Abstract: Blockchain, as an open decentralized ledger technology among a P2P network, is the supporting technology for cryptocurrencies such as Bitcoin and etc. Blockchain enables low-cost trust among counterparts and is considered promising in cross-border payment, credentials, supply chain and etc., attracting wide attention from financial and government institutions. However, while the blockchain guarantees trust via transparency, privacy issue occurs. When all the transactions are exposed to the public and maliciously explored, user privacy will be heavily threatened. Recently, various work have been done to address the privacy issue, leading to the necessity of a survey paper. In this paper, we will first figure out the privacy leakage by examples. Then, comprehensive introduction and analysis of the state-of-the-art solutions, such as Dash, Monero, Zcash, Hawk, Quorum and Coco Framework will be present. Last, we will summarize the technologies and give an outlook.

Key words: blockchain, privacy, cryptocurrency, Monero, Zcash, zero-knowledge proof

摘要： 区块链是一种P2P网络中的共享账本技术，是比特币等密码学货币的支撑性技术．区块链是一种低成本让参与各方达成信任的方式，被认为能应用在跨境支付、凭据业务、供应链等领域，因而受到了金融机构、政府等部门广泛的关注．然而，在保证数据透明可验证的同时，区块链系统却也同时带来了一个新的问题：隐私如何得到保护？当用户的所有交易信息都暴露在大众面前，如果这些交易信息被恶意挖掘及利用，将给用户隐私带来严重的威胁．因此，最近很多团队针对不同的场景和目标提出了相应的隐私解决方案，但是目前并没有将上述方案进行梳理和总结的工作．将对区块链的隐私问题和解决方案做一个全面的介绍和分析．我们将首先结合区块链的基本运行原理和分类，通过若干例子指出目前区块链中存在的隐私问题，例如在公链和联盟链中的隐私泄露场景分别是指什么；然后，将对主流的隐私解决方案做一个综合而全面的介绍，包括达世币（Dash），门罗币（Monero），零钞(Zcash)，Hawk，Quorum以及Coco框架．最后，将对上述方案做一个总结以及阐述我们对区块链隐私技术发展方向的展望．

关键词: 区块链, 隐私, 密码学货币, 门罗币, 零钞, 零知识证明