RFC 1949 (rfc1949) - Page 2 of 18

Scalable Multicast Key Distribution

RFC 1949          Scalable Multicast Key Distribution           May 1996


   Unlike many network layer protocols, the Core Based Tree (CBT)
   multicast protocol [4] makes explicit provision for security; it has
   its own protocol header, unlike existing IP multicast schemes
   [10,11], and other recently proposed schemes [12].

   In this document we describe how the CBT multicast protocol can
   provide for the secure joining of a CBT group tree, and how this same
   process can provide a scalable solution to the multicast key
   distribution problem.  These security services are an integral part
   of the CBT protocol [4]. Their use is optional, and is dependent on
   each individual group's requirements for security. Furthermore, the
   use of the CBT multicast protocol for multicast key distribution does
   not preclude the use of other multicast protocols for the actual
   multicast communication itself, that is, CBT need only be the vehicle
   with which to distribute keys.

   Secure joining implies the provision for authentication, integrity,
   and optionally, confidentiality, of CBT join messages. The scheme we
   describe provides for the authentication of tree nodes (routers) and
    receivers (end-systems) as part of the tree joining process. Key
   distribution (optional) is an integral part of secure joining.

   Network layer multicast protocols, such as DVMRP [7] and M-OSPF [9],
   do not have their own protocol header(s), and so cannot provision for
   security in themselves; they must rely on whatever security is
   provided by IP itself. Multicast key distribution is not addressed to
   any significant degree by the new IP security architecture [2].

   The CBT security architecture is independent of any particular
   cryptotechniques, although many security services, such as
   authentication, are easier if public-key cryptotechniques are
   employed.

   What follows is an overview of the CBT multicasting. The description
   of our proposal in section 6.1 assumes the reader is reasonably
   familiar with the CBT protocol. Details of the CBT architecture and
   protocol can be found in [7] and [4], respectively.

2.  Overview of BCT Multicasting

   CBT is a new architecture for local and wide-area IP multicasting,
   being unique in its utilization of just one shared delivery tree per
   group, as opposed to the source-based delivery tree approach of
   existing IP multicast schemes, such as DVMRP and MOSPF.

   A shared multicast delivery tree is built around several so-called
   core routers. A group receiver's local multicast router is required
   to explicitly join the corresponding delivery tree after receiving an



Ballardie                     Experimental