Challenge "Hill Cipher with Sudoku Key"

Challenge "Hill Cipher with Sudoku Key"  

  By: admin on Sept. 4, 2013, 4:27 p.m.

You find a note with strange characters and an unsolved Sudoku on your brother's desk. You are curious and would like to find out what your brother is working on. Can you decrypt the note using the Sudoku?

Re: Challenge  

  By: Greko on Sept. 5, 2013, 12:32 p.m.

While I was checking if everything is OK with the challenge I found this. The ciphertext must be downloaded in order to get it all correct. What I mean is that sometimes I didn't download the additional file of a challenge but just copy-paste it's content. Here it has to be downloaded. However if you still choose to copy-paste it you will get the first part correct which includes the two codewords so you can still solve the challenge without getting the whole plaintext correct. Although I reccomend reading the plaintext as it refers to an interesting topic in my opinion. I hope that this didn't create any problems.

Re: Challenge  

  By: cruachan on Sept. 8, 2013, 2:43 a.m.

If you want to copy and paste the text and use other software than CrypTool, you have to delete a '-'. It it character number 127 and not part of the alphabet that is used for encryption. You should have a text with 1119 characters after removing it. After decrypting the text. insert the '-' back at position 127 in the plaintext.
I did it that way and was able to decrypt the text with a self-wriiten Matlab function. Took some time to find the character that was causing problems though.

Incorrect additional file  

  By: helmi on Sept. 8, 2013, 4:19 p.m.

Thank you cruachan for giving the key hint for solving this challenge. I am sure most of us counted a cipher text length of 1120 characters, not being aware there is a 96H-"char" at
position 127 which should not be there. So if you (like me) already spent hours entering matrices corresponding to a text length of 1120 I can tell you, this will lead you nowhere. Text length is 1119 char. Delete this extra character and the solution will come easy.

This is another example of a faulty challenge that consumes our time, nerves and points. It's a pity because this could have been a really nice challenge.

Re: Challenge  

  By: Greko on Sept. 8, 2013, 5:25 p.m.

Thank you both of you cruachan and helmi for your posts. I could not imagine that so big problems would come up if somebody didn't use cryptool. I am really sorry about that. I checked it and you are absolutely right.If you ignore that "-"(and put it back after decryption) the message has the appropriate length of 1119 characters and so the challenge can be solved in the way it was designed to be solved. It seems that cryptool ignored that "-" and that caused the problem.

Re: Challenge  

  By: Yokozuna on Sept. 8, 2013, 10:22 p.m.

I also want to thank cruachan. Without his hint it might be possible, that I would have spent some more days for this challenge without any result.

Causal for the problems with this challenge is this character, which looks very similar to the ASCII character 'minus' (= 2Dh) but has the value 96h and is not part of the special character set used by CrypTool. This character 96h is part of the original wikipedia article and the plaintext, which is part of this wikipedia article, also contains this character 96h. The length of the plaintext with this 96h character is 1120. While encrypting this plaintext, CrypTool ignores this character (because it is not part of the special characters used by CrypTool) and does encrypt only 1119 characters, as it was apparently intended. But this character 96h has not been completely ignored. It is true, that it has not been encrypted but instead it has been copied unchanged from the plaintext to the ciphertext and therefore the ciphertext has also the length of 1120 (instead of 1119) and contains this illegal character 96h.

If I decipher this ciphertext (with 96h) with CrypTool and with the correct matrix of the appropriate size, all looks fine. Again this character will be ignored, deciphering 1119 characters. Instead this character will be copied unchanged from the ciphertext to the plaintext and I get the original plaintext with a length of 1120.

But wether I use CrypTool or some other software is not the true problem here. From the visual impression I cannot tell the two characters 2Dh and 96h apart and for me, naturally, it was a 2Dh, because 2Dh belongs to the special character set of CrypTool and it is the only character there, which looks like a 'minus'. There was no reason to assume the presence of any 'illegal' characters (not belonging to the special characters used by CrypTool) in the ciphertext. Therefore I assumed a length of the ciphertext of 1120. Now hint number two in the challenge states:

"The length of the given ciphertext fits to the size of the
sought-after key matrix. The plaintext was encrypted without

Following this hint I tried several different sizes for the matrix according to the length of 1120, but the size of the matrix used by the author is not possible at all with this length. Therefore I could have tried countless matrices of different sizes (according to the length of 1120) until the end of all times. The Queen would say: "I am not amused!"

Re: Challenge  

  By: be on Sept. 9, 2013, 1:32 a.m.

You should have a text with 1119 characters after removing it.

Thanks a lot for revealing this problem and informing all of us at the forum. I am impressed about your analysis.
I'll make the author and Lena, who takes care for the templates of the challenges, to correct the delivered ciphertext. This was no intended difficulty.

Re: Challenge  

  By: michaelm on Sept. 10, 2013, 4:46 p.m.

Please also check the alphabet given in the PDF. I am programming in Basic and had to change/correct the sequence of the 92 characters.

Re: Challenge  

  By: be on Sept. 11, 2013, 7:08 p.m.

Please also check the alphabet given in the PDF.

Where is the problem? Please be a bit more specific: We will correct the PDF if necessary.

Re: Challenge  

  By: Veselovský on Sept. 11, 2013, 8:25 p.m.

Neither "visual image" of alphabet in the PDF is correct:
nor is correct its copy using CTRL+C:
vwxyz0123456789.,]{}@_><# =\ &%$Ÿ

The correct alphabet should be:
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz 0123456789.,]{}@_><#~=\"&%$§

…that is what was michaelm referring to.

Re: Challenge  

  By: michaelm on Sept. 11, 2013, 9:58 p.m.

The correct alphabet should be:
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz 0123456789.,:;!?()-+*/[]{}@_><#~=\"&%$§

that's what I was meaning.

Space asc(32) was in the wrong place, ~ asc(126) and § asc(167) were missing or wrong.

There should be a Space asc(32) between the xyz 012

Re: Challenge  

  By: Yokozuna on Sept. 11, 2013, 10:29 p.m.

An optical inspection of the used alphabet in the PDF shows, that there is obviously the space missing between the lowercase letters and the numerals. Moreover between # and = there is the ~ missing (there is a space instead) and after the " there is a space which should not be there.

If somebody needs this alphabet for own programming its better to copy it from the CrypTool. The alphabet looks then like this:

ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz 0123456789.,:;!?()-+*/[]{}@_><#~=\"&%$§

Copying the alphabet from the PDF looks like this:

vwxyz0123456789.,:;!?()-+*/[]{}@_><# =\ &%$Ÿ

There seems to be two additional spaces between b and c and also between p and q (this spaces are not visible in the PDF) and some special characters will not be displayed correctlyŸ. Therefore this alphabet cannot be used without some manual corrections.

edit: I didn't notice, that two had been faster with their answer, so this one seems to be superfluous

Re: Challenge  

  By: be on Sept. 12, 2013, 12:37 a.m.

I didn't notice, that two had been faster with their answer, so this one seems to be superfluous

Thanks everybody. No comment is superfluous as you used diferent ways to explain it.
We (the authors and the MTC3 team) learned for the future, that we have to check more carefully the PDF file of the challenge (as the alphabet seemed to be correct in the LaTeX source file), or put any text with letters outside the "normal" alphabet into an additional file.
Thanks again for all your contributions – we'll correct the PDF.

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