Cracking the Zodiac killer’s code

Cracking the Zodiac killer’s code

Until 2020, the 340 character cipher remained un-decrypted. There have been no end to the theories about the meaning of the code and the identity of its author from would-be sleuths. With the solution text now out and standing up to scrutiny, it’s a wonderful reminder that internet sleuths need to be taken with a grain of salt.

One of these sleuths, Sam Blake, decided to contact programmer David Oranchak of Roanoke, Virginia after he gave a talk on it at the annual meeting of the American Cryptogram Association. Blake was particularly intrigued by the idea of homophonic substitution where one letter might be swapped for more than one symbol and then re-arranged in a systematic way. This generated a whole host of new ways to read the cypher.

Here’s Oranchak’s talk:

Oranchak took what he’d found to Jarl van Eycke, a Belgian warehouse worker and codebreaker who’d written AZdecrypt, software used for decoding homophonic substitutions. Van Eycke used an updated version of his software to churn through the possibilities. Using misspellings and characteristics from Zodiac’s previous writings things started falling into place.

The code used a tremendous amount of computing power, power that was definitely not available in 1960’s. The techniques involved in cracking it weren’t like the ones used in modern cryptography, so it’s explains why few people have used such statistical models on what is essentially a one-off code.

Oranchak sent their solution to contacts at the FBI, and by the end of 2020, the FBI had verified the methodology and results. In March 2021, Blake wrote about how he’d used Mathematica, a math software package, for his part, and in January, van Eycke made headlines again when he cracked an unsolved 386-year-old code composed by a Dutch scientist.

You can read more about the journey here, or check out the 9 part series about solving the code on Oranchak’s youtube channel.

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