Subject: [AAA-WG]: Proposed Text for Issue 91

From: Pat Calhoun <[email-masked]>
Date: Tue, 17 Jul 2001 06:28:31 -0700

All,

Below is my proposed text for this issue. I'd *really* like some
comments on this ASAP, as my deadline to get the drafts out is 
tomorrow. The changes aren't that major, and include:

1. Changing the Mobile keys to be Grouped AVPs
3. Added text in sub-sections 5.x to state that the mobile proposes
   its keys in the MIP AAA keys subtypes, and the HA uses these SPIs
   in the creation of the MIP AAA key reply extensions.
4. Added text in 5.x stating that the HA is responsible for creating
   the SPI used in the FA-HA key
5. Added two new AVPs, that the HA includes in the HAA. These AVPs
   contain the SPIs that the FA will use with the MN and the HA. These
   SPIs are used by the AAAH to create the grouped key AVPs that are
   sent to the foreign in the AMA.

btw, I am not using my normal nroff environment, so the formatting MAY
be a tad off. I will be out of contact today between 9 and 5 pacific, and
will respond to comments upon my return.

Comments most appreciated,

PatC
----

5.0  Key Distribution Center

   The mobile node and mobility agents use registration keys to compute
   authentication extensions applied to registration messages, as
   defined in [4]: Mobile-Foreign, Foreign-Home and Mobile-Home.  If
   registration keys are requested the AAA server(s) MUST create them
   after the Mobile Node is successfully authenticated and authorized.

   If the AAAH does not communicate directly with the foreign agent, and
   it does not wish for intermediate proxies to have access to the
   session keys, they SHOULD be protected using the CMS security
   application [9].

   The Authorization-Lifetime AVP contains the number of seconds before
   registration keys destined for the Home Agent and/or Foreign Agent
   expire.  A value of zero indicates infinity (no timeout).

   AAA support for key distribution departs slightly from the existing
   SPI usage, as described in [4]. The SPI values are used as key
   identifiers, meaning that each registration key has its own SPI
   value; nodes that share a key also share an SPI. The Mobile Node
   proposes SPIs for use in computing the Mobile-Foreign and Mobile-Home
   authentication extensions, via the Mobile IP AAA Key Request
   extensions [15], while the Home Agent allocates the Mobile-Foreign,
   Mobile-Home and Foreign-Home SPIs.

   Once the registration keys have been distributed, subsequent Mobile
   IP registrations need not invoke the AAA infrastructure until the
   keys expire.  These registrations MUST include the Mobile-Home
   authentication extension.  In addition, subsequent registrations MUST
   also include Mobile-Foreign authentication extension if the Mobile-
   Foreign key was generated and distributed by AAA; similarly for
   subsequent use of the Foreign-Home authentication extensions.

   Each registration key that is generated by AAA will generally be
   distributed to two parties; for instance, a Mobile-Foreign key goes
   to both a mobile node and a foreign agent.  The methods by which the
   key is encoded will depend upon the security associations available
   to the AAA server and each recipient of the key.  These methods will
   often be different for the two recipients, so that the registration

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   key under consideration has to be encoded twice.

   See sections 6.0 for details about the format of the AVPs used to
   transport the registration keys.

5.1  Distributing the Mobile-Home Registration Key

   If the mobile node does not have a Mobile-Home registration key, then
   the AAAH is likely to be the only entity trusted that is available to
   the mobile node.  Thus, the AAAH has to generate the Mobile-Home
   registration key, and encode it for eventual consumption by the
   mobile node and home agent.

   If the home agent is in the home domain, then AAAH can directly
   encode the Mobile-Home registration key into a MIP-HA-to-MN-Key AVP
   and include that AVP in the HAR message for delivery to the home
   agent.

   If, on the other hand, the home agent is to be allocated in the
   visited domain, the AAAH does not transmit the HAR to the home agent,
   but instead transmits the HAR to the AAAF. When the AAAF receives the
   HAR, it first allocates a home agent, and then issues the HAR for
   that home agent.

   The AAAH also has to arrange for the key to be delivered to the
   mobile node.  Unfortunately, the AAA server only knows about Diameter
   messages and AVPs, and the mobile node only knows about Mobile IP
   messages and extensions [4].  For this purpose, AAAH encodes the
   Mobile-Home registration key into a MIP-MN-to-HA-Key AVP, using its
   security association with the mobile node, which is added to the HAR
   message, and delivered either to a local home agent, or to the AAAF
   in the case where the home agent is in the visited network. The AAAH
   has to rely on the home agent (that also understands Diameter) to
   transfer the keying information into a Mobile IP Generalized MN-HA
   Key Reply extension [15] in the Registration Reply message, using the
   SPI proposed by the Mobile Node in the MN-HA Key Request From AAA
   Subtype extension. The home agent can format the Reply message and
   extensions correctly for eventual delivery to the mobile node. The
   resulting Registration Reply is added to the HAA's MIP-Reg-Reply AVP.

   After the HAA message is parsed by the AAAH, and transformed into an
   AMA, the AMA message containing the MIP-Reg-Reply AVP will eventually
   be received by the the foreign agent. The foreign agent can then use
   that AVP to recreate a Registration Reply message, containing the
   Generalized MN-HA Key Reply extension, for delivery to the mobile
   node.

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   In summary, the AAAH generates the Mobile-Home registration key and
   encodes it into a MIP-HA-to-MN-Key AVP and a MIP-MN-to-HA-Key AVP.
   These AVPs are delivered to a home agent by including them in a HAR
   message sent from either AAAH or AAAF. The home agent decodes the key
   for its own use.  The home agent also copies the encoded registration
   key from the MIP-MN-to-HA-Key AVP into a Generalized MN-HA Key Reply
   extension appended to the Mobile IP Registration Reply message. This
   Registration Reply message MUST also include the Mobile-Home
   authentication extension, created using the newly allocated Mobile-
   Home registration key. The home agent then encodes the Registration
   Reply message and extensions into a MIP-Reg-Reply AVP included as
   part of the HAA message to be sent back to the AAA server.

5.2  Distributing the Mobile-Foreign Registration Key

   The Mobile-Foreign registration key is also generated by AAAH (upon
   request), so that it can be encoded into a MIP-MN-to-FA-Key AVP,
   which is added to the HAR, and copied by the home agent into a
   Generalized MN-FA Key Reply Extension [15] to the Mobile IP
   Registration Reply message, using the SPI proposed by the Mobile Node
   in the MN-FA Key Request From AAA Subtype extension. Further, the
   home agent includes the SPI in the HAA's MIP-FA-to-MN-SPI AVP. Most
   of the considerations for distributing the Mobile-Foreign
   registration key are similar to the distribution of the Mobile-Home
   Registration Key.

   Upon receipt of the HAA, if MN-FA keying was requested the AAAH
   creates the MIP-FA-to-MN-Key AVP, using the SPI in the MIP-FA-to-MN-
   SPI, and includes the AVP in the AMA. If the MIP-FA-to-MN-Key AVP was
   present in the AMA, the foreign agent MUST include the Mobile-Foreign
   authentication extension in the Registration Reply, using the newly
   distributed key.

5.3  Distributing the Foreign-Home Registration Key

   If the home agent is in the home domain, then AAAH has to generate
   the Foreign-Home registration key.  Otherwise, it is generated by
   AAAF.

   In either case, the AAA server encodes the registration key into a
   MIP-HA-to-FA-Key AVP and includes that AVP as part of the HAR message
   sent to the home agent, and waits for the HAA message to be returned.

   Upon receipt of the HAR, the home agent recovers the Foreign-Home
   registration key, allocates an SPI to be used with the key, and uses
   this key to create a Foreign-Home authentication extension to the

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   Registration Reply message. The allocated SPI is included in the
   HAA's MIP-FA-to-HA SPI AVP.

   Upon receipt of the HAA, the Diameter server responsible for key
   allocation adds the MIP-FA-to-HA Key AVP, using the SPI in the MIP-
   FA-to-HA-SPI, and includes the AVP in the AMA.

5.4  Key Distribution Example

   Figure 9 provides an example of subsequent Mobile IP message
   exchange, assuming that AAAH distributed registration keys for all
   three MN-FA, FA-HA and HA-MN authentication extensions.

   Mobile Node                Foreign Agent                 Home Agent
   -----------                -------------                 ----------

   Reg-Req(MN-HA-Auth, MN-FA-Auth)-------->

                              Reg-Req(MN-HA-Auth, FA-HA-Auth)-------->

                              <--------Reg-Rep(MN-HA-Auth, FA-HA-Auth)

   <--------Reg-Rep(MN-HA-Auth, MN-FA-Auth)

                   Figure 9: Mobile IP Message Exchange

6.0  Key Distribution Center (KDC) AVPs

   The Mobile-IP protocol defines a set of security associations shared
   between the Mobile Node, Foreign Agent and Home Agents. These three
   security associations (Mobile-Home, Mobile-Foreign, and Foreign-
   Home), can be dynamically created by the AAAH. This requires that the
   AAAH create Mobile-IP Registration Keys, and that these keys be
   distributed to the three mobile entities, via the Diameter Protocol.
   AAA servers supporting the Diameter Mobile IP Application MUST
   implement the KDC AVPs defined in this document. In other words, AAA
   servers MUST be able to create three registration keys: the Mobile-
   Home, Mobile-Foreign, and Foreign-Home keys.

   The names of the KDC AVPs indicate the two entities sharing the
   security association defined by the encrypted key material; the
   intended receiver of the AVP is the first named entity.  So, for
   instance, the MIP-MN-to-HA-Key AVP contains the Mobile-Home key
   encrypted in a way that allows it to be recovered by the mobile node.

   If strong authentication and confidentiality of the registration keys

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   is required, it is recommended that the CMS security application [9]
   be used.

   The following table describes the Diameter AVPs defined in the Mobile
   IP application, their AVP Code values, types, possible flag values
   and whether the AVP MAY be encrypted.

                                             +---------------------+
                                             |    AVP Flag rules   |
                                             |----+-----+----+-----|----+
                    AVP  Section             |    |     |SHLD| MUST|MAY |
    Attribute Name  Code Defined  Value Type |MUST| MAY | NOT|  NOT|Encr|
    -----------------------------------------|----+-----+----+-----|----|
    MIP-Algorithm-   345  6.9     Enumerated | M  |  P  |    |  V  | Y  |
      Type                                   |    |     |    |     |    |
    MIP-FA-to-HA-Key 328  6.2     Grouped    | M  |  P  |    |  V  | Y  |
    MIP-FA-to-HA-SPI 318  6.12    Unsigned32 | M  |  P  |    |  V  | Y  |
    MIP-FA-to-MN-Key 326  6.1     Grouped    | M  |  P  |    |  V  | Y  |
    MIP-FA-to-MN-SPI 319  6.11    Unsigned32 | M  |  P  |    |  V  | Y  |
    MIP-HA-to-FA-Key 329  6.3     Grouped    | M  |  P  |    |  V  | Y  |
    MIP-HA-to-MN-Key 332  6.4     Grouped    | M  |  P  |    |  V  | Y  |
    MIP-MN-to-FA-Key 325  6.5     OctetString| M  |  P  |    |  V  | Y  |
    MIP-MN-to-HA-Key 331  6.6     OctetString| M  |  P  |    |  V  | Y  |
    MIP-Peer-SPI     342  6.7     Unsigned32 | M  |  P  |    |  V  | Y  |
    MIP-Replay-Mode  346  6.10    Enumerated | M  |  P  |    |  V  | Y  |
    MIP-Session-Key  343  6.8     OctetString| M  |  P  |    |  V  | Y  |

6.1  MIP-FA-to-MN-Key AVP

   The MIP-FA-to-MN-Key AVP (AVP Code 326) is of type Grouped, and
   contains the Foreign Agent's session key, which it shares with the
   Mobile Node. Its Data field has the following ABNF grammar:

      MIP-FA-to-MN-Key ::= < AVP Header: 326 >
                           { MIP-Peer-SPI }
                           { MIP-Algorithm-Type }
                           { MIP-Session-Key }
                         * [ AVP ]

6.2  MIP-FA-to-HA-Key AVP

   The MIP-FA-to-HA-Key AVP (AVP Code 328) is of type Grouped, and
   contains the Foreign Agent's session key, which it shares with the
   Home Agent. Its Data field has the following ABNF grammar:

      MIP-FA-to-HA-Key ::= < AVP Header: 328 >

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                           { MIP-Peer-SPI }
                           { MIP-Algorithm-Type }
                           { MIP-Session-Key }
                         * [ AVP ]

6.3  MIP-HA-to-FA-Key AVP

   The MIP-HA-to-FA-Key AVP (AVP Code 329) is of type Grouped, and
   contains the Home Agent's session key, which it shares with the
   Foreign Agent. Its Data field has the following ABNF grammar:

      MIP-HA-to-FA-Key ::= < AVP Header: 329 >
                           { MIP-Algorithm-Type }
                           { MIP-Replay-Mode }
                           { MIP-Session-Key }
                         * [ AVP ]

6.4  MIP-HA-to-MN-Key AVP

   The MIP-HA-to-MN-Key AVP (AVP Code 332) is of type Grouped, and
   contains the Home Agent's session key, which it shares with the
   Mobile Node. Its Data field has the following ABNF grammar:

      MIP-HA-to-MN-Key ::= < AVP Header: 332 >
                           { MIP-Algorithm-Type }
                           { MIP-Replay-Mode }
                           { MIP-Session-Key }
                         * [ AVP ]

6.5  MIP-MN-to-FA-Key AVP

   The MIP-MN-to-FA-Key AVP (AVP Code 325) is of type Grouped, and
   contains the Mobile Node's session key, which it shares with the
   Foreign Agent. The Home Agent uses this AVP in the construction of
   the Mobile IP "Unsolicted MN-FA Key from AAA Subtype" extension [15].
   The SPI in the extension's FA SPI field is allocated by the Home
   Agent, but it SHOULD take into consideration the SPI requested by the
   Mobile Node in the "MN-FA Key Request From AAA Subtype" extension.

      MIP-MN-to-FA-Key ::= < AVP Header: 325 >
                           { MIP-Algorithm-Type }
                           { MIP-Replay-Mode }
                           { MIP-Session-Key }
                         * [ AVP ]

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6.6  MIP-MN-to-HA-Key AVP

   The MIP-MN-to-HA-Key AVP (AVP Code 331) is of type Grouped, and
   contains the Mobile Node's session key, which it shares with the Home
   Agent. The Home Agent uses this AVP in the construction of the Mobile
   IP "Unsolicted MN-HA Key from AAA Subtype" extension [15]. The SPI in
   the extension's HA SPI field is allocated by the Home Agent, but it
   SHOULD take into consideration the SPI requested by the Mobile Node
   in the "MN-HA Key Request From AAA Subtype" extension.

      MIP-MN-to-FA-Key ::= < AVP Header: 331 >
                           { MIP-Algorithm-Type }
                           { MIP-Replay-Mode }
                           { MIP-Session-Key }
                         * [ AVP ]

6.7  MIP-Peer-SPI AVP

   The MIP-Peer-SPI AVP (AVP Code 342) is of type Unsigned32, and
   contains the Security Parameter Index to use to reference the key in
   the associated MIP-Session-Key AVP. The SPI created MUST NOT be a
   value between zero (0) and 255, which is the reserved namespace
   defined in [4].

6.8  MIP-Session-Key AVP

   The MIP-Session-Key AVP (AVP Code 343) is of type OctetString and
   contains the Session Key to be used between two Mobile IP entities.

6.9  MIP-Algorithm-Type AVP

   The MIP-Algorithm-Type AVP (AVP Code 345) is of type Enumerated, and
   contains the Algorithm identifier used to generate the associated
   Mobile IP authentication extension. The following values are
   currently defined:

      1   Prefix+Suffix MD5 [4]
      2   HMAC-MD5 [13]
      3   SHA-1 [17]

6.10  MIP-Replay-Mode AVP

   The MIP-Replay-Mode AVP (AVP Code 346) is of type Enumerated and
   contains the replay mode the Home Agent should use when

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   authenticating the Mobile Node.

   The following values are supported (see [4] for more information):

      0   None
      1   Timestamps
      2   Nonces

6.11  MIP-FA-to-MN-SPI AVP

   The MIP-FA-to-MN-SPI AVP (AVP Code 319) is of type Unsigned32, and
   contains the Security Parameter Index the Foreign Agent is to use to
   refer to the session key it shares with the Mobile Node. The SPI
   created MUST NOT be a value between zero (0) and 255, which is the
   reserved namespace defined in [4]. This AVP MAY be added in the HAA
   message by the Home Agent for the AAAH's use in MIP-Peer-SPI AVP of
   the MIP-FA-to-MN-Key AVP.

6.12  MIP-FA-to-HA-SPI AVP

   The MIP-FA-to-HA-SPI AVP (AVP Code 318) is of type Unsigned32, and
   contains the Security Parameter Index the Foreign Agent is to use to
   refer to the session key it shares with the Home Agent. The SPI
   created MUST NOT be a value between zero (0) and 255, which is the
   reserved namespace defined in [4]. This AVP MAY be added in the HAA
   message by the Home Agent for the AAAH's use in MIP-Peer-SPI AVP of
   the MIP-FA-to-HA-Key AVP.