Research And Application Of Privacy Preference Blockchain Smart Contract

The development of big data technology has brought widespread attention to the issue of data privacy and has rapidly become a hot research topic in recent years.Meanwhile,blockchain and smart contract technology has provided a new means of privacy protection.This makes it quickly become an important technology in the research of data privacy issues.However,due to the workings of the consensus mechanism,all data of smart contracts are public,and the privacy preference problem they have needs to be addressed.In addition,outsourcing computing has become a business model arising from the development of big data technology,which enables data processing at low cost and high efficiency through outsourcing computing.However,the information asymmetry and asynchronous payment in the process make the trust crisis between users and service providers.To address these problems,this thesis designs and implements a privacy-preserving system for smart contracts based on homomorphic encryption,and proposes a transaction protocol for outsourced computing that balances privacy and fairness around the system.The main contributions of this thesis include the following three parts:1.In order to solve the privacy problem of smart contracts,this thesis proposes a privacy-preserving scheme for blockchain smart contracts through precompiled contracts and homomorphic encryption.By theoretically analyzing each part of the system,this thesis designs a system architecture that encrypts smart contract data and replaces arithmetic with homomorphic operations by calling pre-compiled contracts.To verify the feasibility,this thesis conducts comparison experiments on common homomorphic encryption schemes and code bases.The results show that the system is compatible with different encryption schemes and has good feasibility.2.In order to ensure the fairness of outsourcing computation,this thesis creatively proposes a fair transaction protocol based on blockchain and Paillier cryptosystem.The protocol introduces blockchain as a third party and uses smart contracts to ensure that both parties to a transaction receive the correct result or full payment,respectively.To verify the security and usability of the protocol,this thesis tests the actual performance of important steps of the protocol.The results show that the protocol is able to meet the requirements and balance privacy and fairness.3.To verify the practical performance of the scheme proposed in Contribution 1.This thesis implements a privacy-preserving system for Solidity language.First,this thesis analyzes the working principles of the Solidity syntax and the solc compiler,and then implements privacy protection for Solidity code based on these principles.By encrypting the plaintext and using homomorphic operations instead of arithmetic operations,the system achieves privacy protection for smart contracts and preserves the executability of smart contracts intact.The system is tested to verify the working of each module,and the test results show that the system can accomplish the privacy protection of smart contracts,and has good performance and ease of use.