Research On Private Information Retrieval Based On Blockchain

With the rapid development of Internet technology,more and more people access information through the network.While enjoying the convenience brought by various network services,personal privacy has also been greatly challenged.While the user is searching for information on the network,the retrieved content is also exposed to the network service provider.These network service providers use the user's search records to gain benefits.In many cases,users want to be able to protect their privacy when querying sensitive information.Private information retrieval(PIR)is proposed to solve this problem.PIR mainly has two types.information-theoretic private information retrieval(IT-PIR)and computational private information retrieval(C-PIR).IT-PIR can provide infor-mation theory security,requiring multiple servers to store the replicate database.C-PIR provides weaker security and is based on mathmetical hard problems.IT-PIR requires that the servers cannot collude.Once the server colludes,the privacy of the user can-not be guaranteed.C-PIR is not practical due to the computational complexity is too high.How to solve the collusion problem of IT-PIR is a hard problem to many scholars.The main solution to the collusion problem is to turn the protocol into a C-PIR when all servers collude.This thesis combines the blockchain with PIR,use some excellent features of the blockchain to solve the problems in PIR.The specific research contents are as follows:1.Proposed Bitcoin-based PIR payment protocolFrom the perspective of economic interests,let the service provider involved in the conspiracy are subject to loss of profits to suppress the conspiracy of the service providers.This thesis goes from this perspective and proposes a bitcoin-based PIR pay-ment protocol.In this protocol,users pay for service fees for PIR through bitcoin trans-actions.The service provider can get the service fee he deserves according to the normal process.However,if the service provider chooses to collude,most service providers will lose the corresponding service fee,so they will not choose to collude.This paper an-alyzes the security and feasibility of the protocol and simulates the transactions in the protocol.According to the analysis,the payment agreement can hinder the conspiracy of the service party to a certain extent.2.Analyzed blockchain-based PIRPIR requires multiple servers to store the replicate database,which is very com-patible with the distributed ledger of the blockchain.The data of the blockchain comes from each node in the blockchain network,and it is more difficult for different data providers to form collusion behavior.In addition,the blockchain ledger has many ex-cellent features,the non-tempering ledger,traceable history records,etc.,which can ensure the reliability and authority of the data.These advantages make the blockchain a good platform for PIR.This paper analyzes the feasibility of implementing PIR on the public blockchain and the league chain,and proposes a reasonable scheme.It is concluded that the multi-server PIR based on league chain is the most feasible scheme.In addition,a method for PIR when the blockchain node data is not synchronized is proposed in this thesis.3.Implemented PIR based on league chainAccording to the previous analysis,the multi-server PIR based on the league chain is the most feasible scheme.This thesis designs a PIR based on the league chain,and gives an implementation.Multiple service provider jointly maintain a league chain,add their own data to the ledger,and provide PIR services.The user generates the request strings locally,and the server-side calculation process is implemented by a smart contract.This paper builds a league chain based on the Hyperledger Fabric framework to realize the data uploading,data updating and access control.Through client node,the user can access the data of the league chain and query by PIR.