Elementary Information Security, 3rd Edition

▶ 7.2 Encryption and Cryptanalysis

Encryption is deceptively simple. Anyone can create a secret code. The trick is to design a code that resists a sophisticated attack. People have been using codes for thousands of years. It seems likely that others have been breaking codes for almost as long. We call this process cryptanalysis. To understand encryption, we need a basic understanding of cryptanalysis.

Simple encryption is relatively easy to crack. Many newspapers publish cryptograms, short notes encrypted with a simple technique, as a puzzle for readers to crack. Potter’s encryption was not, in fact, much more difficult than a newspaper cryptogram. To understand the basic strategy for cracking simple encryption, consider the following example: ...