The good professor, tapping his decades of hands-on experience, including IBM and the NSA, walks us through an introduction to hashing, with a little history here, a little math there. Its all kept at an elementary level, and is somewhat cursory, now and then eschewing a proof or explanation in favor of providing a reference to another source. There is even some humor, for example regarding perfect hashing: "In a perfect world there would be no crime, deans or collisions...".Unfortunately, the text is at times bizarrely sloppy. You might easily arrive at the conjecture that some chapters were based on notes handed to assistants who cobbled them together, despite having English as a second language. Sometimes this sloppiness engenders incorrectness. Shame on Wiley for not having someone at least skim through and catch errors.On the bright side, many chapters end with a References section, great for those interested in the history of it all.If you want the SHA-256 algorithm, you'll get most of it here, but will have to resort to Wikipedia for the full Monty.