Grille

History

The turning grille was developed by the Italian physician, mathematician and astrologer Girolamo Cardano (1501-1576).

Description

It takes the form of a square grille through which a quarter of the holes are cut out. The plaintext is written through each hole then the grille is turned 90º and the next section of plaintext is entered into the holes. This is repeated twice more to fill each cell. Care must be taken when selecting the position of the holes to ensure that every cell is revealed after rotating the grille in each position. The size of the grille is determined by the plaintext length and if an odd size grille is used, e.g. 5x5, 7x7 etc., the middle square is filled with a random letter.

Using the quote "Action will destroy your procrastination" by American author Og Mandino as an example a 6x6 grid is created and a quarter of the cells (9) are selected, let's say cells 1,2,5,11,21,24,27,28 and 34. The first 9 letters of the plaintext are written into the selected cells of the grid then the grille is rotated to reveal cells 6,12,15,16 etc. and the next 9 letters are entered. This process is repeated until all the plaintext is written into the grid and all the cells are filled. The grille is then removed revealing all 36 letters which are read off horizontally producing the cipher.

If the ciphertext length is a multiple of the length used a message will appear suggesting splitting the text before trying again. For example, a ciphertext of length 72 is not a complete square but two 6x6 grids could have been used to decipher it.

Example

Key: 1,2,5,11,21,24,27,28,34

Plaintext: Action will destroy your procrastination.

Plaintext:  Action will destroy your procrastination.

Ciphertext: ACOST LTIUR IDPES RNATR OTINO OWIOY NCYLR A

Solving

Solving method: Hill Climbing search.