Using Crypto-Currencies to Measure Financial Activities and Uncover Potential Identities of Actors Involve

Bitcoin is a digital currency that has recently gathered significant interest. From ecommerce sites to darkweb marketplaces, merchants accept Bitcoin as a form of payment. Every day, millions of dollars are transacted across Bitcoin's payment network. The value of a single bitcoin has increased from $500 to $3,000 in a one-year period since July 2016.;A part of the interest may stem from the decentralized design of Bitcoin. A peer-to-peer network collectively generates new coins and maintains the distributed transaction ledger, also known as the blockchain. The blockchain records transactions between public keys, rather than between real-world identities. This detachment from real-world identities makes it hard to measure financial activities and identify actors on the network, such as four cases that we study: (i) botnets stealing computational cycles, (ii) speculatively investing in digital currencies, (iii) delaying the processing of Bitcoin payments, and (iv) purchasing ads with illegal contents.;Despite this challenge, the decentralized design of Bitcoin and similar digital currencies offers public information on every transaction and the associated identities. This dissertation demonstrates that, using the four cases as examples, we can leverage this public information to analyze financial activities --- e.g. measuring the cost and revenue --- and to potentially uncover the identities of the actors involved.;In particular, we can measure the revenue and cost for Cases (i) through (iii). For (i), we show that botnets made a modest income of $118,000 between 2012 and 2013, but for some botnets we estimate the cost to victims to be more than twice the botnets' revenue. For (ii), we develop a new way to estimate the profitability of investing in digital currency markets. By simulating multiple investment strategies, we show the drastic variations in profitability and thus the extreme risks associated with digital currency investment. For (iii), we show that an adversary delayed Bitcoin transaction processing time from 0.33 to 2.67 hours, at a modest cost of $4,900 per day. Furthermore, we can uncover the potential identities of the actors involved. For (i), we identify 10 distinct botnet operations. For (iv), we identify ads paid for by potentially the same criminals.