关键词: 区块链, 混币, 交易隐私, 一次性环签名, 混合加密

Abstract:

In order to solve the problems of the current blockchain coin mixing system that are difficult to resist the duplicate transfer attack of users， the leakage of information by the mixing center， and the attack of forged transfer while protecting the privacy of user transactions， a blockchain coin mixing scheme based on one-time ring signature was proposed. Firstly， funds were deposited into the mixing center and a request to join a ring group was made by the user. Then， after being verified by the mixing center， a one-time ring signature was used by the user to apply for a transfer. Finally， the signature and transfer instruction were verified by the mixing center， and the transfer was executed. The nature of one-time ring signature makes it possible for the mixing center to confirm whether the signature is from the user ring group， but not from which user， and one-time ring signature can only be verified once， so while protecting the user’s privacy， the user cannot send the transfer instruction repeatedly， and the mixing center cannot forge the transfer instruction. Besides， hybrid encryption technology was used in the communication between the user and the mixing center， which effectively prevented third-party attackers breaching the sending/verification of signatures and obtaining transaction privacy. Experimental results show that the average response time of the proposed scheme increases linearly with the increase of the number of users， and the response time increases by about 10 ms for each additional ten users， and there will be no sharp decline of the system performance or even system paralysis caused by the increase in the number of users， which can support multiple users in the coin mixing network to complete the transfer efficiently and smoothly under the premise of protecting the privacy of transactions. In the case of the same number of users， the proposed scheme has the response time decreased by about 60 ms compared with CoinJoin， and decreased by about 80 ms compared with CoinShuffle， which is not much different from that of Blindcoin and Blindmixing， but has the advantages of simple implementation and high security. It can be seen that the proposed scheme has practical and application values in protecting the privacy and property security of blockchain users.

Key words: blockchain, coin mixing, transaction privacy, one-time ring signature, hybrid encryption