Code and records for "Passing NPCR Without Diffusion: Exact Signatures, a Detection Benchmark and an Audit of Published Image Ciphers"

Abstract

Version 2.0 adds the code, records and technical report behind the manuscript "Passing NPCR Without Diffusion: Exact Signatures, a Detection Benchmark and an Audit of Published Image Ciphers". Version 1.0 (the XCM-IC cipher, its test vectors, preregistrations, execution freeze, Tier A and battery records) is kept unchanged as XCM_NPCR_artifact_v1.0.zip. Passing_NPCR_code_and_records_v2.0.zip contains: - the closed-form NPCR count for one round of forward and backward chaining, with its moments, power calculation, UACI model and scope checks;- the audit of 21 published image ciphers: transcribed values with table numbers, a structural reimplementation of one regime B diffusion layer, the UACI comparison for one video cipher, and a surrogate model and Python port of one batch cipher, checked byte for byte against the authors' public C code (fetched by commit hash, not redistributed);- the eight-bit, round-count experiment through the XCM-IC implementation, with trial-level values and bootstrap intervals;- the detection benchmark (nine simulated ciphers and independent ciphertexts), its robustness runs and its ablation at recalibrated thresholds;- npcr_check, a checker that reads a published NPCR table, with its input tables, verdicts and validation;- reproduce.sh, which regenerates every record, table and figure, and check_consistency.py, which recomputes 179 printed numbers from the records;- SHA256SUMS for every file. Passing_NPCR_technical_report_v2.0.pdf is the companion report: the full XCM-IC specification, the proofs of the finite-state results, the complete evaluation of the instrument and the audit procedure in full. The image corpora are not included; they are the public Kodak and USC-SIPI sets, pinned by SHA-256 in version 1.0.