Self-stabilizing Byzantine Agreement

TL;DR

This paper introduces a self-stabilizing Byzantine agreement algorithm that operates under severe transient faults, requiring only eventual bounded message delays, and includes novel protocols for time assignment and reliable broadcast.

Contribution

It presents the first self-stabilizing Byzantine agreement algorithm that tolerates transient faults with minimal assumptions, using new protocols for time synchronization and reliable broadcast.

Findings

Achieves agreement in the presence of transient faults.

Operates with only eventual bounded message delays.

Develops novel self-stabilizing protocols for time assignment and broadcast.

Abstract

Byzantine agreement algorithms typically assume implicit initial state consistency and synchronization among the correct nodes and then operate in coordinated rounds of information exchange to reach agreement based on the input values. The implicit initial assumptions enable correct nodes to infer about the progression of the algorithm at other nodes from their local state. This paper considers a more severe fault model than permanent Byzantine failures, one in which the system can in addition be subject to severe transient failures that can temporarily throw the system out of its assumption boundaries. When the system eventually returns to behave according to the presumed assumptions it may be in an arbitrary state in which any synchronization among the nodes might be lost, and each node may be at an arbitrary state. We present a self-stabilizing Byzantine agreement algorithm that reaches agreement among the correct nodes in an optimal ration of faulty to correct, by using only the assumption of eventually bounded message transmission delay. In the process of solving the problem, two additional important and challenging building blocks were developed: a unique self-stabilizing protocol for assigning consistent relative times to protocol initialization and a Reliable Broadcast primitive that progresses at the speed of actual message delivery time.