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Re: VMs: Cardan grille

3/12/2004 9:56:14 AM, elvogt@xxxxxxxxxxx wrote:

>Zitat von Jacques Guy <jguy@xxxxxxxxxxxxxxxx>:
>>Try encrypting "hello world"
>> with a small 7x7 grill with 10 holes in it, filling the spaces
>> in between with text written by hand. Then try again on another
>> sheet of paper, with a different 10-letter plaintext. And again.
>> Now compare the three. The plaintext letters are the only ones
>> to be positioned exactly the same relatively to one another

>Sorry, I don't get it.

The trick is in realizing that the text is _handwritten_,
not printed. Handwriting is irregular. 

Pick 20 letters at random out of a handwritten page,
note their coordinates.  

Take another handwritten page. Look at the letters 
positioned at those same 20 coordinates. You will
see sometimes an entire letter, sometimes part of
a letter.

Now take a Cardan grille with 20 holes. Write the first
20 letters of your plaintext message in those holes. 
Remove the grille, fill in the rest of the page. 

Take another page, lay the same grille on it, write 
the next 20 letters of your message in its 20 holes.
Remove the grille, fill in the page.

There will be a set of 20 squares on the first page
occupied each by one full letter, and those same
20 squares will again be occupied by one full letter
on the second page, third page and so on.

To find them, copy the cypher text _exactly_ onto 
transparent sheets, stack them, shift them so that
they match. Each hole of the original grille will
show as a black blob surrounded by white space,
while the rest of the page will show as a greyish/black
continous jumble of letters all running into one another.

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