Research On Searchable Encryption Scheme Based On Certificateless Cryptosystem

As cloud storage technology matures,a growing number of individuals and companies tend to upload data to cloud servers in order to save local space.After the user uploads sensitive data to the cloud server,he will not be able to fully control the data,causing malicious attackers and cloud server providers to access or steal the data at will.In order to achieve data privacy-preservation,the data owner usually encrypts the data before outsourcing it,but it faces problems such as efficient retrieval of encrypted data.Searchable encryption technology can solve this problem,which allows users to perform keyword retrieval in encrypted data,but most of the existing searchable encryption schemes face problems such as not supporting multi-user and multi-keyword retrieval,integrity verification,and and not being able to resist internal keyword guessing attacks.In order to solve these problems,this thesis proposes the following three searchable encryption schemes based on certificateless cryptosystems for different application scenarios and functional requirements.(1)Baesd on the problems of the existing searchable encryption schemes such as not supporting multi-user ciphertext retrieval and low computational performance,a multi-user certificateless searchable encryption scheme is proposed.The scheme solves the certificate management problem based on traditional cryptosystem and the key escrow problem in identity-based cryptosystems.The data owner does not need to specify the identity of the accessing user in the keyword encryption phase,which realizes multi-user ciphertext retrieval.In addition,the scheme implements functions such as adding and revoking accsee users by accessing the user authorization list.The analysis results show that the scheme is secure against keyword guessing attacks in the random oracle model.(2)Based on the problems that existing searchable encryption schemes only support single keyword ciphertext retrieval and cannot resist inside keyword guessing attacks,a blockchain-based certificateless authenticated searchable encryption scheme is proposed.The scheme achieves precise positioning of encrypted files by supporting multi-keyword retrieval,and uses the private key of the data owner to encrypt the keyword,which can resist inside keyword guessing attacks.In addition,the encrypted index is placed in the blockchain to ensure its anti-tampering,integrity and traceability.The analysis results show that the scheme is secure against inside keyword guessing attacks in the random oracle model.(3)Based on the problems of the existing searchable encryption schemes such as not supporting integrity verification and fair transactions,a blockchain-based multi-user certificateless searchable encryption scheme is proposed.The scheme implements functions such as adding and revoking user rights by updating the user table,uses file rights table and user table to determine the user's access rights to the file.In addition,the scheme utilizes the Merkle tree to verify the integrity of medical data,and use smart contracts to track monetary rewards to ensure fair transactions between data owners and users.The analysis results show that the scheme is secure against keyword guessing attacks in the random oracle model.