Optimization Of Account-Based Blockchain Privacy-Preserving System

The account-based blockchain system provides smart contracts with rich functions,but there is a risk of the disclosure of user privacy data.The account-based privacypreserving blockchain system applies zk-SNARK to protect user privacy data.However,compared with the account-based blockchain system itself,the account-based privacypreserving blockchain system has single function,vulnerable security and no practical availability.This paper analyzed the types of users,transactions and zero-knowledge proof scheme of the account-based privacy-preserving blockchain system and improved the system from these three aspects to enhance the robustness of the system.There is no researches on the user type,transaction type,proof scheme with simulation extractability of the account-based blockchain privacy-preserving system.This paper optimizes the types of users,transactions and zero-knowledge proof scheme of the account-based privacy-preserving blockchain system respectively.This paper takes the account-based blockchain anonymous system BlockMaze as the prototype to optimize.The main optimization schemes are:（1）For transaction types,this paper proposed the first known performance optimization of batch processing of the account-based privacy-preserving blockchain system.Since the transaction information generated by the privacy-preserving blockchain system is slower than that of the blockchain system,there is a lot of redundancy when generating multiple sending and depositing transaction information.In this paper,the functions of batch sending and batch depositing are realized through intermediate value processing,serial number processing and circuit integration and assembly.From the experimental data,compared with the original BlockMaze system,the maximum proof generation time is around 57.24%（batch sending）and around 18.07%（batch depositing）respectively.（2）For user types,this paper proposed the first known multi-signature authentication mechanism under the account-based privacy-preserving blockchain system.BlockMaze system does not provide multi-signature for its users.The scheme designed in this paper is easy understood and easy operated.The proof generation time only increases by around 1.80 seconds（account minting）,around 1.99 seconds（account redeeming）,around 0.99 seconds（sending）and around 2.84 seconds（depositing）respectively.（3）For transaction types,this paper put forward the first known micropayment scheme under the account-based privacy-preserving blockchain system,which solves the problem of fund freezing.Refering the micropayment scheme of the blockchain system,this paper designed a circuit which packages the deadline of depositing when generating proofs.As shown by the results,the proof generation time is only increased by around 1.41 seconds（sending）and about 1.02 seconds（depositing）respectively.（4）For the type of proof scheme,this paper proposed the first known simulation extractability security optimization scheme for the account-based privacy-preserving blockchain system.The proof scheme of the account-based privacy-preserving blockchain system is vulnerable to transaction malleability attack.This paper proposed to replace the original proof scheme with a simulation extractable zk-SNARK.As shown by the results,it is proved that the increase of generation time is within an acceptable range,and the security optimization of simulation extractability achieved in this paper has practical value.The function optimization scheme and security optimization scheme proposed in this paper can effectively improve the robustness,practicability and security of the accountbased privacy-preserving blockchain system.