We show how third-party web trackers can deanonymize users of
cryptocurrencies. We present two distinct but complementary attacks. On most
shopping websites, third party trackers receive information about user
purchases for purposes of advertising and analytics. We show that, if the user
pays using a cryptocurrency, trackers typically possess enough information
about the purchase to uniquely identify the transaction on the blockchain, link
it to the user's cookie, and further to the user's real identity. Our second
attack shows that if the tracker is able to link two purchases of the same user
to the blockchain in this manner, it can identify the user's entire cluster of
addresses and transactions on the blockchain, even if the user employs
blockchain anonymity techniques such as CoinJoin. The attacks are passive and
hence can be retroactively applied to past purchases. We discuss several
mitigations, but none are perfect.

展示了第三方 web 追踪器如何解匿名加密货币的用户，并呈现了两种不同但互补的攻击方法。

当 Cookie 遇上区块链：通过加密货币进行网络支付的隐私风险

When the cookie meets the blockchain: Privacy risks of web payments via  cryptocurrencies

The cryptocurrency market surpassed the barrier of \$100 billion market
capitalization in June 2017, after months of steady growth. Despite its
increasing relevance in the financial world, however, a comprehensive analysis
of the whole system is still lacking, as most studies have focused exclusively
on the behaviour of one (Bitcoin) or few cryptocurrencies. Here, we consider
the history of the entire market and analyse the behaviour of 1,469
cryptocurrencies introduced between April 2013 and June 2017. We reveal that,
while new cryptocurrencies appear and disappear continuously and their market
capitalization is increasing (super-)exponentially, several statistical
properties of the market have been stable for years. These include the number
of active cryptocurrencies, the market share distribution and the turnover of
cryptocurrencies. Adopting an ecological perspective, we show that the
so-called neutral model of evolution is able to reproduce a number of key
empirical observations, despite its simplicity and the assumption of no
selective advantage of one cryptocurrency over another. Our results shed light
on the properties of the cryptocurrency market and establish a first formal
link between ecological modelling and the study of this growing system. We
anticipate they will spark further research in this direction.

通过全面分析加密货币市场的历史，本文发现，虽然新加密货币不断出现、消失且市值在（超级）指数级上升，但市场的许多统计属性已经稳定多年。通过采用生态学视角，本文表明，虽然所谓的中性进化模型的假设是没有证据的，但它仍然能够在一定程度上再现市场的关键经验观察结果。