Over on the ZodiacKillerSite forums, pi is doing some interesting work investigating the use of route patterns in quadrants of the 340-character cipher.
His idea is to split the cipher text into four quadrants, and then rearrange the text in each quadrant based on all of the possible routes. He then measures the resulting cipher text to see if more repeating patterns emerge from the text, with the hope that the underlying rearrangement has more features of a real message.
What he found was that running this search on the 340 increases the repeating patterns in at least 15% of his tests. By contrast, doing the same search on the 408 only increases the patterns 0.0000076% of the time. I found a similar phenomenon when exploring quadrants with a slightly different approach (see here and here).
But this led to more questions: What would happen to other 340-character test ciphers? How hard is it to make a 340-character cipher that has very few repeated patterns, yet still contains a valid message?
To answer this, pi created a test cipher that contains very few repeated patterns.
This means the repeated pattern count alone is not enough to separate good and bad rearrangements. What can we use instead? Dan’s approach avoids measuring the candidate cipher text altogether by skipping directly to trying to solve the rearranged text via the zkdecrypto hillclimber. It is a slow approach, but methodical. But is there some measurement that we can apply as a short cut? I think this is still an open question, and that we still need to generate more test ciphers to answer it.