A Dynamic Searchable Encryption Scheme for Secure Cloud Server Operation Reserving Multi-keyword Ranked Search

Cloud computing is becoming more and more popular day by day due to its maintenance, multitenancy and performance. Data owners are motivated to outsource their data to the cloud servers for resource pooling and productivity where multiple users can work on the same data concurrently. These servers offer great convenience and reduced cost for the computation, storage and management of data. But concerns can persist for loss of control over certain sensitive information. The complexity of security is largely intensified when data is distributed over a greater number of devices and data is shared among unrelated users. So these sensitive data should be encrypted for solving these security issues that many consumers cannot afford to tackle. In this paper, we present a dynamic searchable encryption scheme whose update operation can be completed by cloud server while reserving the ability to support multi-keyword ranked search. We have designed a scheme where dynamic operations on data like insert, update and delete are performed by cloud server without decrypting the data. Thus this scheme not only ensures dynamic operations on data but also provides a secure technique by performing those tasks without decryption. The state-of-the-art methods let the data users retrieve the data, re-encrypt it under the new policy and then send it again to the cloud. But our proposed method saves this high computational overhead by reducing the burden of performing dynamic operation by the data owners. The secure and widely used TF x IDF model is used along with kNN algorithm for construction of the index and generation of the query. We have used a tree-based index structure, so our proposed scheme can achieve a sub-linear search time. We have conducted experiments on Amazon EC2 cloud server with three datasets by updating a file, appending a file and deleting a file from the document collection and compared our result with the state-ofthe- art method. Results show that our scheme has an average running time of 42ms which is 75% less than the existing method.