Fragmentary Cryptosystems and Z32: A Discussion Note in the Philosophy of Cryptography

This paper examines the Zodiac killer’s unsolved 32-symbol cipher (Z32) as an example of what we call a fragmentary cryptosystem. Using a simple simulated annealing algorithm with quadgram scoring, stable anchors such as “TEST HERE” and the digit cluster 6–0–1 emerge consistently. These anchors align with the Zodiac’s own reference to “radians + # inches” on a Mt. Diablo map, suggesting hybrid instructions that point toward San Francisco police sites. Rather than a solvable substitution ci-pher, Z32 appears designed to produce local intelligibility without global resolution. We argue this illustrates a broader philosophical point: cryptographic systems may embody ambiguity by design, functioning as instruments of uncertainty rather than hidden communication.