Once upon a time, you could buy illegal drugs anonymously online from a site called Silk Road. The postman would show up at your door with your gas bill, maybe a birthday card from mom, and some carefully packaged pot or heroin. Even though you had never met the person you bought the drugs from, the delivery came just as you ordered it. The FBI tore up the Silk Road, writes Brian Doherty. But they could not end the practice of selling drugs anonymously on the Dark Web.