There is something fascinating about secret codes. How many children have thrilled to the discovery of a simple substitution code where one letter replaces another such as in the example below.
Using this simple code, the word CAT would be written DBU.
"A B C D E F G H I J K L M N O P Q R S T U V W X Y Z" Original Text
"B C D E F G H I J K L M N O P Q R S T U V W X Y Z A" Coded Text
History is filled with examples of people who have reduced their thoughts to writing and then though ingenious methods, attempted to render these same words unreadable except to those in possession of the decoding mechanism. Cryptography or the study of codes and codebreaking, has taken on increasing importance. It has been said that the efforts of Allied cryptographers attacking the German Enigma and Japanese Purple codes during World War II were responsible for dramatically shortening the war.
If you doubt the importance of cryptography, you need only review the attempts of the US government to regulate Cryptography, from ITAR regulations, to the Clipper Chip, to the prosecution of Phil Zimmerman author of the code called Pretty Good Privacy (PGP), the government has thrown its resources behind slowing the wide deployment of strong encryption.
Applied Cryptography: Protocols, Algorithms, and Source Code in C by Bruce Schneier. The author is the President of Counterpane Systems and the author of the free newsletter Crypto-Gram. This book is an excellent and thorough introduction to modern cryptography. The book covers important ciphers in use up to, but not including the new Advanced Encryption Standard (AES) based on a block cipher called Rijndael. While not diving as deeply into the mathematical theory as some texts, Applied Cryptography provides more than just a review of the subject, it also delves into the politics of Cryptography helping you to understand why Cryptography has become controversial. It has been alleged that the terrorist organization which bombed the World Trade Center used modern Cryptography and Steganography (messages hidden in graphic image files or other objects) in order to communicate. Quoting from a blurb on the cover of Applied Cryptography "...The book the National Security Agency wanted never to be published...".
The Codebreakers; The Comprehensive History of Secret Communication from Ancient Times to the Internet by David Kahn. This is a fascinating and exhaustive history of codes and codebreaking. If you interested in the history of cryptography, this book provides a quite complete look at the subject along with the historical perspective to help you appreciate the importance of the work. The sections of the book dealing with the 20th century provide glimpses of the mathematics behind some of modern cryptographic theory. Codebreakers main strength is in chronicling the importance of codes throughout history. When you realize the fate of nations can hinge on decoding intercepted messages, you can start to appreciate the fascination and significance of the subject.
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