Research On Searchable Encryption Based On Index In Cloud Computing

With the rapid development of information,cloud computing has emerged.Cloud storage service,an emerging network technology extended from cloud computing,combines a large number of different types of storage devices to provide storage services for the public in the network.When the public uses cloud storage services,their outsourcing data may contain some private information.Therefore,these data need to be encrypted before the files are uploaded to the cloud server.However,it is very difficult to do keyword search on encrypted data because encryption can make outsourced data inoperable.Users cannot conveniently use their own files which is stored in the cloud.In 2000,Song et al.firstly proposed the symmetric searchable encryption scheme.The purpose of the searchable encryption technology is to solve the problems of secure keyword search and data secure in cloud computing.Through the searchable encryption technology,the ciphertexts can be safely searched on a semi-trusted cloud server,and the target file is returned according to the query result.There are a lot of researches on the searchable encryption,which can be divided into two categories according to search methods.They are the accurate keyword search and the fuzzy keyword search.This thesis studies the index-based searchable encryption of the two directions in cloud environment.The main work is as follows:Firstly,the thesis proposes a scheme named Character Strings Keyword Search(CSKS)over the encrypted data in cloud environment.The existing keyword search scheme cannot search for a keyword that has not been assigned to documents in a preprocessing stage.And querying the same keyword may return too many results.The thesis proposes a scheme that supports search any strings in the files.As a result,the scope of search is larger,and the returned target is more accurate.In this scheme,the key technology is to divide the character information into the position relation information and the logic relation information of strings,which are stored in the data structure and generate a security index of strings search.In addition,we give the correctness and security of the scheme.We also reduce the times of validation,the scheme's efficiency is improved.And the thesis give the application of the scheme in multi-client environment.Secondly,Character Partition Fuzzy Keyword Search(CP-FKS)scheme is proposed.This scheme uses the concept of gram to construct a fuzzy keyword set,which quantizes the keyword set and constructs a security index by means of quotient filter.According to the match in fuzzy keyword sets,this scheme formulates the retrieval range of fuzzy keyword by setting the misspelling tolerance threshold.Thus this scheme can realize the function of multi-keyword fuzzy search.Since the quotient filter only needs only one hash function each time,the times for inserting elements and searching for elements are both reduced compared with the bloom filter.The scheme also supports chinese keyword search and dynamics.Furthermore,we introduce the detailed process of using quotient filter to construct index,and give the security analysis of the scheme.