An efficient and secure data sharing framework using homomorphic encryption in the cloud

Due to cost-efficiency and less hands-on management, data owners are outsourcing their data to the cloud which can provide access to the data as a service. However, by outsourcing their data to the cloud, the data owners lose control over their data as the cloud provider becomes a third party. At first, encrypting the data by the owner and then exporting it to the cloud seems to be a good approach. However, there is a potential efficiency problem with the outsourced encrypted data when the data owner revokes some of the users' access privileges. An existing solution to this problem is based on symmetric key encryption scheme and so it is not secure when a revoked user rejoins the system with different access privileges to the same data record. In this paper, we propose an efficient and Secure Data Sharing (SDS) framework using homomorphic encryption and proxy re-encryption schemes that prevents the leakage of unauthorized data when a revoked user rejoins the system. Our framework is secure under the security definition of Secure Multi-Party Computation (SMC) and also is a generic approach - any additive homomorphic encryption and proxy re-encryption schemes can be used as the underlying sub-routines. In addition, we also modify our underlying Secure Data Sharing (SDS) framework and present a new solution based on the data distribution technique to prevent the information leakage in the case of collusion between a user and the Cloud Service Provider.