Research On Privacy-preserving Technologies In Transaction Layer Of Blockchain

The continuous development of blockchain technologies has been widely concerned.In the distributed environment,more and more blockchains are used to solve the problem of account consistency.At the same time,public nature of blockchain transaction layer leads to the leakage of user privacy information.How to protect the privacy of the transaction layer in blockchain is a key technical issue that needs to be solved urgently.The current blockchain is threatened by privacy disclosure.There are two types of blockchains,namely,a partially decentralized permissioned blockchain that is jointly managed by several organizations,and a complete decentralization public blockchain.The unique data structure and consensus algorithm of blockchain pose severe challenges to the privacy protection of the above two types of blockchains.First,considering the competitive relationship between members and the high transaction throughput in the permissioned blockchain,this requires fast privacy protection technologies,and prevent everyone else except the traders from obtaining transaction privacy information;Second,some centralized administrators who have a certain trust in the permissioned blockchian can implement privacy protection.However,all participants on the public blockchain are equal,which requires the privacy protection technologies on the public blockchain needs to be completely decentralized;Third,the introduction of privacy protection technologies in the permissioned blockchain or the public blockchain often brings relatively large time and storage overhead,which requires these designed privacy protection technologies being more efficient.At present,the privacy protection technologies for the permissioned blockchain is difficult to prevent the consortium administrators from obtaining the user's private information,and the privacy protection for all participants cannot be realized.Most of the research on the privacy protection technologies for the public blockchain require a trusted third party to implement.Privacy protection makes it difficult to guarantee the complete decentralization of the privacy protection process.In addition,the blockchain faces problems such as low throughput and high storage pressure.The existing privacy protection technologies have a relatively large time and storage overhead,which exacerbate the existing low transaction speed and large storage problem on the blockchain.To this end,this paper focuses on the realization of the privacy protection of the blockchain transaction layer to do research of fast privacy protection for the permissioned blockchain,the decentralized privacy protection for the public blockchain and the fixed storage privacy protection based on the ring signature for the public blockchain.Although the privacy protection on the permissioned blockchain is based on the trust administrators,it does not prevent the administrators from obtaining the user's private information.For this reason,this paper proposes a fast privacy protection technologies FPPB for the permissioned blockchain.Based on the zero-knowledge proof,FPPB encrypts the transaction content and protects the specific content of the transaction,so that the verifier can still verify the consistency of the transaction content between the providers and the customers without knowing the transaction content.FPPB takes advantage of the partial decentralization of administrators.It proposes the “Unspent Request Output List” and “Unspent Money Pool” maintained by the administrators,and encrypts the address of the recipient based on the stealth address to improve the transaction verification speed.FPPB also protects the privacy of the trading relationships and removes the off-blockchain interactions between two parties.Experiments on the blockchain platform EthereumJ show that under the same blockchain parameter settings,the transaction latency of the permissioned blockchain transaction based on FPPB increases only 6.3% compared with the normal transaction.The privacy requirement of the public blockchain is different from that of the permissioned blockchain.The public blockchain is completely decentralized and has no credible foundation.This requires that no trusted third parties should be introduced in the privacy protection technologies for the public blockchain,which brings challenges for privacy protection.To this end,this paper proposes a decentralized privacy protection technologies DPB for the public blockchain.DPB is based on the zero-knowledge proofs to hide the transaction content without compromising the verification of the consistency of the provider and customer transaction content.In addition,DPB draws on the idea of ring signature.The sender combines his identity with other users on the blockchain to form a “ring” without the need of a third party.He sends out his own transaction in the name of the ring so that the verifier does not know the actual relationship of the transaction at the same time that the consistency of the transaction content can be verified.Finally,through the distributed generation of encryption parameters,the trading partners do not affect the encryption process,and each part generates an encryption parameter,which realizes the complete decentralized privacy protection.Experiments show that when the ring size is fixed at about 20,the preparation and verification time of the DPB is about 80% lower than that of the traditional ring signature-based privacy protection technology.Since the size of signature in the privacy protection technologies based on the ring signature increases linearly with the size of the ring,the storage burden of the blockchain is seriously increased,which requires a privacy protection technologies based on the ring signature to reduce storage overhead.To this end,we propose a fixed-storage privacy protection technology PCRB based on the ring signature for the public blockchain.PCRB encrypts the transaction content based on zero-knowledge proof to pass the consistency verification.In addition,PCRB uses the ring signature scheme based on the accumulator and the bilinear mapping to generate the ring signature in transactions so that the signature size of the transaction is fixed to be constant.Under the premise of protecting the transaction content and the transaction relationship,the verifier can check the uniformity of the contents in transactions of the provider and customer,even though he does not know the actual trading relationship.Experiments show that the storage overhead of PCRB is reduced by at least 38.6% compared to the traditional privacy protection technologies when the 128-bit security level and 20 ring members are fixed.