Prehistory of Cryptography - A Classical Introduction to Cryptography: Applications for Communications Security - page 1

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Prehistory of Cryptography

Content

Foundation: history, vocabulary, transpositions, substitutions
Basic ciphers: simple substitution, Vigenere, Vernam
Modern settings: digital communications, Kerckhoffs principles

The Shannon Theory of secrecy: entropy, encryption model, perfect secrecy

Cryptography distinguishes itself from coding theory in the sense that the presence
of random noise in the latter is replaced by malicious adversaries in the former. It uses
a specific vocabulary and relies on some fundamental principles which are presented
in this chapter. We also expose historical cases which are relevant for our analysis, and
survey the Shannon Theory of secrecy which was an attempt to make cryptography rely
on information theory. Unfortunately, the goals of achieving “perfect” secrecy were too
ambitious and impossible to achieve in practice at a reasonable cost.

1.1 Foundations of Conventional Cryptography

1.1.1 The Origins of Cryptography

As an easy introduction, we can say that, strictly speaking, cryptography begins with
history: with the origin of language writing. As an example, the Egyptians were able
to communicate by written messages with hieroglyph. This code was the secret of a
selected category of people: the scribes. Scribes used to transmit the secret of writing
hieroglyph from father to son until the society collapsed. It was only several millenia
later that this secret code was broken by Champollion.

Although Egyptian codes are quite anecdotal, history includes many other cryp-
tographic usages. 1 Communication with secret codes was commonly required

for diplomacy: governments had to communicate with their remote embassies in
suspicious environments,
during war: army headquarters had to communicate through hostile environments,
for individual or corporate privacy: some people wanted to be protected against
their neighborhood (against jealous spouses, against dictatorships, etc.), com-
panies wanted to protect their assets against competitors.

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See Ref. [173] for other examples, or Ref. [98] for references on history.