Research And Design Of Data Privacy Protection Scheme For Blockchain Transactions

Blockchain is a data block structure arranged in chronological order,with transaction as the basic message carrier.It has the characteristics of decentralization,tamper proof and traceability.According to the requirements of privacy rights and application scenarios,currently blockchain technology has mainly derived two major application platforms:public blockchain and consortium blockchain.The most classic application of public blockchain is Bitcoin,whose transaction data is stored in plaintext,which can not ensure data privacy under the condition that any node can access;otherwise,it realizes the consistency of distributed ledger at the cost of low transaction throughput.The most well-known platform of consortium blockchain is Hyperledger Fabric,which implements physical isolation and other strategies to realize privacy protection and performance improvement.However,it is based on the premise of weakening the consistency of blockchain ledger,which brings potential data security issues.Thus,it is of great significance to further study secure and efficient blockchain schemes.Based on the consortium blockchain environment,combined with searchable encryption algorithm,this thesis studies and designs a blockchain scheme(referred to as "Cipherchain")in which transaction data is finally stored in the form of ciphertext.Cipherchain retains the distributed ledger technology commonly implemented in the public blockchain schemes.All transactions are required to be processed by the same consensus mechanism,then updated and stored on the globally consistent distributed ledger.Specifically,the main work of this thesis is as follows:(1)The ciphertext processing scheme of transaction data is designed.Firstly,a searchable encryption scheme called multi-user public key encryption with conjunctive keyword search(mPECK)is used to generate public-private key pairs for transaction processing based on its derived system parameters.Secondly,we introduce the concept of keyword set,and perform ciphertext processing on valid transaction data with its associated keyword set.We also design a state database mechanism for transaction ciphertext participating in consensus mechanism,draw the data structure of transaction and corresponding data block.Finally,two search schemes against transaction ciphertext on blockchain ledger are provided,one of which called trapdoor query mechanism is mainly discussed.It includes trapdoor generation,matching query on blockchain and target transaction decryption.(2)An execution-consensus-update blockchain architecture is designed.Based on the design concept of Hyperledger Fabric,the endorsement mechanism and modular processing mode of transaction function are introduced.Firstly,the paper analyzes the system model of Cipherchain,and discusses the functional characteristics of endorsement node,consensus node and update node.Secondly,we designs an smart contract mechanism suitable for Cipherchain,and discusses the logical relationship between user contract,transaction participants and state database.Finally,this thesis focuses on the four stages of transaction data processing:execution,consensus,update and query.In detail,it includes failure processing strategy of endorsement node,validation processing method of consensus node against transaction ciphertext,and different methods adopted by physical nodes in update and query stage.(3)The performance of Cipherchain is tested and analyzed to verify the feasibility of its system.First of all,the core algorithm related to the transaction processing of Cipherchain is realized by coding.And the computation cost of four modules is tested by using the white box test method,including system parameter generation,transaction encryption,trapdoor generation and transaction data decryption.Besides the feasibility of system operation is analyzed and proved.Secondly,we prove that mPECK algorithm can save the storage capacity to the greatest extent by analyzing the communication and storage cost of transaction ciphertext.We also compare the transaction throughput and security mechanism with Hyperledger Fabric and Bitcoin,and conclude that Cipherchain has advantages in both performance and privacy protection.Finally,we also analyze the application value of the combination of Cipherchain with cloud computing and public blockchain.