Stefan Thomas, a German-born programmer living in San Francisco, has two guesses left to figure out a password that is worth, as of this week, about $220 million, according to a New York Times report.

If he can figure out the password, it will enable him to unlock a small hard drive, known as an IronKey, which contains the private keys to a digital wallet holding 7,002 Bitcoin.

The problem is that Mr. Thomas years ago lost the paper where he wrote down the password for his IronKey, which gives users 10 guesses before it seizes up and encrypts its contents forever. He has since tried eight of his most commonly used password formulations — to no avail.

“I would just lie in bed and think about it,” Mr. Thomas said. “Then I would go to the computer with some new strategy, and it wouldn’t work, and I would be desperate again.”

Thomas’s plight has aroused the attention of hard drive and password crackers, offering their services for a piece of the quarter-billion-dollar pie. Alex Stamos, an internet security expert at Stanford Internet Observatory, claimed he can crack the password within six months. However, Mr Stamos is demanding a 10 per cent cut of the fortune.

“Um, for $220m in locked-up bitcoin, you don’t make 10 password guesses but take it to professionals to buy 20 IronKeys and spend six months finding a side-channel or uncapping,” Mr Stomas said on Twitter.

“I’ll make it happen for 10%. Call me.”

Mr Thomas was paid the Bitcoin for making a video about how the cryptocurrency worked, when it was worth around $5 a coin. Last week, on the back of a record-breaking run, Bitcoin was trading at more than US$40,000.

While the price of Bitcoin dropped sharply on Monday, it is still up more than 50 percent from just a month ago when it passed its previous all-time high around $20,000.

(Vosizneias)