Textbook in PDF format

Fault-tolerant distributed consensus is a fundamental concept, both in cryptography as well as distributed computing. Ever since the inception of the problem by Lamport et al in 1982, the problem has been widely studied, both in cryptography as well as distributed computing community and several fundamental results have been obtained regarding the possibility, feasibility and optimality of the consensus protocols in various network models and adversarial settings. The problem has generated revived interest from several other communities over the last few years, after the advent of Blockchain protocols. Traditionally, the consensus protocols are studied either in the synchronous or in the asynchronous communication setting and very often the protocols in the former category serve as the basis for the protocols in the latter category. The focus of this book will be on the synchronous communication setting. The book presents all the seminal possibility and feasibility results in this model ever since the inception of the consensus problem, with formal security proofs. Even though the synchronous corruption model may seem weaker than the more practical asynchronous communication model, designing protocols in the synchronous model turns out to be non-trivial and demands sophisticated and highly advanced techniques. Moreover, understanding protocols in the synchronous setting often constitutes the first stepping stone to understanding the more complex asynchronous consensus protocols. The topic of synchronous consensus protocols in itself is a very vast and important topic to be covered in a single book. This monogram is self-contained and can be read by those with familiarity with Discrete Mathematics and Algorithms. We assume no background in cryptography or distributed computing. Topics and features: Presents protocols both against computationally bounded and computationally unbounded adversaries Provides detailed security proofs for the seminal protocols Offers freely available companion-video lectures for some of the topics Includes pictorial illustrations for a better understanding of the underlying concepts Presents state-of-the-art efficiency improvement techniques for synchronous consensus protocols Assumes no background in cryptography or distributed computing Introduction Preliminaries EIG Protocol for Byzantine Broadcast Efficient Phase-King Protocols for Distributed Consensus Lower Bound on the Resilience of Consensus Protocols Without Any Set-Up Domain Extension for Distributed Consensus with Perfect Security Lower Bound on the Number of Rounds for Deterministic Consensus Protocols Distributed Consensus with a Constant Expected Number of Rounds Dolev-Strong Protocol for Distributed Consensus Domain Extension for BA with Honest Majority and Statistical Security Domain Extension for BA with Honest Majority and Cryptographic Security Domain Extension for Byzantine Broadcast with Dishonest Majority and Statistical Security Domain Extension for Byzantine Broadcast with Dishonest Majority and Cryptographic Security Distributed Consensus with a Constant Expected Number of Rounds and a Strict Honest Majority