Research On Dynamic Searchable Encryption Scheme In Cloud Storage System

Searchable encryption technology is a feasible way which can search on ciphertext without decryption.Today,many types of searchable encryption schemes have been proposed by many scholars.According to the application environment and security ability,these schemes can be divided into two types.One is the scheme based on CPA security and the other one is under forward privacy security definition.Compared with the scheme based on CPA security,the scheme with forward privacy security is more resistant to attack and is suitable for the environment with higher security requirements,but this scheme also needs extra computation cost and storage space.Considering the problems of existing searchable encryption schemes,such as inefficient update ability and search token generation,lacking ideal query performance and well security ability on updating.This thesis intends to optimize the efficiency of the scheme and improve the security ability,so we propose a searchable encryption scheme based on the aggregate index and a searchable encryption scheme based on the access pattern index.The content of our research work is as follows:First,this thesis analyses the dynamic searchable encryption scheme based on CPA security,and proposes a dynamic searchable encryption scheme based on the aggregate index.Compared with the existing scheme,we have optimized it in two aspects.Firstly,we introduced the aggregate index based on the existing index structure.The aggregate index records the aggregated value of all keywords features in a single file,and the subsequent search process can quickly decrease the scale of the query data.Secondly,considering the random storage used by the forward index in the previous scheme,our scheme uses the file identifier and the search token to determine the storage location of the verification information,which improves the efficiency during the searching process.Finally,this scheme is compared with the existing scheme through the experiment.The experimental results show that the searchable encryption scheme based on the aggregate index takes 68% less time when updating files,the efficiency of the generation of search token has increased by 73%,and the search efficiency has also been greatly improved compared to the existing scheme.Second,this thesis combined the forward privacy security definition to improve the existing scheme,we propose a searchable encryption scheme based on access pattern index.By analyzing the search pattern,this new scheme adopts a new structure to store the verify information.In terms of practical efficiency,the new scheme uses a k-v structure to store the linking information between keywords and files,which improves search efficiency and update efficiency.For the security ability,the new scheme uses the signatures of keyword and file to achieve that the same keywords appeared in different files will be stored in different locations,this way can also ensure forward privacy when updating.Finally,we give a security and efficiency analysis between our scheme and the existing scheme,the experiment results show that the new scheme is more efficient than the existing scheme which under the same security ability.Finally,this thesis summarizes our two searchable encryption schemes,and also prospects the future research directions of the searchable encryption scheme.