Abstract: The combination of blockchain and ciphertext policy sttribute based rncryption(CP-ABE) schemes has been widely used in the access control of sharing data on the cloud,but the privacy protection of data users in these schemes has not been solved.Some studies introduce distributed multi-authority attribute based signature schemes(DMA-ABS) to protect the privacy of data users,but when the data user accesses the data multiple times,it is necessary to perform repeated permission verification,which will cause unnecessary time consumption.And when the attributes and access control policies of data users are relatively unchanged,data users can access shared data repeatedly and infinitely,system overload and affect normal request processing.This may cause the leakage of cloud data, posing a hidden danger to the security of cloud data.At the same time,the behavior of data users changes dynamically.A data user who once perform well may have some malicious behaviors such as frequent access to data,illegal access to data,which brings hidden dangers to data security.Firstly,the smart contract is combined with the CP-ABE scheme of multi-attribute authority center to realize the fine-grained access control of personal privacy data in the cloud,and the distributed multi-authority attribute based signature scheme is introduced.The anonymous identity verification of data users is completed to protect the identity privacy of data users.Secondly,based on the idea of unspent transaction output(UTXO ) of Bitcoin,the digital token is designed to realize once authorization and multiple access.Finally,this scheme implements an access control process based on hyperledger fabric,and compares it with existing schemes in terms of access time overhead.The results indicate that the proposed scheme can effectively reduce access time overhead and improve access efficiency.

Key words: Blockchain, Access control, Ciphertext policy attribute based encryption, Access token, Smart contract