A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <s> A peer-to-peer crypto-currency design derived from Satoshi Nakamoto’s Bitcoin. Proof-of-stake replaces proof-of-work to provide most of the network security. Under this hybrid design proof-of-work mainly provides initial minting and is largely non-essential in the long run. Security level of the network is not dependent on energy consumption in the long term thus providing an energyefficient and more cost-competitive peer-to-peer crypto-currency. Proof-of-stake is based on coin age and generated by each node via a hashing scheme bearing similarity to Bitcoin’s but over limited search space. Block chain history and transaction settlement are further protected by a centrally broadcasted checkpoint mechanism. <s> BIB001 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <s> We study decentralized cryptocurrency protocols in which the participants do not deplete physical scarce resources. Such protocols commonly rely on Proof of Stake, i.e., on mechanisms that extend voting power to the stakeholders of the system. We offer analysis of existing protocols that have a substantial amount of popularity. We then present our novel pure Proof of Stake protocols, and argue that they help in mitigating problems that the existing protocols exhibit. <s> BIB002 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <s> We propose a new protocol for a cryptocurrency, that builds upon the Bitcoin protocol by combining its Proof of Work component with a Proof of Stake type of system. Our Proof of Activity protocol offers good security against possibly practical attacks on Bitcoin, and has a relatively low penalty in terms of network communication and storage space. <s> BIB003 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <s> Proof of Stake Velocity (PoSV) is proposed as an alternative to Proof of Work (PoW) and Proof of Stake (PoS) to secure the peer-to-peer network and conrm transactions of Reddcoin, a cryptocurrency created specically to facilitate social interactions in the digital age. PoSV is designed to encourage both ownership (Stake) and activity (Velocity) which directly correspond to the two main functions of Reddcoin as a real currency: store of value and medium of exchange. Reddcoin can also function as the unit of account in heterogeneous social context. The technological aspects of PoSV are presented after a detailed review of existing designs. The economic aspects of Reddcoin are then analysed. Finally the unique position of Reddcoin as a digital social currency in the competitive landscape of cryptocurrencies is discussed. <s> BIB004 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <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> BIB005 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <s> Bitcoin is the first and most popular decentralized cryptocurrency to date. In this work, we extract and analyze the core of the Bitcoin protocol, which we term the Bitcoin backbone, and prove two of its fundamental properties which we call common prefix and chain quality in the static setting where the number of players remains fixed. Our proofs hinge on appropriate and novel assumptions on the “hashing power” of the adversary relative to network synchronicity; we show our results to be tight under high synchronization. <s> BIB006 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <s> In the paper, we present designs for multiple blockchain consensus primitives and a novel blockchain system, all based on the use of trusted execution environments (TEEs), such as Intel SGX-enabled CPUs. First, we show how using TEEs for existing proof of work schemes can make mining equitably distributed by preventing the use of ASICs. Next, we extend the design with proof of time and proof of ownership consensus primitives to make mining energy- and time-efficient. Further improving on these designs, we present a blockchain using a proof of luck consensus protocol. Our proof of luck blockchain uses a TEE platform's random number generation to choose a consensus leader, which offers low-latency transaction validation, deterministic confirmation time, negligible energy consumption, and equitably distributed mining. Lastly, we discuss a potential protection against up to a constant number of compromised TEEs. <s> BIB007 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <s> We present “Ouroboros”, the first blockchain protocol based on proof of stake with rigorous security guarantees. We establish security properties for the protocol comparable to those achieved by the bitcoin blockchain protocol. As the protocol provides a “proof of stake” blockchain discipline, it offers qualitative efficiency advantages over blockchains based on proof of physical resources (e.g., proof of work). We also present a novel reward mechanism for incentivizing Proof of Stake protocols and we prove that, given this mechanism, honest behavior is an approximate Nash equilibrium, thus neutralizing attacks such as selfish mining. <s> BIB008 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <s> As more applications are built on top of blockchain and public ledger, different approaches are developed to improve the performance of blockchain construction. Recently Intel proposed a new concept of proof-of-elapsed-time (PoET), which leverages trusted computing to enforce random waiting times for block construction. However, trusted computing component may not be perfect and 100% reliable. It is not clear, to what extent, blockchain systems based on PoET can tolerate failures of trusted computing component. The current design of PoET lacks rigorous security analysis and a theoretical foundation for assessing its strength against such attacks. To fulfill this gap, we develop a theoretical framework for evaluating a PoET based blockchain system, and show that the current design is vulnerable in the sense that adversary can jeopardize the blockchain system by only compromising \(\varTheta (\log \log n/\log n)\) fraction of the participating nodes, which is very small when n is relatively large. Based on our theoretical analysis, we also propose methods to mitigate these vulnerabilities. <s> BIB009 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <s> We introduce Casper, a proof of stake-based finality system which overlays an existing proof of work blockchain. Casper is a partial consensus mechanism combining proof of stake algorithm research and Byzantine fault tolerant consensus theory. We introduce our system, prove some desirable features, and show defenses against long range revisions and catastrophic crashes. The Casper overlay provides almost any proof of work chain with additional protections against block reversions. <s> BIB010 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <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> BIB011 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <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> BIB012 </s> A Survey on Consensus Mechanisms and Mining Strategy Management in Blockchain Networks <s> A. Proof of Stake and Virtual Mining <s> We present “Ouroboros Praos”, a proof-of-stake blockchain protocol that, for the first time, provides security against fully-adaptive corruption in the semi-synchronous setting: Specifically, the adversary can corrupt any participant of a dynamically evolving population of stakeholders at any moment as long the stakeholder distribution maintains an honest majority of stake; furthermore, the protocol tolerates an adversarially-controlled message delivery delay unknown to protocol participants. <s> BIB013
The concept of PoS was first proposed by Peercoin BIB001 as a modified PoW scheme to reduce the energy depletion due to exhaustive hash queries. Peercoin proposes a metric of "coin age" to measure the miner's stake as the product between the held tokens and the holding time for them. Miner i solves a PoW puzzle as in (1) with an individual difficulty D(h i ). The Peercoin kernel protocol allows a miner to consume its "coin ages" to reduce the difficulty i.e., h i , for puzzle solution. The public verification of the "coin ages" is done through empirically estimating the holding time of the miner's Unspent Transaction Output 18 (UTXO) based on the latest block on the public chain. By completely removing the structure of PoW-based leader election, the protocols of pure PoS are proposed in BIB002 , BIB008 , BIB003 ,  . To simulate a verifiable random function following the stake distribution (see also BIB011 ), an algorithm, follow-thecoin (a.k.a., follow-the-satoshi), has been proposed by BIB003 and widely adopted by these works BIB012 . Here, the terms "coin" or "satoshi" are used to indicate the minimum unit of the digital tokens carried by the blockchain. Briefly, all the tokens in circulation are indexed, for example, between 0 and the total number of available coins in the blockchain network. A simplified PoS protocol can use the header of block t − 1 to seed the follow-the-coin algorithm and determine the random mining leader for block t. Specifically, the hash function H(·) is queried with the header of block t−1, and the output is used as the random token index to initialize the searching algorithm. The algorithm traces back to the minting block (i.e., the first coinbase transaction BIB002 ) for that token or the UTXO account that currently stores it BIB003 . Then, the creator or the holder of the token is designated as the leader for generating block t. To enable public verification of the block, the valid leader is required to insert in the new block its signature, which replaces the data field "nonce" for PoW-based blockchains. It is worth emphasizing that the pure PoS protocols do not rely on a Poisson process-based puzzle solution competition to simulate the random generator of the block leader. Therefore, the ZK puzzle-solving process can be simply replaced by the process of asymmetric key-based signing and verification, and the proof of resource is no longer needed. For this reason, PoS is also known as a process of "virtual mining" BIB005 since the block miners do not consume any resources. In the literature, a number of protocol proposals are claimed to be able to (partially) achieve the same purpose. However, these protocols either need special hardware support, e.g., Intel SGX-enabled TEEs for proof of luck/elapsed-time/ownership BIB007 , BIB009 , or are still under the framework of PoW, e.g., Proof of Burn (PoB)  , Proof of Stake-Velocity (PoSV) BIB004 and "PoS" using coin age BIB001 . Strictly speaking, they cannot be considered as the real virtual mining schemes in permissionless blockchain networks. Compared with the PoX-based protocols, PoS keeps the longest-chain rule but adopts an alternative approach for simulating the verifiable random function of block-leader generation. For this reason, the same framework for analyzing the properties of Byzantine agreements in PoW-based blockchain networks BIB006 can be readily used for the quantitative analysis of PoS protocols. For example, the investigations in BIB008 ,  mathematically evaluate the properties of common prefix, chain quality and chain growth based on the same definition in Table II . The authors propose in BIB008 the "Ouroboros" protocol, and consider that the stakes are distributed at the genesis block by an ideal distribution functionality. By assuming an uncorrupted ideal sampling functionality, Ouroboros guarantees that a unique leader is elected in each block generation round following the stake distribution among the stakeholders (see also BIB011 ). With Ouroboros, forking no longer occurs when all the nodes are honest. However, when adversary exists, forking may be caused by the adversarial leader through broadcasting multiple blocks in a single round. The study in BIB008 shows that the probability for honest nodes to fork the blockchain with a divergence of k blocks in m rounds is no more than exp(−Ω(k) + ln(m)) under the condition of honest majority. It is further shown that the properties of chain growth and chain quality are also guaranteed with negligible probability of being violated. The studies in BIB003 ,  introduce the mechanism of epoch-based committee selection, which dynamically selects a committee of consensus nodes for block generation/validation during an epoch (i.e., a number of rounds). Compared with the single-leader PoS protocol, i.e., Ouroboros BIB008 and its asynchronous variation BIB013 , the committee-based PoS gears the protocol design toward the leader-verifier framework of traditional BFT protocols (see also Figure 6 ). In BIB003 , the scheme of Proof of Activity (PoA) is proposed with the em-phasis that only the active stake-holding nodes get rewarded. The PoA is featured by the design that the leader is still elected through a standard PoW-based puzzle competition, and is only responsible for publishing an empty block. Using the header of this block to seed the follow-the-coin algorithm, a committee of N ordered stakeholders is elected and guaranteed to be publicly verifiable. The first N − 1 stakeholders work as the endorsers of the new empty block by signing it with their private keys. The N -th stakeholder is responsible for including the transactions into that block. The transaction fees are shared among the committee members and the block miner. In this sense, PoA can be categorized as a hybrid protocol that integrates both PoW and PoS schemes. In  , the authors propose a protocol called "Snow White", which uses a similar scheme to select a committee of nodes as in BIB003 . However, only the selected committee members are eligible for running for the election of the block generation leader. Under the Snow White protocol, the leader of an epoch is elected through a competition based on repeated preimage search with the hash function. At this stage, the difference of Snow White from the standard PoW puzzle in  is that the hash function is seeded with the time stamp instead of an arbitrary nonce. Like PoA, Snow White also pertains the characteristics of a hybrid protocol. The analysis in  shows that the proposed protocol supports frequent committee reconfigurations and is able to tolerate nodes that are corrupted or offline in the committee. The recent proposal by Ethereum, Casper BIB010 provides an alternative design of PoS that is more similar to traditional BFT protocols. The current proposal of Casper does not aim to be an independent blockchain consensus protocol, since it provides no approach of leader election for block proposal. Instead, the stakeholders join the set of validators and work as the peer nodes in a BFT protocol. The validators can broadcast a vote message specifying which block in the blockchain is to be finalized. The validator's vote is not associated with its identity, but with the stake that it holds. According to BIB010 , Casper provides plausible liveness (instead of probabilistic liveness with PoW) and accountable safety, which tolerate up to 1/3 of the overall voting power (weighted by stake) that is controlled by the Byzantine nodes.