| Due to cloud computing has a high degree of scalability and cost-effective characteristics,individuals and enterprises tend to store their privacy data on cloud servers.In order to protect the privacy of client,individuals and enterprises often encrypt their data before uploading them to the cloud.However,it is difficult to manipulate data due to a series of changes to the data structure after it is encrypted.For example,the traditional method of searching is no longer applicable.Searchable encryption was proposed to solve the problem of searching on the ciphertext.The data owner encrypts the data and sends it to the cloud server,and then delivers the key to the data user,who searches on the ciphertext using the key and keyword.However,in the actual situation,there are some problems in traditional searchable encryption schemes:(1)If the key remains unchanged for a long time,it is not secure for data users to use it all the time.Therefore,it is necessary for the data owner to replace the key at an appropriate time to ensure the security of the ciphertext.(2)In most security models,the cloud server is ‘honest’ by default,but in actual situations,the cloud server will not execute the algorithm content correctly due to configuration errors or calculation cost reduction.(3)In most searchable encryption schemes,the client maintains a list for each keyword.As the number of keywords increasing,the memory of the list becomes larger,which could bring storage burden to the client.Based on the above problems,this paper conducts further research on searchable encryption in cloud environment,and the research content is as follows:(1)Updatable searchable encryption scheme that supports verification in the cloud environmentThis paper proposes an updatable searchable encryption scheme which can supports verification.To solve the problem of verification,the encrypted indexes and message authentication codes are sent to the blockchain firstly,the blockchain is used to search the results.Then the data user verifies the results,so as to solve the ‘dishonest’ problem of the cloud server.To solve the problem of key-updating,the data owner uses the generation structure of secret key to generate corresponding key-update token.When the secret key needs to be updated,the data owner sends the key-update token to the blockchain,the blockchain updates the secret key of the encrypted indexes.The security analysis of our scheme shows that it not only satisfies adaptive security,but also achieves forward and backward security.Several experiments show that our scheme not only improves the efficiency of key-update,but also shortens the verification time.(2)Updatable searchable encryption scheme supporting bidirectional verification in cloud environment with constant client storageIn this paper,we propose an updatable searchable encryption scheme with constant client storage supporting bidirectional authentication in the cloud environment.This scheme introduces the form of ‘fish-bone chain’,the encrypted indexes and keywords are stored in the keyword index chains of the fishbone chain and the document index chains respectively.In this way,the data owner does not need to maintain a list for each keyword,which could reduce storage overhead of the client.Then,by uploading the encrypted indexes and message authentication codes to the blockchain,the blockchain can verify the results,so as to avoid the fraudulent behavior of data user or malicious servers to achieve the purpose of two-way verification.In addition,this scheme uses the characteristics of Ethereum to package the authorization information into the transaction,such as search token and secret key,in order to control the access of the data user.The security analysis and experiments show that this scheme not only achieves the forward and backward security,verifies the result sets,but also effectively reduces the storage cost of the client. |
