Polybius Square - Telegraphy and Steganography

Telegraphy and Steganography

Polybius did not originally conceive of his device as a cipher so much as an aid to telegraphy; he suggested the symbols could be signalled by holding up pairs of sets of torches. It has also been used, in the form of the "knock code", to signal messages between cells in prisons by tapping the numbers on pipes or walls. In this form it is said to have been used by nihilist prisoners of the Russian Czars, and also by American prisoners of war in the Vietnam War. Indeed it can be signalled in many simple ways (flashing lamps, blasts of sound, drums, smoke signals) and is much easier to learn than more sophisticated codes like the Morse code. However, it is also somewhat less efficient than the more complex codes.

The simple representation also lends itself to steganography. The figures from one to five can be indicated by knots in a string, stitches on a quilt, letters squashed together before a wider space, or many other simple ways.