As data is having an increasingly relevant role in di erent business fields, ensuring integrity has become fundamental. Modern databases rely on transaction history written on redo logs to allow for data restore. However, if redo logs are (maliciously) forged, data can actually be lost or altered. Due its strong data integrity guarantees, blockchain technology can be employed to ensure log integrity, but its current performance limitations hinder actual exploitations.In previous work, we proposed a layered blockchain-based architecture for distributed (federated) database redo logs: a fast first layer blockchain, anchored to a secure second layer blockchain, based on proof-of-work to achieve strong integrity. Here, we present an implementation and an experimental evaluation of a prototype of that architecture, which employs a total consensus algorithm on the first layer blockchain. Finally, to improve availability and scalability, we refine our solution by investigating, respectively, a Byzantine Fault Tolerant consensus and a Distributed Hash Table solution to shard the first layer blockchain ledger among available nodes.

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, anonymization 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 in which maintaining privacy amounts to controlling the allocation of the so-called privacy budget. In this paper, we propose a blockchain-based approach that enables data owners to control the anonymization process and that enhances the security of the services. Our approach relies on blockchain to validate the usage of the privacy budget and adaptively change its allocation through 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.

Cloud federation is an emergent cloud-computing paradigm where partner organisations share data and services hosted on their own cloud platforms. In this context, it is crucial to enforce access control policies that satisfy data protection and privacy requirements of partner organisations. However, due to the distributed nature of cloud federations, the access control system alone does not guarantee that its deployed components cannot be circumvented while processing access requests. In order to promote accountability and reliability of a distributed access control system, we present a decentralised runtime monitoring architecture based on blockchain technology.