and efficient manner by separating the safety concern and the liveness concern [9]. Additional Paxos algorithm are developed to minimize the resources required, and to reduce the latency for achieving consensus by using a higher redundancy level [10, 18].
Chapter 7 introduces the problem of Byzantine fault tolerance. A Byzantine fault is synonymous with a malicious fault. Because a malicious faulty component may choose to behave like any of the non-malicious faults, the Byzantine fault model encompasses any arbitrary fault. The distributed consensus problem under the Byzantine fault model was first studied several decades ago by Lamport, Shostak, and Pease [11]. A much more efficient algorithm for achieving fault tolerance under the Byzantine fault model (referred to as Practical Byzantine fault tolerance) was proposed by Castro and Liskov in 1999 [5]. Since then, the research on Byzantine fault tolerance exploded. With the pervasiveness of cyberattacks and espionages, dealing with malicious faults becomes an urgent concern now compared with several decades ago.
Chapter 8 provides an overview of cryptocurrency and the blockchain technology, including the early conception of cryptocur rency, the first implementation of cryptocurrency in Bitcoin [12], the concept of smart contract and its implementation in Ethereum [4], as well as the vision of decentralized organizations [16] powered by smart contract and the blockchain technology.
Chapter 9 explains the consensus algorithms used in the blockchain technology in depth. Since the original PoW algorithm was introduced in Bitcoin, there has been great effort on improving PoW in various aspects, and on finding alternative algorithms that do not consume as much energy. A common set of requirements for such algorithms is laid out [22] and different proposals are examined with respect to the requirements [17]. In this chapter, we also discuss the Proof-of-Stake (PoS) consensus algorithm, which is the second most well-known algorithm behind PoW for blockchain. We will explain the PoS implementation in PeerCoin [8]. It is the first implementation of PoS in a practical cryptocurrency (i.e., PeerCoin) in 2013 and it has gone through several revisions to address its initial vulnerabilities.
Chapter 10 presents the applications of the blockchain technology and issues that will directly impact on how widely the blockchain technology can be adopted, including the value of the blockchain technology and the efforts to increase the throughput of blockchain systems [1, 3, 14, 21]. We primarily focus on blockchain applications in the area of cyber-physical systems (CPS) [20]. CPS is evolving rapidly and the integration of blockchain and CPS could potentially transform CPS design for much stronger security and robustness.
Wenbing Zhao
Cleveland, USA
March 2021
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