Cryptography Reference
In-Depth Information
is not to provide an exhaustive account.
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Rather, I aim to situate crypto-
graphic techniques within their material and social context, including
medium of transmission, modes of encoding, operating procedures, politi-
cal and military organization, and the contrary means developed to defeat
their security objectives. Such contextualization highlights how the effec-
tiveness of cryptographic systems cannot be reduced to their mere math-
ematical strength but must necessarily evaluate within the broader
environments of their deployment. At the same time, this historical over-
view provides the opportunity to present basic vocabulary, concepts, and
techniques of cryptography so as to build expertise for the arguments
developed in the rest of the topic.
Paper
Although traces of cryptographic activity have been found in most ancient
civilizations from Mesopotamia to the Roman Empire, the systematic
development of codes and ciphers awaited the flowering of modern Euro-
pean diplomacy in the sixteenth century. In 1542, for example, the Vene-
tian state employed three “cipher secretaries” assigned to the development
of such techniques. Though they enjoyed a relatively high status within
Venetian society, betrayal of the cryptological secrets in their possession
was deemed worthy of punishment by death.
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As ciphers increasingly
gained in sophistication, so did the methods for solving them: by the
eighteenth century, most European nations had established “black cham-
bers,” secret organizations specializing in deciphering foreign diplomatic
dispatches. By the 1850s, the principles of good cipher construction were
fairly well developed, if not widely disseminated and necessarily under-
stood in mathematical terms. Classical ciphers relied on two basic methods,
monoalphabetic
and
polyalphabetic
substitution, often combining the two
in
codebooks.
Monoalphabetic Substitution
For each letter of the alphabet, this technique substitutes another one. For
example, the famous Caesar Cipher constructed the
ciphertext
(the enci-
phered message) by substituting each letter used in the
plaintext
(the origi-
nal message) with the letter located five places after in the alphabet. If the
letters are converted to numbers (A = 1, B = 2, etc.), this corresponds to
