| Alphabet of plain text | abcdefghijklmnopqrstuvwxyz |
| Alphabet of cipher | zyxwvutsrqponmlkjihgfedcba |
and Washington would be spelled dzhsrmtglm.
A letter from John Devoy, an Irish-American, exposing his hand in a plot with the Germans to foment revolution in Ireland
Perhaps the cleverest transposition cipher ever devised—it is so good that the British Army uses it in the field and, moreover, has published text books about it—is the very simple “Playfair” cipher. First a square is drawn, divided into fifths each way. This arrangement gives twenty-five spaces, to contain the letters of the alphabet—I and J being put in one square because there would never be any plain sentence in which it would not be quite obvious which one of them is needed to complete a word of which the other letters are known.
Next a “key word” is chosen—and herein lie the cleverness and the simplicity of this cipher, because every time the key word is changed, the whole pattern of the alphabet is changed. Suppose the key word is Gardenia. It is now spelled out in the squares:
The second A is left out, as there must not, of course, be duplicates on the keyboard. Now the rest of the alphabet is written into the squares in their regular sequence: