In the span of a few years, cryptocurrencies have grown from digital novelties to trillion-dollar technologies with the potential to disrupt the global financial system. Bitcoin and hundreds of other cryptocurrencies are increasingly held as investments and used as currencies to buy a swath of goods and services, such as software, digital real estate, and illegal drugs. To their proponents, cryptocurrencies are a democratizing force, wresting the power of money creation and control from centr...