Ball, W. W. Rouse (Walter William Rouse), 1850-1925 · London, Macmillan · leaf 421
ing, but in it are introduced a number of dummies or nonsignificant letters or digits thus concealmg which of the letters are relevant. , One way of picking out those letters which are relevantis by the use of a perforated card of the shape of (say) asheet of note-paper, which when put over such a… … way may be easily concealed from anyone who does not possessa card of the same pattern. If the recipient possesses such CH. XVIIl] CKYlTOGRAPHS AND CIPHERS 401 a card he has only to apply it in order to read the message.This method was used by Richelieu. The use of the grille may be rendered less…
Geometry · Cryptography · Ciphers
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