For as long as people have been communicating, the Bobs and Alices of the world have looked for secure ways to share and hide meaning. When people began using written language to reveal meaning, fields such as cryptography and cryptanalysis were created by the clever mathematical and linguistic minds among us. These people like to make and solve puzzles and often spend lifetimes doing it. Some make a living at it, whereas others only dabble; many contribute to the field. Over time, many good ideas and systems have been created but not fully understood, recognized, or used until much later.
To stay one step ahead of cryptanalysts, cryptographers have invented various ingenious ways to hide meaning. Although computers have made many older methods obsolete, technology has put cryptographic minds to work in new ways.
If you want to lay a good foundation for looking at computerized disguising techniques, the first step is to understand how complexity affects a cryptographic system. So before we clarify how todays computer methods work, lets take a brief look at the history of the cryptographic craft, starting with simple methods and leading up to the more complex. In the next two chapters well discuss the two major components of ancient and modern secret key cryptography: substitution and transposition.
The Father of American Cryptography
Thomas Jefferson earned the title Father of American Cryptography for a device he called a wheel cipher. It remained undiscovered for nearly a century until two othersa Frenchman and an Americanindependently created the same device. Although the wheel cipher was a good method for its time, Jefferson put it aside and apparently forgot about it. In 1922, the year the device was discovered in the Library of Congress among Jeffersons papers, the U.S. Army adopted an almost identical cipher mechanism others had developed.