Research And Application Of Secure Multi-Party Computation In Privacy Protection Of Loan Systems Based On Smart Contract

With the development of decentralized technology,the appearance of smart contract loan platforms makes up for the shortcomings of traditional loan systems.But the openness and transparency of smart contract loan platforms also have brought the risk of privacy leakage.Nowadays,more and more attentions are paid to the privacy protection of user data.How to protect the privacy of user data when participating in loan transactions has become an urgent problem to be solved.Secure Multi-party Computation(SMPC)has become a potential method to solve this problem due to its feature of correct calculation,independent input,and privacy protection.Considering the particularity of the smart contract loan system,this thesis mainly studies the way that SMPC can be used in the privacy protection of smart contract loan systems.This thesis analyses the reasons for the privacy problems in the system from the aspects of loan process and contract execution mechanism.Then,this thesis proposes three protocols based on SMPC to solve the problems mentioned above.Furthermore,this thesis designs and implements a loan system based on smart contract with function of privacy protection.The main research results of this thesis are shown as follows:(1)To overcome the problem of privacy leakage in loan process and contract execution mechanism,this thesis proposes three protocols and a mechanism.For the problem of privacy leakage in the loan request stage,the Amount and Credit Value Comparison protocol is proposed.This protocol uses the method of secure two-party comparison to solve the problem of comparison of amount and credit value between lenders and borrowers.This protocol transforms the comparison problem into the product problem based on the 1-Random encoding scheme and the ElGamal homomorphic encryption algorithm.This protocol is used to protect both lenders and borrowers'privacy.For the problem of privacy leakage in the loan matching stage,the Interest Rate Minimum Value Selection protocol is proposed.This protocol uses the method of secure multi-party minimum computation and secure multi-party comparison to select the minimum of rates and the lender.First,select the minimum of rates based on 0-1 encoding scheme and the particular ElGamal homomorphic encryption algorithm.Second,find the lender who have the minimum rate value based on 1-Random encoding scheme and the ElGamal homomorphic encryption algorithm.This protocol is used to protect lenders' privacy.For the problem of privacy leakage in the smart contract execution mechanism,combined with the characteristics of loan and taking the loan transfer and repayment stage of loan transaction as an example,this thesis proposes a secure multi-party contract execution protocol.After using ElGamal homomorphic encryption algorithm to encrypt the input data of the participants,the verifiable Shamir secret sharing scheme and secure multi-party outsourcing calculation model are used for addition and subtraction calculation.This protocol transforms the single-party contract into multi-party contract,and protects the input privacy of the contract participants.Based on the above protocol,this thesis proposes a privacy protection mechanism for smart contract loan system from the aspects of loan process and contract execution.From the aspects of theory and experiment,this thesis verifies the correctness,security and applicability of the three protocols.This thesis compares the three protocols with the existing protocols,and proves that the proposed protocols have better applicability and higher efficiency in the privacy protection of smart contract loan systems.(2)This thesis designs an intelligent contract loan system with privacy protection function.Combined with the status of privacy protection of smart contract loan systems,this thesis analyses the system requirements,and designs the overall architecture based on the above protocols.On this basis,the front-end pages,smart contract and a password service platform are designed.Finally,the operation process of the system is designed.(3)This thesis implements an intelligent contract loan system with privacy protection function.According to the preset functions of the system,the dependent environment of the system is set,and then the front-end pages,smart contract and the password service platform are implemented respectively.Finally,the system is tested from two aspects of function implementation and execution cost to verify the availability and privacy of the system.