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Versions: (draft-carrara-newtype-keyid) 00 01 02 03 04 05 RFC 4563

   Internet Engineering Task Force        Carrara, Lehtovirta, Norrman
                                                            (Ericsson)
   INTERNET-DRAFT
   EXPIRES: August 2005                                  February 2005





 The Key ID Information Type for the General Extension Payload in MIKEY
                 <draft-ietf-msec-newtype-keyid-01.txt>



Status of this memo

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   applicable patent or other IPR claims of which I am (we are) aware
   have been disclosed, and any of which I (we) become aware will be
   disclosed, in accordance with RFC 3668 (BCP 79).

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   of Section 3 of RFC 3667 (BCP 78).

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   This document is an individual submission to the IETF. Comments
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Abstract

   This memo specifies a new Type (the Key ID Information Type) for the
   General Extension Payload in the Multimedia Internet KEYing
   Protocol. This is used in, e.g., the Multimedia Broadcast/Multicast
   Service specified in the 3rd Generation Partnership Project.





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   TABLE OF CONTENTS

    1. Introduction...................................................2
    2. Rationale......................................................2
    3. The Key ID Information Type for the General Extension Payload..3
    4. The Key ID Information Type for the General Extension Payload..5
    5. Security Considerations........................................5
    6. IANA Considerations............................................5
    7. Acknowledgements...............................................6
    8. Author's Addresses.............................................6
    9. References.....................................................6


1. Introduction

   The 3rd Generation Partnership Project (3GPP) is currently involved
   in the development of a multicast and broadcast service, the
   Multimedia Broadcast/Multicast Service (MBMS), and its security
   architecture [MBMS].

   [MBMS] requires the use of the Multimedia Internet KEYing (MIKEY)
   Protocol [RFC3830], to convey the keys and related security
   parameters needed to secure the multimedia that is multicast or
   broadcast.

   One of the requirements that MBMS puts on security is the
   possibility to perform frequent updates of the keys. The rationale
   behind this is that it should be inconvenient for subscribers to
   publish the decryption keys enabling non-subscribers to view the
   content. To implement this, MBMS uses a three level key management,
   to distribute group keys to the clients, and be able to re-key by
   pushing down a new group key. As illustrated in the section below,
   MBMS has the need to identify which types of key are involved in the
   MIKEY message, and their identity.

   This memo specifies a new Type for the General Extension Payload in
   MIKEY, to identify the type and identity of involved keys.


2. Rationale

   An application where this extension is used is the MBMS key
   management.

   The key management solution adopted by MBMS uses a three level key
   management. The keys are used in the way described below. "Clients"




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   refers to the clients who have subscribed to a given
   multicast/broadcast service.

   û the MBMS User Key (MUK), point-to-point key between the multicast
      server and each client

   û the MBMS Service Key (MSK), group key between the multicast server
      and all the clients

   û the MBMS Traffic Key (MTK), group traffic key between the
      multicast server and all clients.

   The Traffic Keys are the keys that are regularly updated.

   The point-to-point MUK key (first-level key) is shared between the
   multicast server and the client via means defined by MBMS [MBMS].
   The MUK is used as pre-shared key to run MIKEY with the pre-shared
   key method [RFC3830], to deliver (point-to-point) the MSK key. The
   same MSK key is pushed to all the clients, to be used as a (second-
   level) group key.

   Then, the MSK is used to push to all the clients an MTK key (third-
   level key), the actual group key that is used for the protection of
   the media traffic. For example, the MTK could be the master key for
   SRTP [3711] in the streaming case.

   A Key Domain identifier defines the domain where the group keys are
   valid or applicable. For example it may define a specific service
   provider.

   To allow the key distribution described above, an indication of the
   type and identity of involved keys in the MIKEY message is needed.
   This indication is carried in a new Type of the General Extension
   Payload in MIKEY.

   It is necessary to specify what Crypto Session ID map type is
   associated with a given key. There are cases, for example the
   download case in MBMS, where the required parameters are signalled
   in-band. This implies that a CS ID map type needs to be registered
   to the "empty map" as defined in Table 3, which is to be used when
   the map/policy information is conveyed outside of MIKEY.


3. The Key ID Information Type for the General Extension Payload

   The General Extension payload in MIKEY is defined in Section 6.15 of
   [RFC3830].




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   The Key ID Information Type (Type 3) formats the General Extension
   payload as follows:

                           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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ! Next payload  !      Type     !            Length             !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !                  Key ID Information                           ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Next Payload and Length are defined in Section 6.15 of [RFC3830].

     *  Type (8 bits): identifies the type of the General Payload
     [RFC3830]. This memo adds Type 3 to the ones already defined in
     [RFC3830].

          Type      | Value | Comments
          ------------------------------------------------------------
          Key ID    |     3 | information on type and identity of keys

          Table 1.


     * Key ID Information (variable length): the general payload data
     transporting the type and identifier of a key. This field is formed
     by Key ID Type sub-payloads as specified below.


   The Key ID Type sub-payload is formatted as follows:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !  Key ID Type  ! Key ID Length !            Key ID             ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      * Key ID Type (8 bits): describes the type of the key ID.
      Predefined types are listed in Table 2.


         Key ID Type           | Value | Comment
         --------------------------------------
         MBMS Key Domain ID    |     0 | ID of the group key domain
         MBMS Service Key ID   |     1 | ID of the group key
         MBMS Transport Key ID |     2 | ID of the group traffic key

         Table 2.



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      *  Key ID Length (8 bits): describes the length of the Key ID
         field in bytes.

      *  Key ID (variable length): defines the identity of the key.

   Note that there may be more than one Key ID Type sub-payload in an
   extension, and that the overall length (i.e., the sum of lengths of
   all Key ID Type sub-payloads) of the Key ID information field cannot
   exceed 2^16 bytes. Applications using this general extension payload
   have to define the semantics and usage of the Key ID Type sub-
   payloads.

4. The Key ID Information Type for the General Extension Payload

   When the security policy information is conveyed outside of MIKEY,
   the CS ID map type is set to value defined in Table 3 to indicate
   "empty map".


          CS ID map type | Value | Comments
          ------------------------------------------------------------
          Empty map      |     0 | Used when the map/policy information
                         |       | is conveyed outside of MIKEY

          Table 3.


5. Security Considerations

   This memo is not foreseen to introduce security implications. For
   the security considerations of the MIKEY protocol, see [RFC3830].


6. IANA Considerations

   A new MIKEY General Extension Payload Type needs to be registered
   for this purpose. The registered value is requested to be 3
   according to Section 3.

   The name spaces for the following fields in the General Extensions
   payload (from Sections 3 and 4) are requested to be managed by IANA:

   * Key ID Type (Table 2).

   * New value for CS ID map type (Table 3).




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7. Acknowledgements

   We would like to thank Fredrik Lindholm.


8. Author's Addresses

   Questions and comments should be directed to the authors:

      Elisabetta Carrara
      Ericsson Research
      SE-16480 Stockholm     Phone:  +46 8 50877040
      Sweden                 EMail:  elisabetta.carrara@ericsson.com

      Vesa Lehtovirta
      Ericsson Research
      02420 Jorvas           Phone:  +358 9 2993314
      Finland                EMail:  vesa.lehtovirta@ericsson.com

      Karl Norrman
      Ericsson Research
      SE-16480 Stockholm     Phone:  +46 8 4044502
      Sweden                 EMail:  karl.norrman@ericsson.com


9. References

   Normative

   [RFC3830] Arkko et al., "MIKEY: Multimedia Internet KEYing", RFC
   3830, August 2004.

   Informative

   [RFC3711] Baugher et al., "The Secure Real-time Transport Protocol
   (SRTP)", RFC3711, March 2004.

   [MBMS] 3GPP TS 33.246, Technical Specification 3rd Generation
   Partnership Project; Technical Specification Group Services and
   System Aspects; Security; Security of Multimedia Broadcast/Multicast
   Service.









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   Copyright (C) The Internet Society (2004).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.

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   This draft expires in August 2005.


































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