Differentially private data sharing in Cloud Federation with blockchain

Cloud federation is an emergent Cloud-computing paradigm that allows services from different Cloud systems to be aggregated in a single pool. To support secure data-sharing in a Cloud federation, anonymisation services that obfuscate sensitive datasets under differential privacy have been recently proposed. However, by outsourcing data protection to the Cloud, data owners lose control over their data, raising privacy concerns. This is even more compelling in multi-query scenarios where maintaining privacy amounts to controlling the allocation of so-called privacy budget. In this paper we propose a blockchain-based approach that enables data owners to control the nonymisation process, and enhances the security of the services. Our approach relies on blockchain to validate the usage of privacy budget and adaptively change its allocation via smart contracts, depending on the privacy requirements provided by data owners. Prototype implementation with the Hyperledger permissioned blockchain validates our approach with respect to privacy guarantee and practicality