Cardan Grille

Cardan Grid is a steganographic encryption technique consisting of a cover/mask pierced with windows. Superimposed on a blank sheet of paper, it allows a hidden message to be written, which is then supplemented with innocuous text to disguise the secret content.

Cardan encryption uses another text (understandable or not) of which only a few letters are from the original text.

In practice, Cardan uses a mask, a grille in which some cells are opaque, others empty.

Superimpose the mask cover, write the text in the empty boxes, remove this cover and fill the rest with random letters.

Cardan decryption requires knowledge of the grille. The decrypted text appears by placing the cover on the text.

The encrypted message is very long compared to original plain text.

Cardinal Richelieu encrypted his messages in the same way, but the ciphertext took the classical form of a common text. The secret message consisted of only a few of the letters of the message that were revealed with the cache. Any reference to Cardinal Richelieu can be a clue.

The decryption without grille is very difficult, one should try all the grids.

Using a probable word, it is possible to estimate the coverage mask and deduct the amount of letters to ignore.

Cardan is the name of Jérome Cardan (Gerolamo Cardano) its italian creator.