今年 6 月份，我在bitcoin 的技术和金融缺陷一文中提出了Bitcoin的一些技术上和金融上的缺陷，其中一条是认为 Bitcoin 并不完全是匿名的：
每个人的 bitcoin 无法被冻结，但并不代表它是匿名的。bitcoin 协议可以理解为一个公开账目的银行，大家可以看到里面的每一笔交易信息，而且这个银行可以匿名开户。由于账目公开，很容易查到每个账户的交易信息，甚至画出货币流向图，这比查银行更方便。只要抓住交易网络中的一个节点，然后审问该节点，便能将相关节点一个一个找出来。这对于政府机构而言，难度并不是特别的大。
这篇文章被转载到了不少地方，获得了不少评论。但被反对的最厉害的就是匿名性这一条。
昨天偶然间发现一篇论文《An Analysis of Anonymity in the Bitcoin System》（PDF 地址），今年7 月份公布在 arXiv 上，作者是来自爱尔兰 University College Dublin 的两位学者。这篇长达 13 页的论文里，作者通过通过分析 bitcoin 交易节点的网络结构，检验 bitcoin 用户的匿名性。具体方法请直接参见论文。下面直接摘录它的结论：
Bitcoin is an electronic analog of cash in the online world. It is decentralized: there is no central authority responsible for the issuance of Bitcoins and there is no need to involve a trusted third-party when making online transfers. However, this flexibility comes at a price: the entire history of Bitcointransactions is publicly available. In this paper we investigated the structure of two networks derived from this dataset and their implications for user anonymity. Using an appropriate network representation, it is possible to map many users to public-keys. This is performed using a passive analysis only.Active analyses, where an interested party can potentially deploy marked Bitcoins and collaborating users can discover even more information. We also believe that large centralized services such as the exchanges and wallet services are capable of identifying considerable portions of user activity.
Technical members of the Bitcoin community have cautioned that strong anonymity is not a prominent design goal of the Bitcoin system. However, casual users need to be aware of this, especially when sending Bitcoins to users and organizations they would prefer not to be publicly associated with.
Q. E. D.
