Encryption experts, How Did They Crack One of the Zodiac Killer's Most Difficult Ciphers?

    The 'Z340' letter sent by the Zodiac Killer on November 8, 1969. Photo: FBI/Public domain

A new report provides a detailed look at how the Z340 was deciphered 51 years later.

A new report released by an international research team of encryption experts sheds light on the monumental effort, massive crowdsourcing, and digital programming required to translate the cryptic message of a notorious serial killer that remained a mystery for half a century. While one of the experts uploaded a video summary of their method to YouTube in 2020, the new report from the research team provides a more comprehensive view of the extensive effort involved in accomplishing this feat.

A man who called himself Zodiac in 1968-69 had killed at least five people in the northern region of California, USA. During that time and in the following years, the killer had sent a series of letters to local newspapers along with a total of four encrypted messages. Authorities have yet to officially identify the Zodiac Killer's identity, and only two of the encrypted writings had been deciphered so far.

However, one of these, considered for a long time to be the most challenging to decipher, was the 340-character encrypted text, first published in newspapers on November 12, 1969, and often referred to as "Z340." This cryptic message puzzled both amateur and professional codebreakers for years. However, an international research team announced in December 2020 that they believed they had finally cracked Zodiac's encrypted message. This solution was later examined by the FBI and confirmed, provided by David Oranchak, Sam Blake, and Jarl Vay Eycke, thus ending a 51-year-old mystery.

Beginning with the phrase "HOPE YOU ARE TRYING TO CATCH ME WHEN I WILL HAVE MY FUN," the Z340 message disclosed that the caller who dialed into the A.M. San Francisco television talk show on October 22, 1969, was not him.

Cracking the Z-340 Cipher

In November 1969, the Zodiac sent a 340-character cipher known as the "Z-340 Cipher." For over 51 years, it remained one of the few unsolved ciphers in the world, with both amateur and professional cryptographers, as well as cryptanalysts at the FBI, working on it. On December 12, 2020, it was announced that David Oranchak, a software developer from Virginia, along with Jarl Van Eycke, a Belgian computer programmer, and Sam Blake, an Australian mathematician, had solved the problem. The Z-340 Cipher consists of 63 unique symbols. Oranchak, using a suggestion from Van Eycke, divided the cipher into three sections: the first two sections with nine lines each, and the last section with two lines. Oranchak then utilized a computer program called AZ Decrypt, written by Van Eycke, to examine 650,000 different permutations of the encrypted text.

The three sections of the Z-340 Cipher

The individuals became entrenched in a transposition scheme where they followed a pattern starting from the top left corner, moving down one letter and right two letters until reaching the right edge of the cipher. Subsequently, they would restart the same pattern from the second letter. Even envisioning the solution was challenging given the complexity.

In the end, the plaintext of the first section of the cipher became visible; however, the second and third sections remained unreadable. Later, the three men noticed that some words in the second section were written backward, realizing it was likely a coding error made by the Zodiac in this section. Rectifying this error and rearranging the words "LIFEIS" seen in the top right corner led to a solution.

On December 5, 2020, Oranchak, Van Eycke, and Blake presented their findings to the FBI's Cryptanalysis and Racketeering Records Unit, and on December 12, 2020, the solution was confirmed. The Z-340 Cipher states:

"I hope you are having lots of fun in trying to catch me. That wasn't me on the TV show which brings up a point about me. I am not afraid of the gas chamber because it will send me to paradice (sic) all the sooner because I now have enough slaves to work for me where everyone else has nothing when they reach paradice so they are afraid of death. I am not afraid because I know that my new life will be an easy one in paradice death."

The current status of the Zodiac

On December 12, 2020, the FBI tweeted the following statement:

In May 2018, the Vallejo Police Department announced that they were trying to collect Zodiac's DNA from the backs of the stamps he used to send letters. If he is still alive, Zodiac should now be in his 70s or 80s. The question of how someone smart enough to construct these ciphers could misspell so many words in Zodiac's letters remains unanswered. Were the spelling errors intentional?

Given that in most cases, Zodiac's female victims were treated worse than his male victims, did Zodiac's hatred towards women end temporarily in the early 1970s? Did Zodiac eventually find love, get married, have children, or grandchildren?

Zodiac's grandchildren would now be at a similar age to when his victims were killed. Express these writings differently.