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Versions: (draft-krishnan-csi-proxy-send) 00 01 02 03 04 05 RFC 6496

CGA & SEND maintenance Working                               S. Krishnan
Group                                                           Ericsson
Internet-Draft                                               J. Laganier
Intended status: Experimental                              QUALCOMM Inc.
Expires: April 1, 2011                                         M. Bonola
                                             Rome Tor Vergata University
                                                      A. Garcia-Martinez
                                                                    UC3M
                                                      September 28, 2010


                    Secure Proxy ND Support for SEND
                      draft-ietf-csi-proxy-send-05

Abstract

   Secure Neighbor Discovery (SEND) specifies a method for securing
   Neighbor Discovery (ND) signaling against specific threats.  As
   defined today, SEND assumes that the node sending a ND message is the
   owner of the address from which the message is sent and/or posses a
   key which authorizes the node to act as a router, so that it is in
   possession of the private key or keys used to generate the digital
   signature on each message.  This means that the Proxy ND signaling
   performed by nodes that do not possess knowledge of the address
   owner's private key and/or knowledge of a router's key cannot be
   secured using SEND.  This document extends the current SEND
   specification in order to secure Proxy ND operation.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on April 1, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the



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   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, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Secure Proxy ND Overview . . . . . . . . . . . . . . . . . . .  6
   5.  Secure Proxy ND Specification  . . . . . . . . . . . . . . . .  8
     5.1.  Proxy Signature Option . . . . . . . . . . . . . . . . . .  8
     5.2.  Modified SEND processing rules . . . . . . . . . . . . . . 10
       5.2.1.  Processing rules for senders . . . . . . . . . . . . . 10
       5.2.2.  Processing rules for receivers . . . . . . . . . . . . 11
     5.3.  Proxying Link-Local Addresses  . . . . . . . . . . . . . . 13
   6.  Application Scenarios  . . . . . . . . . . . . . . . . . . . . 14
     6.1.  Scenario 1: Mobile IPv6  . . . . . . . . . . . . . . . . . 14
     6.2.  Scenario 2: Proxy Mobile IPv6  . . . . . . . . . . . . . . 15
     6.3.  Scenario 3: RFC 4389 Neighbor Discovery Proxy  . . . . . . 18
   7.  Backward Compatibility with RFC3971 nodes and non-SEND
       nodes  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     7.1.  Backward Compatibility with RFC3971 nodes  . . . . . . . . 20
     7.2.  Backward Compatibility with non-SEND nodes . . . . . . . . 20
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 27
     11.2. Informative References . . . . . . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29











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1.  Requirements notation

   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].














































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2.  Introduction

   Secure Neighbor Discovery (SEND) [RFC3971] specifies a method for
   securing Neighbor Discovery (ND) signaling [RFC4861] against specific
   threats [RFC3756].  As defined today, SEND assumes that the node
   sending a ND message is the owner of the address from which the
   message is sent and/or posses a key which authorizes the node to act
   as a router, so that it is in possession of the private key or keys
   used to generate the digital signature on each message.  This means
   that the Proxy ND signaling performed by nodes that do not possess
   knowledge of the address owner's private key and/or knowledge of a
   router's key cannot be secured using SEND.

   This document extends the current SEND specification with support for
   Proxy ND.  From this point on we refer to such extension as "Secure
   Proxy ND Support for SEND".



































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3.  Terminology

   Secure ND Proxy

      A node authorized to secure a Neighbor Discovery Protocol (NDP)
      message without knowing the private key related to the source
      address of the node, or the key related to the router
      authorization, for which the node acts on behalf.

   Proxied IPv6 address

      An IPv6 address that does not belong to the Secure ND Proxy and
      for which the Secure ND Proxy is performing advertisements.

   Non-SEND node

      An IPv6 node that does not implement the SEND [RFC3971]
      specification but uses the ND protocol defined in [RFC4861] and
      [RFC4862], without additional security.

   RFC3971 node

      An IPv6 node that does not implement the specification defined in
      this document for Secure Proxy ND support, but uses the SEND
      specification as defined in [RFC3971].

   SPND node

      An IPv6 node that receives and validates messages according to the
      specification defined in this document for Secure Proxy ND
      support.

   Translated NDP message

      A NDP message issued by a Secure ND Proxy as a result of a
      received NDP message originated by the owner of the address or
      originated by another node acting on behalf of the owner of the
      address.

   Synthetic NDP message

      A NDP message issued by a Secure ND Proxy that is not the result
      of a received NDP message.








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4.  Secure Proxy ND Overview

   The original SEND specification [RFC3971] has implicitly assumed that
   only the node sending a ND message is the owner of the address from
   which the message is sent.  This assumption does not allow proxying
   of ND messages since the advertiser is required to generate a valid
   RSA Signature option, which in turns requires possession of the
   public-private key pair that was used to generate a CGA, or that was
   associated to a router certificate.

   To be able to separate the roles of ownership and advertiser the
   following extensions to the SEND protocol are defined:

   o  A Secure Proxy ND certificate, which is a certificate authorizing
      an entity to act as an ND proxy.  It is a X509v3 certificate in
      which the purpose for which the certificate is issued has been
      specified explicitly as described in a companion document
      [I-D.ietf-csi-send-cert].  Briefly, Secure Proxy ND certificates
      include one or more KeyPurposeId values which can be used for
      authorizing proxies to sign RA and Redirect messages, or to sign
      NA, NS or RS messages on behalf or other nodes.  The inclusion of
      this value allows the certificate owner to perform proxying of
      SEND messages for a range of addresses indicated in the same
      certificate.  This certificate can be exchanged through the
      Authorization Delegation Discovery process defined in [RFC3971].

   o  A new Neighbor Discovery option called Proxy Signature (PS)
      option.  This option contains the hash value of the public key of
      the proxy, and the digital signature of the SEND message computed
      with the private key of the proxy.  The hash of the public key of
      the proxy is computed over the public key contained in the Secure
      Proxy ND's certificate.  When a ND message contains a PS option,
      it MUST NOT contain CGA or RSA Signature options.  This option
      MUST be appended to any NDP message (NA, NS, RS, RA and Redirect)
      to secure it.

   o  A modification of the SEND processing rules for all ND messages:
      NA, NS, RS, RA, and Redirect.  When any of these messages
      containing a Proxy Signature option is validated, it is considered
      as secure.

   These extensions are applied in the following way:

   o  A Secure ND Proxy which proxies ND messages on behalf of a node
      can use the PS option to protect the proxied messages.  This
      Secure ND Proxy becomes part of the trusted infrastructure just
      like a SEND router.




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   o  In order to allow nodes to successfully validate secured proxied
      messages, the nodes MUST be aware of the Secure Proxy ND
      certificate (in the format described in [I-D.ietf-csi-send-cert])
      and MUST apply the modified processing rules specified in this
      document.  We call these nodes 'SPND nodes'.  Note that the rules
      for generating ND messages in SPND nodes do not change, so these
      nodes behave as defined in [RFC3971] when they send ND messages.

   o  To allow SPND nodes to know the certificate path required to
      validate the public key of the proxy, devices responding to CPS
      (Certification Path Solicitation) messages with CPA (Certification
      Path Advertisements) as defined in Section 6 of SEND specification
      [RFC3971] are extended to support the certificate format specified
      in [I-D.ietf-csi-send-cert], and are configured with the
      appropriate certification path.




































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5.  Secure Proxy ND Specification

   A Secure ND Proxy performs all the operations described in the SEND
   specification [RFC3971] with the addition of new processing rules to
   ensure that the receiving node can identify an authorized proxy
   generating a translated or synthetic SEND message for a proxied
   address.

   This is accomplished by signing the message with a private key of the
   authorized Secure ND Proxy.  The signature of the ND Proxy is
   included in a new option called Proxy Signature (PS) option.  The
   signature is performed over all the Neighbor Discovery Protocol (NDP)
   options present in the message and the PS option is appended as the
   last option in the message.

5.1.  Proxy Signature Option

   The Proxy Signature option allows public key-based signatures to be
   attached to NDP messages.  The format of the PS option is described
   in the following diagram:


        0                   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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |    Length     |          Reserved             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                          Key Hash                             |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                       Digital Signature                       .
       .                                                               .
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       .                                                               .
       .                           Padding                             .
       .                                                               .
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                        Figure 1: PS option layout




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   Type

      TBA

   Length

      The length of the option (including the Type, Length, Reserved,
      Key Hash, Digital Signature, and Padding fields) in units of 8
      octets.

   Reserved

      A 16-bit field reserved for future use.  The value MUST be
      initialized to zero by the sender, and MUST be ignored by the
      receiver.

   Key Hash

      A 128-bit field containing the most significant (leftmost) 128
      bits of a SHA-1 [SHA1] hash of the public key used for
      constructing the signature.  Its purpose is to associate the
      signature to a particular key known by the receiver.  Such a key
      MUST be the same one within the corresponding Secure Proxy ND's
      certificate.

   Digital Signature

      A variable-length field containing a PKCS#1 v1.5 signature,
      constructed by using the sender's private key over the following
      sequence of octets:

      1.  The 128-bit CGA Message Type tag [RFC3972] value for Secure
          Proxy ND, 0x09F5 2BE5 3B62 4C76 CB96 4E7F CDC9 2804 (The tag
          value has been generated randomly by the editor of this
          specification).

      2.  The 128-bit Source Address field from the IP header.

      3.  The 128-bit Destination Address field from the IP header.

      4.  The 8-bit Type, 8-bit Code, and 16-bit Checksum fields from
          the ICMP header.

      5.  The NDP message header, starting from the octet after the ICMP
          Checksum field and continuing up to but not including NDP
          options.





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      6.  All NDP options preceding the Proxy Signature option.

      The signature value is computed with the RSASSA-PKCS1-v1_5
      algorithm and SHA-1 hash, as defined in [RSA].

      This field starts after the Key Hash field.  The length of the
      Digital Signature field is determined by the ASN.1 BER coding of
      the PKCS#1 v1.5 signature.

   Padding

      This variable-length field contains padding.  The length of the
      padding field is determined by the length of the Proxy Signature
      Option minus the length of the other fields.

5.2.  Modified SEND processing rules

   This specification modifies the sender and receiver processing rules
   defined in the SEND specification [RFC3971].

5.2.1.  Processing rules for senders

   A Secure ND Proxy MUST NOT use a key to sign NDP message types which
   do not correspond to the authorization granted to the considered key.
   NA, NS and RS messages MUST be signed with a key corresponding to a
   Secure Proxy ND certificate with a KeyPurposeId value
   [I-D.ietf-csi-send-cert] of id-kp-sendProxiedOwner, and the source
   addresses of the messages MUST be encompassed in the prefix
   associated to the certificate.  RA and Redirect messages MUST be
   signed with a key corresponding to a Secure Proxy ND certificate with
   a KeyPurposeId value of id-kp-sendProxiedRouter.  The prefix included
   in the RA message for on-link determination and/or stateless address
   autoconfiguration, and the Target Address of the Redirect message,
   MUST be encompassed in the prefix associated to that certificate.

   A secured NDP message sent by a Secure ND Proxy for a proxied address
   MUST contain a PS option and MUST NOT contain either CGA or RSA
   Signature options.  Section 7 discusses in which cases a NDP message
   has to be secured in an scenario including non-SEND nodes.

   A Secure ND Proxy sending a secured message on behalf of other node
   MUST construct the message as follows:

   1.  The SEND message is constructed without the PS option as follows:

       A.  If the Secure ND Proxy is generating a synthetic SEND message
           for a proxied address, the message MUST be constructed as
           described in Neighbor Discovery for IP version 6



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           specification [RFC4861].

       B.  If the Secure ND Proxy is generating a translated SEND
           message, first the authenticity of the intercepted message
           MUST be verified as specified in SEND specification
           [RFC3971], Section 5.  If the SEND message is valid, any CGA
           or RSA option MUST be removed from the message.  The
           intercepted message is finally modified as described in
           Section 4 of the ND Proxy specification [RFC4389].

       C.  If the Secure ND Proxy is translating a SEND message already
           containing a PS option, first the authenticity of the
           intercepted message is verified as specified in Section 5.2.2
           of this specification.  If the SEND message is valid, the
           original PS option MUST be removed from the message.  The
           intercepted message is finally modified as described in
           Section 4 of the ND Proxy specification [RFC4389].

   2.  Timestamp and Nonce options MUST be included according to the
       rules specified in SEND [RFC3971].  The value in the Timestamp
       option MUST be generated by the proxy.  If the proxy is
       translating a message which includes a Nonce, the Nonce value in
       the proxied message MUST be the same as in the intercepted
       message.  If the proxy is synthesizing a solicitation message,
       the Nonce value MUST be generated by the proxy.  If the proxy is
       synthesizing an advertisement message, the Nonce value MUST
       correspond to the solicitation message to which the proxy is
       responding.

   3.  The Proxy Signature option MUST be added as the last option in
       the message.

   4.  The data MUST be signed as explained in Section 5.1.

5.2.2.  Processing rules for receivers

   Any SEND message without a Proxy Signature option MUST be treated as
   specified in the SEND specification [RFC3971].

   A SEND message including a Proxy Signature option MUST be processed
   as specified below:

   1.  The receiver MUST ignore any RSA and CGA options, as well as any
       options that might come after the first PS option.  The options
       are ignored for both signature verification and NDP processing
       purposes.





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   2.  The Key Hash field MUST indicate the use of a known public key.
       A valid certification path (see [I-D.ietf-csi-send-cert] Section
       9) between the receiver's trust anchor and the sender's public
       key MUST be known.  The Secure Proxy ND's X509v3 certificate MUST
       contain an extended key usage extension including the appropriate
       KeyPurposeId value and prefix for the message to validate:

       *  For RA messages, a KeyPurposeId value of id-kp-
          sendProxiedRouter MUST exist for the certificate, and the
          prefix included in the RA message for on-link determination
          and/or stateless address autoconfiguration MUST be encompassed
          in the prefix associated to that certificate.

       *  For Redirect messages, a KeyPurposeId value of id-kp-
          sendProxiedRouter MUST exist for the certificate, and the
          prefix included in the Target Address of the Redirect message
          MUST be encompassed in the prefix associated to that
          certificate.

       *  For NA, NS and RS messages, a KeyPurposeId value of id-kp-
          sendProxiedOwner MUST exist for the certificate, and the
          source addresses of the messages MUST be encompassed in the
          prefix associated to the certificate.

       If any of these tests fails, the verification fails.

   3.  The Digital Signature field MUST have correct encoding, otherwise
       the verification of the message including the PS option fails.

   4.  The Digital Signature verification MUST show that the signature
       has been calculated as specified in Section 5.1, otherwise the
       verification of the message including the PS option fails.

   5.  The Nonce option MUST be processed as specified in [RFC3971]
       Section 5.3.4, except for replacing 'RSA Signature option' by 'PS
       option'; if these tests fail, the verification of the message
       including the PS option fails.

   6.  The Timestamp option MUST be processed as specified in [RFC3971]
       Section 5.3.4, except for replacing 'RSA Signature option' by 'PS
       option'.  If these tests fail, the verification of the message
       including the PS option fails.  The receiver SHOULD store the
       peer-related timing information specified in [RFC3971] Section
       5.3.4.1 and 5.3.4.2 (RDlast, TSlast) separately for each
       different proxy (which could be identified by the different Key
       Hash values of the proxied message) and separately from the
       timing information associated to the IP address of a node for
       which the message is proxied.  In this way, a message received



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       for the first time from a proxy (i.e. for which there is no
       information stored in the cache) for which the Timestamp option
       is checked, SHOULD be checked as a message received from a new
       peer (as in [RFC3971] section 5.3.4.2).

   7.  Messages with the Override bit [RFC4861] set MUST override an
       existing cache entry regardless if it was created as a result of
       a RSA Signature option or a PS option validation.  When the
       Override bit is not set, the advertisement MUST NOT update a
       cached link-layer address created securely by means of RSA
       Signature option or PS option validation.

   Messages for which the verification fails MUST be silently discarded
   if the node has been configured to accept only secured ND messages.
   The messages MAY be accepted if the host has been configured to
   accept both secured and unsecured messages but MUST be treated as an
   unsecured message.

5.3.  Proxying Link-Local Addresses

   Secure Neighbor Discovery [RFC3971] relies on certificates to prove
   that routers are authorized to announce a certain prefix.  However,
   Neighbor Discovery [RFC4861] states that routers do not announce the
   Link-Local prefix (fe80::/64).  Hence, it is not required for a SEND
   certificate to hold a X.509 extension for IP addresses that
   authorizes the fe80::/64 prefix.  However, some Secure Proxy ND
   scenarios ([RFC4389], [RFC5213]) impose providing the proxying
   function for the Link-Local address of a node.  When Secure ND proxy
   functionality for a Link-Local address is required, either a list of
   link-local addresses, or the fe80::/64 prefix MUST be explicitly
   authorized to be proxied in the corresponding certificate.




















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6.  Application Scenarios

   In this section we describe three different application scenarios for
   which Secure Proxy ND support for SEND can be applied.  Note that the
   particular way in which Secure Proxy ND support is applied (which ND
   messages are proxied, in which direction, how the interaction with
   non-SEND hosts and RFC3971 hosts is handled, etc.) largely depends on
   the particular scenario considered.  In the first two scenarios
   presented below, ND messages are synthesized on behalf of off-link
   nodes.  In the third one, ND messages are translated from the
   messages received in other interfaces of the proxy.

6.1.  Scenario 1: Mobile IPv6

   The description of the problems for deploying SEND in this scenario
   is presented in [I-D.ietf-csi-sndp-prob].

   The Mobile IPv6 protocol (MIPv6) [RFC3775] allows a Mobile Node (MN)
   to move from one link to another while maintaining reachability at a
   stable address, the so-called MN's Home Address (HoA).  When a MN
   attaches to a foreign network, all the packets sent to the MN's HoA
   by a Correspondent Node (CN) on the home link or a router, are
   intercepted by the Home Agent (HA) on that home link, encapsulated
   and tunneled to the MN's registered Care-of Address (CoA).

   To deploy Secure Proxy ND in this scenario, i.e. to secure the HA
   operation, a Secure Proxy ND certificate with a KeyPurposeId value of
   id-kp-sendProxiedOwner for the prefix of the home link is required.
   The Secure ND Proxy is configured with the private key associated to
   this certificate.  When a NS is intercepted by the HA on the home
   link, the HA checks if the Target address within the NS matches with
   any of the MN's Home Address in the Binding Cache and if so, it
   replies with a Neighbor Advertisement (NA) constructed as described
   in [RFC4861], containing its own link-layer address (HA_LL) as the
   Target Link Layer Address Option (TLLAO).  Then a timestamp
   (generated by the proxy) and nonce (if appropriate, according to
   [RFC3971]), MUST be included.  Finally, a PS option signing the
   message MUST be included as the last option of the message.













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         Node (N)                Home Agent (HA)        Mobile Node (MN)
         on Home Link             on Home Link          on Foreign Link
           |                          |                          |
           | SRC = N                  |                          |
           | DST = solicited_node(MN) |                          |
           | ICMPv6 NS                |                          |
           | TARGET = MN              |                          |
           | SLLAO = N_LL             |                          |
           | [CGA]                    |                          |
           | RSA signature            |                          |
           |------------------------->|                          |
           |                          |                          |
           | SRC = HA                 |                          |
           | DST = N                  |                          |
           | ICMPv6 NA                |                          |
           | TARGET = MN              |                          |
           | TLLAO = HA_LL            |                          |
           | PS signature             |                          |
           |<-------------------------|                          |
           |                          |                          |
           | traffic                  |                          |
           | dest= MN HoA             |                          |
           |------------------------->|                          |
           |                          |                          |
           |                          | tunneled traffic         |
           |                          | dest= MN CoA             |
           |                          |------------------------->|
           |                          |                          |



            Figure 2: Proxy ND role of the Home agent in MIPv6

   A node receiving the NA containing the PS option (e.g.: the CN in the
   home link, or a router) MUST apply the rules defined in
   Section 5.2.2.  Note that in this case the Override bit of the NA
   message is used to control which messages should prevail on each
   case: the message generated by the proxy when the MN moves from the
   home network, or the MN if it comes back to the home link, as defined
   in the MIPv6 specification [RFC3775].

6.2.  Scenario 2: Proxy Mobile IPv6

   Proxy Mobile IPv6 [RFC5213] is a network-based mobility management
   protocol that provides IP mobility management support for MNs without
   requiring MNs being involved in the mobility related signaling.  The
   IP mobility management is totally hidden to the MN in a Proxy Mobile
   IPv6 domain and it is performed by two functional entities: the Local



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   Mobility Anchor (LMA) and the Mobile Access Gateway (MAG).

   When the MN connects to a new access link, it sends a muliticast
   Router Solicitation (RS).  The MAG on the new access link, upon
   detecting the MN's attachment, signals the LMA requesting an update
   of the binding state of the MN (by means of a Proxy Binding Update -
   PBU).  Once the signaling is completed (it receives a Proxy Binding
   Ack - PBA), the MAG replies to the MN with a Router Advertisement
   (RA) containing the home network prefix(es) that were assigned to
   that mobility session, making the MN believe it is still on the same
   link, so the IPv6 address reconfiguration procedure is not triggered
   (Figure 3).


             MN                   new MAG                  LMA
              |                      |                      |
          MN Attached                |                      |
              |                      |                      |
              |       MN Attached Event from MN/Network     |
              |                      |                      |
              | SRC = MN             |                      |
              | DST = all-routers    |                      |
              | ICMPv6 RS            |                      |
              | [CGA]                |                      |
              | RSA signature        |                      |
              |--------------------->|                      |
              |                      |                      |
              |                      |--- PBU ------------->|
              |                      |                      |
              |                      |                  Accept PBU
              |                      |                      |
              |                      |<------------- PBA ---|
              |                      |                      |
              |                 Accept PBA                  |
              |                      |                      |
              |                      |==== Bi-Dir Tunnel ===|
              |                      |                      |
              |        SRC = MAG4MN  |                      |
              |            DST = MN  |                      |
              |           ICMPv6 RA  |                      |
              |        SLL = MAG_LL  |                      |
              |            PS        |                      |
              |<---------------------|                      |
              |                      |                      |
              |                      |                      |
              |                      |                      |





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                Figure 3: Mobile node's handover in PMIPv6


   To avoid potential link-local address collisions between the MAG and
   the MN after a handoff to a new link, the Proxy Mobile IPv6
   specification requires the MAG's link-local address on the link to
   which the MN is attached to be generated by the LMA when the MN first
   attaches to a PMIPv6 domain, and to be provided to the new MN's
   serving MAG after each handoff.  Thus, from the MN's point of view,
   the MAG's link-local address remains constant for the duration of
   that MN's session.

   The approach described above and the current SEND specification are
   incompatible since sharing the same link-local address on different
   MAGs would require all MAGs of a PMIPv6 domain to construct the CGA
   and the RSA Signature option with the same public-private key pair,
   which is not an acceptable security policy.

   Using different public-private key pairs on different MAGs would mean
   different MAGs use different CGAs as link-local address.  Thus the
   serving MAG's link-local address would change after each handoff of
   the MN, which is in contradiction with the way MAG link-local address
   assignment occurs in a PMIPv6 domain.

   To provide SEND protection, each MAG MUST be configured to act as a
   proxy by means of a certificate associated to the PMIPv6 domain,
   authorizing each MAG to proxy securely NA and RS messages by means of
   a KeyPurposeId value of id-kp-sendProxiedOwner.  In addition, the
   certificate MUST also authorize the MAG to advertise prefixes by
   associating to the same certificate a KeyPurposeId value of id-kp-
   sendProxiedRouter.  Note that the inclusion of multiple KeyPurposeId
   values is supported by [I-D.ietf-csi-send-cert].

   When a MAG replies to a RS with a RA, the source address MUST be
   equal to the MAG link-local address associated to the MN in this
   PMIPv6 domain, with its own link-layer address as Source link-layer
   address.  Then a timestamp (generated by the proxy) and nonce (if
   appropriate, according to [RFC3971]), MUST be included.  Finally, a
   PS option signing the message MUST be included as the last option of
   the message.  This procedure is followed for any other ND message
   that could be generated by the MAG to the MN.

   A node receiving a message from the MAG containing the PS option MUST
   apply the processing rules defined in Section 5.2.2.  Note that
   unsolicited messages sent by the MAG should be validated by the host
   according to timestamp values specific to the MAG serving the link,
   not to any other MAG to which the host has been connected before in
   other links, according to processing step number 6 of Section 5.2.2.



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6.3.  Scenario 3: RFC 4389 Neighbor Discovery Proxy

   The description of the problems for deploying SEND in this scenario
   is presented in [I-D.ietf-csi-sndp-prob].



          Link 1                                               Link 2

          Host A                   ND Proxy (P)                Host B
            |                          |                          |
            | SRC = A                  |                          |
            | DST = solicited_node(B)  |                          |
            | ICMPv6 NS                |                          |
            | TARGET = B               |                          |
            | SLLAO = A_LL             |                          |
            |------------------------->|                          |
            |                          | SRC = A                  |
            |                          | DST = solicited_node(B)  |
            |                          | ICMPv6 NS                |
            |                          | TARGET = B               |
            |                          | SLLAO = P_LL             |
            |                          |------------------------->|
            |                          |                          |
            |                          | SRC = B                  |
            |                          | DST = A                  |
            |                          | ICMPv6 NA                |
            |                          | TARGET = B               |
            |                          | TLLAO = B_LL             |
            |                          |<-------------------------|
            | SRC = B                  |                          |
            | DST = A                  |                          |
            | ICMPv6 NA                |                          |
            | TARGET = B               |                          |
            | TLLAO = P_LL             |                          |
            |<-------------------------|                          |
            |                          |                          |


           Figure 4: RFC 4389 Neighbor Discovery Proxy operation

   The Neighbor Discovery (ND) Proxy specification [RFC4389] provides a
   method by which multiple link-layer segments are bridged into a
   single segment and specifies the IP-layer support that enables
   bridging under these circumstances.

   A Secure ND Proxy MUST parse any IPv6 packet it receives on a proxy
   interface to check whether it contains one of the following NDP



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   messages: NS, NA, RS, RA, or Redirect.  The Secure ND Proxy MUST
   verify the authenticity of the received ND message, according to
   [RFC3971].  If the SEND message is valid, then it proxies the
   original message with the following changes:

   1.  The message MUST be processed according to [RFC4389].  This
       includes changing the source link-layer address to the address of
       the outgoing interface, maintaining the destination link-layer
       address as the address in the neighbor entry corresponding to the
       destination IPv6 address, etc.  In particular any link-layer
       address within the payload (that is, in a Source Local Link
       Address option - SLLAO, or a Target Local Link Address option -
       TLLAO) is substituted with the link-layer address of the outgoing
       interface.

   2.  Any CGA or RSA option MUST be removed.

   3.  If a Nonce option existed in the original message, its value MUST
       be preserved in the proxied message.  The Timestamp MUST be
       generated by the proxy.

   4.  The PS option MUST be added as the last option in the message,
       signing all the information contained so far in the message.  To
       be able to sign any NS, NA, RS, RA o Redirect message, the key
       used must correspond to a certificate with KeyPurposeId values of
       id-kp-sendProxiedOwner and id-kp-sendProxiedRouter.

   When any other IPv6 unicast packet is received on a proxy interface,
   if it is not locally destined then it is forwarded unchanged (other
   than using a new link-layer header) to the proxy interface for which
   the next-hop address appears in the neighbor cache.  If no neighbor
   cache entry is present, the Secure ND Proxy SHOULD queue the packet
   and initiate a Neighbor Discovery signaling as if the NS message were
   locally generated.

   In order to deploy this scenario, nodes in proxied segments MUST know
   the certificate authorizing proxy operation.  To do so it could be
   required to configure at least one device per each proxied segment
   (may be the proxy itself) to propagate the required certification
   path to authorize proxy operation by means of a CPS/CPA exchange.











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7.  Backward Compatibility with RFC3971 nodes and non-SEND nodes

   In this section we discuss the interaction of Secure ND Proxies and
   SPND nodes with RFC3971 nodes and non-SEND nodes.  As stated in
   [RFC3971], network operators may want to run a mixture of nodes
   accepting secured and unsecured NDP messages at the same time.
   Secure ND Proxies and SPND nodes SHOULD support the use of secured
   and unsecured NDP messages at the same time.

7.1.  Backward Compatibility with RFC3971 nodes

   RFC3971 nodes, i.e.  SEND nodes not compliant with the modifications
   required in Section 5, cannot interpret correctly a PS option
   received in a proxied ND message.  These SEND nodes silently discard
   the PS option, as specified in [RFC4861] for any unknown option.  As
   a result, these messages will be treated as unsecured as described in
   Section 8 "Transitions Issues" of the SEND specification [RFC3971].

   When RFC3971 nodes and SPND nodes exchange ND messages (without proxy
   intervention), in either direction, messages are generated according
   to the SEND specification [RFC3971], so these nodes interoperate
   seamlessly.

   In the scenarios in which the proxy translates ND messages, the
   messages to translate can either be originated in a RFC3971 node or
   in an SPND node, without interoperability issues (note that the
   difference between RFC3971 nodes and SPND nodes only affect to the
   ability to process received NDP messages containing a PS option, not
   in the way they generate messages secured by SEND).

7.2.  Backward Compatibility with non-SEND nodes

   Non-SEND nodes receiving NDP packets silently discard PS options, as
   specified in [RFC4861] for any unknown option.  Therefore, these
   nodes interpret messages proxied by a Secure ND Proxy as any other ND
   message.

   When non-SEND nodes and SPND nodes exchange ND messages (without
   proxy intervention), in either direction, the rules specified in
   section 8 of [RFC3971] apply.

   A Secure ND Proxy SHOULD support the use of secured and unsecured NDP
   messages at the same time, although it MAY have a configuration that
   causes not to perform proxying for unsecured NDP messages.  A Secure
   ND Proxy MAY also have a configuration option whereby it disables
   secure ND proxying completely.  This configuration SHOULD be switched
   off by default, that is security is provided by default.  In the next
   paragraphs we discuss the recommended behavior of the Secure ND Proxy



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   regarding to the protection level to provide to proxied messages in a
   mixed scenario involving SPND/RFC3971 nodes and non-SEND nodes.  In
   particular, two different situations occur depending on if the
   proxied nodes are RFC3971 or SPND, or if they are non-SEND nodes.

   As a rule of thumb, if the proxied nodes can return to the link in
   which the proxy operates, the Secure ND Proxy MUST only generate PS
   options on behalf of nodes with SEND capabilities (i.e. that they
   could use SEND to defend their messages if present on the same link
   as the proxy, i.e. being either RFC3971 nodes or SPND nodes).  This
   is relevant to allow nodes to prefer secured information over
   unsecured one, and to properly execute the DAD procedure, as
   specified in [RFC3971].  Therefore, in this case the Secure ND Proxy
   MUST synthesize/translate messages containing the PS option for SPND
   and RFC3971 hosts, and MUST NOT synthesize/translate messages
   containing the PS option for non-SEND nodes.  Note that ND
   advertisements in response to solicitations generated by a Secure ND
   Proxy must be secured or not according to the previous considerations
   (i.e. to the nature of the proxied node), and not according to the
   secure or unsecure nature of the solicitation message.

   In order to apply this rule, the Secure ND Proxy needs to know the
   security capabilities of the proxied node.  The way this information
   is acquired depends on the application scenario, and it is discussed
   next:

   o  For scenarios in which ND messages are translated for nodes that
      can arrive to the link in which the proxy operates, the rule can
      be easily applied: only for messages validated in the Secure ND
      Proxy according to the SEND specification [RFC3971], or according
      to Section 5.2.2 of this specification for messages containing a
      PS option (which means that another proxy previously checked that
      the original message was secured), the message MUST be proxied
      securely by the inclusion of a PS option.  Unsecured ND messages
      could be proxied if unsecured operation is enabled in the proxy,
      but the message generated by the Secure ND Proxy for the received
      message MUST NOT include a PS option.

   o  For scenarios in which ND messages are synthesized on behalf of
      remote nodes, different considerations should be made according to
      the particular application scenario.

      *  For MIPv6, if the MN can return to the home link, it is
         required for the proxy to know if the node could use SEND to
         defend its address or not.  A HA including the PS option for
         proxying a non-SEND MN would make ND messages sent by the proxy
         to be more preferred than a ND message of the non-SEND MN when
         the MN returns to the home link (even if the proxied messages



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         have the Override bit set to 1).  Not using the PS option for a
         RFC3971 or SPND MN would make the address in the home link more
         vulnerable when the MN is away than when it is in the home
         link, defeating the purpose of the Secure Proxy ND mechanism.
         Therefore, in this case the HA MUST know the SEND capabilities
         of the MN, MUST use the PS option if the MN is a SPND or
         RFC3971 host, and MUST NOT use PS option for non-SEND hosts.

      *  For the Proxy Mobile IPv6 scenario, a node moving from a link
         in which PS option has been used to protect a link-layer
         address to a link in which ND messages are not protected by
         SEND would prevent the MN from adquiring the new information
         until the cached information expires.  However, in this case it
         is reasonable to consider that all MAGs provide the same
         security for protecting ND messages, and that either all MAGs
         will behave as Secure ND Proxy, or none, so configuration is
         expected to be easier.


































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8.  Security Considerations

   The mechanism described in this document introduces a new Proxy
   Signature (PS) option allowing a Secure ND Proxy to synthesize or
   translate a SEND message for a proxied address, to Redirect traffic
   for given target addresses or to advertise prefix information by
   means of RA messages.  A SPND node only accepts such a message if it
   includes a valid PS option generated by a properly authorized Secure
   ND Proxy (with a certificate containing a KeyPurposeId with value id-
   kp-sendProxiedOwner for protecting NA, NS and RS messages, or
   containing a KeyPurposeId value of id-kp-sendProxiedRouter for
   protecting RA and Redirect messages).  Such a message has equivalent
   protection against the threats presented in section 9 of [RFC3971] as
   a message signed with a RSA Signature option.

   The security of proxied ND messages not including a PS option is the
   same as an unsecured ND message.  The security of a proxied ND
   message received by a non-SEND host or RFC3971 host is the same as an
   unsecured ND message.

   When a message including a PS option is received by a SPND node, any
   CGA or RSA options also included in the message are removed and the
   remaining message further processed.  Altough properly formed proxied
   messages MUST NOT include at the same time PS and CGA/RSA options,
   discarding them if they appear does not affect to the security.  If
   the PS option is validated, then the information included in the
   message has been validly generated by a proxy, and should be honored
   (remember that anti-replay protection is provided by means of nonce
   and timestamp options).  If the PS option is not validated, then it
   is treated as an unsecured message.  In any case, there is no gain
   for an attacker from appending false or old CGA/RSA information to a
   message secured by a Secure ND Proxy.

   A compromised Secure ND Proxy provisioned with an authorization
   certificate with a KeyPurposeId value of id-kp-sendProxiedRouter is
   able, like a compromised router to siphon off traffic from the host,
   or mount a man-in-the-middle attack, for hosts communicating to off-
   link hosts.  A compromised Secure ND Proxy provisioned with an
   authorization certificate with a KeyPurposeId value of id-kp-
   sendProxiedOwner can siphon off traffic or mount a man-in-the-middle
   attack for communication between on-link hosts, even if the hosts use
   SEND.  Note that different application scenarios may require one type
   of authorization, the other, or both.  To minimize security risks,
   authorization capabilities SHOULD NOT exceed the ones strictly
   required by the application scenario to be deployed.

   The messages for which a Secure ND Proxy performs its function and
   the link for which this function is performed MUST be configured



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   appropriately for each proxy and scenario.  This configuration is
   specially relevant if Secure Proxy ND is used for translating ND
   messages from one link to another.

   Section 7 discusses the security considerations resulting from the
   decision of appending or omitting the PS option depending on the
   SEND-awareness of the proxied nodes.

   Protection against replay attacks from unsolicited messages such as
   NA, RA, and Redirects is provided by means of the Timestamp option.
   When Secure ND Proxy is used, each proxy and the host for which a
   proxy acts on behalf are considered to be different peers in terms of
   Timestamp verification.  Since the information provided by the host
   and a proxy maybe different, including different link-layer
   addresses, a replay attack could affect the operation of a third
   node: replaying messages issued by a host that is no longer in the
   link can prevent the use of a proxy, and replaying messages of a
   proxy when the host is back in the link can prevent communication
   with the host.  This kind of attacks can be performed until the
   timestamp of the peer (either the host or a proxy) is no longer valid
   for the receiver.  The window of vulnerability is in general larger
   for the first message received from a new peer than for subsequent
   messages received from the same peer (see [RFC3971]).  A more
   detailed analysis of the possible attacks related with the Timestamp
   option is described in section 7.3 of [I-D.ietf-csi-sndp-prob].


























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9.  IANA Considerations

   IANA is requested to allocate:

      A new IPv6 Neighbor Discovery Option type for the PS option, as
      TBA.  The value need to be allocated from the namespace specified
      in the IANA registry IPv6 NEIGHBOR DISCOVERY OPTION FORMATS
      located at http://www.iana.org/assignments/icmpv6-parameters.

      A new 128-bit value under the CGA Message Type [RFC3972]
      namespace, 0x09F5 2BE5 3B62 4C76 CB96 4E7F CDC9 2804.








































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10.  Acknowledgements

   The text has benefited from feedback provided by Jari Arkko, Jean-
   Michel Combes, Roque Gagliano, Tony Cheneau, Marcelo Bagnulo, Alexey
   Melnikov and Sandra Murphy.

   The work of Alberto Garcia-Martinez was supported in part by T2C2
   project (TIN2008-06739-C04-01, granted by the Spanish Science and
   Innovation Ministry).










































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11.  References

11.1.  Normative References

   [I-D.ietf-csi-send-cert]
              Gagliano, R., Krishnan, S., and A. Kukec, "Certificate
              profile and certificate management for SEND",
              draft-ietf-csi-send-cert-07 (work in progress),
              September 2010.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, March 2005.

   [RFC4389]  Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
              Proxies (ND Proxy)", RFC 4389, April 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

   [RSA]      RSA Laboratories, "RSA Encryption Standard, Version 2.1",
              PKCS 1 , November 2002.

   [SHA1]     National Institute of Standards and Technology, "Secure
              Hash Standard", FIPS PUB 180-1 , April 1995.

11.2.  Informative References

   [I-D.ietf-csi-sndp-prob]
              Combes, J., Krishnan, S., and G. Daley, "Securing Neighbor
              Discovery Proxy: Problem Statement",
              draft-ietf-csi-sndp-prob-04 (work in progress),
              January 2010.



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   [RFC3756]  Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
              Discovery (ND) Trust Models and Threats", RFC 3756,
              May 2004.
















































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Authors' Addresses

   Suresh Krishnan
   Ericsson
   8400 Decarie Blvd.
   Town of Mount Royal, QC
   Canada

   Phone: +1 514 345 7900 x42871
   Email: suresh.krishnan@ericsson.com


   Julien Laganier
   QUALCOMM Incorporated
   5775 Morehouse Dr
   San Diego, CA  92121
   USA

   Phone: +1 858 658 3538
   Email: julienl@qualcomm.com


   Marco Bonola
   Rome Tor Vergata University
   Via del Politecnico, 1
   Rome  I-00133
   Italy

   Phone:
   Email: marco.bonola@gmail.com


   Alberto Garcia-Martinez
   U. Carlos III de Madrid
   Av. Universidad 30
   Leganes, Madrid  28911
   Spain

   Phone: +34 91 6248782
   Email: alberto@it.uc3m.es
   URI:   http://www.it.uc3m.es/










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