Summary form only given. Information has always been valuable, never more so than in recent decades, and throughout history people have turned to cryptography in an attempt to keep important information secret. Coherent manipulation of quantum states promises to rearrange the lists of possible and impossible cryptographic tasks. The author gives an overview of the changes, including Shor's algorithm to break classical codes with a quantum computer and protocols for quantum key distribution using single photons to perform unbreakable encryption. One useful classical technique is the idea of a public key, which can be safely handed out even to an adversary. The author shows how to create quantum protocols with similar properties, and how they can be used to create unbreakable digital signatures.