Vinegar - refined Vigenère - can you break my cipher? | Hacker News Reader

Vinegar - refined Vigenère - can you break my cipher?

blog.hackensplat.com

21 pointsbillpg11 comments

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.

"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.

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.

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".

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.

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

Interesting read. Thanks.

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

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

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...

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

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