Research And Scheme Design On Scenario-oriented Reputation-based Consensus Algorithm

Since the advent of bitcoin in 2008,the underlying technology of bitcoin,blockchain,has developed from the digital currency to a core technology which impacts the traditional business model.Blockchain has received high attention from governments,financial institutions and technology enterprises which have launched their own blockchain projects to solve the drawbacks of traditional industries.However,most of public blockchain-based projects are using Proof of Work(Po W)mechanism based on hash calculation,which results in low system throughput and poor availability.Consortium blockchain-based projects have poor security due to the presence of super nodes.Aiming at the above problems,Repu Coin propose a reputation-based consensus algorithm which combines the advantages of public blockchains and consortium blockchains.But there are two problems in this algorithm:(1)when calculating reputation values,only the number of blocks is considered,the quality of the blocks is not taken into consideration;(2)Repu Coin is not friendly to miners newly joining the system.In response to this problem,this paper proposes an improved reputationbased consensus algorithm Po SR.Based on the consensus algorithm,we propose a general model of the scenario-oriented reputation consensus mechanism.In this mechanism,we use blockchain technology to solve the problems of scenarios.The detailed descriptions are as follows.1.Aiming at the problem that new miners in Repu Coin cannot join in the consensus group and the measurement of miners’ reputation value is not comprehensive,we propose a general model of scenario-oriented reputation consensus algorithm,including the scenario-based reputation consensus algorithm Po SR and its application in cryptocurrencies.Firstly,we propose a scenario-based reputation consensus algorithm Po SR.The algorithm measures the quality of the generated blocks by considering the numbers of transactions in a block.Then,a reputation conversion function is proposed to improve the accumulation rate of new miners’ reputation values.Finally,we apply the Po SR algorithm to the cryptocurrency field.The experiments show that the algorithm can achieve the same level of throughput as RepuCoin,and can resist 51% attacks,selfish mining attacks and Sybil attacks.2.Aiming at the problems that the current photo forensics schemes cannot uniformly achieve photo authentication,photo copyright protection and photo traceability with permissible transformations,we propose a blockchain-based photo forensics system with permissible transformations.Firstly,we design photo transactions to map photos to blockchain transactions.On the basis of photo transactions,we propose a photo authentication-based consensus algorithm.This algorithm allows miners to use photo transactions to authenticate transformed photos.We design the register smart contract,owner management smart contract,verifier management smart contract and trace smart contract to deal with the registration of users and the management of photos.Through the trace smart contract,users can trace the history of any authenticated photo.We use Ethereum to test the performance of the proposed system and analyze the security of it.Compared with existing schemes,our system supports more permissible transformation operations,and can simultaneously achieve photo authentication,photo copyright protection and photo traceability.3.Aiming at the problems of low throughput,serious centralization and poor retrieval efficiency of the current blockchain-based e Health systems,we propose a reputation-based medical data sharing and privacy-preserving e Health system.Firstly,we design special block structures by leveraging chameleon hash functions,which can improve the retrieval efficiency to O(log n).A reputation system is also constructed to motivate medical institutions to participate in SPChain.By using proxy re-encryption schemes,SPChain achieves medical data sharing for patients in a privacy-preserving manner.To evaluate SPChain,we leverage the distribution of miners in the real world to test the system’s performance.The results show that SPChain can achieve high throughput with low storage overhead.Compared with the existing schemes,SPChain achieves lower time complexity in terms of data retrieving,and can resist proposed blockchain attacks as well as SPChain attacks.4.Aiming at the problems that c Mix is vulnerable to blocking attacks,collusion attacks and Man-in-the-Middle attacks,we propose a reputation-based dynamic self-reconfigurable mixnet called BCMIX.Firstly,we design reputation-based voting,IP sharding and VRF voting algorithms to select mix nodes from blockchain miners.With these voting algorithms,BCMIX can mitigate blocking attacks and blockchain Sybil attacks.Then we present an additive homomorphic mixnet protocol altered from c Mix.Furthermore,we design a transaction-based key-exchange protocol for users and mix nodes to negotiate keys with each other,which resists Man-in-the-Middle attacks that exist in c Mix.We also demonstrate the security and anonymity of BCMIX under formal security models.To evaluate BCMIX,we leverage the distribution of mining pools in the real world to test the system.The results show that with the proper mining difficulty,the probability of an attacker launching collusion attacks and Sybil attacks is negligible.Compared with the existing anonymous systems,BCMIX provides better resilience to the known attacks while achieving low latency anonymous communication without significant bandwidth or storage resources.