3.1. Introduction

Cryptography is a vast and difficult field that we cannot hope to cover in this book. Nevertheless, an understanding of the basics and an appreciation of some of the subtleties of cryptography are necessary for an understanding of what is to follow. Fortunately, just as with TCP/IP, several excellent texts are available for those who wish to delve deeper into its mysteriessee [Schneier 1996], [Ferguson and Schneier 2003], and [Menezes, Oorschot, and Vanstone 1996], for example.

In this chapter, we are concerned mainly with three major subjects:

Along the way, we shall also examine Diffie-Hellman key exchange and the use of certificates for authentication and key exchange.

As we shall see, there are two main types of ciphers used for encryption: symmetric and asymmetric. These two types generally serve different purposes but work together to provide a total solution. The symmetric ciphers are again divided into two main classes: block and stream. Both of these classes have their strengths and weaknesses, and we shall examine examples of each as we go along.

This chapter is more mathematical than the others, so some readers may want to skip the details and take in just the major points. On the other hand, the chapter covers the bare minimum needed for a reasonable understanding of modern cryptography, so interested readers may want to consult the references cited in the chapter.