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Abstract
With the block chain receiving extensive attention in recent years, many storage schemes based on the blockchain havebeenproposed as alternative meansocloudstoragefordata 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 (CPABE). 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). 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 CPABE 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 centre.