Privacy Protection Scheme Of Application Scenario-oriented Blockchain Systems

Blockchain systems are widely used in finance,medical care,education and other fields,openness of which leads to the risk of privacy disclosure.This master dissertation focuses on main work and its results of privacy protection of public chain and consortium chain which are as follows.(1)Aiming at that it is difficult to find a single trusted KGC for distributing keys in public chain systems,and the signature is easy to be forged by malicious KGC,a“multi-KGC ring signature scheme based on the SM9 algorithm” is proposed,in which there are correctness being verified,and unconditional anonymity.Owing to their maintaining system parameters together,multi-KGCs restrict each other,and any single KGC cannot obtain the ring signature private key in the above mentioned scheme in this master dissertation.Therefore,it cannot be forged by users and KGC members.In addition,it also reduces probability of KGCs' being attacked,which is suitable for privacy protection of decentralized and distrusted public chains.(2)In order to solve that there is untrustworthy server of centralized coin mixing scheme and that it is difficult to deploy decentralized coin mixing scheme,a“multi-KGC ring signature coin mixing scheme based on SM9 algorithm” is proposed to enhance anonymity of bitcoin systems,being combined the above mentioned“multi-KGC ring signature scheme based on SM9 algorithm” with the existing centralized coin mixing scheme.There is unlinkability internally and externally in the above mentioned coin mixing scheme,and it is easy to be expanded and to be deployed.Furthermore,it is compatible with bitcoin systems.The above mentioned multi-KGC ring signature scheme is used to hide input-output relationships of transactions,which can prevent privacy leakage behaviors such as stealing coins and tracking transactions by coin mixing servers.(3)In order to combine the privacy protection with its supervision of the alliance chain in its application,a “supervised transaction privacy protection scheme based on consortium chain” is designed to protect privacy of transaction amount,its receiver and sender.The trusted supervisor is introduced as the trusted node,which is responsible for distributing and managing homomorphic keys and group signature keys,and for supervising transactions.The Paillier homomorphic encryption algorithm is used to encrypt and hide the transaction amount,and the “range proof” is used to verify legitimacy of transaction.There are correctness,security,anonymity and traceability in the above mentioned scheme,where there are more comprehensive protection scope and supervision function,compared with related schemes.In summary,some above mentioned blockchain privacy protection schemes for the application scenario-oriented in this master dissertation can meet privacy protection of public chain and supervisable privacy protection of consortium chain,they can be applied in practical application scenarios.