Cryptography (from Greek , hidden, and , writing), in one form or another has probably been practiced ever since man has communicated his thoughts in speech or writing.
One of the oldest known examples is the Spartan scytale.
Over 2500 years ago, Spartan goverment sent secret messages to its generals in the following clever way.
Sender and recipient each had a cylinder (called a scytale) of exactly the same radius. The sender wound a narrow ribbon of parchment around his cylinder, then wrote on it lengthwise. After the ribbon is unwound, the writing could be read only by a person who had a cylinder of exactly the same circumference.
Try it out yourself! The Spartan Scytale * The circumference has to be smaller than the message, otherwise, the message will stay the same.
Considerable interest and adeptness in cryptography were developed during the sixteenth, seventeenth, and eighteenth centuries. It was the custom in those days for people of importance to have private ciphers. For the most part they were based on substitution, either with letters of phonetic symbols, and were nearly always so complicated that the key could not be memorized but had to be reduced to writing. In this respect they had a disadvantage inherent in codes -- both correspondents had to have copies of the key.
The story of the development of military cryptography through the eighteenth, nineteenth, and twentieth centuries would fill volumes. The effects of secret writings upon the outcome of wars, and the devices used have ranged from the writing of hidden messages in a musical score to the arrangement of the fifty-two cards in a pack so that their order carried information.
However, the employment of cryptography has not been confined to the purposes of diplomacy and warfare. It has been widely used for the sake of economy [...to be continued...]