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MIP6 Working Group                                             F. Dupont
Internet-Draft                                                       ISC
Intended status: Standards Track                             J-M. Combes
Expires: February 26, 2009                               Orange Labs R&D
                                                         August 25, 2008


        Using IPsec between Mobile and Correspondent IPv6 Nodes
                    draft-ietf-mip6-cn-ipsec-08.txt

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   This Internet-Draft will expire on February 26, 2009.

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 and protection of mobility signaling for Route
   Optimization.  The configuration details for IPsec and IKE are also
   provided.


1.  Introduction

   Mobile IPv6 documents [RFC3775][RFC3776][RFC4877] specify IPsec



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   [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 for
   Mobile IPv6 route optimization based on strong authentication and
   IPsec.

   It 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.

   Note when the design goal of the return routability procedure was to
   be "not worse than the current Internet", the design goal of this
   document is "not worse than deployed IPsec".

   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] [IKEv2bis].


2.  Applicability

   The purpose of this document is not to replace the return routability
   procedure, specified in [RFC3775], 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.  This explicit configuration involves turning
   on the mechanism specified in this document and turning off the
   Mobile IPv6 Return Routability mechanism.  It does not support
   automatic capability negotiation at this time.

   It is expected that certificate enrollment supports the inclusion of
   the Home Address of a node in the node certificate when the Home
   Address is known in time.

   It is REQUIRED that nodes conforming to this specification implement
   the base Mobile IPv6 as specified in RFC 3775 [RFC3775] (either in



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   Mobile or Correspondent Node role or in both).


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:
   o  IPsec Security Association pairs MUST be between the Mobile Node
      and one of its Correspondent Nodes.
   o  origin authentication, payload integrity and anti-replay services
      MUST be enabled.
   o  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).
   o  IPsec transport mode MUST be used.
   o  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 IPsec to
   provide a proof of origin.  The third one enforces the use of the
   proper Home Address.


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:
   o  an IPsec header was processed according to [RFC4301] section 5.2
      with a suitable IPsec Security Association, or
   o  a Binding Cache Entry check is successfully performed, or
   o  the packet contains a Binding Update, or
   o  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



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   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:
   o  Nonce Indices and Binding Authorization Data options SHOULD NOT be
      sent by the Mobile Node and MUST be ignored by the Correspondent
      Node.
   o  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:
   o  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

6.1.  Introduction

   This section should be understandable (so applicable) from both the
   mobility and IPsec/IKE points of view:
   o  IKE is an application like any other, mobility is not directly
      visible by IKE.  This is different and simpler than the Mobile
      Node - Home Agent [RFC3776] [RFC4877] situation.
   o  the key point in the use of IKE by the mobility is to enforce the
      Section 3 requirements.

   In particular, it is REQUIRED the Home Address of the Mobile Node
   matches exclusively the address of the Mobile Node in the Traffic



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   Selector.  So this section can use one of these two terms to indicate
   this address.

6.2.  Requirements

   Addresses IKE runs over (aka. the peer addresses) are the addresses
   seen at the transport or application layer.  With this definition,
   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.

   Note the PKI profile for IKE [RFC4945] applies so when the Mobile
   Node uses an Identification payload with the ID_IPV6_ADDR type, the
   Mobile Node MUST put the Home Address in it and the Correspondent
   Node MUST verify that the address in the Identification payload will
   be the Home Address.

6.3.  Authorization

   The IPsec/IKE configuration MUST constraint the authorized traffic,
   in particular the Child SA Authorization Data [RFC4301] [IKEv2bis]
   SHOULD authorize the Home Addresses per Mobile Node and per Address.
   This requirement applies to the whole IPsec/IKE configuration, not
   only the mobility related part.

   The Correspondent Node MUST verify the authorization of the Home
   Address, and it MUST refuse to established IPsec SAs with a not-
   authorized Home Address.  For instance, this check is REQUIRED when
   the Home Address can be the address in an iPAddress field in the
   SubjectAltName extension [RFC3280] of the Mobile Node certificate; or
   when the Home Address can be the address used to lookup a pre-shared
   key.

   Dynamically assigned Home Addresses are not known a priori so it is
   not possible to individually authorize them.  In this case the
   authorization SHOULD be done using the ranges of the possible
   dynamically assigned Home Addresses.


7.  IANA Considerations

   This document makes no request of IANA.



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   Note to RFC Editor: this section may be removed on publication as an
   RFC.


8.  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 a strong
   defense against this threat.

   Where the means to create suitable IPsec security associations exist,
   this mechanism provides origin authentication, integrity protection,
   replay protection and optional confidentiality services for the
   Mobile IPv6 signaling.  This improves the security over RFC 3775
   route optimization, as the signaling packets in the latter are
   vulnerable to man-in-the-middle attacks.  The implications of this
   vulnerability are that an attacker performing the man-in-the-middle
   attack can have access to the security material needed to create
   MIPv6 signaling instead of the Mobile Node.  On the other hand, an
   attacker in the same position is also capable of seeing all the
   payload packets and could launch other attacks with similar
   implications.  For instance, such an attacker could see or modify the
   contents of payload packets not protected with end-to-end security
   and cause denial-of-service for others.  However, the RFC 3775
   mechanism allows such attacks in a short time window even after the
   attacker is no longer in a position to see the payload packets
   themselves.  The mechanism defined in this specification removes this
   vulnerability.

   However, unlike RFC 3775 this mechanism should only be used when the
   correspondent node has good reason to trust the actions of the mobile
   node.  In particular, the correspondent node needs to be certain that
   the mobile node will not launch flooding attacks against a third
   party as described in [RFC4225].  Without such trust the only
   protection comes from the application of ingress filtering in the
   network where the attacker resides.  However, at the moment ingress
   filtering has not been universally deployed.  This mechanism is
   vulnerable to flooding attacks as it does not verify the validity of
   a claimed new care-of address.  Note, however, the following:
   o  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.
   o  The attack can be easily traced back to the Mobile Node.

   In order to avoid granting extra privileges by a side effect, the
   application of this mechanism must not lead to allowing any new,



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   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.

   Although the protection of static addresses is not mandatory in IPsec
   or Home Addresses do not introduce a specific issue, this document
   requires authorized Home Addresses, and recommends individual or
   range authorization according to what is possible.  This protects a
   Mobile Node using a static so likely known Home Address against the
   theft of its Home Address, both when the security associations are
   established and without limitations when they are used.  Dynamic
   addresses are not protected against spoofing but the spoofing is
   limited to the dynamic address ranges, i.e., Mobile Nodes using
   dynamically assigned Home Addresses can be attacked between them.
   Finally the authorization requirement applies to the whole
   configuration so mobility is protected against other usages of IPsec.


9.  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 Mohan
   Parthasarathy for the peer address clarification and to Jari Arkko
   for the time he spent to improve the document.


10.  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.  [RFC4651]
   describes many proposals for the general Route Optimization problem.

   [I-D.dupont-mipv6-rrcookie] is an alternate approach to testing
   Care-of Addresses.

   When the Home Address is bound to a public key, for instance when the
   Home Address is a Cryptographically Generated Address [RFC3972],
   [I-D.laganier-ike-ipv6-cga] describes an alternative approach to the
   use of strong authentication.






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11.  Changes from the previous version

   To be removed prior to publication as an RFC.

   None.


12.  References

12.1.  Normative References

   [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.

   [RFC3280]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
              X.509 Public Key Infrastructure Certificate and
              Certificate Revocation List (CRL) Profile", RFC 3280,
              April 2002.

   [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.

   [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.

   [RFC4877]  Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with
              IKEv2 and the Revised IPsec Architecture", RFC 4877,
              April 2007.

   [RFC4945]  Korver, B., "The Internet IP Security PKI Profile of
              IKEv1/ISAKMP, IKEv2, and PKIX", RFC 4945, August 2007.

12.2.  Informative References

   [I-D.dupont-mipv6-rrcookie]
              Dupont, F. and J-M. Combes, "Care-of Address Test for
              MIPv6 using a State Cookie",
              draft-dupont-mipv6-rrcookie-05.txt (work in progress),



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              November 2007.

   [I-D.laganier-ike-ipv6-cga]
              Laganier, J. and G. Montenegro, "Using IKE with IPv6
              Cryptographically Generated Addresses",
              draft-laganier-ike-ipv6-cga-02.txt (work in progress),
              July 2007.

   [IKEv2bis]
              Kaufman, C., Hoffman, P., and P. Eronen, "Internet Key
              Exchange Protocol: IKEv2", draft-hoffman-ikev2bis-02.txt
              (work in progress), November 2007.

   [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.

   [RFC4651]  Vogt, C. and J. Arkko, "A Taxonomy and Analysis of
              Enhancements to Mobile IPv6 Route Optimization", RFC 4651,
              February 2007.

   [RFC4843]  Nikander, P., Laganier, J., and F. Dupont, "An IPv6 Prefix
              for Overlay Routable Cryptographic Hash Identifiers
              (ORCHID)", RFC 4843, April 2007.


Appendix A.  IKE running over a Care-of Address

   In special circumstances where the Home Address can be unusable, as
   when the Home Address is ORCHID [RFC4843] based and not routable, IKE
   must be run over a Care-of Address but this has many known drawbacks:
   o  a Care-of Address can not be used for authentication nor
      authorization.
   o  Security Associations do not survive handoffs.
   o  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.











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Authors' Addresses

   Francis Dupont
   ISC

   Email: Francis.Dupont@fdupont.fr


   Jean-Michel Combes
   Orange Labs R&D
   38 rue du General Leclerc
   92794 Issy-les-Moulineaux Cedex 9
   France

   Email: jeanmichel.combes@gmail.com




































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