In 1881, Colonel Eduard
Fleissner von Wostrowitz of
Austria published an essay entitled "New Secret Writing Template". This template was a square with a number of holes punched out. There are an even number of rows and columns (thus the total number of fields is divisible by 4). One fourth of these
fields is cut out. This template is used for both encoding and decoding the message.
X X X
X XXXX
XXX XX
X XX X
XXXXX
XX XXX
This template is used as part of a
transposition cipher. Transposition ciphers, as opposed to
substitution ciphers, keep the same character - an 'e' is always an 'e'. The key to the
encoding and
decoding is moving the letters around. Not every template is suitable - the rotations of the template must expose every spot once, and only once.
Encoding and Decoding
Take the plain text of 'wow, you are beautiful. How about dinner?'. This becomes 'wowyouarebeautifulhowaboutdinner'. This is 32 characters, so four extra random characters should be added (for grins, 'xoxo') to make 36. Using the above template, the letters are written in the empty spots, and the the template is rotated once and repeated. The following example uses the template above.
W.O.W. | .B...E | ...H.. | ......
.Y.... | ..A.U. | .....O | I..N..
...O.. | T....I | .W..A. | ..N...
.U..A. | ...F.. | ..B... | E....R
R..... | ..U..L | ....O. | .X.O..
..E... | ...... | .U.T.D | X...O.
W O W | WBO WE | WBOHWE | WBOHWE
Y | YA U | YA UO | IYANUO
O | T O I | TW OAI | TWNOAI
U A | U FA | UBFA | EUBFAR
R | R U L | R U OL | RXUOOL
E | E | UET D | XUETOD
The cipher can potentially be flipped over part way through, or encoding the ciphertext once again. This second encrypting is called superencryption.
Construction
Create a nxn grid where 'n' is even. In the following example n=6. Divide this grid up into 4 sections of size n/2.
...|...
...|...
...|...
---+---
...|...
...|...
...|...
Number each section - rotating the numbering by 90 degrees in each section.
123|741
456|852
789|963
---+---
369|987
258|654
147|321
To choose the fields to cut out, select one field of each number 1-9 to remove. In all, there are 262,144 possibilities for a 6x6 grill.
..3|..1
...|8..
7.9|.6.
---+---
...|...
.5.|..4
...|.2.
Weaknesses
One of the key giveaways for the turning grill method of enciphering is the length of the text - a multiple of a square of a even number. Never the less, this system was used as recently as World War II by German spies in South America.