The field of cryptography was already of great importance before the advent of the computer. People have always had the wish to send messages in such a form that only the recipient could read them. Julius Caesar is known to have devised a method for encoding messages. In the course of centuries, other and better methods were developed. The famous ENIGMA cypher machine comprised a step in the direction of the efficient mechanization of encoding. Its messages could only be successfully decoded with the help of the first computers. Today’s encoding techniques with computers are much more complicated and, moreover, must be changed and developed constantly because decoding methods are keeping pace with them.