Byzantine fault-tolerance techniques are useful because they tolerate arbitrary faults regardless of cause: bugs, hardware glitches, even hackers. These techniques have recently gained popularity after it was shown that they could be made practical.
Most of the dissertation builds on Byzantine fault-tolerance (BFT) and extends it with new results for Byzantine fault-tolerance for both quorum systems and state machine replication. Our contributions include proving new lower bounds, finding new protocols that meet these bounds, and providing new functionality at lower cost through a new architecture for state machine replication.
The second part of the dissertation goes beyond Byzantine fault-tolerance. We show that BFT techniques are not sufficient for networks that span multiple administrative domains, propose the new BAR model to describe these environments, and show how to build BAR-Tolerant protocols through our example of a BAR-Tolerant terminating reliable broadcast protocol.