Just over a decade ago, Bitcoin appeared to many of its adherents to be the crypto-anarchist holy grail: truly private digital cash for the internet.Satoshi Nakamoto, the cryptocurrency’s mysterious and unidentifiable inventor, had stated in an email introducing Bitcoin that “participants can be anonymous.” And the Silk Road dark-web drug market seemed like living proof of that potential, enabling the sale of hundreds of millions of dollars in illegal drugs and other contraband for bitcoin while...