Re: cracking the vigenere cipher when the key is non-alphabetic

From: Dave Neubelt (surftherocks2002_at_yahoo.com)
Date: 08/20/03 

Date: 19 Aug 2003 23:12:49 -0700

> Congrats. You can still use frequency analysis on it -- for each column
> you've identified, the characters in it will be from a single alphabet.
> This alphabet will be shifted from one column to the next, but they'll
> be in the same order. If the plaintext uses full ASCII, it's actually
> *better* for you this way, because you'll see from the frequencies where
> the printable characters start and stop, and the space character will
> stand out like a Fed at a hacker convention. Line 'em up and you're done!
>
> If the plaintext isn't full ASCII, then proceed the same way, keeping in
> mind that numbers will typically be low frequency (if they're not, as with
> an Excel spread***, then you'll get a big hint from having *lots* of them
> in a block of 10). If space is used, that should be the biggy; if not, then
> do the standard vig attack, looking at the pattern of high-frequency letters
> (A...E and so on).
Ok I'm sorry I'm so new at this I am a little confused on everything.
I am trying to write a program to take the cipher and crack the
message, so I think the easiest way would be to apply a chi-square
statistic and choose the lowest number out of all the possible shifts.
But the recourse I have for the chi-square statistic is a little
confusing to me so I just want to double check here that I am applying
this correctly.

*reminder about my encryption algorithm
-the message is normal ascii plaintext, a long letter i wrote
-the key is monkey123!@#isthekey

I'm real confused here(so bear with me if this is totally off)
I take all the frequencies of the different ASCII charectors

then I take the sqr of one particular ASCII char in message plus a
shift of 1 to 128 mod% 128 all divided by a frequency of what? I'm
real confused here because this chi-square statistic uses the english
alphabet, and my cipher text is just a char between 0-128. I don't
know how to apply this formula. Or maybe I'm going about it the wrong
way please help out an ansipiring cryptoanalys

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