I see that quite a few people stumble across this space on a given week, so I figured I'd give an update since it's been nearly a month since my last post.
As noted earlier, when treating the D'Agapeyeff cipher as a numerical version of ADFGX (treating the 6-0 digits as nulls) the max attainable phi value is 600 which is associated with an IC of 1.64 (6.3%).
From tests I've run, the fact that the IC tops somewhere below the value expected for English leads me to believe that if the D'Agapeyeff cipher is in ADFGX form, the plaintext has a lower IC much like the cipher D'Agapeyeff decoded from his friend in the cryptanalysis section of his book.
Thus far I've eliminated all key variants from 600 down to 538. This represents 215 key variants and 1,083,600 total keys. The program I'm working with allows me to input one key variant, and it then checks the 5,040 permutations of the 7 column pairings and scores the potential plaintext with log tetragraphs. It's a slick program, but does require me to input keys. If I make it down to a phi value of 520 with no plaintext the key distinct variants do get tougher to distinguish. And by tougher I just mean time consuming. I've not come up with a great programmatic way to sort through all the keys that fall into a given phi/IC and pick out just the unique column pairings.
That's all for now.
As noted earlier, when treating the D'Agapeyeff cipher as a numerical version of ADFGX (treating the 6-0 digits as nulls) the max attainable phi value is 600 which is associated with an IC of 1.64 (6.3%).
From tests I've run, the fact that the IC tops somewhere below the value expected for English leads me to believe that if the D'Agapeyeff cipher is in ADFGX form, the plaintext has a lower IC much like the cipher D'Agapeyeff decoded from his friend in the cryptanalysis section of his book.
Thus far I've eliminated all key variants from 600 down to 538. This represents 215 key variants and 1,083,600 total keys. The program I'm working with allows me to input one key variant, and it then checks the 5,040 permutations of the 7 column pairings and scores the potential plaintext with log tetragraphs. It's a slick program, but does require me to input keys. If I make it down to a phi value of 520 with no plaintext the key distinct variants do get tougher to distinguish. And by tougher I just mean time consuming. I've not come up with a great programmatic way to sort through all the keys that fall into a given phi/IC and pick out just the unique column pairings.
That's all for now.
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