THE art of transmitting information by means of writings designed to be understood only by the persons who have especially agreed upon the significance of the characters employed was known and practised by the ancients long before the Christian era. It has many high-sounding names, among which will be found cryptography, cryptology, polygraphy, stenganography, cipher, etc. The first is what might be styled its scientific name; the latter the one commonly used by the foreign offices.
The oldest example of secret writing is the Spartan scytale. According to Plutarch, the Lacedæmonians had a method which has been called the scytale, from the staff employed in constructing and deciphering the message. When the Spartan ephors, who, in the fourth century B.C., were the supreme power of the state, controlling alike its civil and military administration, wished to forward their orders to their commanders abroad, they wound slantwise a narrow strip of parchment upon a staff so that the edges met close together, and the message was then written in such a way that the center of the line of writing was on the edges of the parchment. The parchment was then unwound and sent to the general, who, by winding it upon a similar staff, was enabled to read the message.
Various other devices of secret writing were practised by the old Greeks and Romans. All served their purpose, and some of them were remarkably ingenious. One, by reason of its being not only very ingenious, but at the same time highly ludicrous, seems worthy of mention. It was the one which Histiæus, while at the Persian court, employed to advise Aristagoras, who was in Greece, to revolt. As the roads were well guarded, there seemed to Histiæus only one safe way of making his wishes known. He chose one of his most faithful slaves, and, having shaved his head, tattooed it with his advices; then keeping him till the hair had grown again, Histiæus despatched him to Aristagoras with this message: “Shave my head and look thereon.”
Among the Greeks many systems of cipher were employed to transmit messages during war-times. To illustrate one, let us suppose that the English alphabet, by omitting the letter j, consists of twenty-five letters; then arrange these thus:
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