Research On Blockchain-oriented Searchable Encryption Scheme

With unique advantages such as decentralization,traceability and tamper resistance,blockchain has been studied and applied in many fields such as digital finance and supply chain.The volume of data stored on the blockchain has been increasing continuously with the increase in the scale of blockchain applications and the number of users.However,due to the transparency of the data on blockchain,users usually encrypt data before uploading it to blockchain for security reasons.While encryption protects the privacy of data,it also poses challenges for data retrieval.Searchable Encryption enables users to retrieve ciphertext data securely and efficiently,but much of existing research on Searchable Encryption is for cloud environments,Searchable Encryption for blockchain environments has not been fully studied.Existing Searchable Encryption schemes in blockchain environment have some deficiency.On the one hand,existing schemes achieve ciphertext retrieval by storing large indexes on blockchain.However,due to the limited storage space of blockchain,users want to store unnecessary data on blockchain as little as possible,these schemes are therefore less practical;on the other hand,there is a lack of a Searchable Encryption scheme on blockchain that supports data sharing to meet the demand of users to share or sell their data.This thesis conducts research on the above problems,and the main research contents are as follows.1.A lightweight Symmetric Searchable Encryption scheme on blockchain is proposed.For the problem of storage space limitation on blockchain,the index structure is improved to reduce the space overhead of the scheme and improve the space efficiency.The scheme firstly analyzes the characteristics of real datasets and finds that there is duplicate data storage in the inverted index.By constructing the Inverted Index Forest structure,the duplicate data stored in the index is merged and the space overhead is reduced.In addition,a Hierarchical Encrypted Index structure is constructed to provide a flexible solution to the existing Symmetric Searchable Encryption,which requires redundant padding of data.The specific construction of the scheme is given,and the security of the scheme is demonstrated by security analysis.A prototype of the scheme is implemented on the Hyperledger Fabric platform,and it is demonstrated through comparative experiments that the scheme has lower space overhead and high practical application value in blockchain environments with limited storage space.2.An Attribute-Based Searchable Encryption scheme on blockchain is proposed.By introducing Attribute-Based Encryption,one-to-many data sharing and fine-grained access control are achieved in blockchain environment and the interaction between data owners and data demanders is avoided.The access control tree structure ensures that only users who satisfy the specified attributes can search and decrypt the data.An Index Chain structure is designed to improve the efficiency of retrieval by linking file indexes with the same keywords.The security and feasibility of the scheme are proved by security analysis and experimental analysis.The scheme has lower search efficiency compared with the previous scheme but can achieve richer functions and can meet different needs of users.