Stupid Questions March 2015

Gondolinian

This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.

Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.

To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.

Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.

To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.

I finally did get round to taking a look at this, and it isn't yielding to the usual methods. In fact, it's sufficiently unyielding that I am wondering whether it's really the result of Vigenere-ciphering something that resembles ordinary English text with a key of reasonable length. I find the following:

The text is 146 characters long. I would expect that, with "ordinary" plaintext, to be enough to identify a key of at most about 7 characters without too much pain. I actually tried lengths up to 10.
For no key length k does the distribution of { (a-b) mod 26 : a,b are characters at the same position mod k } much resemble the distribution of differences mod 26 of randomly chosen letters with typical English letter frequencies.
For no key length k does the result of the following procedure produce something that looks as if most of the shifts are correct:
- For each offset, count letter frequencies, and choose a shift that maximizes the sum of log(typical_prob) where typical_prob are those typical English letter frequencies again.

JRMayne, if you happen to be reading this and happen to have either a record or a memory of the message and how you encrypted it: can you confirm that (1) this really is the output of a Vigenere cipher, (2) the plaintext isn't (statistically) outrageously unlike ordinary English, and (3) the key length is at most, let's say, 10?

(If the key is much longer than that, there isn't enough information for these simple methods to work with. Perhaps, e.g., doing a more expensive search and looking at digraph frequencies might be worth considering, but I'm too lazy.)

Gah. I don't remember the solution or the key. And I just last week had a computer crash (replaced it), so, I've got lots of nothing. Sorry.

I am sure of (1) and (2). I don't remember (3), and it's very possible it's longer than 10 (though probably not much longer.) But I don't remember clearly. That's the best I can do.

Drat.