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Turning Grille

Tool for encryption and decryption of messages using the rotating grid (Fleissner) technique. Find out how to secure your communications with this historic cryptographic method.

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Turning Grille -

Tag(s) : Transposition Cipher

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# Turning Grille

## Turning Grille Decoder

 Rotation ⟳ Clockwise ⟲ Counter-Clockwise
 End After 4 rotations After all letters are done

## Turning Grille Encoder

 Grille Generate a random grid Use the following grid: (X = Hole)
 Rotation ⟳ Clockwise ⟲ Counter-Clockwise

### What is a turning grid cipher? (Definition)

The turning grille cipher, also known as the Fleissner grille, is a transposition encryption technique which consists of hiding a message by arranging its letters in a grid on which a removable and rotating cover allows the letters to be read/written to be selected.

### How to encrypt using a turning grid?

To encode a message with a rotating grid, the user places a perforated grid or sheet with holes on top of a blank grid.

Example: Encrypt the message FLEISSNERGRILLE with the grid

 ▮ ▮ ▮ ▮ ▮ ▮ ▯ ▯ ▮ ▮ ▮ ▯ ▯ ▮ ▮ ▮

The locations visible through the holes are then filled with the letters of the plain message.

Example:

 ▮ ▮ ▮ ▮ ▮ ▮ F L ▮ ▮ ▮ E I ▮ ▮ ▮

Once filled, the perforated grid is then turned a quarter turn, revealing new free spaces, which are in turn filled with the letters of the plain message.

Example:

1⟳
 S ▮ ▮ ▮ ▮ ▮ ▮ ▮ ▮ ▮ S ▮ ▮ N E ▮
2⟳
 ▮ ▮ ▮ R G ▮ ▮ ▮ R I ▮ ▮ ▮ ▮ ▮ ▮
3⟳
 ▮ L L ▮ ▮ E ▮ ▮ ▮ ▮ ▮ ▮ ▮ ▮ ▮ ▯

After 4 rotations, the grid is supposed to be full.

Reading the letter grid online constitutes the encrypted message.

Example: The message is encrypted SLLRGEFLRISEINEG from the grid obtained:

 S L L R G E F L R I S E I N E G

If the message contains more letters, then repeat the steps with the following letters and a new blank grid (but keeping the same perforated grid).

If the grid is not completely filled, insert random/neutral letters to fill in the holes.

The grid must respect certain rules so that the holes do not end up on the same letters after rotation.

### How to decrypt a message with a turning grid?

To decode a message encrypted with a spinning grid, the player places the perforated grid over the encoded text, aligning the holes with the characters.

The characters visible through the holes reveal the letters of the original message.

After 4 hourly rotations, the original message is completely reconstituted.

If the message contains more letters, then repeat the steps with the following letters.

### How to generate a valid grid?

The grid must have a quarter hole for every 3/4 non-hole. Since the holes successively occupy 4 positions, only one of these positions can contain a hole.

An easy way to avoid having duplicate holes is to separate the grid into 4 quadrants, then number the boxes as follows:

Make holes for each value, but limiting yourself to 1 hole per value (at any random location among the 4).

For odd-sized grids, ignore the central box.

### Why are these grids called Fleissner grilles?

The rotating grid method was detailed by the Austrian Colonel Edouard Fleissner von Wostrowitz, who detailed it in his work entitled Handbuch der Kryptographie. Although it cannot be said with certainty that he was the inventor, because encryption techniques using grids had existed for a long time, Fleissner's name remained associated with this method.

Jules Verne, in 1885, incorporated this cryptographic technique into his novel Mathias Sandorf, crediting it to Fleissner.

This type of grilles was used during the First World War by the German army. Each grid size had a code name: Anna 5×5, Berta 6×6, Clara 7×7, Dora 8×8, Emil 9×9, Franz 10×10.

### How to recognize a turning grid ciphertext? (Identification)

The encrypted message is a transposition of the letters, the coincidence index is similar to that of the plain text.

The presence of a punched card (or any other similar object) should bring to mind this method or the Cardan cipher.

Any reference to Mathias Sandorf or Jules Verne is a clue.

### How to decipher without grid? (Attacks)

Deciphering a message without having the corresponding grid is difficult.

Potential attacks include searching for recurring patterns in the ciphertext, statistical analysis of letters, but especially brute force methods. The number of permutations of the grid is relatively limited if its size is small.

### What are the variants of the turning grid cipher?

There are several variations of the rotating grille, including different sized racks or methods of rotating the grille clockwise or counterclockwise.

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Turning Grille on dCode.fr [online website], retrieved on 2023-09-27, https://www.dcode.fr/turning-grille-cipher

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