Storekeeper: A Security-Enhanced Cloud Storage Aggregation Service

Cloud storage services are currently a commodity that allows users to store data persistently, access the data from everywhere, and share it with friends or co-workers. However, due to the proliferation of cloud storage accounts and lack of interoperability between cloud services, managing and sharing cloud-hosted files is a nightmare for many users. To address this problem, specialized cloud aggregator systems emerged that provide users a global view of all files in their accounts and enable file sharing between users from different clouds. Such systems, however, have limited security: not only they fail to provide end-to-end privacy from cloud providers, but they require users to grant full access privileges to individual cloud storage accounts. In this paper, we present Storekeeper, a privacy-preserving cloud aggregation service that enables file sharing on multi-user multi-cloud storage platforms while preserving data confidentiality from cloud providers and from the cloud aggregator service. To provide this property, Storekeeper decentralizes most of the cloud aggregation logic to the client side enabling security sensitive functions to be performed only on the trusted client endpoints. This decentralization brings new challenges related with file update propagation, access control, user authentication, and key management that are addressed by Storekeeper. This is provided at a low cost (7% on average) when compared with the underlining cloud providers.