Crack the Zodiac Killer's Z-408 Cipher: A Step-by-Step Cryptanalysis 🕵️‍♂️

#cryptology, #cryptography, #cryptanalysis

In this video, we present how to break the infamous Zodiac Killer's Z-408 cipher. The Zodiac killer killed five people between 1968 and 1969 in the San Francisco Bay Area. He also sent different (bizarre) letters to local newspapers. Four of those messages were encrypted, and one (Z-408) has been already solved in 1969 (by hand!). The letters were encrypted homophonically using different symbols. The content of the broken message can only be described as ill.

Here, we first give a short introduction of the Zodiac killer and his messages. Also, we briefly introduce homophonic substitution ciphers.

After that, we create our own homophonic substitution cipher in CrypTool 2. Finally, we use CrypTool 2's homophonic substitution analyzer to actually break the cipher.

We highly suggest, if you are interested in this topic, to also have a look at the "zodiac killer ciphers" webpage [1], which is a great source of information on the cases and the ciphers.

Also, please have a look at the forum on [2]. It is also a great source, a place to meet knowledgable code breakers, and you can also download great and powerful cryptanalytic tools, e.g. for homophonic substitution ciphers.

If you want to know more about how CrypTool 2's analyzer, which we use in the video, works, have a look at our paper of the HistoCrypt 2019 [3].

Finally, you may download the latest version of CrypTool 2 from here: https://www.cryptool.org/en/ct2/downloads

[1] http://www.zodiackillerciphers.com/
[2] http://zodiackillersite.com/
[3] Kopal, Nils. "Cryptanalysis of Homophonic Substitution Ciphers Using Simulated Annealing with Fixed Temperature." Proceedings of the 2nd International Conference on Historical Cryptology, HistoCrypt 2019, June 23-26, 2019, Mons, Belgium. No. 158. Linköping University Electronic Press, 2019.

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