Flexible Synchronization Protocol to Prevent Illegal Information Flow in Peer-to-Peer Publish/Subscribe Systems

In the peer-to-peer type of topic-based publish/subscribe (P2PPS) model, each peer (process) can publish event messages and event messages are notified to target peers with no centralized coordinator. Some information of a peer may flow to target peers by publishing an event message. Here, a target peer recognizes an event message to be related with topics which are in a publication of the event message and the peer subscribes. On the other hand, the peer forgets topics which are in a publication of the event message but not in a set of topics which the peer subscribes. We have to prevent illegal information flow to occur by flowing the forgotten topics. In this paper, we newly propose a flexible synchronization (FS) protocol and a relevance concept of topics to prevent illegal information flow to be caused by the forgotten topics. In the FS protocol, even if an event message carries forgotten topics, a peer accepts the event message if the forgotten topics are related with the subscription topics. In the evaluation, the number of illegal information flows decreases in the FS protocol.