Computer Security Basics, 2nd Edition

Chapter 7. Encryption

The study of encryption is called cryptography, from the Greek kryptos meaning “hidden,” and graphia, meaning “writing.” The process of trying to decrypt encrypted information without the key (to “break” an encrypted message) is called cryptanalysis. The study of code creation and breaking together is sometimes referred to as cryptology. To write something in a cipher so that only those authorized to do so can decode and read it is called encryption.

Encryption is an ancient form of information protection that dates back 4,000 years. Encryption has taken on new significance in the modern computer age. It’s a particularly effective way to protect sensitive information—for example, passwords —that’s stored in a computer system, as well as information that’s being transmitted over radio or microwave channels and communications lines.

By changing or substituting or scrambling the order of letters and words, encryption has through the ages protected communications while they were being transmitted through a hostile environment—usually one involving war or diplomacy. Of course, once the message is received, it must be unencrypted to be meaningful. Thus begins the fascinating story of cryptography, literally “secret writing,” much of which forms the basis for computer and network security today.

Hundreds or even thousands of years ago, messages worthy of encryption might have included letters from a battlefield general to the home front. Encryption protected the communication ...