





Network Working Group                                         C. Perkins
Request for Comments: 3957                         Nokia Research Center
Category: Standards Track                                     P. Calhoun
                                                               Airespace
                                                              March 2005


          Authentication, Authorization, and Accounting (AAA)
                   Registration Keys for Mobile IPv4

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   Authentication, Authorization, and Accounting (AAA) servers, such as
   RADIUS and DIAMETER, are in use within the Internet today to provide
   authentication and authorization services for dial-up computers.
   Mobile IP for IPv4 requires strong authentication between the mobile
   node and its home agent.  When the mobile node shares an AAA Security
   Association with its home AAA server, however, it is possible to use
   that AAA Security Association to create derived Mobility Security
   Associations between the mobile node and its home agent, and again
   between the mobile node and the foreign agent currently offering
   connectivity to the mobile node.  This document specifies extensions
   to Mobile IP registration messages that can be used to create
   Mobility Security Associations between the mobile node and its home
   agent, and/or between the mobile node and a foreign agent.














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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Terminology. . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Overview of Operations with Key Generation Nonce Extensions. .  5
   4.  Mobility Security Associations . . . . . . . . . . . . . . . .  7
   5.  Key Generation Nonce Creation and Key Derivation . . . . . . .  8
   6.  Key Generation Extensions. . . . . . . . . . . . . . . . . . .  9
       6.1.  Generalized MN-FA Key Generation Nonce Request Extension 10
       6.2.  Generalized MN-FA Key Generation Nonce Reply Extension . 11
       6.3.  Generalized MN-HA Key Generation Nonce Request Extension 13
       6.4.  Generalized MN-HA Key Generation Nonce Reply Extension . 14
   7.  Error Values . . . . . . . . . . . . . . . . . . . . . . . . . 16
   8.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 16
   9.  Security Considerations. . . . . . . . . . . . . . . . . . . . 17
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
       11.1. Normative References . . . . . . . . . . . . . . . . . . 18
       11.2. Informative References . . . . . . . . . . . . . . . . . 19
   Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
       A. AAA Infrastructure. . . . . . . . . . . . . . . . . . . . . 20
       B. Message Flow for Requesting and Receiving Registration Keys 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 27

1.  Introduction

   AAA servers, such as RADIUS [11] and DIAMETER [12], are in use within
   the Internet today to provide authentication and authorization
   services for dial-up computers.  Such services are likely to be
   valuable for mobile nodes using Mobile IP for IPv4 [1], when the
   nodes are attempting to connect to foreign domains with AAA servers.
   In this document Mobile IP for IPv4 is called "Mobile IPv4" or just
   "Mobile IP" for short, since no confusion with other versions is
   expected.  Requirements for interactions between AAA and Mobile IP
   are outlined in RFC 2977 [13]; that document describes an
   infrastructure which enables AAA servers to authenticate and
   authorize network access requests from mobile nodes.  See also
   appendix A.  The Mobile IP Registration Request is considered to be a
   request for network access.  It is then possible to augment the
   functionality of the Mobile IP mobility agents so that they can
   translate between Mobile IP registration messages and the messages
   used within the AAA infrastructure, as described in RFC 2977.
   Mobility agents and AAA servers that conform to the requirements of
   RFC 2977 can be considered as appropriate network entities to support
   the message types specified in this document.  Please consult RFC
   2977 [13] for further details.




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   This specification makes use of a single AAA Security Association to
   create derivative Mobility Security Associations.  A Mobility
   Security Association in this specification is a simplex connection
   that serves to authenticate MIPv4 control traffic between a MN and HA
   and/or a MN and FA.  A Mobility Security Association is identified by
   the two end points, such as a MN IP address and a HA IP address, and
   a SPI.  Two nodes may have one or more Mobility Security Associations
   established between each other; however, typically there is no reason
   to have more than one Mobility Security Association between two
   nodes.

   This document specifies extensions to Mobile IP registration messages
   that can be used to create Mobility Security Associations between the
   MN and FA and/or MN and HA based on the AAA Security Association
   between the MN and AAA server.  These new Mobility Security
   Associations may then be used to calculate the Authentication Data
   needed by authentication extensions used in Mobile IP control
   messages.

   It is assumed that the security association between the mobile node
   and its AAA server has been appropriately configured so that the AAA
   server can provide key material to be used as the basis for the
   necessary Mobility Security Association(s) between the mobile node
   and its prospective mobility agents.

   AAA servers typically use the Network Access Identifier (NAI) [2] to
   uniquely identify the mobile node; the mobile node's home address is
   not always necessary to provide that function.  Thus, it is possible
   for a mobile node to authenticate itself, and be authorized for
   connection to the foreign domain, without having any home address.
   However, for Mobile IP to work, the mobile node is required to have a
   home address and a Mobility Security Association [1] with its home
   agent.  When the Mobile IP Registration Reply packet is authenticated
   by the MN-AAA Authentication Extension [3], the mobile node can
   verify that the key material contained in the extensions were
   produced by the AAA server, and thus may be reliably used to create
   Mobility Security Associations with the home agent and/or the foreign
   agent.

   It is also assumed that the AAA entities involved (i.e., the AAAH,
   AAAL, and the AAA interface features of the foreign agents and home
   agents) all have means outside of the scope of this document for
   exchanging keys.  The extensions within this document are intended to
   work with any AAA protocol suite that allows for such key exchange,
   as long as it satisfies the requirements specified in RFC 2977 [13].
   One such AAA protocol is defined within the Diameter framework [14].





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2.  Terminology

   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 [4].

   AAA           Authentication, Authorization, and Accounting (see
                 [10]).

   AAA entity    A network node processing AAA messages according to the
                 requirements for AAA protocols (see [10]).

   AAA Security Association
                 A security association between a AAA entity and another
                 node needing the services of that AAA entity.  In this
                 document all AAA Security Associations are between a
                 mobile node and its home AAA server (AAAH).  A mobile
                 node's AAA Security Association with its home AAA
                 server (AAAH) may be based either on the mobile node's
                 IP address or on its NAI [2].  The key is referred to
                 as "AAA-key" in this specification.

   Key           A number, kept secret.  Only nodes in possession of the
                 key have any hope of using the security transform to
                 obtain correct results.

   Key Generation Nonce
                 Nonce data used for the purpose of creating a key.

   Mobility Security Association
                 A Mobility Security Association is a simplex connection
                 that applies security services to RFC 3344 MIPv4
                 control traffic between a MN and HA (or MN and FA)
                 using RFC 3344 Authentication Extensions.  A Mobility
                 Security Association is uniquely identified by the peer
                 source and destination IP addresses and an SPI.  Two
                 nodes may have one or more Mobility Security
                 Associations; however, typically there is no reason to
                 have more than one Mobility Security Association
                 between two nodes, except as a transient condition
                 during re-keying events.

   Registration Key
                 A key used in the MN-FA or MN-HA Mobility Security
                 Association.  A registration key is typically only used
                 once or a very few times, and only for the purposes of
                 verifying a small volume of Authentication data.




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   Security Algorithm
                 A set of rules for using input data and a secret key
                 for producing data for use in security protocols.

   SPI           Security Parameters Index.  The SPI is an arbitrary
                 32-bit value that assists in the identification of an
                 AAA, IP, or Mobility Security Association.

   Other terminology is used as defined in the base Mobile IP
   specification [1].  Furthermore, in order to simplify the discussion,
   we have used the word "Extension" instead of "Subtype of the
   Generalized Extension" in many cases.  So, for instance, instead of
   using the phrase "The MN-FA Key Generation Nonce From AAA Subtype of
   the Generalized MN-FA Key Generation Nonce Reply Extension", we would
   instead use the phrase "The MN-FA Key Generation Nonce From AAA
   Extension".

3.  Overview of Operations with Key Generation Nonce Extensions

   When a mobile node depends on an AAA infrastructure to obtain
   authorization for network connectivity and Mobile IP registration, it
   may lack any pre-existing Mobility Security Associations with either
   its home agent, or the foreign agent controlling the access to the
   foreign network.  The extensions defined in this document allow a AAA
   entity to supply key material to mobile nodes to be used as the basis
   of its Mobility Security Association with mobile agents.  The AAA
   entity that will act on these extensions is part of the AAA
   infrastructure, and is typically identified within the foreign domain
   by methods outside the scope of this specification (see appendix A).

   The key material may be requested by the mobile node in new
   extensions (defined below) to Mobile IP Registration Request
   messages, and supplied to the mobile node in extensions to the Mobile
   IP Registration Reply messages.  Alternatively, the AAA server MAY
   provide unsolicited key material via mobility agents to mobile nodes;
   the mobile node MUST then calculate new keys and update or create its
   relevant Mobility Security Association.  The method by which key
   material is supplied to the mobility agents themselves is out of
   scope for this document, and would depend on the particular details
   of the security architecture for the AAA servers in the foreign and
   home domains (see RFC 2977 and appendix A).  For the purposes of this
   document, we assume that there is a suitable AAA infrastructure
   available to the home and foreign agents, and that the mobile node
   does have an AAA Security Association with at least one AAA server in
   its home domain.






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   When a mobile node travels away from home, it may not have a Mobility
   Security Association with its home agent, perhaps because it does not
   yet have a home address [5].  The protocol and messages in this
   document are intended to facilitate the following operations which
   may occur between the mobile node, foreign agent, home agent, and AAA
   servers in the visited (local) domain (Authentication, Authorization
   and Accounting Local or AAAL) and in the home domain (Authentication,
   Authorization, and Accounting Home or AAAH).  In the following
   sequence of messages, the only message flows specified in this
   document are the Registration Request between the mobile node and the
   foreign agent, and Registration Reply between the foreign agent and
   the mobile node.  The other messages described here result from the
   presumed action of the AAA entities as described in RFC 2977.  See
   also appendix B.

   1.  If the mobile node does not have a Mobility Security Association
       with the foreign agent, it SHOULD include an MN-FA Key Generation
       Nonce Request extension (see Section 6.1) as part of its
       Registration Request that it sends to the Foreign Agent.

   2.  If the mobile node does not have a Mobility Security Association
       with the home agent, it MUST add an MN-HA Key Generation Nonce
       Request extension (see Section 6.3) as part of its Registration
       Request that it sends to the Foreign Agent.

   3.  If one or more AAA Key Generation Nonce Request extensions were
       added, the mobile node MUST add the MN-AAA Authentication
       extension to its Registration Request.

   4.  By action of the foreign agent, which is presumed to be also a
       AAA entity, the mobile node's key requests and authentication
       data are transferred to the local AAA server (AAAL), typically
       after reformatting to fit into the appropriate AAA messages,
       which are out of scope for this document.

   5.  After the information within the MN-AAA Authentication extension
       is verified by the AAA server in the home domain (AAAH), it then
       also generates the key material that has been requested by the
       mobile node, for the necessary Mobility Security Associations.

   6.  The respective keys for the Mobility Security Associations are
       distributed to the Home Agent and Foreign Agent via the AAA
       protocol.

   7.  The mobile node receives the Registration Reply message from the
       Foreign Agent.





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   8.  If a MN-HA Key Generation Nonce Request From AAA extension is
       present in the Registration Request message, then the mobile node
       MUST create or update its Mobility Security Association with the
       Home Agent indicated in the corresponding Registration Reply,
       using the key computed from the key material in the MN-HA Key
       Generation Nonce From AAA extension.  In this case, if no MN-HA
       Key Generation Nonce Reply extension is present, the mobile node
       MUST discard the Registration Reply.

   9.  Using its (perhaps newly created) Mobility Security Association
       with the home agent, the mobile node authenticates the
       Registration Reply message by checking the Authentication Data in
       the Mobile-Home Authentication extension.  If the check fails,
       the MN MUST discard the Registration Reply and the new Mobility
       Security Association, reverting to the old Mobility Security
       Association with the home agent, if any.

   10. If the Registration Reply passes authentication and contains a
       MN-FA Key Generation Nonce From AAA extension (see section 6.2),
       the mobile node generates the registration key using the Key
       Generation Nonce provided, according to its AAA Security
       Association with the AAA.  The resulting registration key is used
       to establish the mobile node's Mobility Security Association with
       its foreign agent, and is used to compute the authentication data
       used in the Mobile-Foreign authentication extension.

       If verification of the Mobile-Foreign authentication extension
       fails, and if the MN-FA Key Generation Nonce Reply extension was
       not protected by another, valid authentication extension, the MN
       MUST discard the new Mobility Security Association, reverting to
       the old Mobility Security Association with the foreign agent, if
       any.

   Any registration reply containing the MN-HA Key Generation Nonce From
   AAA extension MUST also contain a subsequent Mobile Home
   Authentication extension, created using the generated MN-HA key.
   Similarly, a reply containing the MN-FA Key Generation Nonce From AAA
   extension MUST also contain a subsequent Mobile Foreign
   Authentication extension, created using the registration key.

4.  Mobility Security Associations

   Mobility Security Associations between Mobile IP entities (mobile
   nodes, home agents, foreign agents) contain both the necessary
   cryptographic key information and a way to identify the cryptographic
   transform that uses the key to produce the authentication information
   that is present in the Mobile-Home Authentication extension or the
   Mobile-Foreign Authentication extension.  In order for the mobile



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   node to make use of key material created by the AAA server, the
   mobile node also has to be able to identify and select the
   appropriate cryptographic transform that uses the key to produce the
   authentication.

   The transform identifiers are the same as those used in IPsec.  They
   are tabulated in the list of Authentication Algorithms allowable as
   values for the "Attribute Type" (5) (i.e., "Authentication
   Algorithm"), one of the classifications in the tabulated Attribute
   Types for "IPsec Security Association Attributes".  See
   http://www.iana.org/assignments/isakmp-registry for the full listing
   of all Attribute Types and other Attributes for IPsec Security
   Associations.

   Mobility Security Associations shared between mobile nodes and home
   agents also require a replay protection method.  The following table
   contains the supported replay detection methods.

      Replay Method       Name           Reference
      --------------    ------------   --------------
      0,1               Reserved
      2                 Timestamps       RFC 3344 [1]
      3                 Nonces           RFC 3344 [1]
      4-65535           Unallocated

5.  Key Generation Nonce Creation and Key Derivation

   This section contains the procedures followed in the creation of the
   Key Generation Nonce by AAA servers, and the key derivation
   procedures used by mobile nodes.  Note that the AAA servers will also
   deliver the keys to the mobility agents (home agent, foreign agent)
   via the AAA protocol.  AAA servers that follow these procedures will
   produce results that can be understood by mobile nodes.  The mobility
   agents will faithfully transcribe the results into the appropriate
   Mobile IP extensions.

   The following example uses HMAC-SHA1 [6].  All mobile nodes and
   mobility agents implementing Mobile IP [1] and implementing the
   extensions specified in this document MUST implement HMAC-SHA1 [1].
   Other message authentication codes or keyed hash functions MAY also
   be used.  The particular algorithm used is configured as part of the
   AAA Security Association between the MN and the AAAH server, which is
   in turn indexed by the AAA SPI.








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   The following steps are performed on the AAAH server:

   1. The AAA server identifies the mobile node.  If the NAI field is
      present in the Registration Request, then the NAI is used as the
      mobile node identifier.  Otherwise, the Home Address field of the
      Registration Request is used.

   2. The AAA server generates a random [7] value of at least 128 bits
      to be used as the Key Generation Nonce.

   3. The AAA server inserts the random value into the Key Generation
      Nonce Reply extension in the "Key Generation Nonce" field.

   The following steps are performed by the mobile node (here ||
   represents concatenation):

   1. The mobile node calculates

         key = HMAC-SHA1 (AAA-key, {Key Generation Nonce || mobile node
         identifier})

      Here the Key Generation Nonce is from the extension in the
      Registration Reply, and the mobile node identifier is the MN's
      NAI, if present in the Registration Request, or the Home Address
      from the Registration Request otherwise.

   2. The mobile node creates the Mobility Security Association(s),
      using the resulting key and the other relevant information in the
      Key Generation Nonce Extension.

   The secret key used within the HMAC-SHA1 computation is indicated by
   the AAA Security Association indexed by the AAA SPI, which has been
   previously configured as the basis for the AAA Security Association
   between the mobile node and the AAA server creating the key material.

6.  Key Generation Extensions

   This section defines new Extensions to Mobile IP Registration
   Requests and Replies [1].












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6.1.  Generalized MN-FA Key Generation Nonce Request Extension

   Figure 1 illustrates the Generalized MN-FA Key Generation Nonce
   Request Extension (MN-FA KeyGen Request for short).

    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      |    Subtype    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Mobile Node SPI                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           MN-FA Key Generation Nonce Request Subtype Data ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


     Figure 1: The Generalized Mobile IP MN-FA Key Generation
               Nonce Request Extension

   Type             40 (not skippable) (see [1] and section 8)

   Subtype          A number assigned to identify the way in which the
                    MN-FA Key Generation Nonce Request Subtype Data is
                    to be used when generating the registration key.

   Length           The 16-bit Length field indicates the length of the
                    extension.  It is equal to the number of bytes in
                    the MN-FA Key Generation Nonce Request Subtype Data
                    plus 4 (for the Mobile Node SPI field).

   Mobile Node SPI  The Security Parameters Index that the mobile node
                    will assign for the Mobility Security Association
                    created for use with the registration key.

   MN-FA Key Generation Nonce Request Subtype Data
                    Data needed to carry out the creation of the
                    registration key on behalf of the mobile node.

   The MN-FA KeyGen Request defines a set of extensions, identified by
   subtype, which may be used by a mobile node in a Mobile IP
   Registration Request message to request that some other entity create
   a Registration Key for use by the mobile node with the mobile node's
   new foreign agent.








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   This document defines the subtype 1 for the MN-FA Key Generation
   Nonce >From AAA Request (MN-FA AAA KeyGen Request for short).  The
   MN-FA AAA KeyGen Request has a zero-length Subtype Data field and
   MUST appear in the Registration Request before the MN-AAA
   Authentication extension.

6.2.  Generalized MN-FA Key Generation Nonce Reply Extension

   The Generalized MN-FA Key Generation Nonce Reply extension (MN-FA
   KeyGen Reply for short) supplies keying material requested by the
   MN-FA KeyGen Request extension.  Figure 2 illustrates the format of
   the Generalized MN-FA Key Generation Nonce Reply Extension.

    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      |    Subtype    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             MN-FA Key Generation Nonce Reply Subtype Data ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 2: The Generalized Mobile IP MN-FA Key
                    Generation Nonce Reply Extension

   Type       41 (not skippable) (see [1] and section 8)

   Subtype    A number assigned to identify the way in which the MN-FA
              Key Generation Nonce Reply Subtype Data is to be used to
              obtain the registration key.

   Length     The 16-bit Length field is equal to the number of bytes in
              the MN-FA Key Generation Nonce Reply Subtype Data.

   MN-FA Key Generation Nonce Reply Subtype Data
              An encoded copy of the keying material, along with any
              other information needed by the recipient to create the
              designated Mobility Security Association.

   For each subtype, the format of the MN-FA Key Generation Nonce Reply
   Subtype Data has to be separately defined according to the particular
   method required to set up the Mobility Security Association.

   For the subtype defined in this document, the MN-FA Key Generation
   Nonce supplied in the data for a subtype of this extension may come
   as a result of a request which was sent using a subtype of the
   Generalized MN-FA Key Generation Nonce Request Extension.  In such





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   cases, the SPI to be used when employing the Mobility Security
   Association defined by the registration key is the same as given in
   the original request.

   Once the mobile node creates the Mobility Security Association with
   the foreign agent, by using the transform indexed by the AAA SPI, it
   stores that Mobility Security Association indexed by the FA SPI in
   its list of Mobile Security Associations.

   If the foreign agent receives a Registration Reply that has no MN-FA
   Key Generation Nonce Reply extension, and if it has no existing
   Mobility Security Association with the mobile node, the foreign agent
   MAY change the Code value of the Registration Reply to MISSING_MN_FA
   (see section 7), effectively causing the registration to fail.

   This document defines subtype 1 of the MN-FA KeyGen Reply for the
   MN-FA Key Generation Nonce From AAA extension (MN-FA AAA KeyGen Reply
   for short), shown in figure 3.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Lifetime                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            AAA SPI                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             FA SPI                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Algorithm Identifier     |      Key Generation Nonce ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 3: The MN-FA Key Generation Nonce From AAA
                  Subtype-Specific Data

   lifetime   This field indicates the duration of time (in seconds) for
              which the keying material used to create the registration
              key is valid.

   AAA SPI    A 32-bit opaque value, indicating the SPI that the mobile
              node must use to determine the transform to use for
              establishing the Mobility Security Association between the
              mobile node and its prospective foreign agent.

   FA SPI     The SPI for the Mobility Security Association to the FA
              that the mobile node creates using the Key Generation
              Nonce.





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   Algorithm Identifier
              This field indicates the transform to be used (stored as
              part of the Mobility Security Association with the foreign
              agent, and selected from among the values in the
              "Authentication Algorithm" table cited in section 4), for
              future computations of the Mobile-Foreign Authentication
              Extension.

   Key Generation Nonce
              A random [7] value of at least 128 bits.

   The MN-FA AAA KeyGen Reply extension MUST appear in the Registration
   Reply before the Mobile-Foreign Authentication extension.

   The Key Generation Nonce is provided by the AAA server for use by the
   mobile node in creating the registration key, which is used to secure
   future Mobile IP registrations with the same foreign agent.

6.3.  Generalized MN-HA Key Generation Nonce Request Extension

   Figure 4 illustrates the Generalized MN-HA Key Generation Nonce
   Request Extension (MN-HA KeyGen Request for short).

   Type             42 (not skippable) (see [1] and section 8)

   Subtype          a number assigned to identify the way in which the
                    MN-HA Key Generation Nonce Request Subtype Data is
                    to be used when generating the registration key.

   Length           The 16-bit Length field indicates the length of the
                    extension.  It is equal to the number of bytes in
                    the MN-HA Key Generation Nonce Request.

    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      |    Subtype    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Mobile Node SPI                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            MN-HA Key Generation Nonce Request Subtype Data ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 4: The Generalized Mobile IP MN-HA Key Generation
               Nonce Request Extension

   Subtype Data plus 4 (for the Mobile Node SPI field).




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   Mobile Node SPI  The Security Parameters Index that the mobile node
                    will assign for the Mobility Security Association
                    created for use with the registration key.

   MN-HA Key Generation Nonce Request Subtype Data
                    Data needed to carry out the creation of the MN-HA
                    key on behalf of the mobile node.

   The MN-HA KeyGen Request Extension defines a set of extensions,
   identified by subtype, which may be used by a mobile node in a Mobile
   IP Registration Request message to request that some other entity
   create an MN-HA key for use by the mobile node with the mobile node's
   new home agent.

   This document defines the subtype 1 for the MN-HA Key Generation
   Nonce from AAA Request (MN-HA AAA KeyGen Request for short).  The
   MN-HA AAA KeyGen Request has a zero-length Subtype Data field and
   MUST appear in the Registration Request before the MN-AAA
   Authentication extension.

6.4.  Generalized MN-HA Key Generation Nonce Reply Extension

   The Generalized MN-HA Key Generation Nonce Reply extension (MN-HA
   KeyGen Reply for short) supplies keying material requested by the
   MN-HA KeyGen Request extension.  Figure 5 illustrates the format of
   the Generalized MN-HA Key Generation Nonce Reply Extension.

    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      |    Subtype    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Lifetime                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              MN-HA Key Generation Nonce Reply Subtype Data ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 5: The Generalized Mobile IP MN-HA Key
                    Generation Nonce Reply Extension

   Type       43 (not skippable) (see [1] and section 8)

   Subtype    a number assigned to identify the way in which the MN-HA
              Key Generation Nonce Reply Subtype Data is to be used to
              obtain the MN-HA key.






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   Length     The 16-bit Length field indicates the length of the
              extension.  It is equal to the number of bytes in the MN-
              HA Key Generation Nonce Reply Subtype Data plus 4 (for the
              Lifetime field).

   Lifetime   This field indicates the duration of time (in seconds) for
              which the MN-HA key is valid.

   MN-HA Key Generation Nonce Reply Subtype Data
              Data used to derive the MN-HA key, along with any other
              information needed by the mobile node to create the
              designated Mobility Security Association with the home
              agent.

   For each subtype, the format of the MN-HA Key Generation Nonce Reply
   Subtype Data has to be separately defined according to the particular
   method required to set up the Mobility Security Association.

   This document defines subtype 1 of the MN-HA KeyGen Reply for the
   MN-HA Key Generation Nonce From AAA extension (MN-HA AAA KeyGen Reply
   for short), shown in figure 6.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            AAA SPI                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             HA SPI                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Algorithm Identifier      |         Replay Method         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Key Generation Nonce ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 6: The MN-HA Key Generation Nonce From AAA
                  Subtype-Specific Data

   AAA SPI    A 32-bit opaque value, indicating the SPI that the mobile
              node must use to determine the transform to use for
              establishing the Mobility Security Association between the
              mobile node and its home agent.

   HA SPI     The SPI for the Mobility Security Association to the HA
              that the mobile node creates using the Key Generation
              Nonce.






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   Algorithm Identifier
              This field indicates the transform to be used for future
              computations of the Mobile-Home Authentication Extension
              (see section 4).

   Replay Method
              This field contains the replay method to be used for
              future Registration messages (see section 4).

   Key Generation Nonce
              A random [7] value of at least 128 bits.

   The MN-HA AAA KeyGen Reply subtype-specific data is shown in figure
   6.  The Mobile Node calculates the MN-HA key using the Key Generation
   Nonce provided by the AAA server.  The calculation proceeds by using
   the key shared between the mobile node and the AAA server that has
   previously been configured for securing all such communication
   requirements with the AAA server which will be contacted within the
   AAA infrastructure (see appendix A).  The MN-HA key is intended for
   use by the mobile node to secure future Mobile IP registrations with
   its home agent.  The MN-HA AAA KeyGen Reply extension MUST appear in
   the Registration Reply before the MN-HA Authentication extension.

   Once the mobile node creates the MN-HA Key, by using the transform
   specified in the AAA SPI, it stores the HA Security Information
   indexed by the HA SPI in its list of Mobile Security Associations.
   The mobile node uses the Identification field data from the
   Registration Reply as its initial synchronization data with the home
   agent.

7.  Error Values

   Each entry in the following table contains the name of the Code [1]
   value to be returned in a Registration Reply, the value for that
   Code, and the section in which the error is first mentioned in this
   specification.

      Error Name               Value   Section
      ----------------------   -----   ---------
      MISSING_MN_FA             107      6.2

8.  IANA Considerations

   This document defines 4 new extensions (see Section 6) taken from the
   (non-skippable) numbering space defined for Mobile IP registration
   extensions defined in RFC 3344 [1] as extended in RFC 2356 [8].  The
   values for these extensions are:




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      Name                   Value   Section
      --------------------- ------- ---------
      MN-FA-KeyGen Request    40      6.1
      MN-FA-KeyGen Reply      41      6.2
      MN-HA-KeyGen Request    42      6.3
      MN-HA-KeyGen Reply      43      6.4

   IANA has created and will maintain a new registry for the KeyGen
   Request/Reply subtypes.  The initial contents of the registry is a
   single entry for the subtypes defined in this document:

      Name                           Value   Section
      ----------------------------- ------- ---------
      KeyGen Request/Reply from AAA    1        6

   New subtypes for these two registries are assigned through Standards
   Action as defined in [9].

   IANA has assigned a code value for error MISSING_MN_FA, listed in
   section 7.  This value has been taken from the space of error values
   conventionally associated with rejection by the foreign agent (i.e.,
   64-127).

   IANA has created and will maintain a namespace for the Replay Method
   Identifier.  This specification makes use of 2 and 3; all other
   values other than zero (0) and (1) are available for assignment,
   pending review and approval by a Designated Expert [9].

9.  Security Considerations

   The extensions in this document are intended to provide the
   appropriate level of security for Mobile IP entities (mobile node,
   foreign agent, and home agent) to calculate the Authentication Data
   needed by authentication extensions used with Mobile IP registration
   messages.  The Mobility Security Associations resulting from use of
   these extensions do not offer any higher level of security than what
   is already implicit in use of the AAA Security Association between
   the mobile node and the AAAH.  In order to deny any adversary the
   luxury of unbounded time to analyze and break the secrecy of the AAA
   Security Association between the mobile node and the AAA server, that
   AAA Security Association MUST be refreshed periodically.

   The provisioning and refreshing of the AAA key in the MN and AAA
   server is outside the scope of this document.

   Since the Reply extensions defined in this specification only carry
   Key Generation Nonces, which are used to derive keys, they do not
   expose any data that could be used in an attack aimed at recovering



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   the key shared between the mobile node and the AAA.  The authors do
   not believe this specification introduces any new security
   vulnerability.

10.  Acknowledgements

   Thanks to Fredrik Johansson, Tom Hiller, and the members of the IESG
   for their useful comments.  Thanks especially to Tom Hiller who has
   contributed many textual improvements to later revisions of this
   document.

11.  References

11.1.  Normative References

   [1]  Perkins, C., Ed., "IP Mobility Support for IPv4", RFC 3344,
        August 2002.

   [2]  Aboba, B. and M. Beadles, "The Network Access Identifier", RFC
        2486, January 1999.

   [3]  Perkins, C. and P. Calhoun, "Mobile IPv4 Challenge/Response
        Extension", RFC 3012, November 2000.

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

   [5]  Calhoun, P. and C. Perkins, "Mobile IP Network Access Identifier
        Extension for IPv4", RFC 2794, March 2000.

   [6]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
        for Message Authentication", RFC 2104, February 1997.

   [7]  Eastlake, D., Crocker, S., and J. Schiller, "Randomness
        Recommendations for Security", RFC 1750, December 1994.

   [8]  Montenegro, G. and V. Gupta, "Sun's SKIP Firewall Traversal for
        Mobile IP", RFC 2356, June 1998.

   [9]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.










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11.2.  Informative References

   [10] Mitton, D., St.Johns, M., Barkley, S., Nelson, D., Patil, B.,
        Stevens, M., and B. Wolff, "Authentication, Authorization, and
        Accounting: Protocol Evaluation", RFC 3127, June 2001.

   [11] Rigney, C., Willens, S., Rubens, A., and A. Simpson, "Remote
        Authentication Dial In User Service (RADIUS)", RFC 2865, June
        2000.

   [12] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko,
        "Diameter Base Protocol", RFC 3588, September 2003.

   [13] Glass, S., Hiller, T., Jacobs, S., and C. Perkins, "Mobile IP
        Authentication, Authorization, and Accounting Requirements", RFC
        2977, October 2000.

   [14] Calhoun, P. and C. Perkins, "DIAMETER mobile IP extensions",
        Work in Progress, February 2004.
































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Appendix A.  AAA Infrastructure

   In this appendix, we attempt to capture the main features of a basic
   model for operation of AAA servers that is assumed for understanding
   of the use of the Mobile IP registration extensions described in this
   document.  This information has been adapted from the discussion in
   RFC 2977 [13].

   Within the Internet, a mobile node belonging to one administrative
   domain (called the home domain) often needs to use resources provided
   by another administrative domain (called the foreign domain).  A
   foreign agent that handles the mobile node's Registration Request is
   likely to require that the mobile node provide some credentials that
   can be authenticated before access to the resources is permitted.
   These credentials may be provided as part of the Mobile-AAA
   Authentication extension [3], relying on the existence of an AAA
   infrastructure such as is described in this section, and also
   described in RFC 2977 and RFC 3012 [3].  Such credentials are
   typically managed by entities within the mobile node's home domain.
   They may be also used for setting up secure communications with the
   mobile node and the foreign agent, or between the mobile node and its
   home agent if necessary.

                Local Domain                  Home Domain
              +--------------+           +----------------------+
              |   +------+   |           |   +------+           |
              |   |      |   |           |   |      |           |
              |   | AAAL |   |           |   | AAAH |           |
              |   |      +-------------------+      |           |
              |   +---+--+   |           |   +------+           |
              |       |      |           |                      |
              |       |      |           +----------------------+
   +------+   |   +---+--+   |
   |      |   |   |      |   |       MN   =  mobile node
   |  MN  |- -|- -|  FA  |   |       FA   =  foreign agent
   |      |   |   |      |   |       AAAL =  local authority
   +------+   |   +------+   |       AAAH =  home authority
              |              |
              +--------------+

          Figure 7: AAA Servers in Home and Local Domains

   The foreign agent often does not have direct access to the data
   needed to verify the credentials.  Instead, the foreign agent is
   expected to consult an authority (typically in the same foreign
   domain) in order to request proof that the mobile node has acceptable
   credentials.  Since the foreign agent and the local authority (AAAL)
   are part of the same administrative domain, they are expected to have



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   established, or be able to establish for the necessary lifetime, a
   secure channel for the purposes of exchanging sensitive (access)
   information, and keeping it private from (at least) the visiting
   mobile node.

   The local authority (AAAL) itself may not have enough information
   stored locally to carry out the verification for the credentials of
   the mobile node.  In contrast to the foreign agent, however, the AAAL
   is expected to be configured with enough information to negotiate the
   verification of mobile node credentials with its home domain.  The
   home and foreign domains should be configured with sufficient IP
   Security Associations (i.e., IPsec) and access controls so that they
   can negotiate the authorization, and also enable the mobile node to
   acquire Mobility Security Associations with the mobility agents
   within the foreign domain.  For the purposes of the key exchanges
   specified within this document, the authorization is expected to
   depend only upon secure authentication of the mobile node's
   credentials.

   Once the authorization has been obtained by the local authority, and
   the authority has notified the foreign agent about the successful
   negotiation, the foreign agent can deliver the Registration Reply to
   the mobile node along with the key material.

   In figure 7, there might be many mobile nodes from many different
   Home Domains.  Each Home Domain provides a AAAH that can check
   credentials originating from mobile nodes administered by that Home
   Domain.  There is a security model implicit in figure 7, and it is
   crucial to identify the specific security associations assumed in the
   security model.  These IP Security Associations are illustrated in
   figure 8, and are considered to be relatively long-lived security
   associations.

   First, it is natural to assume that the mobile node has an AAA
   Security Association with the AAAH, since that is roughly what it
   means for the mobile node to belong to the home domain.

   Second, from the model illustrated in figure 7 it is clear that AAAL
   and AAAH have to share an IP Security Association, because otherwise
   they could not rely on the authentication results, authorizations,
   nor even the accounting data which might be transacted between them.
   Requiring such bilateral IP Security Associations is, however, in the
   end not scalable; the AAA framework must provide for more scalable
   mechanisms, but the methods by which such a broker model is to be
   created are out of scope for this document.  See RFC 2977 for more
   details.





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   Finally, from figure 7, it is clear that the foreign agent can
   naturally share an IP Security Association with the AAAL.  This is
   necessary in order for the model to work because the foreign agent
   has to have a way to find out that it is permissible to allocate the
   local resources to the mobile node, and further to transmit any
   successful Registration Reply to the mobile node.

   Figure 8 illustrates the IP Security Associations we understand from
   our proposed model.  Note that there may be, by mutual agreement
   between AAAL and AAAH, a third party inserted between AAAL and AAAH
   to help them arbitrate secure transactions in a more scalable
   fashion.  The broker model which has been designed to enable such
   third-party processing should not have any effect on the Mobile IP
   extensions specified in this document, and so no description is
   provided here; see RFC 2977 [13] for more details.

                               +------+              +------+
                               |      |              |      |
                               | AAAL +--------------+ AAAH |
                               |      |              |      |
                               +---+--+              +--+---+
                                   |                    |
                                   |                    |
                               +---+--+              +--+---+
   MN   =  mobile node         |      |              |      |
   FA   =  foreign agent       |  FA  |              |  MN  |
   AAAL =  local authority     |      |              |      |
   AAAH =  home authority      +------+              +------+

                   Figure 8: IP Security Associations

   Nodes in two separate administrative domains (for instance, AAAH and
   AAAL) often must take additional steps to verify the identity of
   their communication partners, or alternatively to guarantee the
   privacy of the data making up the communication.  While these
   considerations lead to important security requirements, as mentioned
   above in the context of security between servers, we consider the
   exact choice of IP Security Associations between the AAA servers to
   be beyond the scope of this document.  The choices are unlikely to
   depend upon Mobile IP, or any specific features of the general model
   illustrated in figure 7.  On the other hand, the Mobility Security
   Associations needed between Mobile IP entities are of central
   importance in the design of the key derivation extensions in this
   document.







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   One further detail deserves mention.  The Mobility Security
   Association to be established between the mobile node and the foreign
   agent has to be communicated to the foreign agent as well as to the
   mobile node.  The following requirements are placed on the mechanism
   used by the AAA infrastructure to effect key distribution:

   -  The AAAH must establish strong, fresh session keys.

   -  The mechanism must maintain algorithm independence, allowing for
      the distribution of authentication algorithm identification along
      with the keys.

   -  The mechanism must include replay detection.

   -  The mechanism must authenticate all parties, including the AAA
      servers and the FA and HA.

   -  The mechanism must provide for authorization of the client, FA,
      and HA.

   -  The mechanism must not rely on plaintext passwords.

   -  The mechanism must maintain confidentiality of session keys.

   -  The mechanism must uniquely name session keys.

   -  The mechanism must be such that the compromise of a single FA and
      HA cannot compromise any other part of the system, including
      session keys and long-term keys

   -  The mechanism must bind key(s) to an appropriate context

   -  The mechanism must not expose the keys to entities other than the
      AAAH and FA (or HA in the case of key distribution to the HA).

   The way that the key is distributed to the foreign agent (or home
   agent) is expected to be handled as part of the AAA protocol
   processing between the AAAH and AAAL, and the further AAA protocol
   processing between the AAAL and the foreign agent.  Such processing
   is outside the scope of this document, but must satisfy the above
   requirements.










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Appendix B.  Message Flow for Requesting and Receiving Registration Keys

   In this section, we show message flows for requesting and receiving a
   registration key from the AAA infrastructure, described in section A.
   Challenge values, as specified in [3], might be added to the
   Advertisement and Registration messages for additional replay
   protection, but are not illustrated here.

   Diagram 9 illustrates the message flow for the case when the mobile
   node explicitly requests keying material to create registration keys.

   MN                     FA                  AAA Infrastructure
    |                       |                           |
    |<--- Advertisement-----|                           |
    |      (if needed)      |                           |
    |                       |                           |
    |-- RReq+AAA Key Req.-->|                           |
    |                       |--- RReq + AAA Key Req.--->|
    |                       |                           |
    |                       |<--- RRep + AAA Key Rep.---|
    |<-- RRep+AAA Key Rep.--|                           |
    |                       |                           |

          Figure 9: Message Flows for Requesting and
                    Receiving Key Generation Nonce

   In diagram 9, the following message flow is illustrated:

   1. The foreign agent disseminates an Agent Advertisement.  This
      advertisement MAY have been produced after receiving an Agent
      Solicitation from the mobile node (not shown in the diagram).

   2. The mobile node creates a Registration Request including the MN-HA
      AAA KeyGen Request and/or MN-FA AAA KeyGen Request, as needed,
      along with an authorization-enabling authentication extension as
      required by Mobile IP [1].

   3. The foreign agent relays the Registration Request and/or Key
      Request(s) to its locally configured AAA Infrastructure (see
      appendix A), according to local policy.

   4. The foreign agent receives a AAA Response with the appropriate
      indications for authorizing connectivity for the mobile node.
      Along with this AAA Response, the foreign agent may also receive
      key material by some secure method appropriate for communications
      between it and its local AAA infrastructure.  At this point if the





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      foreign agent has not relayed the Registration Request, it
      forwards it directly to the Home Agent and waits for a
      Registration Reply (not shown in the figure).

   5. The foreign agent relays the Registration Reply to the mobile
      node, along with the new AAA KeyGen Reply extensions to be used by
      the mobile node to establish Mobility Security Associations with
      the relevant mobility agents (foreign agent and/or home agent).

   Diagram 10 illustrates the message flow for the case when the mobile
   node receives unsolicited keying material from the AAA
   Infrastructure.

   MN                     FA                  AAA Infrastructure
    |                       |                           |
    |<--- Advertisement-----|                           |
    |      (if needed)      |                           |
    |                       |                           |
    | ------ RReq --------->|                           |
    |                       |------- RReq ------------->|
    |                       |                           |
    |                       |<--- RRep + AAA Key Rep.---|
    |<-- RRep+AAA Key Rep.--|                           |
    |                       |                           |

      Figure 10: Message Flow for Receiving Unsolicited
                 Key Generation Nonce

   In diagram 10, the following message flow is illustrated:

   1. The foreign agent disseminates an Agent Advertisement.  This
      advertisement MAY have been produced after receiving an Agent
      Solicitation from the mobile node (not shown in the diagram).

   2. The mobile node creates a Registration Request including an
      authorization-enabling authentication extension as required by
      Mobile IP [1].

   3. The foreign agent sends a AAA Request (possibly containing the
      Registration Request) to its locally configured AAA Infrastructure
      (see appendix A), according to local policy.

   4. The foreign agent receives a AAA Response with the appropriate
      indications for authorizing connectivity for the mobile node.
      Along with this AAA Response, the foreign agent may also receive
      key material by some secure method appropriate for communications
      between it and its local AAA infrastructure.  At this point, if
      the foreign agent has not relayed the Registration Request, it



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      forwards it directly to the Home Agent and waits for a
      Registration Reply (not shown in the figure).

   5. The foreign agent relays the Registration Reply to the mobile
      node, along with the new KeyGen Reply extensions to be used by the
      mobile node to establish Mobility Security Associations with the
      relevant mobility agents (foreign agent and/or home agent).

Authors' Addresses

   Charles E. Perkins
   Nokia Research Center
   313 Fairchild Drive
   Mountain View, California 94043
   USA

   Phone:  +1 650 625-2986
   Fax:    +1 650 625-2502
   EMail:  charles.perkins@nokia.com


   Pat R. Calhoun
   Airespace, Inc.
   110 Nortech Parkway
   San Jose, CA 95134
   USA

   Phone:  +1 408 635 2000
   Fax:    +1 408 635 2020
   EMail:  pcalhoun@airespace.com





















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Full Copyright Statement

   Copyright (C) The Internet Society (2005).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.







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