A Privacy-Preserving and Fully Decentralized Storage and Sharing System on Blockchain

Abstract

With the blockchain receiving extensive attention in recent years, many storage schemes based on the blockchain have been proposed as alternative means of cloud storage for data outsourcing. However, the conventional access control methods in the current sharing schemes require either individual permission granting via symmetric keys or a trusted central attribute authority for ciphertext-policy attribute-based encryption (CP-ABE). Moreover, due to the transparency of the blockchain, the data query logs are recorded in public ledgers. Nevertheless, the problem of privacy protection for data consumers has not been properly addressed. In this paper, we propose a fully decentralized data storage and sharing system on a blockchain by using multi-authority CP-ABE and decentralized multi-authority attribute-based signatures (DMA-ABSs). In our system, every party can securely store and share its data with a set of individuals satisfying a policy with no need to grant separate permissions individually. Additionally, the data owners can fully control their data, know how their data are accessed due to the nature of the blockchain and have the ability to opt-out at any time. The public ledger of the blockchain provides immutable logs of data address pointers, access policies, attribute public keys and data queries. In addition, data consumers' attributes are publicly verifiable through the DMA-ABS scheme without revealing more private information. Finally, the combination of the multi-authority CP-ABE with the blockchain guarantees the integrity, confidentiality, and accessibility of the data without the need for trusted third parties, such as a central authority or a data center.