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Basis of Cryptography • Chapter 9 541

Concepts of Using Cryptography

Cryptography is a word derived from the Greek kryptos (“hidden”), and the use of
cryptography pre-dates the computer age by thousands of years. In fact, the history
of cryptography was documented over 4000 years ago, where it was first allegedly
used in Egypt. Julius Caesar even used his own cryptography called Caesar’s Cipher.
Basically, Caesar’s Cipher rotated the letters of the alphabet to the right by three
(e.g., S moves to V and E moves to H). By today’s standards, the Caesar Cipher is
extremely simplistic, but it served Julius just fine in his day. Keeping secrets has long
been a concern of human beings, and the purpose of cryptography is to hide infor-
mation or change it so that it is incomprehensible to people for whom it is not
intended. Cryptographic techniques include:

■ Encryption Involves applying a procedure called an algorithm to plaintext
to turn it into something that will appear to be gibberish to anyone who
doesn’t have the key to decrypt it.
■ Steganography A means of hiding the existence of the data, not just its
contents.This is usually done by concealing it within other, innocuous
data.

EXAM WARNING

The words cryptography and encryption are often used interchangeably,
but cryptography is a much broader term than encryption; encryption is
a form of cryptography. In other words, all encryption is cryptography,
but not all cryptography is encryption.

This section looks at some of the concepts and motivating factors behind the
use of cryptography.

Confidentiality

The first goal of cryptography is confidentiality (covered in Chapter 1).Through the
use of cryptography, users are able to ensure that only an intended recipient can
“unlock” (decrypt) an encrypted message. Most modern algorithms are secure
enough that those without access to the message “key” cannot read the message.
Thus, it is extremely important to keep the secret key (when using symmetric algo-

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