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

摘要：

针对当前区块链混币系统在保护用户交易隐私的同时存在的难以抵御用户重复转账攻击、混币中心泄露信息和伪造转账攻击等问题，提出一种基于一次性环签名的区块链混币方案。首先，用户向混币中心存款并请求加入环组；其次，在混币中心验证通过后用户使用一次性环签名申请转账；最后，混币中心对签名和转账指令进行验证并转账。一次性环签名的性质使混币中心只能确认签名是否来自用户环组内，而无法获知具体来自哪位用户，且一次性环签名只能被验证一次，因此在保护用户隐私的同时使得用户无法重复发送转账指令，且混币中心也无法伪造转账指令。此外，用户和混币中心之间的通信使用混合加密技术，从而有效地防止第三方攻击者破坏签名的发送/验证并获取交易隐私。实验结果显示，该方案的平均响应时间随用户数量增多呈线性增长，每增加10个用户响应时间约增加10 ms，不会出现用户数量增长导致系统性能急剧下降甚至系统瘫痪的情况，可以支持混币网络中的多个用户在保护交易隐私的前提下高效顺利地完成转账。在用户数量相同的情况下，该方案的响应时间与CoinJoin相比缩短了约60 ms，和CoinShuffle方案相比缩短了约80 ms，与Blindcoin和Blindmixing方案相比响应时间相差不大但具有实现简单和安全性高等优点。可见，该方案在保护区块链用户隐私及财产安全方面具有实践及应用价值。

关键词: 区块链, 混币, 交易隐私, 一次性环签名, 混合加密