“I first heard about Bitcoin in 2011,” Green says. “I downloaded the code, which was a mess, tried to understand it, and I couldn’t believe that it worked. One of the places that it didn’t do things very well is privacy—every time you make a transaction, you’re leaving a trail.

“I started looking for interesting things to do with it. I was just a researcher looking for research problems, and this was one of them. I fooled around with it a bit until my wife yelled at me to stop using the computer on vacation.”

When the vacation expired, Green’s curiosity about what he calls “the real currency/digital currency interface” did not.

“One of the biggest things that Bitcoin offers is that we can take these things and spend them, and the system is not going to allow you to make copies of them,” he says. “The problem with electronic data in general is that it can be copied. In fact, computers are the ultimate copying machines since that’s basically all they do.

“However, most physical cash relies on the idea that you can’t make copies of coins and bills. This is the reason that electronic cash is a hard problem. What Bitcoin does is make it hard for someone to spend the same money twice.

“The other part is that it’s easy to transact bitcoins. You can have lots of other unique and valuable things in limited quantities—like, say, the Alps—but they are large things that you can’t move around.”

It was Miers, Green says, who came up with “the really good idea I wish I had—“why don’t we just fix Bitcoin using its own software to make a better version?”

“We are building an entirely new Bitcoin protocol,” Green says. “We are not going to mess with the block chain, peer-to-peer features that Bitcoin was built on. Zerocoin is a technology that you can paste into something like Bitcoin so that it still has everything that Bitcoin has, and now it’s completely anonymous.

“We are going to use the same technology to make it possible for Alice to transfer money to Bob without anyone knowing who Alice and Bob are.”

“People have been predicting the demise of paper currency for decades,” says John Driscoll an adjunct professor of economics at Johns Hopkins’ Krieger School of Arts and Sciences. “Bitcoin is just the latest in a long string of how we make payments. To some people, the privacy aspect is very appealing, for the same reason why people use currency because it’s anonymous.”

Driscoll recognizes that “there may be people who just aren’t comfortable with the government’s knowing what they’re doing. These people may be looking for an alternate store of value—a way to hold their wealth.” (True believers remain a small minority. Driscoll surveyed 150 of his students and found that only three had experience in “mining” Bitcoin.)

“When I think about Bitcoin,” Driscoll says, “I am reminded of the situation in the United States in the early 19th century when there was no central bank. When you got a note, say it was from the First National Bank of Wichita, the first thing you asked yourself was, ‘Is this counterfeit or not?’ With Bitcoin, if I’m convinced that it’s not fake, my next question is, ‘Is this exchange going to give me full value for it?’

“On the privacy issue, paper currency has this privacy feature built into it. If these [Bitcoin] people can solve the privacy issue and create a currency that is private from the government, then you’re trusting that the people who create it aren’t sneaking in the back door.”

“We’re building a system that will not have a back door,” Matt Green insists. “We’re building a system that even we don’t know how to break.

“We’re going to make a clone of Bitcoin, make it up and play with it. Build a technology, write a code, and put it out there. Maybe the government comes down on it like a ton of bricks. Or maybe nobody will want it; maybe we’re overselling ourselves.

“This is a bunch of grad students and university professors. We’re not looking for investment, and we’re not looking to get rich.”

(“Well, for the record, I wouldn’t mind getting rich,” Green says. Funding for his research comes from sources that include U.S. Naval Research Labs, DARPA, and U.S. Air Force Research Labs grants.)

“I don’t know if it’s going to replace MasterCard and VISA because there is one particular problem that MasterCard and VISA solve, which is what happens when somebody steals your wallet.”

This is not idle conjecture. Green was mugged in Palo Alto, California, of all places, about a dozen years ago, but his wallet was full of refundable traveler’s checks. “Always carry traveler’s checks,” his father would preach, back in Vermont. “It’ll be much safer.”

“What about cash? Will cash fade away?” the go-to guru is asked.

“Electronic money is so much more convenient,” he answers. “Cash is a real pain.”