One of the most remarkable achievements in the Zodiac story occurred in 2020, when David Oranchak, Sam Blake and Jarl Van Eycke collaborated to finally break the 51 year resistance of the infamous 340 cipher on December 3rd. But what inspired the added complexity and the diagonal shift employed by the Zodiac Killer in his encryption technique on November 8th 1969. The trigger may have been his 408 cipher and the detailed attempt to break it in the Vallejo News Chronicle on August 4th 1969, at a time when the Zodiac Killer would undoubtedly have been scrutinizing the newspapers for progress on his 408 cipher. This was pointed out to me by the forum contributor known as Cragle, who made this astute observation recently.
The cryptogram fan from San Francisco, a graduate student, made some observations regarding the 408 cipher (shown on the left). While his analysis wasn't wholly accurate, it is this newspaper article that may have bearings on the technique employed by the Zodiac Killer when designing his 340 cipher. On page two of this newspaper article it continued The pattern beginning to take shape apparently will end up a three-tiered diagonal structure composed of sections, of each of the three ciphers. Work with the patterns of the ciphers, which he calls complex and the work of a very intelligent person, has yielded eight doublets of symbols which are equals. He remarked that he didn't feel the ciphers were a hoax because they are too complicated and required too much effort to devise. "A computer may have been used" he said. He thinks the person who made them is intelligent, scheming and imaginative, but not really unusual. "I know kids in school who could do better" on cryptograms.
The next communication mailed by the Zodiac Killer on October 13th 1969 promised to target young children, threatening that "School children make nice targets, I think I shall wipe out a school bus some morning. Just shoot out the front tire + then pick off the kiddies as they come bouncing out". But the most important section in the Vallejo News Chronicle article was "The pattern beginning to take shape apparently will end up a three-tiered diagonal structure composed of sections". The Zodiac Killer's 340 cipher, that followed the October 13th 1969 letter, was three-tiered just like the 408 cipher, but crucially it was structured diagonally for the majority of the coding, as postulated in the newspaper. The title of the newspaper article was Text Of Letter May Offer Clues, but did it offer the inspiration for the Zodiac Killer to create a diagonal shift in his 340 cipher just three months later?
The next communication mailed by the Zodiac Killer on October 13th 1969 promised to target young children, threatening that "School children make nice targets, I think I shall wipe out a school bus some morning. Just shoot out the front tire + then pick off the kiddies as they come bouncing out". But the most important section in the Vallejo News Chronicle article was "The pattern beginning to take shape apparently will end up a three-tiered diagonal structure composed of sections". The Zodiac Killer's 340 cipher, that followed the October 13th 1969 letter, was three-tiered just like the 408 cipher, but crucially it was structured diagonally for the majority of the coding, as postulated in the newspaper. The title of the newspaper article was Text Of Letter May Offer Clues, but did it offer the inspiration for the Zodiac Killer to create a diagonal shift in his 340 cipher just three months later?
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