HTTP Developer’s Handbook

Symmetric Cryptography

When two parties want to send and receive information that only they can interpret, the traditional method is for the two parties to share a secret that explains how to encode and decode the messages. For example, assume that the messages only consist of capital letters of the Latin alphabet (A-Z). The two parties could agree to an encoding system where each letter is exchanged with another letter according to the following chart:

Decoded   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 
Encoded   Q W E R T Y U I O P A S D F G H J K L Z X C V B N M 

Thus, a message that is encoded using this format can be decoded as long as the receiving party has this secret chart. The following example illustrates this encoding:

 Decoded ...