Zero-Trust Spectrum — Files (ZS-1 → ZS-6): CyBOK, NCSC, and NIST-aligned framework for file assurance classification and decision guidance.

Defines six assurance levels (ZS-1 → ZS-6) describing how digital files are validated, sanitized, or rebuilt within a Zero-Trust architecture. The framework maps to operational controls in NCSC Zero-Trust guidance, NIST SP-800-207, and the Cyber Security Body of Knowledge (CyBOK). Content includes: • Level definitions and evaluation criteria • Deployment and integration patterns (Email, Web, Storage, API, SDK, Air-Gap/CDS, Automation) • Decision Quick Picks for architecture and procurement • Alignment signals to CyBOK, NCSC, and NIST principles • Licensing and governance for reuse (CC BY 4.0) Intended as an open reference for governments, integrators, and researchers seeking measurable file assurance standards within Zero-Trust programs.