My objective in writing this book was to produce a general, comprehensive textbook that treats all the essential core areas of cryptography. Although many books and monographs on cryptography have been written in recent years, the majority of them tend to address specialized areas of cryptography. On the other hand, many of the existing general textbooks have become out-of-date due to the rapid expansion of research in cryptography in the past 15 years.

I have taught a graduate level cryptography course at the University of Nebraska-Lincoln to computer science students, but I am aware that cryptography courses are offered at both the undergraduate and graduate levels in mathematics, computer science and electrical engineering departments. Thus, I tried to design the book to be flexible enough to be useful in a wide variety of approaches to the subject.

Of course there are difficulties in trying to appeal to such a wide audience. But basically, I tried to do things in moderation. I have provided a reasonable amount of mathematical background where it is needed. I have attempted to give informal descriptions of the various cryptosystems, along with more precise pseudo-code descriptions, since I feel that the two approaches reinforce each other. As well, there are many examples to illustrate the workings of the algorithms. And in every case I try to explain the mathematical underpinnings; I believe that it is impossible to really understand how a cryptosystem works without understanding the underlying mathematical theory.

The book is organized into three parts. The first part, Chapters 1-3, covers private-key cryptography. Chapters 4–9 concern the main topics in public-key cryptography. The remaining four chapters provide introductions to four active research areas in cryptography.