Cryptography (secret writing) has an intriguing history, and forms part of the history of intrigue. It has always also had a business application, since business people have wanted to keep secrets from their competitors. More recently it has entered the world of business in a more mundane way, because of public key cryptography, which allows businesses, banks, and credit card companies to broadcast to the world the key by which consumers can send them secret messages to transfer money or charge a credit card. How is it possible for them to do this without also giving away the secret to decoding those secret instructions? In this talk we will survey the history of cryptography and outline the principles of public key cryptography. The talk is intended to be intelligible to the general public.