Published Paper Details:

The rapid progress of quantum computing threatens the security of classical cryptographic systems such as RSA and ECC, making the transition to quantum-resistant solutions essential. This research proposes a hybrid key exchange protocol built explicitly on a Defense-in-Depth security model, where multiple independent cryptographic layers are integrated to provide robust and resilient protection. The protocol combines classical methods like Elliptic Curve Diffie-Hellman (ECDH) with post-quantum mechanisms such as ML-KEM, along with the incorporation of Quantum Key Distribution (QKD). In this layered architecture, each component acts as an independent security barrier, ensuring that even if one mechanism is compromised, the remaining layers continue to protect the session key and maintain system integrity. The framework introduces a dual-handshake mechanism and adaptive parameter selection to achieve both backward compatibility with existing infrastructure and enhanced forward secrecy. The Defense-in-Depth strategy is realized through the combination of classical, post-quantum, and quantum-based security assumptions, significantly reducing the risk of single-point failure and strengthening resistance against both classical and quantum adversaries. Performance is evaluated across diverse deployment scenarios, considering metrics such as CPU utilization, and memory overhead. Experimental results prove that the hybrid design maintains near-classical efficiency while improving security, achieving up to a 30% reduction in latency compared to purely post-quantum approaches. Overall, This system establishes a practical and standards-compliant framework for secure communication, effectively mitigating emerging threats such as "harvest now, decrypt later" attacks in the post-quantum era through a comprehensive Defense-in-Depth approach.