Chapter 1 Historical Introduction Cryptology, the process of concealing messages, has been used for the last 4,000 years. It started at least as long ago as the Egyptians, and continues today and into the foreseeable future. The term cryptology is from the Greek κρυπτω or krypt´ os, meaning secret or hidden, and λoγoζ or log´ os, meaning science. The term cryptology has come to encompass encryption (cryptography, which conceals a message) and decryption (revelation by cryptanalysis). In this chapter we give a quick introduction to the main terms and goals of cryptology. Our intent here is not to delve deeply into the mathemat- ics we’ll do that in later chapters. Instead, the purpose here is to give a broad overview using historical examples to motivate the issues and themes. Thus the definitions are less formal than later in the book. As this is a cryptography book, we of course highlight the contributions of the field and individuals in the stories below, though of course this cannot be the entire story. For example, even if you know the enemy’s plan of attack, men and women must still meet them in the field of battle and must still fight gal- lantly. No history can be complete without recalling and appreciating the sacrifices many made. Below we provide a brief introduction to the history of cryptography there are many excellent sources (such as [45]) which the interested reader can consult for additional details. Later chapters will pick up some of these historical themes as they develop the mathematics of encryption and decryp- tion. This chapter is independent of the rest of the book and is meant to be an entertaining introduction to the subject the later chapters are mostly mathematical, with a few relevant stories. For the most part, we only need some elementary number theory and high school algebra to describe the problems and techniques. This allows us to cast a beautiful and important theory in accessible terms. It’s impossible to live in a technologically complex society without encountering such is- sues, which range from the obvious (such as military codes and deciphering terrorist intentions) to more subtle ones (such as protecting information for online purchases or scanning purchases at a store to get the correct price 1 http://dx.doi.org/10.1090/mawrld/029/01

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