Research On Privacy Protection Methods In Blockchain-enabled Distributed System

With the development of blockchain technology,the traditional centralized system is undergoing revolutionary changes and upgrades,and its applications in finance,Internet of Things,medical and health care,government affairs,intellectual property,and other fields are also accelerating.However,blockchain-related security incidents are also on the rise in recent years,and the user privacy security of blockchain-based distributed systems is particularly prominent.Besides,with the development of quantum computers and quantum computing,the vulnerability of traditional cryptographic algorithms based on computational complexity to quantum attacks has become increasingly prominent.Therefore,it is of great research value and significance to study the privacy protection methods for the blockchain-enabled distributed system,especially the anti-quantum attack cryptographic algorithms,to improve user privacy security.In view of the problems existing in the traditional centralized system,especially the user privacy and data security in the medical service system,and the user privacy security in the blockchain-enabled distributed system,this thesis studies the privacy protection methods against quantum attacks.The research content of this thesis mainly revolves around the following four aspects:(1)Secure medical big data sharing based on consortium blockchainAiming at data island problems and information loss existing in the traditional centralized medical service system,a blockchain-based distributed storage and sharing scheme for big medical data is proposed.By utilizing the consortium blockchain technology,a secure storage and management mode called Healthchain has been established,which can break the barrier of data decentralization of various medical institutions in the traditional healthcare service system,and solve the problem of information loss caused by human or natural factors.Simultaneously,A Steinberg data resource pricing game is proposed to promote data resource sharing among different medical institutions and improve the medical big data's benefit value.The performance analysis shows that:compared with the fixed average pricing strategy,the proposed scheme can increase the profit value of resource consumers by 80%,and the maximum benefit of the system by 103%,while the benefit value of the resource consumer is only reduced by 15%.Therefore,this scheme not only protects the security of users' privacy information,but also improves the utilization value of medical big data resources.(2)User signature authentication based on lattice cryptographyAiming at the problem that the authentication protocol in the current blockchain-enabled distributed system cannot effectively resist the attack from quantum computing,single protocol function,and lack of practicality,a blockchain-enabled distributed anti-quantum security signature authentication scheme has been proposed.By lattice cryptography theory,two kinds of anti-quantum blind signature schemes and proxy blind signature schemes suitable for different environments are designed.The proposed two schemes can effectively enhance the anti-quantum attack security of transaction authentication in the blockchain-enabled distributed system,and establish different secure signature authentication mechanisms according to various business function requirements,thus improving the security of user and transaction verification in the system.The comparative analysis of efficiency shows that the schemes' signature size is reduced by more than 50%compared with similar schemes,which reduces the storage space required for a signature,reduces the computational complexity of the transaction signature process,and improves the efficiency of transaction execution.(3)Bonsai trees empowered transaction privacy protectionAiming at the transaction privacy leakage problem existing in the current blockchain-enabled distributed system,a Bonsai trees empowered transaction privacy protection scheme is proposed.A lightweight blockchain wallet model is constructed using the Bonsai trees algorithm.The root key pair generates the leaf key pair,which is used for transaction signature and verification.Users only need to save the root key pair,which greatly reduces the difficulty of key management in distributed system.In order to improve the security of distributed system against quantum computing attacks,a transaction signature verification algorithm based on the lattice difficulty hypothesis is designed.The security proof shows that the scheme can resist the strong unforgability under adaptive selection message attack.The storage space required to generate N transactions of this scheme is only 1/N of that of the traditional method,and with the increase of the number N of transactions,this scheme will save more wallet space.(4)Searchable encryption empowered data security managementAiming at the problems of significant redundancy of ledger,poor searchability of data,and quantum attack threat in the blockchain-based medical service system,a searchable encryption empowered data security management scheme is proposed.A lightweight medical big data security management model called On-chain and Off-chain storage is designed,which only requires the electronic medical record index to be uploaded to the blockchain ledger and the real electronic medical record data to be stored on the local server.This model can find the data by index,effectively avoid the security problem caused by direct contact with the data,and significantly reduce public accounts' bloated phenomenon.Simultaneously,a keyword-searchable attribute-based encryption scheme based on lattice assumption is proposed,and a flexible attribute-based access policy is established to achieve fine-grained access control of data.The keyword mechanism is used to ensure the searchable security of the electronic medical record data,and the post-quantum lattice cryptography is used to improve the security of the system against quantum computing attacks.