The Zodiac Z13 and Z32 Ciphers as a Structural Anti-Cipher System: NANNANLA as Closure Signature and Z32 as Terminal Operator

The Zodiac Killer’s Z13 (“My name is—”) and Z32 (map/bomb code) ciphers remain unsolved despite decades of analysis. This paper proposes that they are not conventional homophonic substitution puzzles, but instead form a deliberately constructed self-closing disclosure system encoding permanent structural ambiguity rather than recoverable plaintext content. Z13 is interpreted as the residue of constraint propagation from the solved Z340 cipher lattice, collapsing to a closed corridor (Row 14, Columns 10–17) and stabilizing as the invariant signature NANNANLA (A1Z26 vector: 14-1-14-14-1-14-12-1). This sequence functions as a fixed-point seed in the Z32 parameter space P= (θ, d, ϕ, s) P = (, d, , s) P= (θ, d, ϕ, s), reducing the dimensionality of the solution manifold from ≥2 to approximately 1–2, but never to zero—preserving irreducible ambiguity under admissible transformations. A key result is the modular anchoring of this seed: the vector sum 71 yields θanchor=71 mod 2π≈1. 885 rad≈108∘, ₀₍₂₇₎ₑ = 71 2 1. 885 rad 108^, θanchor=71mod2π≈1. 885 rad≈108∘, providing an invariant angular constraint without collapsing the system to a unique solution. Z32 is thus interpreted as a terminal operator, sealing the identity-disclosure pathway. The system qualifies as an anti-cipher: a symbolic structure resembling a cipher but encoding terminal undecidability. Major external solution claims (geometric, confessional, and anagrammatic) are rejected via algebraic consistency tests. The system is further interpreted through the Convexity Principle and Recursive Survival Law, framing the ciphers as self-protecting informational artifacts analogous to resilience structures in complex systems. No decryption is claimed. Instead, the paper explains why decryption is structurally precluded.