Cryptography Reference
In-Depth Information
Chapter 2
Cryptology from the Romans
to World War II
Now that we have talked about the cryptology landscape more than about
cryptology itself, let's get to the point. We begin with pretty simple algorithms,
which, unfortunately, still play a role. But first, let's define several terms. You
will probably be familiar with some of them:
Plaintext: This is the original text to be encrypted.
Ciphertext: This is the encrypted text.
Cryptography: This is the science of designing encryption algorithms.
Cryptanalysis: This is the art of recovering an encrypted text (or at
least clues about it) without knowing the key. The process is called code
breaking or compromising . An algorithm that doesn't resist cryptanaly-
sis (except perhaps for an uninteresting special case) is said to have been
broken, compromised ,or cracked .
A plaintext attack is the cryptanalysis of a ciphertext, where parts of the plain-
text are known. This type of attack is generally much more effective than the
pure analysis of a ciphertext. Plaintext attacks play a major role in this chapter.
Enough theory for the time being. Just check out the Glossary if you have
problems with one term or another. You should find it there (and if you don't,
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