ABSTRACT
Throughout the history of human civilization, the need for secure communication has been one of the top priorities. The word cryptography comes from two Greek words (kryptos = hidden) and (graphein = writing). In fact, the need to send concealed messages dates back to the Stone Age, when human beings started living in groups. As soon as these groups evolved, the level of trust among them deteriorated. Hence, the need to send messages among the allied groups/tribes in a hidden manner increased. As early as 1900 b.c., the Greeks wrapped a tape on a stick and wrote a message on the tape in a sequential manner. Upon unwinding the tape from the stick and reading the message, the text would be meaningless. To decipher the message, the receiver needed a stick with the same diameter as that of the sender. However, breaking this code was simply a matter of trying sticks with different diameters.
