Fleissner's stencil is a grille cipher to encrypt text by reordering characters using a rotating stencil.
It has been named after the Austrian cavalry colonel Edouard Fleissner von Wostrowitz, who described it back in 1881.
It gained popularity as it has been part of the novel Mathias Sandorf by Jules Verne (1885).
The classical stencil is of size 6x6 fields, hence capable to encrypt at most 36 characters. For longer texts a second matrix is required. That point is addressed by this project, which generates bigger grilles, based on the same mathematical principle.
The stencil of correct size has to be layed over the text, where the cut out (white) fields are used for writing and reading. When all free fields are filled, the stencil has to be rotated by 90° clockwise to continue writing or reading. This is repeated until the stencil is back in its initial orientation, so every field has been used once.