Grille
The grille method, was developed by the French Cardinal Richelieu in the 1600's. Its purpose was to send a secret message that could only be deciphered by a special card punched with holes in strategic locations. While it is no longer feasible for use in computers, it is still an effective method for sending physical, encrypted messages today. The picture below shows a plain message and the associated grille card that is used to decipher the secret message from the plain message.



A grille message can be created in two different ways: Write a message and then create a grille card just for that message, then create a master grille card and write message to fit within the predetermined hole punched locations.

In the example above the message was written out and the grille card was punched out as needed to create the secret message. Since the message was fairly long it was easy to get all the necessary characters to create the secret message "Is it not human to err." However, the encipherer now needs to create a second grille card for the recipient and must get both the grille card and the secret message to the recipient using separate means. Otherwise an interception could easily mean the message is successfuly deciphered.

A better, but more complicated method, for creating a grille method is to make up a set of master grille cards that have hole punches in the same location on each card. Then the message is written in so that the letters for the secret message land in the grille punched locations.