It’s not clear if bitcoin is legal, but there is no company in control and no one to arrest. Illustration by Grafilu

There are lots of ways to make money: You can earn it, find it, counterfeit it, steal it. Or, if you’re Satoshi Nakamoto, a preternaturally talented computer coder, you can invent it. That’s what he did on the evening of January 3, 2009, when he pressed a button on his keyboard and created a new currency called bitcoin. It was all bit and no coin. There was no paper, copper, or silver—just thirty-one thousand lines of code and an announcement on the Internet.

Nakamoto, who claimed to be a thirty-six-year-old Japanese man, said he had spent more than a year writing the software, driven in part by anger over the recent financial crisis. He wanted to create a currency that was impervious to unpredictable monetary policies as well as to the predations of bankers and politicians. Nakamoto’s invention was controlled entirely by software, which would release a total of twenty-one million bitcoins, almost all of them over the next twenty years. Every ten minutes or so, coins would be distributed through a process that resembled a lottery. Miners—people seeking the coins—would play the lottery again and again; the fastest computer would win the most money.

Interest in Nakamoto’s invention built steadily. More and more people dedicated their computers to the lottery, and forty-four exchanges popped up, allowing anyone with bitcoins to trade them for official currencies like dollars or euros. Creative computer engineers could mine for bitcoins; anyone could buy them. At first, a single bitcoin was valued at less than a penny. But merchants gradually began to accept bitcoins, and at the end of 2010 their value began to appreciate rapidly. By June of 2011, a bitcoin was worth more than twenty-nine dollars. Market gyrations followed, and by September the exchange rate had fallen to five dollars. Still, with more than seven million bitcoins in circulation, Nakamoto had created thirty-five million dollars of value.

And yet Nakamoto himself was a cipher. Before the début of bitcoin, there was no record of any coder with that name. He used an e-mail address and a Web site that were untraceable. In 2009 and 2010, he wrote hundreds of posts in flawless English, and though he invited other software developers to help him improve the code, and corresponded with them, he never revealed a personal detail. Then, in April, 2011, he sent a note to a developer saying that he had “moved on to other things.” He has not been heard from since.

When Nakamoto disappeared, hundreds of people posted theories about his identity and whereabouts. Some wanted to know if he could be trusted. Might he have created the currency in order to hoard coins and cash out? “We can effectively think of ‘Satoshi Nakamoto’ as being on top of a Ponzi scheme,” George Ou, a blogger and technology commentator, wrote.

It appeared, though, that Nakamoto was motivated by politics, not crime. He had introduced the currency just a few months after the collapse of the global banking sector, and published a five-hundred-word essay about traditional fiat, or government-backed, currencies. “The root problem with conventional currency is all the trust that’s required to make it work,” he wrote. “The central bank must be trusted not to debase the currency, but the history of fiat currencies is full of breaches of that trust. Banks must be trusted to hold our money and transfer it electronically, but they lend it out in waves of credit bubbles with barely a fraction in reserve.”

Banks, however, do much more than lend money to overzealous homebuyers. They also, for example, monitor payments so that no one can spend the same dollar twice. Cash is immune to this problem: you can’t give two people the same bill. But with digital currency there is the danger that someone can spend the same money any number of times.

Nakamoto solved this problem using innovative cryptography. The bitcoin software encrypts each transaction—the sender and the receiver are identified only by a string of numbers—but a public record of every coin’s movement is published across the entire network. Buyers and sellers remain anonymous, but everyone can see that a coin has moved from A to B, and Nakamoto’s code can prevent A from spending the coin a second time.

Nakamoto’s software would allow people to send money directly to each other, without an intermediary, and no outside party could create more bitcoins. Central banks and governments played no role. If Nakamoto ran the world, he would have just fired Ben Bernanke, closed the European Central Bank, and shut down Western Union. “Everything is based on crypto proof instead of trust,” Nakamoto wrote in his 2009 essay.

Bitcoin, however, was doomed if the code was unreliable. Earlier this year, Dan Kaminsky, a leading Internet-security researcher, investigated the currency and was sure he would find major weaknesses. Kaminsky is famous among hackers for discovering, in 2008, a fundamental flaw in the Internet which would have allowed a skilled coder to take over any Web site or even to shut down the Internet. Kaminsky alerted the Department of Homeland Security and executives at Microsoft and Cisco to the problem and worked with them to patch it. He is one of the most adept practitioners of “penetration testing,” the art of compromising the security of computer systems at the behest of owners who want to know their vulnerabilities. Bitcoin, he felt, was an easy target.

“When I first looked at the code, I was sure I was going to be able to break it,” Kaminsky said, noting that the programming style was dense and inscrutable. “The way the whole thing was formatted was insane. Only the most paranoid, painstaking coder in the world could avoid making mistakes.”

Kaminsky lives in Seattle, but, while visiting family in San Francisco in July, he retreated to the basement of his mother’s house to work on his bitcoin attacks. In a windowless room jammed with computers, Kaminsky paced around talking to himself, trying to build a mental picture of the bitcoin network. He quickly identified nine ways to compromise the system and scoured Nakamoto’s code for an insertion point for his first attack. But when he found the right spot, there was a message waiting for him. “Attack Removed,” it said. The same thing happened over and over, infuriating Kaminsky. “I came up with beautiful bugs,” he said. “But every time I went after the code there was a line that addressed the problem.”

He was like a burglar who was certain that he could break into a bank by digging a tunnel, drilling through a wall, or climbing down a vent, and on each attempt he discovered a freshly poured cement barrier with a sign telling him to go home. “I’ve never seen anything like it,” Kaminsky said, still in awe.

Kaminsky ticked off the skills Nakamoto would need to pull it off. “He’s a world-class programmer, with a deep understanding of the C++ programming language,” he said. “He understands economics, cryptography, and peer-to-peer networking.”

“Either there’s a team of people who worked on this,” Kaminsky said, “or this guy is a genius.”

Kaminsky wasn’t alone in this assessment. Soon after creating the currency, Nakamoto posted a nine-page technical paper describing how bitcoin would function. That document included three references to the work of Stuart Haber, a researcher at H.P. Labs, in Princeton. Haber is a director of the International Association for Cryptologic Research and knew all about bitcoin. “Whoever did this had a deep understanding of cryptography,” Haber said when I called. “They’ve read the academic papers, they have a keen intelligence, and they’re combining the concepts in a genuinely new way.”