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A World War II steganography competition

Von / 9. März 2019 / 4 Kommentare / Seite 1 von 2 / Auf einer Seite lesen
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A few years ago, online magazine “Naked Security” ran a steganography competition. The participants had to hide a given message in an inconspicuous letter using a method developed by British cipher experts in WW2. The results were quite impressing. Can a reader do better anyway?

In the Second World War, British cipher specialists developed a steganographic method that was to be used by soldiers in case they were captured by the Germans. This method allowed for hiding a secret message in an unsuspicious letter a soldier would send to his family back home (British prisoners of war usually were allowed to write such letters; these messages were transported by the Red Cross or similar organisations).

I have blogged about this method before (in German).

 

How the method works

To explain how the method works, we first need a message. Here’s an example:

WE PLAN ESCAPE NEXT MONDAY AT 8. GOAL IS TO REACH SWITZERLAND BY NOON.

This message consists of 14 words. For clearity, we numerate them:

1WE 2PLAN 3ESCAPE 4NEXT 5MONDAY 6AT 78. 8GOAL 9IS 10TO 11REACH. 12SWITZERLAND 13BY 14NOON.

Now, the order of the words is changed according to a rule based on a rectangle. The following diagram shows how this works with 15 words:

PoW-Code

Our message doesn’t have 15 words but only 14. We take the following rectangle instead:

PoW-Code-2

Now, the message is written in the order indicated by the diagram (14, 13, 12, 11, 10, …). In our case, this is equivalent to writing the text backwards:

NOON BY SWITZERLAND REACH TO IS GOAL 8 AT MONDAY NEXT ESCAPE PLAN WE

In the next step, we extend the message with filling words. After the first, third, fifth, seventh etc. word, six filling words are positioned. After the second, fourth, sixth etc. word, three filling words follow (the method allows for other distance patterns as well, for example 5-4-5-4-5…, but this is not relevant here). Now, we get:

NOON xxxx xxxx xxxx xxxx xxxx xxxx BY xxxx xxxx xxxx SWITZERLAND xxxx xxxx xxxx xxxx xxxx xxxx REACH xxxx xxxx xxxx TO xxxx xxxx xxxx xxxx xxxx xxxx IS xxxx xxxx xxxx GOAL xxxx xxxx xxxx xxxx xxxx xxxx 8 xxxx xxxx xxxx AT xxxx xxxx xxxx xxxx xxxx xxxx MONDAY xxxx xxxx xxxx NEXT xxxx xxxx xxxx xxxx xxxx xxxx ESCAPE xxxx xxxx xxxx PLAN xxxx xxxx xxxx xxxx xxxx xxxx WE

Next, we add a line at the beginning. The length of the first two words indicates the size of the rectangle. As we have used a 2×7 retangle, the first word needs to have two and the second needs to have seven letters. I have chosen ON TUESDAY. The rest of the line is irrelevant:

ON TUESDAY xxxxxxxxx
NOON xxxx xxxx xxxx xxxx xxxx xxxx BY xxxx xxxx xxxx SWITZERLAND xxxx xxxx xxxx xxxx xxxx xxxx REACH xxxx xxxx xxxx TO xxxx xxxx xxxx xxxx xxxx xxxx IS xxxx xxxx xxxx GOAL xxxx xxxx xxxx xxxx xxxx xxxx 8 xxxx xxxx xxxx AT xxxx xxxx xxxx xxxx xxxx xxxx MONDAY xxxx xxxx xxxx NEXT xxxx xxxx xxxx xxxx xxxx xxxx ESCAPE xxxx xxxx xxxx PLAN xxxx xxxx xxxx xxxx xxxx xxxx WE

The next step is the most difficult one. The placeholders need to be replaced by words, such that we get a meaningful text. Here is my proposal:

ON TUESDAY WEATHER WAS COLD.
NOON BROUGHT COLD RAIN WHICH GOT WORSE BY LATE AFTERNOON IN SWITZERLAND TEMPERATURES ARE MUCH HIGHER THEY WILL REACH MORE THAN TWENTY TO TWENTY TWO DEGREES TOMORROW WHICH CERTAINLY IS QUITE HOT OUR GOAL IS TO STAY WARM FOR ANOTHER 8 DAYS BECAUSE HERE AT THE CAMP COAL WILL COME NEXT MONDAY OR AT LEAST NEXT TUESDAY I REALLY WISH I COULD NOW ESCAPE FROM THIS WEATHER PLAN TO WRITE AGAIN ON THE NEXT WE

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Kommentare (4)

  1. #1 Magnus
    Borensberg
    10. März 2019

    In the winning entry, isn’t there one word too many in between HOUR and BUNGALOWS?

  2. #2 Klaus Schmeh
    12. März 2019

    Mark Romo via Facebook:
    This is amazing! Much easier than the subtraction method. [If 5 is the numerator, then DIFFERENT = 4] What a headache that is! This method is much simpler, which drastically decreases the chances of making mistakes.

  3. #3 Klaus Schmeh
    13. März 2019

    Mark Romo via Facebook:
    I tried this, thank you Klaus. Once the recipient has received the letter, how do the discern a message word from a filler?

  4. #4 Klaus Schmeh
    13. März 2019

    @Mark:
    The first word in the text is a message word. In my example a 5-4-5-4-5 pattern was used. This means that there are five filler words between the first and the second message word and that there are four filler words between the second and the third message word etc.