Research On Attribute-based Multi-keyword Searchable Encryption Scheme

Explosive data growth has produced data outsourcing cloud storage services in the era of big data,and users' inability to directly control the outsourcing data has led to the risk of privacy data leakage.Therefore,encrypting private data before uploading to cloud storage can effectively ensure the security of private data.Attribute-based encryption is widely used in encryption of cloud storage shared data due to its fine-grained access control.However,the encrypted data loses its semantics,and users cannot search effectively in a large number of ciphertexts,which limits the flexibility of data sharing to a certain extent.Searchable encryption is of vital significance in encryption field.It realizes fast and effective retrieval of encrypted data without decrypting the ciphertext.Attributebased searchable encryption,as a combination of attribute-based encryption and searchable encryption technology,realizes secure data sharing and fine-grained search authorization,and can search for ciphertexts more flexibly and quickly while ensuring the security of ciphertexts.In addition,the attribute-based multi-keyword searchable encryption allows users to search for multiple keywords in combination,which effectively improves the accuracy and efficiency of the search.This thesis studies on the attribute-based multi-keyword searchable encryption algorithm.The main contributions are as follows:1.Aiming at the problem that most of the current searchable encryption schemes cannot support the user to customize the access strategy in the trapdoor,this thesis proposes a secure and efficient attribute-based multi-keyword searchable encryption scheme which can support trapdoor LSSS(Linear Secret Sharing Scheme)access structure.Firstly,the trapdoor in our scheme,based on the LSSS access structure,supports construction of arbitrary conjunctive,disjunctive or threshold multi-keyword search access strategy.The user generates the trapdoor for the LSSS access structure using private key.The cloud server can search for the ciphertexts that satisfy access structure in the trapdoor;secondly,our scheme can realize fine-grained access control of encrypted data in the cloud through combining with the attribute-based encryption;in addition,our scheme divides the keywords into keyword names and keyword values and "linear splitting" technology that makes it impossible for attackers to infer sensitive information from ciphertexts and trapdoors.Finally,by transferring part of the decryption work to the cloud server,the user's computational burden gets reduced.The safety of the scheme is proved under the DBDH(Decisional Bilinear Diffie-Hellman)assumption,the(q-2)assumption and the decisional linear assumption.Theoretical analysis and experimental results also show the effectiveness of the scheme.2.In view of the hierarchical relationship between keywords in some application scenarios,this thesis,based on trapdoor LSSS access structure,introduces the idea of keyword hierarchy from attribute hierarchy and proposes the attribute-based hierarchical multi-keyword searchable encryption scheme in the cloud environment.The scheme forms a keywords hierarchy tree according to the hierarchical relationship between keywords.The cloud server can search the ciphertext containing the same level and low-level keywords through the keyword hierarchy information hidden in the trapdoor,which can not only reduce the size of the trapdoor,but also reduce the search computational overhead.The safety of the scheme is proved under the decisional BDH assumption,the(q-2)assumption and the decisional linear assumption.Theoretical analysis and experimental results also show the effectiveness of the scheme.