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Consensus mechanism (CM) is the heart and soul of blockchain, for it allows nodes in a blockchain network to reach an agreement on the state of system execution. Among the CMs, the right for constructing the next new block is regarded as the most important one since it is required for the blockchain to grow so that transaction data can be recorded in it. Proof-of-work (PoW) is an efficient CM since it allows all the nodes to participate equally in the competition for the right. However, high energy consumption makes PoW less desirable for applications. Moreover, application-oriented blockchains should employ CMs that could reflect some main characteristics of the applications to facilitate the development of other mechanisms, such as the incentive mechanisms. Proof-of-contribution (PoC) is an effective, application-oriented CM since the right for constructing the next new block is determined by contributions made by the nodes and the node that has accumulated the highest contribution value (CV) gets the right. PoC is a general-purpose CM since the behavior of nodes can be characterized in the form of contributions. However, the deterministic nature of PoC as the result of ranking nodes based on CVs may lower efficiency since nodes could fail to function due to network delay, node failure or node's simply dropping out of the network. This paper proposes to design highly effective and efficient CMs by integrating PoC with PoW, which we refer to as PoCW. In PoCW, nodes compete for the right for constructing the next new block based on PoW after being assigned different difficulty values (DVs) based on the ranking of their CVs. Since assigning DVs strictly according to the ranking of CVs would make PoCW resemble PoC while assigning the same DV to all the nodes would make PoCW the same as PoW, PoCW could be designed as a class of CMs through applying different DV assignment strategies to meet the effectiveness and efficiency requirements of a variety of applications. We can further apply the same principle at finer levels of granularity by dynamically grouping nodes along the ranking of CVs and then applying different DV assignment strategies to different groups. The paper will first describe a generic PoCW without involving node grouping and then present the design of a general PoCW through applying an example node grouping method to demonstrate the feasibility of PoCW as a general-purpose CM for blockchain-based applications. Experiments were also conducted to demonstrate the effectiveness and the efficiency of PoCW as well as its advantages over comparable CMs. [ABSTRACT FROM AUTHOR]

Blockchain is a technology that is rapidly gaining prominence and finding applications in various sectors such as banking, supply chain, healthcare, and e-governance. The consensus algorithm employed in a blockchain network is crucial as it directly impacts the network's performance and security. Different consensus techniques exist, including Proof of Work (PoW), Proof of Stake (PoS), Robust Proof of Stake (RPoS), and Delegate Proof of Stake (DPoS), each with its own set of advantages and disadvantages. In this work, we propose a new consensus algorithm called Delegated Proof of Stake with Exponential Back-off (DPoSEB). DPoSEB utilizes a stake-based selection of delegates and employs an exponential back-off technique to mitigate collisions among nodes within the network. Each delegate is assigned a random sleep time, and the node with the shortest wake-up time is chosen to mine the block for that particular round. However, collisions among nodes can still occur. To provide a fair chance for each delegate node, collided nodes are assigned an exponential back-off time. We implement our proposed algorithm on an Ethereum-based private blockchain network. To evaluate the effectiveness of our proposed work, we compare it with existing consensus mechanisms such as PoS (version 2) and Delegated RPOS with downgrading (DDRPOS) using different scenarios in terms of transaction latency, waiting time, and fairness as evaluation metrics. The results reveal that DPoSEB performs better than POS and DDRPOS. [ABSTRACT FROM AUTHOR]

In healthcare systems, blockchain technology plays a crucial role in transmitting COVID-19 data among multiple entities. Over time, various blockchain-based medical applications have emerged to handle medical information confidentially. One such system is the Scalable eHealthChain system (SeHealthChain), which utilizes a sharding scheme consisting of transaction chain and reputation chain structures to enhance throughput and security. However, the system employs a modified Raft-based Synchronous Consensus Scheme (RSCS) for generating the transaction blockchain, which can potentially introduce illegitimate transactions to the Hyperledger fabric network if a rogue node transfers them to the orderer. This poses a significant security risk in the worst-case scenarios. Additionally, as the hash rate fluctuates exponentially, the generation period of transaction blocks and computation difficulty increase. To address these issues, this article proposes an Optimized SeHealthChain (OSeHealthChain) system. It integrates a Tuna Swarm Optimization Algorithm (TSOA) with the modified RSCS to dynamically adjust the blockchain parameters in response to significant changes in the hash rate. The TSOA optimizes two variables, namely the Block Interval (BI) and Difficulty Adjustment Interval (DAI) of the Proof-of-Work (PoW) for the transaction blockchain, based on objective functions that consider the Standard Deviations (SD) of the mean BI and difficulty. By selecting appropriate variables, the system generates new transaction blocks with minimal nodes and overhead, effectively validating transactions and blocks to enhance the security level. Extensive simulations show that the OSeHealthChain achieves a throughput of 3918tps and a user-perceived latency of 63.8s for 1000 nodes, outperforming the SeHealthChain, eHealthChain, Permissionless Proof-of-Reputation-X (PL-PoRX), and hybrid Proof of Stake-Practical Byzantine Fault Tolerance (POS-PBFT) algorithms in blockchain systems. It also achieves throughputs of 7051tps, 6418tps, and 6290tps for simple, camouflage, and observe-act attacks, respectively, with 1000 nodes and a shard dimension of 200 during 20 epochs. [ABSTRACT FROM AUTHOR]

The increasing complexity of cloud computing has prompted a greater emphasis on protecting the privacy, integrity, and security of data stored and processed in the cloud. Data privacy is safeguarded through access control, but existing models such as Role Based Access Control (RBAC) and Attribute Based Access Control (ABAC) rely on a centralized server. If this server is compromised, it poses significant risks to data security. To address this issue, there is a need for Distributed ABAC (DABAC) system for OpenStack services based on blockchain. The unique features of blockchain enables access control systems which ensures data integrity and privacy. Additionally, blockchain offers a level of transparency for both the resource owner and a user. In this work, we propose a smart contract based ABAC system. We implemented the proposed work using an Ethereum blockchain and OpenStack cloud. Furthermore, we evaluated two consensus algorithms for scalability analysis of DABC mechanism. The results demonstrate that DABAC performs better than ABAC in ensuring fine-grade access control with proof of stake consensus algorithm providing better scalability. [ABSTRACT FROM AUTHOR]

Proof of work (PoW) is one of the most widely used consensus algorithms in blockchain networks. It mainly uses the competition between mining nodes to obtain block rewards. However, this competition for computational power will allow malicious nodes to obtain illegal profits, bringing potential security threats to blockchain systems. A distributed denial of service (DDoS) attack is a major threat to the PoW algorithm. It utilizes multiple nodes in the blockchain network to attack honest miners to obtain illegal rewards. To solve this problem, academia has proposed a DDoS attack detection mechanism based on reinforcement learning methods and static game modeling methods based on mining pools. However, these methods cannot effectively make miners choose the strategy with the best profit over time when facing DDoS attacks. Therefore, this paper proposes a dynamic evolutionary game model for miners facing DDoS attacks under blockchain networks to solve the above problems for the first time. We address the model by replicating the dynamic equation to obtain a stable solution. According to the theorem of the Lyapunov method, we also obtain the only stable strategy for miners facing DDoS attacks. The experimental results show that compared with the static method, the dynamic method can affect game playing and game evolution over time. Moreover, miners' strategy to face DDoS attacks gradually shifts from honest mining to launching DDoS attacks against each other as the blockchain network improves. [ABSTRACT FROM AUTHOR]

Internet of Things (IoT) is used to describe devices with sensors that connect and exchange data with other devices or systems on the Internet or other communication networks. Actually, the data not only represent the concrete things connected but also describe the abstract matters related. Therefore, it is expected to support trust on IoT since blockchain was invented so that trusted IoT could be possible or, recently, even metaverse could be imaginable. However, IoT systems are usually composed of a lot of device nodes with limited computing power. The built-in unsolved performance and energy-consumption problems in blockchain become more critical in IoT. The other problems such as finality, privacy, or scalability introduce even more complexity so that trusted IoT is still far from realization, let alone the metaverse. With general Proof of Work (GPoW), the energy consumption of Bitcoin can be reduced to less than 1 billionth and proof of PowerTimestamp (PoPT) can be constructed so that a global even ordering can be reached to conduct synchronization on distributed systems in real-time. Therefore, trusted IoT is possible. We reintroduce GPoW with more mathematic proofs so that PoPT can be optimal and describe how PoPT can be realized with simulation results, mining examples and synchronization scenario toward trusted IoT. [ABSTRACT FROM AUTHOR]

Data management becomes essential component of patient healthcare. Internet of Medical Things (IoMT) performs a wireless communication between E-medical applications and human being. Instead of consulting a doctor in the hospital, patients get health related information remotely from the physician. The main issues in the E-Medical application are lack of safety, security and privacy preservation of patient's health care data. To overcome these issues, this work proposes block chain based IoMT Processed with Hybrid consensus protocol for secured storage. Patients health data is collected from physician, smart devices etc. The main goal is to store this highly valuable health related data in a secure, safety, easy access and less cost-effective manner. In this research we combine two smart contracts such as Practical Byzantine Fault Tolerance with proof of work (PBFT-PoW). The implementation is done using cloud technology setup with smart contracts (PBFT-PoW). The accuracy rate of PBFT is 90.15%, for PoW is 92.75% and our proposed work PBFT-PoW is 99.88%. [ABSTRACT FROM AUTHOR]

Blockchain technology considers the central technology that is used within many applications used frequently with human life. And the primary core of the blockchain is the consensus algorithm which may affect the security of the chain as well as the required resource consumption which affect mainly the blockchain performance directly. In recent years many consensus algorithms have been used and proposed such as proof of work (PoW) and proof of stake (PoS) and many others. However, these algorithms still need some improvement to the security and system resource consumption which will reduce the need for a huge amount of energy and save the environment as well as let the blockchain be useable within low computation ability devices such as the internet of things devices (IoT). This paper proposes a new consensus algorithm that ensures the integrity and authorization of nodes participating in the validation of the transaction and only a predefined number of nodes chosen randomly to participate in block addition which reduces the need for high computations power for mining and voting. The proposed algorithm needs lower time and computation costs comparable to the standard POW algorithm. [ABSTRACT FROM AUTHOR]

Technological advancements in block chain (BC)-based frameworks have empowered scientists to create innovative inventions such as e-casting ballots. The traditional agreement models utilized proof-of-work (PoW) in the Bitcoin that affected energy utilization and bargained the adaptability for the ballot framework. The existing works evaluates the trust basically only on the centralized party as it was not feasible because of the dynamic changes in the pervasive social networking (PSN) topology and their characteristics. The present research work proposes a block chain based trust evaluation model for the PSN based BC. The proposed hybrid proof of stake-trust (PST) BC is based on the proof-of trust (PoT) and also the proof of stake (PoS) overcomes the issues that are occurring in the e-vote casting. The trust evaluation is performed for public verification and becomes transparent for each node of PSN. The advantage of the proposed method is that a new block will be designed for trust evaluation during the block generation. The process of sharding erases the workload when the network works fast for the individual nodes provides the sum of their alternative parts. Therefore, the model utilizes the agreements for generating the safe process that guarantee the precision to vote it from the time of the election results. The present research work utilizes the proof of stake-trust based BC resulted in security improvement. The model improves the adaptability and execution of the BC based on the ballot framework provided a secured voting system for the government. The proposed PST-BC model showed better results in terms of latency as 15/s when compared with the existing models merkle hash tree -bloom filter that obtained 107.3/s and performance constraints based electron of 18/s. [ABSTRACT FROM AUTHOR]

Decentralization for data storage is a challenging problem for blockchain-based solutions as the blocksize plays a key role for scalability. In addition, specific requirements of multimedia data call for various changes in the blockchain technology internals. Considering one of the most popular applications of secure multimedia streaming, i.e., video surveillance, it is not clear how to judiciously encode incentivization, immutability, and compression into a viable ecosystem. In this study, we provide a genuine scheme that achieves this encoding for a video surveillance application. The proposed scheme provides a novel integration of data compression, immutable off-chain data storage using a new consensus protocol namely, Proof-of-WorkStore (PoWS) in order to enable fully useful work to be performed by the miner nodes of the network. The proposed idea is the first step towards achieving greener application of a blockchain-based environment to the video storage business that utilizes system resources efficiently. [ABSTRACT FROM AUTHOR]

Copyright of Romanian Journal of Information Technology & Automatic Control / Revista Română de Informatică și Automatică is the property of National Institute for Research & Development in Informatics - ICI Bucharest and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to improve the revenue of attacking mining pools and miners under block withholding attack, we propose the miner revenue optimization algorithm (MROA) based on Pareto artificial bee colony in blockchain network. MROA establishes the revenue optimization model of each attacking mining pool and revenue optimization model of entire attacking mining pools under block withholding attack with the mathematical formulas such as attacking mining pool selection, effective computing power, mining cost and revenue. Then, MROA solves the model by using the modified artificial bee colony algorithm based on the Pareto method. Namely, the employed bee operations include evaluation value calculation, selection probability calculation, crossover operation, mutation operation and Pareto dominance method, and can update each food source. The onlooker bee operations include confirmation probability calculation, crowding degree calculation, neighborhood crossover operation, neighborhood mutation operation and Pareto dominance method, and can find the optimal food source in multidimensional space with smaller distribution density. The scout bee operations delete the local optimal food source that cannot produce new food sources to ensure the diversity of solutions. The simulation results show that no matter how the number of attacking mining pools and the number of miners change, MROA can find a reasonable miner work plan for each attacking mining pool, which increases minimum revenue, average revenue and the evaluation value of optimal solution, and reduces the spacing value and variance of revenue solution set. MROA outperforms the state of the arts such as ABC, NSGA2 and MOPSO. [ABSTRACT FROM AUTHOR]

As the core of a blockchain system, the consensus mechanism not only helps to maintain the consistency of node data, but also gets involved in the issuance of tokens and prevention of attacks. Since the first blockchain system was born, it has been continuously improved with the development of blockchain technology and evolved into multiple new branches. Starting with the basic introduction of consensus and the classic Byzantine Generals Problem in distributed computing area, this survey utilizes a thorough classification to explain current consensus protocols in the blockchain system, presents the characteristics of mainstream protocols (PoW, PoS, DPoS, PBFT, etc.) and analyzes the strengths and weaknesses of them. Then we evaluate the performance qualitatively and quantitatively. In the end, we highlight several research directions for developing more practical consensus protocols for the future. [ABSTRACT FROM AUTHOR]

Blockchain is not widely applied in various fields due to the critical issue of scalability as part of the blockchain trilemma. This issue arises during consensus among the nodes in a public blockchain. To address the issue of low scalability with proof-of-work (PoW) consensus, various methods have been proposed for transaction per second (TPS) improvement. However, no such methods include an improvement in the consensus step. Therefore, to improve PoW public blockchain scalability, it is important to shorten the time required for PoW consensus. This paper proposes a method for minimizing the block intervals that occur during consensus over a PoW blockchain network. A shortened block interval leads to an increase in the probability of three different attacks: selfish mining, double-spending, and eclipse attacks. According to an experiment using Ethereum, with a typical PoW blockchain, it is inevitable to provide rewards for stable block mining in competition between mining pools. To find an optimal block interval in the PoW consensus algorithm, we conducted a four-step experiment. The purpose of this experiment was to verify the difficulty level and issues with Mainnet security. Therefore, considering stale block mining rewards, an optimal block interval is proposed. The Ethereum TPS was improved by at least 200%. Given this finding, it is considered possible to achieve a similar improvement in a different PoW blockchain. On balance, even if the block interval is shorter than that of the PoW Mainnet, network security falls by only 1.21% in Testnet, even with a rise in the stale block rate, while performance is increased at up to 120 TPS, which is three times higher than that in Mainnet. [ABSTRACT FROM AUTHOR]