Italian cryptologist Luigi Sacco left behind a text encrypted with a Fleissner grille. Paolo Bonavoglia and Bart Wenmeckers, both readers of this blog, solved it.
The Fleissner grille is one of the most popular encryption tools. In spite of its popularity, surprisingly little has been published about deciphering a Fleissner grille. I wonder if a reader can break the Fleissner challenge I am going to present today.