How a 27-Year-Old Codebreaker Busted the Myth of Bitcoin’s Anonymity

Just over a decade ago, Bitcoin appeared to many of its adherents to be the crypto-anarchist holy grail: truly private digital cash for the internet.

Satoshi Nakamoto, the cryptocurrency’s mysterious and unidentifiable inventor, had stated in an email introducing Bitcoin that “participants can be anonymous.” And the Silk Road dark-web drug market seemed like living proof of that potential, enabling the sale of hundreds of millions of dollars in illegal drugs and other contraband for bitcoin while flaunting its impunity from law enforcement.

This is the story of the revelation in late 2013 that Bitcoin was, in fact, the opposite of untraceable—that its blockchain would actually allow researchers, tech companies, and law enforcement to trace and identify users with even more transparency than the existing financial system. That discovery would upend the world of cybercrime. Bitcoin tracing would, over the next few years, solve the mystery of the theft of a half-billion dollar stash of bitcoins from the world’s first crypto exchange, help enable the biggest dark-web drug market takedown in history, lead to the arrest of hundreds of pedophiles around the world in the bust of the dark web’s largest child sexual abuse video site, and result in the first-, second-, and third-biggest law enforcement monetary seizures in the history of the US Justice Department.

That 180-degree flip in the world’s understanding of cryptocurrency’s privacy properties, and the epic game of cat-and-mouse that followed, is the larger saga that unfolds in the book Tracers in the Dark: The Global Hunt for the Crime Lords of Cryptocurrency, out this week in paperback.

All of it began with the work of a young, puzzle-loving mathematician named Sarah Meiklejohn, the first researcher to pull out traceable patterns in the apparent noise of Bitcoin’s blockchain. This excerpt from Tracers in the Dark reveals how Meiklejohn came to the discoveries that would launch that new era of crypto criminal justice.

In early 2013, the shelves of a windowless storage room in a building of the University of California, San Diego, began to fill up with strange, seemingly random objects. A Casio calculator. A pair of alpaca wool socks. A small stack of Magic: The Gathering cards. A Super Mario Bros. 3 cartridge for the original Nintendo. A plastic Guy Fawkes mask of the kind popularized by the hacker group Anonymous. An album by the classic rock band Boston on CD.

Periodically, the door would open, the light would turn on, and a petite, dark-haired graduate student named Sarah Meiklejohn would enter the room and add to the growing piles of miscellaneous artifacts. Then Meiklejohn would walk back out the door, down the hall, up the stairs, and into an office she shared with other graduate students at the UC San Diego computer science department. One wall of the room was almost entirely glass, and it looked out onto the sunbaked vista of Sorrento Valley and the rolling hills beyond. But Meiklejohn’s desk faced away from that expanse. She was wholly focused on the screen of her laptop, where she was quickly becoming one of the strangest, most hyperactive Bitcoin users in the world.