Byzantine replication under attack

Existing Byzantine-resilient replication protocols satisfy two standard correctness criteria, safety and liveness, in the presence of Byzantine faults. In practice, however, faulty processors can, in some protocols, significantly degrade performance by causing the system to make progress at an extremely slow rate. While ldquocorrectrdquo in the traditional sense, systems vulnerable to such performance degradation are of limited practical use in adversarial environments. This paper argues that techniques for mitigating such performance attacks are needed to bridge this ldquopracticality gaprdquo for intrusion-tolerant replication systems. We propose a new performance-oriented correctness criterion, and we show how failure to meet this criterion can lead to performance degradation. We present a new Byzantine replication protocol that achieves the criterion and evaluate its performance in fault-free configurations and when under attack.