Bitcoin offers privacy -- as long as you don't cash out or spend it

Most users do not use sophisticated methods that would more deeply mask their transactions

By , IDG News Service |  Security

Not the best way to launder your ill-gotten gains

Image credit: flickr/BTC Keychain

On the surface, Bitcoin seems to be a great way to hide cash. Actually, it's a terrible way to launder money.

That's the conclusion of a new academic study that analyzed Bitcoin's blockchain, or the public ledger that records bitcoin transactions. The ledger shows how bitcoins move from one person to another, represented by 34-character alphanumeric addresses.

It's a sea of numbers without names. But researchers from the University of California at San Diego and George Mason University found it is a lot harder to convert bitcoins to cash -- or spend the bitcoins with a service -- and stay anonymous due to the ledger.

Most bitcoin users interact with a service to buy or sell the virtual currency. These days, most of those services want to know exactly who they're dealing with, especially as regulators around the world take an increasing interest in bitcoin.

Using special algorithms, the researchers were able to associate large numbers of seemingly anonymous bitcoins addresses with certain major services such as exchanges and payment processors, said Sarah Meiklejohn, a doctoral candidate in computer science at UC San Diego, who assisted in the research.

By analyzing those transactions, they found it is possible to somewhat deanonymize bitcoin users, opening up avenues through which investigators could reveal the people behind them.

For example, they linked more than 500,000 Bitcoin addresses with Mt. Gox, a popular exchange in Japan where users buy and sell bitcoins. Mt. Gox requires identification from its users, often including a scan of their passport. It wouldn't make sense for a hacker to cash out a large number of bitcoins there.

"We haven't uncovered the identity of the thief, but we've paved the way for law enforcement or an agency with subpoena power to do exactly that," Meiklejohn said.

The researchers analyzed details from bitcoin thefts. While there are sophisticated methods that can be used to cloud whether a bitcoin is indeed still held by a thief, many thieves became lazy after initially moving stolen funds around, Meiklejohn said.

"Maybe thieves and other criminals in the future are going to become a lot more sophisticated, but I think so far, people have not been particularly careful," she said.

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