Byzantine agreement protocol using hierarchical groups

Peer-to-peer (P2P) systems are composed of large number and various types of peer processes interconnected in networks. Peers may not only stop by fault but also be arbitrarily faulty by attacks like hacking. We have to discuss how to make a system tolerant of Byzantine faults of processes. Byzantine agreement protocols imply large communication overhead. In order to reduce the overhead, we consider a hierarchical group composed of subgroups. Each subgroup shares at least one of correct processes named gateway ones with other subgroups. Even if a leader process of a subgroup is faulty, all the correct processes can make an agreement on the correct value in a whole group because correct gateway processes forward correct values to the subgroup. We evaluate the protocol compared with traditional protocols in terms of number of messages and rounds.