Internet paranoiacs drawn to Bitcoin have long indulged fantasies of American spies subverting the booming, controversial digital currency. Increasingly popular among get-rich-quick speculators, Bitcoin started out as a high-minded project to make financial transactions public and mathematically verifiable — while also offering discretion. Governments, with a vested interest in controlling how money moves, would, some of Bitcoin’s fierce advocates believed, naturally try and thwart the coming techno-libertarian financial order.
It turns out the conspiracy theorists were on to something. Classified documents provided by the whistleblower Edward Snowden show the National Security Agency indeed worked urgently to target Bitcoin users around the world — and wielded at least one mysterious source of information to “help track down senders and receivers of Bitcoins,” according to a top-secret passage in an internal NSA report dating to March 2013. The data source appears to have leveraged NSA’s ability to harvest and analyze raw, global internet traffic while also exploiting an unnamed software program that purported to offer anonymity to users, according to other documents.
Although the agency was interested in surveilling some competing cryptocurrencies, “Bitcoin is #1 priority,” a March 15, 2013 internal NSA report stated.
The documents indicate that “tracking down” Bitcoin users went well beyond closely examining Bitcoin’s public transaction ledger, known as the Blockchain, where users are typically referred to through anonymous identifiers; the tracking may also have involved gathering intimate details of these users’ computers. The NSA collected some Bitcoin users’ password information, internet activity, and a type of unique device identification number known as a MAC address, a March 29, 2013 NSA memo suggested. In the same document, analysts also discussed tracking internet users’ internet addresses, network ports, and timestamps to identify “BI