Cryptography has emerged as an enormously important component of the networked world. People are hesitant to trust the World Wide Web and e-commerce without the protections crypto provides. As companies build Virtual Private Networks, demand secure communications and require stronger authentication techniques, more and more applications are built with crypto as core components. Many cryptographic algorithms are virtually unbreakable ... if used properly. If applied incorrectly, it doesn't matter how strong an algorithm or key is, the tools of crypto will provide no protection. This paper will describe some of the blunders people have made over the years in their use of cryptography. Some of these mistakes made headlines, some did not. Some might even be a little humorous -- to those not involved. If nothing else, readers will learn what not to do in their products.