

Vinegar - refined Vigenère - can you break my cipher? - billpg
http://blog.hackensplat.com/2011/02/vinegar.html

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gonnakillme
A big problem with these types of ciphers is that you need to transmit the key
somehow. If you have had no previous encrypted contact with the intended
receiver, you have to get the key to that person in plaintext. This is why
public key cryptography was invented.

As a side note, isn't this just a less secure Enigma cipher? Alan Turing would
have your u-boats for dinner.

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billpg
"isn't this just a less secure Enigma cipher?"

Talk is cheap, my friend. I've described the algorithm and supplied some
cipher-text. What's the plain text?

Seriously though, if you know what the Enigma cipher is without having to look
it up, you're probably over qualified for this sort of puzzle.

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swolchok
Well, the first word is probably THE. I have doubts as to whether this is
broken enough in practice if you follow standard cryptographic practice and
remove spacing and punctuation; the key space size is still 26^17, assuming
"random codeword" means a random string of letters and not a randomly selected
string of one or more dictionary words.

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billpg
The key is 17 random letters generated using the password generator at
GRC.COM.

I don't think I'm giving away anything by confirming that at least one of
those three letter groups is "THE".

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billpg
Hi everyone.

In summary, the cipher is Vigenère with 2,3,5 and 7 key lengths. The four keys
won't synchronise for 210 letters, so it's only "good" for that much.

It's very flawed. If you know cryptography its easy to spot, but the article
isn't for you. It's for people who don't know cryptography, with the long
description of Vigenère in the article.

Enjoy.

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losvedir
Fun little problem. I think I'm on the right track towards the solution,
though I'm not positive. So as not to spoil it for others wanting to work on
it, I've put my thoughts and progress here:

<https://gist.github.com/828496>

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billpg
Interesting read. Thanks.

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swolchok
This cipher is just 4 rounds of Vigenere with progressively shorter keys...

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billpg
Exactly. It's a very flawed cipher which I invented when I was young and
naive.

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swolchok
I realized that; I was just hoping that this observation would lead to an
attack, but it's not clear to me that there's a particularly easy/reliable
extension of the Vigenere attacks...

~~~
billpg
Gotcha. The vulnerability I thought of could be applied to Vigenere but in a
roundabout sort of way.

