Research On Blockchain-assisted Fine-grained Data Sharing Mechanism

With the vigorous development of the big data era,data sharing has become an effective way to release the value of massive data,and has received extensive attention in fields like healthcare and the Internet of Things.In order to achieve flexible data sharing while protecting the privacy of user data,attribute-based encryption technology that can support fine-grained data access control is considered to be promising.However,the process of attribute-based encryption will lead to huge computing overhead.Users with limited resources usually have to outsource the complex decryption to a third party(i.e.,a proxy),which leads to the fairness problem in outsourcing transactions,that is,whether the user and proxy can obtain the correct calculation results and rewards if they honestly obey the transaction protocol,respectively.Besides,in the traditional data sharing scheme based on cloud storage and attribute-based encryption,the data tampering of malicious cloud and problems like key escrow caused by the authority holding private keys of all users in single-authority attribute-based encryption will lead to the security risks of the system.In order to solve the above two kinds of issues,this paper mainly focuses on the fairness problem in attribute-based outsourcing decryption transaction and the exploration of a secure and efficient data sharing scheme.The major results of work are as follows:1.Achieve robust fairness in attribute-based outsourcing decryption payment.In the outsourcing decryption payment scenario,fairness is usually guaranteed by the public verifiability of the decryption scheme,and the key to achieving robust fairness is to use zero knowledge proof or the decentralized characteristics of blockchain technology to replace the trusted third party for verification.For the attribute-based outsourcing decryption payment scenario,this paper first points out that the existing schemes have defects in fairness and correctness.Then,we construct an attribute-based outsourcing decryption scheme which supports both private and public verifiability.To achieve robust fairness in the transaction,smart contract in blockchain is introduced to make a judge when a dispute occurs.Besides,the introduction of Interplanetary File System is applied to handle the average storage overhead on chain and assist in the judgement of smart contract due to the non-repudiation.Through detailed theoretical analysis and experimental comparison,we prove that the scheme is secure and effective.2.Realize a data sharing scheme with strong scalability,security and user friendliness.The traditional data sharing scheme based on cloud storage has underlying dangers of data tampering and disclosure,while the decentralized and tamperproof features of blockchain enable data to be stored and shared in a more transparent and secure way.For this purpose,we propose an attribute-based encryption scheme with blockchain outsourcing decryption function that supports large attribute domains and multiple authorities,which improves the flexibility of system and reduces the risk of key disclosure and escrow attacks.In the scheme,we introduce the decentralized execution provided by the blockchain chaincode to replace cloud computing for outsourced decryption.While further reducing the local decryption cost of users,we reduce the risk of key abuse through the key owner and robustness check mechanism,and Interplanetary File System is also applied to store the encrypted data to reduce the average storage cost on chain.Through theoretical analysis and experimental simulation,we prove the feasibility,security and efficiency of client decryption.