Chapter Two. Fundamentals of Cryptography

This chapter introduces many of the basic ideas that are required for fully understanding several subsequent chapters. Our purpose is to introduce terminology and concepts, and we consider several simple, classical cryptographic algorithms as examples. These concepts are used in later chapters where more sophisticated algorithms are discussed.

This chapter also gives some interesting historical perspectives on cryptography. The remainder of the book provides a great deal more current, practical information, covering many modern cryptographic and security techniques. Some chapters also delve into the use of the Microsoft .NET Security Framework for implementing many aspects of cryptography and security. Of course, if you are already familiar with basic cryptographic terminology and concepts, you may safely skip this chapter.

The title of this book refers to security and cryptography, which are closely interrelated at a fundamental level. Security comes in many flavors, but the basic idea is always the same: preventing something dangerous or undesirable from happening. For example, you may wish to ensure that only authorized users are permitted to perform certain operations on certain computing resources or to control access to sensitive information. Computer security is ultimately based on the science of cryptography. For example, Kerberos, ^[1] which is a powerful network security protocol for authenticating users, and .NET evidence-based security, which is used to secure executable code, are both based on strong underlying cryptographic technologies.

^[1] Kerberos is the authentication system of MIT's Project Athena, based on symmetric key cryptography. The Greek name Kerberos (also known by the Latin spelling Cerberus ) was the name of the three-headed guard dog at the entrance to Hades in Greek mythology. With a name like that, it's got to be secure!