Ensuring Privacy and Data Freshness for Public Auditing of Shared Data in Cloud

The cloud offers storage services where users can store a huge amount of data. Users are given flexible amounts of storage space along with the certain number of processors and primary memory where they can perform the required operations. Users can also share their data with other users whom they trust. This sharing of data is usually done by forming groups of users who share a common interest. Data shared by any user (known as the data owner) can be accessed by other users in the group, in which the data owner is a part of. The data which is stored in the cloud needs to be protected from theft, misuse, eavesdropping, etc. Since the user may store critical and sensitive data in the cloud, it is the responsibility of the cloud service provider (CSP) to ensure that the data is secure and also to preserve the identity (Privacy) of the users who share the data in the group. Users in a group can also make changes to the data which is shared in the group. Moreover when a user accesses the data, most up-to-date (fresh) data should be made available so that valid inferences and operation can be done. For this purpose in this paper, we propose a novel method for ensuring privacy and data freshness of shared data in cloud using Homomorphic authenticable ring signature (HARS) scheme to preserve the user privacy and Overlay tree algorithm is used for ensuring that users the data with required level of freshness. Also Third Party Auditor (TPA) audits the data stored in the cloud. He should be able to verify the trustworthiness of the CSP without disclosing the identity of the users in the group.