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| Shorte Code | |
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| Tweet Topic Started: Feb 5 2006, 09:58 PM (1,296 Views) | |
| Boulemans | Feb 5 2006, 09:58 PM Post #1 |
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Just registered
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Hi, I need to show my math teacher how to crack following code: XF GTLTD UIUJHFVRA DTC VVGY FKUE YPMRFUV H UYCD IBXCJ anyone who knows how to begin? I think it isn't so difficult, but, since I am a n00b, I don't know were to start. My teacher got an extra hint; here it is in white: The code is in Vinegere, the language is (of course) English |
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| Revelation | Feb 6 2006, 03:28 PM Post #2 |
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Administrator
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Sure, if it is a Vigenere, you should check this out. Finding the key length is probably the hardest part. You should try to find the IOC. Here is a tool.
Good luck
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RRRREJMEEEEEPVKLWENFNVJKEEEEEAOLKAFKLXCFZAASDJXZTTTTTTTLSIOWJXMOKLAFJNNKFNXN RAGRBAQEMHIGDJVDSEOXVIYCELFHWLELJFIENXLRATALSJFSLCYTKLASJDKMHGOVOKAJDNMNUITN RRRRLJVEEEEECLYVYHNVPFTAEEEEEMWLMEIRNGLARWJAKJDFLWNTIERJMIPQWOTZEOCXKNUBNXCN RJIRPOWEANFUSNCZVDVZNMSFEKLOEPZLDKDJWSAAAAAAAOERHJCTNCKFRIMVKSOFOMKMANREWNBN RZUDRGXEEEEENFQIDVLQNCKNEEEEEDGLLLLLLAWIOSNCDARLODMTOEJXMILDFJROTKJSDNLVCZNN | |
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| Donald | Feb 7 2006, 03:34 AM Post #3 |
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NSA worthy
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The problem is that this cipher is VERY short for a Vigenere. It's under the minimum ACA recommended length for even a simple substitution cipher. It's not very far above the point where you can no longer guarantee a unique solution. The short length will make Kasiski or IOC very difficult to determine I fear. Of course, having the word divisions should help. I made a quick attempt at it and wasn't getting anywhere. I'll do some more looking at it later if I get time. Of course, one of the better cryptographers here may be able to show you how to rip it open in no time. |
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| rot13 | Feb 7 2006, 01:37 PM Post #4 |
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Elite member
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The word breaks are definitely the thing I needed to break it. I used trial and error, and a bit of guessing. The single-letter word was the first point of attack. I kept trying various key lengths until the other letters seemed at least normal. Then I took a guess for the letters near it in the key. After that it came apart. I'd say it took about 10 minutes. |
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| Donald | Feb 7 2006, 01:44 PM Post #5 |
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NSA worthy
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EXCELLENT! That was where I started, The two letter word at the begining also looked promising. But I'm not as good at recognizing when "the other letters seem at least normal" yet.
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| rot13 | Feb 7 2006, 10:01 PM Post #6 |
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Elite member
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Here's how I went about the first part (SPOILER): I made a guess that H was A, since there are only 2 common 1-letter words. It was between A and I. In Vigenere A -> H when the key is H, I -> H when the key is Z. I figured that H is more likely to be in the keyword than Z, so I went with that. Then I tried various combinations: Key: H qy zmemw nbncayokt wmv oozr ydnx rifkyno a nrvw buqvc XF GTLTD UIUJHFVRA DTC VVGY FKUE YPMRFUV H UYCD IBXCJ Definitely no good Key: H. <span style='font-family:Courier'> q. z.e.w .b.c.y.k. w.v .o.r .d.x .i.k.n. a .r.w .u.v XF GTLTD UIUJHFVRA DTC VVGY FKUE YPMRFUV H UYCD IBXCJ Key: .H doesn't touch the single-letter word - only 1 position in each key length will hit the single letter word Key: .H. .y ..e.. n..c..o.. w.. o..r ..n. .i..y.. a ..v. .u..c XF GTLTD UIUJHFVRA DTC VVGY FKUE YPMRFUV H UYCD IBXCJ This at least looks possible. The first word could be My or By. The 4-letter word with V could end with E. Trying any of those possibilities yields garbage words, though. Key: ..H. .. z...w ...c...k. ..v ...r ...x ...k... a ...w ...v XF GTLTD UIUJHFVRA DTC VVGY FKUE YPMRFUV H UYCD IBXCJ Nope. Key: ....H .. ..e.. ..n....k. ... o... .d.. ..f.... a .... b XF GTLTD UIUJHFVRA DTC VVGY FKUE YPMRFUV H UYCD IBXCJ This looks a little promising. The 4-letter word with D second is a good point of attack because there should be a vowel there. I tried A,E,I and O and got garbage. Key: ....H. .. ..e.. ...c..... w.. ...r .... .i..... a .... .u XF GTLTD UIUJHFVRA DTC VVGY FKUE YPMRFUV H UYCD IBXCJ This also looks promising. The 3-letter word beginning with W is a good next point. Once I got that word, it really fell apart quickly. </span> As you can see, the word breaks really make a difference here. |
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| Donald | Feb 8 2006, 01:42 PM Post #7 |
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NSA worthy
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Thank you rot13, that was an excellent lesson! |
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