Is there a test to distinguish a Gromark cipher (letters only, no primer given) from a running key cipher? I think this is the ultimate useless ID test. In the Cryptogram, a Gromark is always accompanied by its primer, there’s no question about what type it is. Also according to ACA rules a running key is about 50 letters, always shorter then a Gromark cipher.
Nevertheless I got interested in IDing Gromark ciphers when only the letters are given — no primer. But my ID tests gave poor results. The most common error was misidentifying a Gromark as a Progressive key cipher. I came up with a progressive key ID test using logs of digraphs that worked pretty well at IDing progressive key ciphers. But it didn’t help ID Gromark ciphers. When I ran my improved ID test on a Gromark cipher, the test no longer misidentified them as progressive keys. Instead it misidentified them as Running key ciphers.
I have a feeling there is a test based only on ciphertext letter frequencies that will distinguish running keys from Gromarks. In case anybody wants to try coming up with such a test, I generated 10,000 Gromarks and 10,000 running keys. They are in a zip file with the link below:
Each line has 7 fields separated by commas: (1) The running key’s “key” which is just the first half of its plaintext, (2) the second half of the running key’s plaintext, which is equal to the Gromark’s entire plaintext, (3) Gromark key, (4) Gromark primer, (5) Gromark ciphertest (6) running key type: 0 is vegenere, 1 is variant, (7) Running key ciphertext.
The running key plaintext is twice as long as the Gromark plaintext so their ciphertext lengths are equal.