Super Sudoko

By Win Noren

Cracking coded messages has been a target of spies – both industrial and otherwise – since the beginning of time. Surely as a kid you created your own secret code to pass along messages to a special friend, I know that I did. Of course my code doesn’t come close to the code used by Britain during World War II to communicate with officers held by Germany as prisoners of war.

Apparently taught to officers either before heading out to the field or passed along by other prisoners, the MI9 code was recently cracked by researchers at Plymouth University. Dr. Bennett, Associate Professor of History and one of the members of the research team which cracked the code, describes the MI9 code as a “bit more like crosswords or puzzles – a form of super-Sudoko for the 1940’s generation” compared to the German approach to cryptography which “was mechanical and industrial and they would typically use a machine, like the Enigma machine, to encode stuff for them.”

The details of their research are fascinating for a numbers geek like me and you may also want to read the in-depth description of how the code was cracked.

The content of these coded messages, which were hidden in routine messages home that talked about vegetable gardens and other daily activities of the prisoners show that the PoWs were passing on vital information about the war as well as asking for materials to engineer their own escapes. In one letter, Sub-Lieutenant John Pryor wrote “Many seeds are left, being saved from several plants which did very well some time ago…Our last year’s harvest was extremely good. Well worth repeating again for this year.” Once decoded the letter containing this message provided details about the sinking of a British submarine.

I am astonished by the complexity of this code that the prisoners used in constructing these letters. The rules for the MI9 code were (more or less) the following:

  1. The date was written in a certain way indicating that a letter contained a secret message. This was confirmed by underlining the signature.
  2. The length of the message is determined by multiplying the number of letters in the first two words on the line following the salutation. So if the first two words were “lucky again” the coded message contained 25 words (5×5) using a 5×5 grid.
  3. Starting on the next line select the fifth and fourth word alternatively
  4. However if either the fourth or fifth word was the word “the” this was the signal that a complex alphabetic code started.
  5. Once all the words in the message were placed in the proper sized grid, the message would be read by starting in the lower right corner and reading the message in a diagonal pattern towards the upper left corner. This means that the first coded word in the letter would be the last word in the un-coded message.

Of course modern cryptography use sophisticated computer methods to thwart hackers and this modern discipline is an intersection of computer science, mathematics and engineering. Applications of encryption that touch our daily lives include computer passwords, electronic commerce, ATMs not to mention business and government communications.

Perhaps next time I will talk about my old and new way of handing my personal passwords in my own personal battle against hackers and phishers. Or perhaps I will just be content thinking about how PoWs like John Pryor continued the battle using their super puzzle solving skills.

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Posted on May 8, 2013, in Uncategorized. Bookmark the permalink. Leave a comment.

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