Issues in Multicast Security

Extended Abstract Multicast communications have generated increasing interest during the past few years. This is due, in principle, to the obvious potential for improvement in the use of network resources: data is sent to a number of diierent recipients in just one transmission, instead of requiring the setup and the maintenance of distinct unicast connections. This means substantial savings both in terms of network load and in terms of server operation. However, multicast communications are generally more complicated and cause a number of diicult problems at diierent levels. In particular, the lack of multicast support in most Internet routers has made related technologies largely unavailable. Today, the widespread use of multicast-enabled applications and networks is possible and even likely. The reasons for this are twofold. has pushed the technology by demonstranting that, although many problems remain to be solved, the technology is mature and suucient for supporting high quality applications. The MBONE is overlayed to the standard Internet by tunneling multicast communications via IP unicast, and having routers at each end of the tunnel support multicast routing. Although this was initially done with normal workstations, the main commercial routers are now supporting this function. On the other hand, the technology is being pulled by changes in the size of the Internet and in the way people use it. Some Web sites report receiving millions of requests each day: this means tremendous duplication of data being trasmitted over the same physical media, and sometimes leads to the denial of service that follows excessive load at the server. This is aggravated by the constant increase in multimedia content: images and animations of diierent kinds populate most Web pages, and this is more true for the most popular 1