Layered Cryptographic Trust for Open Digital Systems: A Conceptual Framework Linking Private-Key Limitations, Public-Key Exchange and Post-Quantum Migration

Abstract

Modern digital infrastructures rely on cryptography to establish confidentiality, integrity, authentication, non-repudiation and secure key establishment over networks that cannot be assumed trustworthy. Yet the relationship between private-key limitations, public-key exchange, computational security, pseudorandomness, chosen-plaintext security and post-quantum migration is often presented in fragmented form. This study develops a layered design-science framework for cryptographic trust in open digital systems. The work adopts a conceptual review method supported by standards-based triangulation. Core techniques were analysed against their security role, mathematical basis, computing requirements, application domain, operational risk and post-quantum relevance. The resulting framework shows that symmetric encryption remains the most practical mechanism for high-volume data protection, but it depends on reliable key establishment and lifecycle governance. Public-key cryptography provides scalable trust and authentication, while Diffie-Hellman exchange and key derivation functions connect mathematical shared-secret construction to deployable session keys. Pseudorandomness and chosen-plaintext security give formal discipline to encryption design, whereas post-quantum cryptography introduces migration requirements for long-term confidentiality and identity assurance. The study contributes an integrated architecture that connects cryptographic theory, implementation practice and institutional readiness. Its main implication is that secure systems should be designed as hybrid, lifecycle-aware and algorithm-agile infrastructures rather than as isolated deployments of individual cryptographic primitives.