Blog reader Jozef Krajčovič has sent me a turning grille ciphertext he found in an 1870 scientific journal. Can a reader decipher it?
The turning grille (also known as Fleissner grille) is a popular encryption tool that has been known at least since the 17th century. Here’s an example from Sweden, provided to me by Andreas Önnerfors:
The following turning grille is a replica, which is on display at the Heinz Nixdorf MuseumsForum in Paderborn, Germany:
The following diagram shows how a turning grille encryption works (the stencil is used four times, each step is followed by a 90 degree turn):
A turning grille encryption represents a transposition cipher. This means that no letter substitution takes place. Instead, the order of the letters is changed. To construct a Fleissner grille you can proceed as follows (start with a square matrix and fill it with numbers from 1 to 4 at random):
Here’s a turning grille ciphertext my friend Karl de Leeuw published over 20 years ago in Cryptologia:
As my readers (especially Armin Krauß) have shown, even a message encrypted with a 20×20 grille can be solved with hill climbing. More information about breaking a turning grille ciphertext will be available in my next book, Codebreaking: A Practical Guide.
A challenge from 1870
Jozef Krajčovič from Slovakia, who writes the blog Katkryptolog, has recently made me aware of two reader’s letters published in the scientific journal English Mechanic and World of Science in 1870. Both notes refer to an article titled Secret Writing, which had been contained in an earlier issue of the same journal. This article describes an encryption system invented by a Mr. Flamm. Apparently, The Times had covered this cipher, too. The reader’s letters don’t provide a description of the system, but I assume that it’s the turning grille cipher or at least something similar.
The first letter, written by a person with the pseudonym Kryptograph, states that the cipher allegedly invented by Mr. Flamm is far from new. The author writes that he has seen the same method nine years before at a seminar in Heidelberg, Germany.
The second reader’s letter was written by somebody named Tekew. It contains the following challenge cipher encrypted in the Flamm system:
Here’s a transcription Jozef provided:
NVRDIEMHNEAT IRVOAEINFYIU BRNTTTEHSEUA FHSEREPEFDRF OORRMOSVTOHO EIDFNOTSHTUH RETRTEEEAMLE EUGGSTSRIELA TARIEGTEAMRY OBSFOUCTTOHT EMTRPHCOLIIE XPSIHRTEIEYN
Now, there are a few obvious questions:
- Is the Flamm system identical with the turning grille cipher I described above? Or is it just a similar system?
- Can a reader find the English Mechanic and World of Science article that describes the Flamm cipher?
- Can a reader solve the challenge created by Tekew?
If you can answer one of these questions, please let Jozef and me know.
Further reading: The Turning Grille message described in Jules Verne’s novel „Mathias Sandorf“