Of the existing 18.5 million Bitcoin, around 20 percent — currently worth around $140 billion — appear to be in lost or otherwise stranded wallets, according to the cryptocurrency data firm Chainalysis. Wallet Recovery Services, a business that helps find lost digital keys, said it had received 70 requests a day from people who wanted help recovering their riches, three times the number of a month ago.

The cryptocurrency’s unusual nature has meant that many people are locked out of their Bitcoin fortunes as a result of lost or forgotten keys. They have been forced to watch, helpless, as the price has risen and fallen sharply, unable to cash in on their digital wealth.

Bitcoin owners who are locked out of their wallets speak of endless days and nights of frustration as they have tried to get access to their fortunes. Many have owned the coins since Bitcoin’s early days a decade ago, when no one had confidence that the tokens would be worth anything.

The quandary is a stark reminder of Bitcoin’s unusual technological underpinnings, which set it apart from normal money and give it some of its most vaunted — and riskiest — qualities. With traditional bank accounts and online wallets, banks like Wells Fargo and other financial companies like PayPal can provide people the passwords to their accounts or reset lost passwords.