The Hunt for the Zodiac's 340 Cipher: 51 Years to Crack It

In November 1969, the Zodiac Killer mailed a 340-character coded message to the San Francisco Chronicle. For 51 years, professional cryptographers, FBI analysts, and thousands of amateur sleuths tried and failed to crack it. On December 5, 2020, three men announced they had solved it.

THE CIPHER: The "Z340" — named for its 340 characters — used a complex substitution cipher with multiple alphabets and deliberate misdirection. Unlike the earlier Z408 cipher (solved in 1969), the Z340 had been carefully constructed to resist standard frequency analysis.

THE SOLVERS:

• David Oranchak, a software developer from Virginia who had been studying the cipher for 14 years
• Jarl Van Eycke, a Belgian programmer who built specialized software
• Sam Blake, an Australian mathematician

THE BREAKTHROUGH: Oranchak hypothesized that the Zodiac had written the message in a complex diagonal reading pattern rather than left-to-right. He and Van Eycke programmed their decryption software to test thousands of possible transposition patterns. Blake's mathematical analysis narrowed the search space.

A computing cluster ran through 650,000 possible configurations. One returned readable English.

THE DECODED MESSAGE: "I HOPE YOU ARE HAVING LOTS OF FUN IN TRYING TO CATCH ME... I AM NOT AFRAID OF THE GAS CHAMBER BECAUSE IT WILL SEND ME TO PARADICE ALL THE SOONER..."

The decoded message — riddled with the Zodiac's characteristic misspellings — was confirmed authentic by professional cryptographers.

THE MYSTERY CONTINUES: Two other Zodiac ciphers (Z13 and Z32) remain unsolved. The killer's identity remains unknown.

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