Maxim Integrated’s introduction to SHA security. Link here (PDF)
This application note goes over the basics of Secure Hash Algorithms (SHA) and discusses the variants of the algorithm. It then briefly touches on how the algorithm is used for authentication, including the concept of a Hashed Message Authentication Code (HMAC). It concludes by looking at some of the Maxim secure authenticators that can be used to very easily deploy SHA algorithms for security applications.