People laughed at the Winklevoss twins in 2012 when they started buying up bitcoin – lots of it.

The two Harvard-educated entrepreneurs bought about 120,000 bitcoins when they were less than $10 each, using funds they got from settling a lawsuit against Mark Zuckerberg over their claim that they came up with the idea for Facebook.

But nobody’s laughing at Cameron and Tyler Winklevoss anymore. They confirmed in an interview with The New York Times that they had held on to their bitcoins as the price has skyrocketed – a coin was worth about $17,800 on Tuesday afternoon.

Their bitcoin fortune is now worth about $1.3 billion, The Times reported.

“We’ve turned that laughter and ridicule into oxygen and wind at our back,” Tyler Winklevoss told The Times.

A fortune that large needs protection. Because bitcoin is a digital currency, it can be stolen in a hack. Earlier this month, for example, one cryptocurrency-mining service said hackers had taken $80 million in bitcoin.

The Winklevoss twins use what’s called a “cold wallet” system to store their bitcoin fortune.

Bitcoin resides in electronic “wallets,” and each has a private key. If someone has that key, they can take your bitcoin. Printing the key – and keeping it off the internet – helps protect it from people trying to steal it.

The Winklevoss twins take it one step further – they cut up a paper printout of their private key, then stored the pieces in banks around the country.

Here’s how The Times explains it:

“The Winklevosses came up with an elaborate system to store and secure their own private keys. They cut up printouts of their private keys into pieces and then distributed them in envelopes to safe deposit boxes around the country, so if one envelope were stolen the thief would not have the entire key.”

The Winklevosses say they use a similar system for Gemini, the bitcoin exchange they created that’s licensed in New York to hold the cryptocurrency on behalf of banks and traders. That’s because if the Winklevosses were to lose their bitcoin billions, that would be a tragedy for them – but if their exchange were hacked, there would be a lot of angry financiers looking for answers.

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