Research On Several Issues In Blockchain Applications

In recent years,with the development and popularization of Bitcoin,the application and research of blockchain technology have shown explosive growth,which has received wide attention from governments,technology companies and research institutions.Initially,blockchain technology was only the core support of the digital currency trading system.At present,blockchain technology has been extended to various fields such as finance,trade,credit reporting,Internet of Things,traceability,entertainment and medical health,and has been initially applied.Because the blockchain has the characteristics of decentralization,reliable database,trust,transaction anonymity,collective maintenance,open source and programmable,it can safely and transparently track the data stored in the block,and can effectively guarantee the accuracy and consistency of the data among the participating nodes.Blockchain applications encounter a variety of problems and challenges in the development process.On the one hand,for the existing blockchain applications,there are many problems about throughput,consensus efficiency,block capacity,energy consumption,and data availability.On the other hand,it is of great practical significance to study how to solve the problems in real application scenarios through multiple characteristics of blockchain technology.Based on the above two aspects,this paper firstly designs a consensus algorithm based on the proof of contribution to the problem of low mining efficiency and high energy consumption in the typical application of blockchain.Secondly,in order to improve the data availability of blockchain application,this paper also took Bitcoin as an example and proposed a model to evaluate user's participation and importance objectively and mechanically by adapting LeaderRank algorithm.According to the development of the medical industry,clinical data verification,storage and synchronization are difficult between institutions to become a challenging task.There are many restrictions in the process of data access and sharing for patients,doctors and even researchers,which results in a huge cost of both resources and time for authority authentication and verification.Finally,this paper proposed a Blockchain-based medical data sharing model.This paper conducted in-depth research on several problems with blockchain applications.The main work results are as follows:First,in order to enhance the usability of data in Blockchain applications,this paper proposed a user participation evaluation model based on Heuristic rules in the Bitcoin network.The problem of Blockchain availability includes two aspects.On the one hand,it is difficult for developers to build third-party services based on data in Blockchain.On the other hand,from the perspective of users,Blockchain applications lack models and tools that facilitate users to analyze data and use data.The model defines multiple dimensions of transaction amount stability and transaction quantity stability to evaluate node value.The improved LeaderRank algorithm measures the participation of each node in the address-based trading network.After then,this paper calculated the mapping relationship between the address and user entity through Heuristic rules and completed the evaluation of the user transaction network.This paper analyzed the importance and accuracy of the participation ranking node,and further verified the reliability of the algorithm by comparing the bitcoin well-known address list.The user's participation score refl ects the degree of satisfaction of the users to the system.For the decentralized application,it will directly affect the value and security of the application.At the same time,the user's participation score can provide auxiliary tools and evaluation basis for third-party services and network supervision.Second,Proof-of-Work based Blockchain wastes an enormous amount of electricity and requires expensive mining equipment.Because each node needs to consume a lot of power to complete the hash calculation to find the hash value smaller than the target.This paper proposed a new consensus algorithm built on top of the Bitcoin protocol,which combines Proof-of-Work(PoW)with Proof-of-Stake(PoS),called Proof-of-Contribution(PoC).PoC algorithm reduces the energy consumption for mining and improves mining efficiency by rewarding the calculation difficulty of a cryptographic puzzle.The algorithm balances the virtual computing power required by the consensus with the actual computing power by adjusting the reward coefficient r.Then the paper analyzed the impact of POC on the mining difficulty coefficient under different reward coefficients,and explored different attacking scenarios and show that the network resilient to these attacks is comparable to PoW.Finally,two simulation experiments are designed.The variation of mining difficulty and the change of mining efficiency in the blockchain based on PoW and PoC are compared and analyzed with the increase of the number of nodes.Third,the paper proposed a blockchain-based medical data sharing model to solve the problems faced by data sharing in medical scenarios.At present,the Informatization of the medical industry has been basically completed,but there are still many challenges for safe storage and secure sharing of medical data,including the information islands,unclear data ownership,data tampering,data omission,data disclosure and privacy data grey trading,etc.This paper reviewed existing solutions for medical data sharing issues and some solutions based on blockchain technology.The proposed model achieved the consistency of data accuracy and consistency through improved DPoS.The VRF cryptographic algorithm is used between the representative nodes to increase the randomness of the generated blocks and increase the cost of attackers.In addition,according to the characteristics of medical data,this paper designed two proxy re-encryption schemes for different scenarios,which effectively realized the user's secure sharing of data decryption permissions.The hash algorithm-based proxy encryption scheme can be applied to most scenarios,and the smart contract is used as a third-party proxy to provide re-encryption services,which facilitates users to achieve offline low-cost data sharing.Finally,the paper evaluated the security of the consensus algorithm and the encryption scheme in the model,then analyzed the advantages and characteristics of the model against the existing solutions and models.This paper studies the energy consumption,mining efficiency,data availability and other related issues of blockchain applications,and designs the corresponding models and algorithms as well as simulation experiments.In addition,the paper designs a blockchain-based solution for practical problems in medical application scenarios.All solution have achieved good results.