A seemingly run-of-the-mill trial is playing out in Florida: The family of a deceased man is suing his former business partner over control of their partnership’s assets. In this case, the assets in question are a cache of about one million bitcoins, equivalent to around $64 billion today, belonging to bitcoin’s creator, the pseudonymous Satoshi Nakamoto. The family of the dead man says he and his business partner together were Nakamoto, and thus the family is entitled to half of the fortune. For bitcoiners, there is only one piece of evidence that could conclusively prove the identity of Satoshi Nakamoto:...