Thesis Defense - Tanaraksiritavorn

Group communication middleware is widely used for constructing high-level distributed applications to provide reliable services through the redundancy approach. The main goal of this dissertation is to build a practical fault-tolerant group communication system that can sustain arbitrary failure and support strong confidentiality while still be able to provide continuous services. These two features are inherently conflicting in their nature. This thesis addresses the confidentiality and reliability issues by presenting a unified architecture that incorporates fault masking and fault detection.

A new group communication system that offers high availability via replication and provides secured service in asynchronous systems under byzantine failure assumption is presented. This system combines a suspicion containment mechanism with traditional detect-response mechanism. This dissertation makes three important contributions. First, the proposed group communication system complements the usage of existing intrusion detection systems with a peer-level intrusion detector that specifically targets group communication traffic. This aids in detecting failures that traditional intrusion detection systems do not. Second, a new group membership protocol is presented that introduces a new suspended state to reduce the effect of intrusion detector's false-positives and the overhead of running group membership protocol. Third, the system provides support for preventing data leakage from compromised servers and supporting inexact match comparison of replies from servers.

The proposed group communication system has been extensively evaluated using simulation as well as a prototype implementation. Experimental results demonstrate the system's feasibility and practicality.