HistoCrypt 2019 – Really good papers
HistoCrypt 2019, an annual conference on historical cryptology, convenes this week. The proceedings have been published and include many fascinating papers:
Those here who like to tinker with solvers and the Zodiac ciphers need to read these:
Nils Kopal, “Cryptanalysis of Homophonic Substitution Ciphers Using Simulated Annealing with Fixed Temperature” (This paper in particular is the first to formally acknowledge and accurately describe the long-available solvers such as ZKDecrypto and AZDecrypt)
Tom S Juzek, “Using the Entropy of N-Grams to Evaluate the Authenticity of Substitution Ciphers and Z340 in Particular” Notable conclusion:
We applied those two SVM models to the the Zodiac Killer’s two major ciphers, z408 and z340. z408, which has been solved, is correctly predicted to be a real substitution cipher. z340, which remains unsolved, is predicted to not be a substitution cipher. We think that it is likely that z340 is either another type of cipher, e.g. a transpose cipher or a Vigenere cipher, or that it might not be a bona fide substitution cipher after all.
Also, while this one is about PlayFair ciphers, the algorithmic techniques described in the paper would well apply to homophonic solvers:
George Lasry, “Solving a 40-Letter Playfair Challenge with CrypTool 2”
The proceedings are definitely worth a read if you have any technical interest in cryptology in general and the Zodiac ciphers in particular!
What is more important, is what is your opinion on the 340 cipher Dave. Have your views shifted over the years on the possibility of a clear and coherent message being encoded in the cipher. If you had to give a percentage on ‘message or ruse’ what would you attribute to the 340 cipher. As you discussed on Zodiac Killer Roundtable, one of the most interesting aspects of the 340 is the corrected sixth line. Was this just a ploy by Zodiac to give the impression he had made an error from his draft to finalized cipher and the impression by correcting it was to convince us it was genuine? – especially when we consider the errors he never bothered correcting in the 408.
The short answer is it’s very difficult to prove that there is no message, especially since there are still so many possibilities that haven’t been adequately and exhaustively explored.
Here are my longer thoughts about it:
Over time, I think the needle has moved a tiny bit more towards “there’s not a message” when I ponder how much of Zodiac’s communications were him trying to portray himself as a supervillain mastermind. His elaborate bomb never materialized so maybe the 340’s message will also never materialize because it is window dressing for his persona. What prevents the needle from moving even more is the fact that we know he’s capable of creating a real cipher with a real message (the 408).