Research On Secure Searchable Encryption In Cloud Storage System

The rapid development of cloud storage technology allows enterprises and users to store data information on the cloud storage platform in order to use high-capacity storage resources and efficient cloud computing technology.For the security of private data information,enterprises and users encrypt the data but the way to search from a large amount of ciphertext data of the cloud storage server is an important question.Searchable encryption technology can directly search from encrypted ciphertext data without decryption,it is an important research hotspot of data security under cloud storage system.The data scale is huge and the information is various in the current period of big data.The scheme that only supports single-keyword search or single-group user communication is gradually not applicable to the actual application scenarios.According to whether to support the file update dynamically,the scheme of searchable encryption can be divided into static searchable encryption scheme and dynamic search encryption scheme.The static scheme is suitable for the application scenarios where the files are relatively fixed,so the privacy files are relatively safe but lack of controllability.The dynamic scheme is advantageous to the dynamic update of the file,but it is easy to be attacked when updating.This thesis studies and analyzes the defects of both static and dynamic scheme,and proposes corresponding solutions.The main work and research results of this paper are as follows:(1)In the static searchable encryption scheme under the multi-user scenario,in view of the security authentication defects of users and cloud servers as well as the lack of controllability of the search keyword authority,a public key encryption scheme with multi-keyword search of authority control(AC-PEKS)is put forward.AC-PEKS generates an additional keyword authority based on the level of different users by using equality test technology.In the search process,only the search keywords within the authority can be allowed.Through the analysis and experimental verification of AC-PEKS scheme,the AC-PEKS scheme can achieve the authority control function of different level.Besides,low index and authority storage space is provided.AC-PEKS scheme can achieve the security requirement of keywords indistinguishable,trapdoor indistinguishable and secure search authority.(2)Aiming at the problems of dynamic security and low accuracy of search results in dynamic searchable encryption scheme,a multi-keyword rank searchable encryption scheme with dynamic security(DS-MRSE)is proposed.DS-MRSE adopts the trie tree as index structure and uses preprocessing method to improve the efficiency of search and update on cloud storage platform.Each node in index contains two parts,including linked list of newly added file identifier and the array of existing file identifier.In search process,the time complexity is only related to the number and the average character length of search keywords.Moreover,the algorithmic complexity of dynamic update is only O(1).Besides,DS-MRSE scheme achieves dynamic forward privacy and backward privacy in dynamic security.Based on practical considerations,the scheme adds a custom search results sorting function.Through analysis and experimental verification,DS-MRSE scheme has better computing efficiency in search and update process and is more suitable for the application scenarios of multi-user and multi-keyword.