Efficient Dynamic Symmetric Searchable Encryption With Forward And Backward Security

Due to the expanding amount of data in the era of big data,local computing and storage resources can no longer meet people's needs.More and more companies and users choose to upload data to cloud servers.At the same time,the privacy issue of cloud storage has become the biggest factor restricting its development.Encrypting the private data before uploading them can effectively solve this problem,but it also reduces the availability of the data,and it is difficult to perform common operations such as keyword search on the ciphertext.Symmetric searchable encryption allows users to safely outsource the database to an semi-trusted cloud server,and retains the function of keyword search for encrypted databases.Taking into account the needs of adding and deleting files in practical applications,dynamic symmetric searchable encryption also adds the function of dynamically updating the database.However,the introduction of the update operation brings additional information leakage.In this case,two security definitions are proposed to restrict the leakage under different operations: forward security and backward security.The former mainly restricts the update operation from revealing the association between the updated documents and the previous search keywords.The latter mainly ensures that the search operation should not reveal the information of the deleted files.According to the amount of information leaked,the backward security is divided into three types.Among the existing research work,the solutions that meets the second type of backward security has a larger communication and storage overhead,and the solutions that meets the third type of backward security has the best communication and storage overhead but the lowest security.In the work of this thesis,we define a weak type two backward security by leakage function on the basis of existing security definition,and use logical deletion combined with physical deletion to construct a DSSE scheme based on symmetric puncturable encryption and its incremental property.At the same time,we use obfuscation technology to resist the leakage of special cases.On the basis of this scheme,the deletion operation is optimized without reducing security.Through security proof and efficiency analysis,the two schemes proposed in this paper can not only meet the second type of backward security,but also achieve the same level of overhead as the third type of backward security scheme.Compared with existing backward security solutions,our schemes strikes a balance between efficiency and security.