Preprint / Version 3

JCCDB v1.2 — Cryptographic Audit Hash and Macroeconomic Price Correction for Reproducible LLM-Based Construction Cost Diagnostics(v1.2.1)

##article.authors##

DOI:

https://doi.org/10.31224/7007

Keywords:

construction cost estimation, Japan, consumer protection, cryptographic audit hash, AI reproducibility, EU AI Act compliance, macroeconomic correction, Hormuz Strait crisis, deterministic LLM systems, residential renovation, SHA-256, Cloudflare Workers, Bank of Japan CGPI

Abstract

We present JCCDB v1.2, a substantive extension to the Japan Construction Cost Database (JCCDB), an open structured dataset supporting LLM-based construction cost diagnostic systems for consumer protection.

First, we introduce a cryptographic audit hash mechanism based on SHA-256 that provides reproducibility guarantees for diagnostic outputs: identical inputs always produce the same 12-character (48-bit) audit hashes printed on consumer-facing PDF reports, enabling vendor-neutral, client-side verification during contractor negotiations.

Second, we describe a War Price Coefficient (WPC) subsystem that automatically incorporates manufacturer price-change announcements into monthly price corrections, addressing the documented exploitation of material price volatility in renovation contractor fraud. The current deployed coefficient is ×1.0935 (+9.35%, Hormuz Strait/Iran-conflict baseline), computed from a weighted composite of seven CGPI series and four manufacturer announcements.

We demonstrate the production deployment of both mechanisms within HORIZON SHIELD, a Cloudflare Workers-based diagnostic service, and validate hash output stability. Theoretical collision analysis using the birthday-bound approximation indicates collision probability below 2×10⁻⁵ for realistic deployment scales within the 48-bit truncated hash space.

The mechanisms described are designed to align with the recording and human-oversight principles of EU AI Act Article 12 and Article 14 (Regulation 2024/1689, applicable to high-risk systems from August 2, 2026), and are released under CC-BY 4.0 to support independent replication.

[v1.2.1 May 2026] This revision corrects 8 implementation discrepancies between manuscript and production code, adds Section 3.8 documenting OpenTimestamps Bitcoin blockchain anchoring, Section 4.5 deployment epoch theorem, and Section 7.4 practitioner observations from n=98 operational cases. Core contributions are unaffected.

Downloads

Download data is not yet available.

Downloads

Posted

2026-05-06 — Updated on 2026-05-15

Versions

License

Copyright (c) 2026 Toshikatsu Oga

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.

Version justification

v1.2.2 corrects a numerical inconsistency between the collision-probability tables in Section 3.4 and Section 6.2. Section 3.4 previously reported values computed from the closed-form approximation n²/(2·2⁴⁸), while Section 6.2 used the exact birthday-bound formula 1−exp(−n(n−1)/(2·2⁴⁸)), producing inconsistent figures at large n (17.8% vs. 16.28% at n=10⁷). Both tables are now unified on the exact formula, with an added clarifying note. All audit-hash values in Sections 6.3, 6.4, 6.5 have been independently re-verified against a reference Python 3 hashlib implementation. No other content has been substantively altered. We thank Prof. Pang-jo Chun (The University of Tokyo) for identifying the inconsistency.