EVID-DGC -- Blockchain-Based Evidence Management System

The integrity of digital evidence in law enforcement and legal proceedings depends fundamentally on maintaining an immutable chain of custody and cryptographic proof of non-tampering. Traditional centralized evidence management systems suffer from critical vulnerabilities: manual documentation prone to manipulation, limited auditability, fragmented custody records, and difficulty proving authenticity in court. This paper presents EVID-DGC (Evidence Digital Guardian (2) decentralized IPFS storage with content-addressed verification; (3) Polygon blockchain recording all evidence handling transactions with ~2-second finality and 0. 001 average cost. The system supports eight specialized roles (Public Viewer, Investigator, Forensic Analyst, Legal Professional, Court Official, Evidence Manager, Auditor, Administrator) with granular permissions enforced at the database kernel level through Supabase Row-Level Security policies. Empirical results demonstrate: 100/100 chain of custody integrity score, 100/100 evidence preservation score, zero unauthorized access incidents across 847 test cases, 99. 2% production uptime, and compliance with ISO/IEC 27037, NIST SP 800-86, and Federal Rules of Evidence standards. The system achieves a 95/100 Forensic Soundness Score, indicating production readiness for law enforcement deployment. This research demonstrates that blockchain technology fundamentally transforms evidence management from a trust-based model (reliant on institutional oversight) to a verification-based model (reliant on mathematical cryptography), reducing tampering incidents by providing provable n