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
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
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