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Modern Cryptanalysis: Techniques for Advanced Code Breaking by Christopher Swenson

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Chapter 1. Simple Ciphers

As long as there has been communication, there has been an interest in keeping some of this information confidential. As written messages became more widespread, especially over distances, people learned how susceptible this particular medium is to being somehow compromised: The messages can be easily intercepted, read, destroyed, or modified. Some protective methods were employed, such as sealing a message with a wax seal, which serves to show the communicating parties that the message is genuine and had not been intercepted. This, however, did nothing to actually conceal the contents.

This chapter explores some of the simplest methods for obfuscating the contents of communications. Any piece of written communication has some set of symbols that constitute allowed constructs, typically, words, syllables, or other meaningful ideas. Some of the simple methods first used involved simply manipulating this symbol set, which the cryptologic community often calls an alphabet regardless of the origin of the language. Other older tricks involved jumbling up the ordering of the presentation of these symbols. Many of these techniques were in regular use up until a little more than a century ago; it is interesting to note that even though these techniques aren't sophisticated, newspapers often publish puzzles called cryptograms or cryptoquips employing these cryptographic techniques for readers to solve.

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