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| Simple Substiution Along With Grille Cipher | |
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| Tweet Topic Started: Oct 3 2005, 06:49 PM (1,614 Views) | |
| Colly | Oct 3 2005, 06:49 PM Post #1 |
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Unregistered
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Im new to cryptoanalysis and I know that in a few months I will need to be able to break this example without using a pc in a few minutes. I barely have a clue where to start so I was hoping someone could please break it and give me an idea of how it's done. This should be simple. Here's my problem: The following ciphertext has been found in a file called topsecret.txt on an employee's desktop, ----------------------------- | A | T | O | Y | |---------------------------- | O | O | G | R | |----------------------------- | E | K | P | S | |----------------------------- | M | U | D | T | ----------------------------- It is known that the employee favours substitution or grille ciphers. It is also known that the word "mark" appears in the plaintext. Find the origional message. Thanks. |
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| rot13 | Oct 3 2005, 07:42 PM Post #2 |
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Elite member
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Since this is a grille and there are 16 letters, you are looking at a grille with 4 holes (4 positions of the grille * 4 holes = 16 letters). In a 4x4 square, the letters rotate like this: ABCA CDDB BDDC ACBA That is, a hole at any position A rotates through all the other A's, a hole at B rotates through all the other B's, etc. You need to find a combination of holes at A, B, C and D that might write out MARK. Since both M and A appear at the A spot, one hole will be responsible for writing both those letters. That suggests that M is at the end of one position, and ARK gets written out by the next position. Also, since A, R and K must be in a row, you should start there. K appears in the D spot, R appears in the B spot, A appears in the A spot, so you only need to figure out which C spot to use. The grille is read off from left to right, starting at the top, so when the grille is in the ARKx position, there can be no holes before A (since it must come after the M from the previous position), and nothing between A and R, or between R and K (because then it wouldn't be written out as ARK). That substantially reduces the choices and you should be able to go from there. I can tell you the complete solution, but since I have gotten you this far, maybe you can come up with it. If you start with the position that writes out ARK, I think there are only two possible guesses for the last hole. |
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| Colly | Oct 3 2005, 08:43 PM Post #3 |
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Unregistered
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Thanks, I cut out the grill and got the message. I thought there may have been a substitution in that as well but there wasn't. |
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| Donald | Oct 3 2005, 09:41 PM Post #4 |
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NSA worthy
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Congratulations! May I ask what puzzle/game this is that you are working on? Donald |
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12:26 AM Jul 11