A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> A new digital signature based only on a conventional encryption function (such as DES) is described which is as secure as the underlying encryption function -- the security does not depend on the difficulty of factoring and the high computational costs of modular arithmetic are avoided. The signature system can sign an unlimited number of messages, and the signature size increases logarithmically as a function of the number of messages signed. Signature size in a 'typical' system might range from a few hundred bytes to a few kilobytes, and generation of a signature might require a few hundred to a few thousand computations of the underlying conventional encryption function. <s> BIB001 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> The state machine approach is a general method for implementing fault-tolerant services in distributed systems. This paper reviews the approach and describes protocols for two different failure models—Byzantine and fail stop. Systems reconfiguration techniques for removing faulty components and integrating repaired components are also discussed. <s> BIB002 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Our growing reliance on online services accessible on the Internet demands highly available systems that provide correct service without interruptions. Software bugs, operator mistakes, and malicious attacks are a major cause of service interruptions and they can cause arbitrary behavior, that is, Byzantine faults. This article describes a new replication algorithm, BFT, that can be used to build highly available systems that tolerate Byzantine faults. BFT can be used in practice to implement real services: it performs well, it is safe in asynchronous environments such as the Internet, it incorporates mechanisms to defend against Byzantine-faulty clients, and it recovers replicas proactively. The recovery mechanism allows the algorithm to tolerate any number of faults over the lifetime of the system provided fewer than 1/3 of the replicas become faulty within a small window of vulnerability. BFT has been implemented as a generic program library with a simple interface. We used the library to implement the first Byzantine-fault-tolerant NFS file system, BFS. The BFT library and BFS perform well because the library incorporates several important optimizations, the most important of which is the use of symmetric cryptography to authenticate messages. The performance results show that BFS performs 2p faster to 24p slower than production implementations of the NFS protocol that are not replicated. This supports our claim that the BFT library can be used to build practical systems that tolerate Byzantine faults. <s> BIB003 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Distributed systems: an algorithmic approach is an important addition to the distributed computing literature. The book offers a broad overview of important distributed computing topics, and, where relevant, a touch of networking topics as well. <s> BIB004 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Understanding distributed computing is not an easy task. This is due to the many facets of uncertainty one has to cope with and master in order to produce correct distributed software. Considering the uncertainty created by asynchrony and process crash failures in the context of message-passing systems, the book focuses on the main abstractions that one has to understand and master in order to be able to produce software with guaranteed properties. These fundamental abstractions are communication abstractions that allow the processes to communicate consistently (namely the register abstraction and the reliable broadcast abstraction), and the consensus agreement abstractions that allows them to cooperate despite failures. As they give a precise meaning to the words "communicate" and "agree" despite asynchrony and failures, these abstractions allow distributed programs to be designed with properties that can be stated and proved. Impossibility results are associated with these abstractions. Hence, in order to circumvent these impossibilities, the book relies on the failure detector approach, and, consequently, that approach to fault-tolerance is central to the book. Table of Contents: List of Figures / The Atomic Register Abstraction / Implementing an Atomic Register in a Crash-Prone Asynchronous System / The Uniform Reliable Broadcast Abstraction / Uniform Reliable Broadcast Abstraction Despite Unreliable Channels / The Consensus Abstraction / Consensus Algorithms for Asynchronous Systems Enriched with Various Failure Detectors / Constructing Failure Detectors <s> BIB005 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Bit coin has emerged as the most successful cryptographic currency in history. Within two years of its quiet launch in 2009, Bit coin grew to comprise billions of dollars of economic value despite only cursory analysis of the system's design. Since then a growing literature has identified hidden-but-important properties of the system, discovered attacks, proposed promising alternatives, and singled out difficult future challenges. Meanwhile a large and vibrant open-source community has proposed and deployed numerous modifications and extensions. We provide the first systematic exposition Bit coin and the many related crypto currencies or 'altcoins.' Drawing from a scattered body of knowledge, we identify three key components of Bit coin's design that can be decoupled. This enables a more insightful analysis of Bit coin's properties and future stability. We map the design space for numerous proposed modifications, providing comparative analyses for alternative consensus mechanisms, currency allocation mechanisms, computational puzzles, and key management tools. We survey anonymity issues in Bit coin and provide an evaluation framework for analyzing a variety of privacy-enhancing proposals. Finally we provide new insights on what we term disinter mediation protocols, which absolve the need for trusted intermediaries in an interesting set of applications. We identify three general disinter mediation strategies and provide a detailed comparison. <s> BIB006 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Bitcoin cryptocurrency demonstrated the utility of global consensus across thousands of nodes, changing the world of digital transactions forever. In the early days of Bitcoin, the performance of its probabilistic proof-of-work (PoW) based consensus fabric, also known as blockchain, was not a major issue. Bitcoin became a success story, despite its consensus latencies on the order of an hour and the theoretical peak throughput of only up to 7 transactions per second. <s> BIB007 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Besides attracting a billion dollar economy, Bitcoin revolutionized the field of digital currencies and influenced many adjacent areas. This also induced significant scientific interest. In this survey, we unroll and structure the manyfold results and research directions. We start by introducing the Bitcoin protocol and its building blocks. From there we continue to explore the design space by discussing existing contributions and results. In the process, we deduce the fundamental structures and insights at the core of the Bitcoin protocol and its applications. As we show and discuss, many key ideas are likewise applicable in various other fields, so that their impact reaches far beyond Bitcoin itself. <s> BIB008 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Emerging smart contract systems over decentralized cryptocurrencies allow mutually distrustful parties to transact safely without trusted third parties. In the event of contractual breaches or aborts, the decentralized blockchain ensures that honest parties obtain commensurate compensation. Existing systems, however, lack transactional privacy. All transactions, including flow of money between pseudonyms and amount transacted, are exposed on the blockchain. We present Hawk, a decentralized smart contract system that does not store financial transactions in the clear on the blockchain, thus retaining transactional privacy from the public's view. A Hawk programmer can write a private smart contract in an intuitive manner without having to implement cryptography, and our compiler automatically generates an efficient cryptographic protocol where contractual parties interact with the blockchain, using cryptographic primitives such as zero-knowledge proofs. To formally define and reason about the security of our protocols, we are the first to formalize the blockchain model of cryptography. The formal modeling is of independent interest. We advocate the community to adopt such a formal model when designing applications atop decentralized blockchains. <s> BIB009 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Motivated by the recent explosion of interest around blockchains, we examine whether they make a good fit for the Internet of Things (IoT) sector. Blockchains allow us to have a distributed peer-to-peer network where non-trusting members can interact with each other without a trusted intermediary, in a verifiable manner. We review how this mechanism works and also look into smart contracts—scripts that reside on the blockchain that allow for the automation of multi-step processes. We then move into the IoT domain, and describe how a blockchain-IoT combination: 1) facilitates the sharing of services and resources leading to the creation of a marketplace of services between devices and 2) allows us to automate in a cryptographically verifiable manner several existing, time-consuming workflows. We also point out certain issues that should be considered before the deployment of a blockchain network in an IoT setting: from transactional privacy to the expected value of the digitized assets traded on the network. Wherever applicable, we identify solutions and workarounds. Our conclusion is that the blockchain-IoT combination is powerful and can cause significant transformations across several industries, paving the way for new business models and novel, distributed applications. <s> BIB010 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Technological innovation and consequential decentralisation are driving forces in the ongoing evolution and increasing openness of digital infrastructures and services. One of the most discussed and allegedly disruptive innovations is the distributed database technology referred to as blockchain. Although it is still in its technological infancy, experimental adoption and customization seem to be in full progress in various potential fields of application ranging from decentralized grids for computation and storage to global financial services. However, the technology and its path of development still entail a lot of common unknowns for practitioners and researchers alike. Especially regarding the question how the technology could amend or be incorporated into the existing landscape of digital services, processes and infrastructures. Hence, in this article we develop an ontology that (1) clearly delineates common terminology, core concepts and components, their relationships as well as innovative features of blockchain technology. It further (2) connects these insights with implications for relevant types of digital market models. Our framework is of high theoretical and practical value as it provides researchers and practitioners a common basis for communication and means for guided analysis of blockchain applicability. <s> BIB011 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> This column evaluates blockchain’s roles in strengthening security in the Internet of Things (IoT). Key underlying mechanisms related to the blockchain–IoT security nexus are covered. From a security standpoint, the article highlights how blockchain-based solutions could be, in many aspects, superior to the current IoT ecosystem, which relies mainly on centralized cloud servers. Using practical applications and real-world examples, the article argues that blockchain’s decentralized nature is likely to result in a low susceptibility to manipulation and forgery by malicious participants. Special consideration is given to how blockchain-based identity and access management systems can address some of the key challenges associated with IoT security. The column provides a detailed analysis and description of blockchain’s roles in tracking the sources of insecurity in supply chains related to IoT devices. Using blockchain, it is also possible to contain an IoT security breach in a targeted way after it is discovered. The column also discusses and evaluates initiatives of organizations, interorganizational networks, and industries on the frontlines of blockchain. <s> BIB012 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> The blockchain technology is gaining momentum because of its possible application to other systems than the cryptocurrency one. Indeed, blockchain, as a de-centralized system based on a distributed digital ledger, can be utilized to securely manage any kind of assets, constructing a system that is independent of any authorization entity. In this paper, we briefly present blockchain and our work in progress, the VMOA blockchain, to secure virtual machine orchestration operations for cloud computing and network functions virtualization systems. Using tutorial examples, we describe our design choices and draw implementation plans. <s> BIB013 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Smart contracts are computer programs that can be correctly executed by a network of mutually distrusting nodes, without the need of an external trusted authority. Since smart contracts handle and transfer assets of considerable value, besides their correct execution it is also crucial that their implementation is secure against attacks which aim at stealing or tampering the assets. We study this problem in Ethereum, the most well-known and used framework for smart contracts so far. We analyse the security vulnerabilities of Ethereum smart contracts, providing a taxonomy of common programming pitfalls which may lead to vulnerabilities. We show a series of attacks which exploit these vulnerabilities, allowing an adversary to steal money or cause other damage. <s> BIB014 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Blockchain technologies are gaining massive momentum in the last few years. Blockchains are distributed ledgers that enable parties who do not fully trust each other to maintain a set of global states. The parties agree on the existence, values and histories of the states. As the technology landscape is expanding rapidly, it is both important and challenging to have a firm grasp of what the core technologies have to offer, especially with respect to their data processing capabilities. In this paper, we first survey the state of the art, focusing on private blockchains (in which parties are authenticated). We analyze both in-production and research systems in four dimensions: distributed ledger, cryptography, consensus protocol and smart contract. We then present BLOCKBENCH, a benchmarking framework for understanding performance of private blockchains against data processing workloads. We conduct a comprehensive evaluation of three major blockchain systems based on BLOCKBENCH, namely Ethereum, Parity and Hyperledger Fabric. The results demonstrate several trade-offs in the design space, as well as big performance gaps between blockchain and database systems. Drawing from design principles of database systems, we discuss several research directions for bringing blockchain performance closer to the realm of databases. <s> BIB015 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> With the exponential rise in the number of devices, the Internet of Things (IoT) is geared toward edge-centric computing to offer high bandwidth, low latency, and improved connectivity. In contrast, legacy cloud-centric platforms offer deteriorated bandwidth and connectivity that affect the quality of service. Edge-centric Internet of Things-based technologies, such as fog and mist computing, offer distributed and decentralized solutions to resolve the drawbacks of cloud-centric models. However, to foster distributed edge-centric models, a decentralized consensus system is necessary to incentivize all participants to share their edge resources. This paper is motivated by the shortage of comprehensive reviews on decentralized consensus systems for edge-centric Internet of Things that elucidates myriad of consensus facets, such as data structure, scalable consensus ledgers, and transaction models. Decentralized consensus systems adopt either blockchain or blockchainless directed acyclic graph technologies, which serve as immutable public ledgers for transactions. This paper scrutinizes the pros and cons of state-of-the-art decentralized consensus systems. With an extensive literature review and categorization based on existing decentralized consensus systems, we propose a thematic taxonomy. The pivotal features and characteristics associated with existing decentralized consensus systems are analyzed via a comprehensive qualitative investigation. The commonalities and variances among these systems are analyzed using key criteria derived from the presented literature. Finally, several open research issues on decentralized consensus for edge-centric IoT are presented, which should be highlighted regarding centralization risk and deficiencies in blockchain/blockchainless solutions. <s> BIB016 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> Blockchain has numerous benefits such as decentralisation, persistency, anonymity and auditability. There is a wide spectrum of blockchain applications ranging from cryptocurrency, financial services, risk management, internet of things (IoT) to public and social services. Although a number of studies focus on using the blockchain technology in various application aspects, there is no comprehensive survey on the blockchain technology in both technological and application perspectives. To fill this gap, we conduct a comprehensive survey on the blockchain technology. In particular, this paper gives the blockchain taxonomy, introduces typical blockchain consensus algorithms, reviews blockchain applications and discusses technical challenges as well as recent advances in tackling the challenges. Moreover, this paper also points out the future directions in the blockchain technology. <s> BIB017 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> I. INTRODUCTION <s> The core technical component of blockchains is consensus: how to reach agreement among a distributed network of nodes. A plethora of blockchain consensus protocols have been proposed---ranging from new designs, to novel modifications and extensions of consensus protocols from the classical distributed systems literature. The inherent complexity of consensus protocols and their rapid and dramatic evolution makes it hard to contextualize the design landscape. We address this challenge by conducting a systematization of knowledge of blockchain consensus protocols. After first discussing key themes in classical consensus protocols, we describe: (i) protocols based on proof-of-work; (ii) proof-of-X protocols that replace proof-of-work with more energy-efficient alternatives; and (iii) hybrid protocols that are compositions or variations of classical consensus protocols. This survey is guided by a systematization framework we develop, to highlight the various building blocks of blockchain consensus design, along with a discussion on their security and performance properties. We identify research gaps and insights for the community to consider in future research endeavours. <s> BIB018
In the past decade, blockchain networks have gained tremendous popularity for their capabilities of distributively providing immutable ledgers as well as platforms for data-driven autonomous organization. Proposed by the famous grassroot cryptocurrency project "Bitcoin"  , the blockchain network was originally adopted as the backbone of a public, distributed ledger system to process asset transactions in the form of digital tokens between Peer-to-Peer (P2P) users. Blockchain networks, especially those adopting open-access policies, are Wenbo distinguished by their inherent characteristics of disintermediation, public accessibility of network functionalities (e.g., data transparency) and tamper-resilience BIB015 . Therefore, they have been hailed as the foundation of various spotlight Fin-Tech applications that impose critical requirement on data security and integrity (e.g., cryptocurrencies BIB008 , BIB006 ). Furthermore, with the distributed consensus provided by blockchain networks, blockchains are fundamental to orchestrating the global state machine 1 for general-purpose bytecode execution. Therefore, blockchains are also envisaged as the backbone of the emerging open-access, trusted virtual computers BIB009 for decentralized, transaction-driven resource management in communication networks and distributed autonomous systems BIB010 , BIB016 . For these reasons, blockchain technologies have been heralded by both the industry and academia as the fundamental "game changer" BIB011 in decentralization of digital infrastructures ranging from the financial industry BIB006 to a broad domain including Internet of Things (IoTs) BIB012 and selforganized network orchestration BIB013 . Generally, the term "blockchain networks" can be interpreted from two levels, namely, the "blockchains" which refer to a framework of immutable data organization, and the "blockchain networks" on top of which the approaches of data deployment and maintenance are defined. The two aspects are also considered as the major innovation of blockchain technologies. For data organization, blockchain technologies employ a number of off-the-shelf cryptographic techniques BIB001 -  and cryptographically associate the users' on-chain identities with the transactions of their tokenized assets. Thus, blockchains are able to provide the proofs of authentication for asset (i.e., token) transfer and then the proofs of asset ownerships. Furthermore, a blockchain maintains an arbitrary order of the transactional records by cryptographically chaining the record subsets in the form of data "blocks" to their chronic predecessors. With the help of cryptographic references, any attempt of data tampering can be immediately detected. From the perspective of network organization, the problem of replicated agreement BIB005 , BIB002 on a single/canonical transaction history among trustless nodes is creatively tackled by the blockchain consensus protocols in an open-access, weakly synchronized network. Blockchain consensus protocols are able to offer the agreement on the global blockchain-data state among a large number of trustless nodes with no identity authentication and low messaging overhead BIB018 . To achieve this, a number of blockchain networks, e.g., Bitcoin, choose to incorporate an incentive-based block creation process known as "block mining" in their protocols. With distributed consensus, the blockchain can be viewed as a universal memory of the blockchain network. Meanwhile, the blockchain network can be viewed as a virtual computer (i.e., distributed VM) comprised by every node therein. With the rapid evolution in blockchain technologies, the demand for the higher-level quality of services by blockchainbased applications presents more critical challenges in designing blockchain protocols. Particularly, the performance of blockchain networks significantly relies on the performance of the adopted consensus mechanisms, e.g., in terms of data consistency, speed of consensus finality, robustness to arbitrarily behaving nodes (i.e., Byzantine nodes BIB002 ) and network scalability. Compared with the classical Byzantine consensus protocols allowing very limited network scalability in distributed systems BIB002 , BIB003 , most of the existing consensus protocols in open-access blockchain networks (e.g., Bitcoin) guarantee the better network scalability at the cost of limited processing throughput. Also, to achieve decentralized consensus among poorly synchronized, trustless nodes, a number of these protocols incur huge consumption of physical resources (e.g., computing power) BIB008 . Moreover, to ensure a high probability of consensus finality, the protocols may also impose high latency for transaction confirmation. Out of such concerns, a large volume of research has been conducted with the aim of improving the performance of the open-access blockchain consensus protocols in specific aspects. However, in spite of a few short surveys BIB018 , BIB007 , a comprehensive study on the development of these consensus protocols and the related problems is still missing. Especially, there is a lack of a concise overview on how such a development can be interpreted under a uniform framework and how it impacts the potential applications of blockchain networks. During the past decade, the scope of blockchain networks has been expanded way further from tamper-evident distributed ledgers. However, due to the recent market frenzy about cryptocurrencies, most of the existing general reviews and surveys on blockchains emphasize narrowly the scenarios of using blockchain networks as the backbone technologies for cryptocurrencies, especially the market-dominant ones such as Bitcoin and Ethereum BIB015 - BIB006 , BIB007 - BIB010 . For example, the issues regarding the client (user)-side application (i.e., wallet), P2P network protocols, consensus mechanisms and user privacy in the scope of Bitcoin are discussed in BIB008 , BIB006 . In BIB017 , a brief summary of the emerging blockchain-based applications ranging from finance to IoTs is provided. A systematic survey is conducted in  with respect to the security in the Bitcoin network including the identified attacks on the consensus mechanisms and the privacy/anonymity issues of the Bitcoin clients. In BIB014 , BIB010 , the special issues regarding the design, application and security of the smart contracts 2 are reviewed in the context of the Ethereum network. In BIB016 , BIB018 , two brief surveys on consensus protocols in blockchain networks are provided. The existing surveys on the fast-developing studies of blockchain technologies rarely provide a global view on the issues related to consensus protocols. Our work aims to fill this gap by providing a comprehensive survey on this specific topic. To distinguish our study from the existing works, we present our survey on blockchain networks from the perspective of consensus formation, especially in open-access 3 P2P networks. In analogy to the distributed database, blockchain consensus is perceived as a process of collaborative state transitions among distributed nodes in the framework of blockchain-specified data organization. We emphasize that such a viewpoint brings the taxonomy of blockchain networks into a paradigm that is comparable to the classical problems of global state maintenance in distributed systems BIB004 . Therefore, we are able to cast our analysis of blockchain networks into the context of classical fault-tolerant studies by focusing on the standard consensus properties in distributed systems (i.e., the Agreement-Validity-Termination properties BIB004 Chapter 13.1] ). We provide a uniform view of blockchain networks by presenting a number of implementation stacks and revealing the interconnection between different protocol components therein. We align our survey on blockchain consensus protocols with a uniform framework based on Zero-Knowledge (ZK) prover-verifier systems  ,  in Section III. By focusing on the blockchain protocols for data organization, network organization, and consensus maintenance, our survey contributes in the following aspects: (1) providing a brief overview on the data organization and network protocols of blockchain networks, (2) providing a generic paradigm for the consensus mechanisms using cryptographic techniques in open-access blockchain networks, (3) reviewing the studies on the behaviors of the rational (profit-driven) nodes in the consensus processes of blockchain networks, (4) providing an in-depth review on the research effort toward addressing the concerns (e.g., performance vs. scalability) for blockchain networks with different roadmaps of consensus protocol design, and BIB010 providing an outlook of the research in the emerging decentralized applications built on top of the consensus layer, which may not be limited to the framework of the prevalent blockchain technologies (cf. our discussion in Sections III-VI). The rest of this survey is organized as follows. Section II provides an introductory overview on the protocol organization of blockchain networks. Section III provides an indepth survey on the popular approaches of consensus protocol design for open-access networks using linear blockchains. Consequently, Section IV provides a survey on the studies of the rational nodes' strategies in these consensus processes and their impact on the performance of blockchain networks. Section V extends our survey on blockchain consensus protocols to the emerging fields including virtual block-mining (i.e., blockchain-extension) mechanism and hybrid consensus. Section VI briefly reviews the emerging cross-layer design regarding the data organization and consensus protocols, namely, the "next-generation blockchains" which may have different roadmaps for scalability and performance other than the prevalent blockchain paradigm. Section VII provides a short review of the emerging applications of blockchains as well as an outlook of the potential research directions in the context of telecommunication networks. Section VIII concludes this survey by summarizing the contributions.