A secure multicast protocol for the internet's multicast backbone

I n recent years, the Internet has seen an increase in the number of new applications that rely on multicast transmission. Multicast is a technology that conserves bandwidth in point-to-multipoint transmission. With the development of Mbone technology, an Internet-wide virtual network for point-to-multipoint transmission, group communication becomes possible NetMeeting, NetShow and many other applications for group communications are available on the Internet. The Internet’s Multicast Backbone (Mbone) is the small subset of Internet routers and hosts that are interconnected and are capable of forwarding IP multicast traffic. The MBone constructs a virtual network that is divided into sub-networks called islands. The islands are connected by multicastcapable routers via virtual point-to-point links called ‘tunnels’. The tunnels enable multicast traffic to pass through the non-multicast-capable parts of the Internet. Multicast packets sent to a local island are captured by a local Multicast router (MRouter), then the MRouter encapsulates these packets in IPover-IP format and unicasts to other MRouters in remote islands via tunnels. The remote MRouters then strip the encapsulated packets and multicast to their local islands. Since the Internet is an open environment, multicast messages may be eavesdropped easily. In order to prevent intruders from cracking group communications, a secure multicast environment must be provided. Confidential data have to be encrypted before transmission and only legal group members can acquire communication contents. The basic requirement is that all group members need to know the common group key that is used to encrypt communication data. Then the main problem is how to distribute secret information or a common key to the members distributed across the Internet and a secure key-establishment process is required. Key-establishment schemes can be classified into two categories: one is key agreement and the other is key distribution. Key agreement allows all members to determine the common key securely and collaboratively. The Diffie–Hellman key exchange1 is an example of key agreement techniques for two parties. Key distribution is simpler, it only needs someone to select the common key and securely distribute it to others. There are two kinds of key distribution: centralized and decentralized. Centralized schemes usually