Prototyping of Secure and Reliable Multicast System

最近，随着计算机网络的发展，分散式应用程序的使用已经变得普遍。完全有序的群通信服务是有效的，是设计分布式应用程序的必要和不可或缺的。针对全序组通信服务中的隐私保护问题，提出了考虑所有成员同步的全序组播协议的组密钥更新方法。该方法将组播组由两个或多个域中的两个或多个成员和一个密钥传递服务器（KDS）组成，KDS负责将组密钥传递给自己管理域中的成员。在满足一定条件的情况下，该方法可以应用于任何全有序组播协议。然而，由于实际通信而可能发生的数据包丢失在该方法中没有考虑。发送组密钥时，如果报文丢失，则成员的组密钥请求会增加。同时，组密钥请求成为系统的瓶颈，降低了整个系统的性能。然后，为了有效地传递组密钥，本研究在密钥传递中加入FEC（Forward Error Correction，前向纠错）功能，并在存在丢包的环境下事先添加繁琐的奇偶校验包，改进了基于推送的组密钥传递方法。然而，实际网络上的损耗率是变化的。如果在低损失率的环境中给出大量的奇偶校验包，则会消耗带宽。而且，如果在丢包率较高的环境中校验包较少，则大多数校验包成员都不能恢复原始包。提出了根据丢包率的变化动态改变奇偶校验包的方法，并对其有效性进行了评价。

Recently, the use of a decentralized application has become general by the development of the computer networks. The totally-ordered group communication service is effective and it is necessary and indispensable to design a decentralized application. For the privacy protection in the totally-ordered group communication service, we have proposed the method of renewing the group key of the totally-ordered multicast protocol which considers synchronization by all members. The multicast group is composed of two or more domains with two or more members and one key delivery server (KDS) in the method, and KDS takes the responsibility of delivering the group key to the member in the domain that oneself manages. If some assumptions are filled, this method can be applied to any totally-ordered multicast protocol. However, the loss of the packet which can happen because of an actual communication is not considered in this method. The group key request of the member increases if the packet is lost when the group key is delivered. And, the group key request becomes a bottleneck, and the performance of the entire system is downed. Then, to deliver the group key efficiently by adding the function of FEC(Forward Error Correction) to the key delivery in this research, and adding a tedious parity packet beforehand under the environment with the packet loss, the group key delivery method based on the push has been improved. However, the loss, rate on an actual network changes. If a lot of parity packets are given in the environment with a low loss rate, the bandwidth is consumed. Moreover, if the parity packet is few in the environment with a high loss rate, most members are not original packet restorable. It proposed the method of dynamically changing the parity packet to correspond to the change in such a loss rate, and the effectiveness was evaluated.