Introduction to Encryption

Encryption is said to occur when data is passed through a series of mathematical operations that generate an alternate form of that data. The sequence of these operations is called an algorithm. To help distinguish between the two forms of data, the unencrypted data is referred to as the plaintext and the encrypted data as ciphertext. The security of encryption lies in the ability of an algorithm to generate ciphertext that is not easily reverted to the original plaintext.

In a very simple example, encryption of the word "secret" could result in "terces." Reversing the order of the letters in the plaintext generates the ciphertext. This is a very simple encryption - it is quite easy for an attacker to retrieve the original data. A better method of encrypting this message might be to create an alternate alphabet by shifting each letter by some arbitrary number. This is known as a substitution cipher, a form of encryption that is still used in puzzle books today.

For example, encrypting the word "secret" with an alphabet shifted by 3 letters to the right (Figure 1.) produces "vhfuhw." A substitution cipher simply exchanges one letter or word with another. This particular algorithm is called the "Caesar Cipher."

Normal alphabet: a b c d e f g h i j k l m n o p q r s t u v w x y z Alphabet shifted by 3: d e f g h i j k l m n o p q r s t u v w x y a b c Figure 1. The Caesar Cipher and the encryption of the word "secret"