update and acknowledgment message types. This SHOULD be the default policy when authentication or authorization can be considered as being weak, for instance when the previous paragraph is applied. Dupont & Combes Expires December 29, 2005 [Page 4] Internet-Draft Using IPsec between MN and CN June 2005 6. Security Considerations IPsec is far more secure than the return routability procedure, thus it should be used where it is applicable. So this document can increase at least the overall security of Mobile IPv6. Note that some operators can not propose Mobile IPv6 based services knowing that the Mobile IPv6 security is based on assumptions. Two points are worthy of special considerations: - no care-of address test is required when ingress filtering can reject fake care-of addresses from a rogue mobile node but a correspondent node can use the return routability state cookie procedure to get extra insurance as well as the support of real alternate care-of addresses. - in order to avoid granting any extra privilege by a side effect of using IPsec, the peers (i.e., the mobile and correspondent nodes) may restrict the traffic selectors to the protection of mobility signaling only. This should be applied to any dubious cases, including by default when security administration is known to be too light. 7. 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. Thanks to the Mobile IPv6 IETF working group for discussions about the third party bombing issue, including for no convincing arguments in favor of a requirement for the care-of address test in all cases. No thanks to router vendors who do not support ingress filtering with reasonable performance on some models, and to Internet service provider managers who could enable ingress filtering but do not. 8. Changes from previous versions 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. 9. References Dupont & Combes Expires December 29, 2005 [Page 5] Internet-Draft Using IPsec between MN and CN June 2005 9.1 Normative References [IKEv2] Kaufman, C., Ed., "Internet Key Exchange (IKEv2) Protocol", draft-ietf-ipsec-ikev2-17.txt (work in progress), September 2004. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP 14, March 1997. [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998. [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. [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. [cookie] Dupont, F. and J-M. Combes, "Care-of Address Test for MIPv6 using a State Cookie", draft-dupont-mipv6-rrcookie-01.txt (work in progress), June 2005. 9.2 Informative References [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, March 2005. [bombing] Dupont, F., "A note about 3rd party bombing in Mobile IPv6", draft-dupont-mipv6-3bombing-02.txt (work in progress), June 2005. Dupont & Combes Expires December 29, 2005 [Page 6] Internet-Draft Using IPsec between MN and CN June 2005 Authors' Addresses Francis Dupont Point6 c/o GET/ENST Bretagne 2 rue de la Chataigneraie CS 17607 35576 Cesson-Sevigne Cedex France Fax: +33 2 99 12 70 30 Email: Francis.Dupont@enst-bretagne.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@francetelecom.com Dupont & Combes Expires December 29, 2005 [Page 7] Internet-Draft Using IPsec between MN and CN June 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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