Research On Privacy-preserving Technology For Blockchain Applications

Blockchain is a tamper-proof digital distributed ledger with the characteristics of decentr alization,traceability,pseudonymity,and transparency.However,on the one hand,although t he transaction addresses of blockchain users are pseudonymous,malicious users can still use t he techniques such as transaction graph analysis attacks,address reuse attacks,and timestamp analysis attacks to track blockchain users and obtain their real identities.On the other hand,to achieve consensus,the nodes in the blockchain need to make the data stored in public,which causes the data privacy leakage concerns.The frequent occurrence of privacy breaches has ser iously affected the application and promotion of the blockchain technology.To address these i ssues,this thesis focuses on these two aspects of privacy preservation in blockchain applicatio ns,i.e.,transaction user identity privacy and data privacy.Specifically,the thesis designs the f ollowing two solutions:(1)To balance the contradictory requirements of identity privacy preservation and transa ction supervision,this thesis proposes a privacy-preserving and supervised scheme for blockc hain transaction user identity.First,the scheme combines the knowledge signature with one-ti me public key and anonymous certificate to achieve user identity anonymity and authenticity.Second,by designing the tracking tags,the transaction identity traceability is achieved,which satisfies the transaction supervision requirement.In addition,the scheme introduces the key sh aring technology,to realize multi-party supervision.It avoids single point of failure caused by one-party supervision.Finally,the security analysis and performance evaluation demonstrate that the scheme achieves both privacy preservation and supervision of the transaction user ide ntities,with a slightly higher supervision cost.(2)Considering that it will results in privacy leakage if storing the sensitive data directly on the blockchain in plaintext,this thesis utilizes the smart contract to design a secure,efficien t,and searchable data privacy-preserving sharing scheme based on the ciphertext-policy attrib ute-based encryption(CP-ABE)algorithm.First,the scheme utilizes the outsourced CP-ABE t o reduce the computation burden on the user side.Second,the scheme uses smart contract to i mplement data search on ciphertext,which is secure against the malicious servers.In addition,the scheme not only supports data sharing under different levels of precision,but also reduces the data update complexity to O(1)for dynamic data sharing scenarios.Finally,the security a nalysis and performance evaluation prove that the scheme is secure and feasible.