Grille Cipher Tool

About this calculator

A Cardan grille (named after 16th-century Italian polymath Girolamo Cardano) is a transposition cipher that uses a physical card with cut-out holes. In the 4×4 turning-grille variant, a quarter of the 16 cells are cut open; the grille is laid over a blank grid, letters are written through the holes, then the grille is rotated 90° four times, filling all 16 cells in a scrambled but reversible order to produce the ciphertext.

Because the grille itself — not a mathematical key — determines the permutation, decrypting the message requires physically possessing (or precisely reconstructing) the same grille and rotation sequence, making it historically popular for hand-delivered military and diplomatic messages before modern cryptography. Cryptography students, puzzle and escape-room designers, and history-of-cryptography enthusiasts use this calculator to encode short messages exactly the way the original Cardan grille worked, without cutting a physical card.