ABSTRACT: The foundational security architecture of the global digital economy, currently sustained by public-key cryptographic frameworks such as RSA and Elliptic Curve Cryptography (ECC), faces an existential vulnerability from the advent of quantum computing. The eventual realization of a Cryptanalytically Relevant Quantum Computer (CRQC)—projected for the 2030s—will leverage Shor’s algorithm to solve integer factorization and discrete logarithms in polynomial time, effectively rendering modern asymmetric encryption obsolete. Furthermore, Grover’s algorithm will quadratically degrade the security margins of symmetric standards like AES. This computational paradigm shift introduces immediate risks via "Harvest Now, Decrypt Later" (HNDL) attacks, where adversarial actors passively intercept and store encrypted data for retroactive decryption, compromising long-term data confidentiality today.

To mitigate this systemic risk, global cybersecurity frameworks are evolving along two parallel trajectories: Post-Quantum Cryptography (PQC) and Quantum Key Distribution (QKD). While PQC replaces vulnerable algorithms with quantum-resistant mathematical structures, QKD represents a fundamental shift from computational hardness assumptions to information-theoretic security rooted in the laws of quantum mechanics. By transmitting cryptographic keys via the quantum states of single photons, QKD ensures that any eavesdropping attempt inherently alters the physical states, immediately alerting communicating parties.

This report provides a comprehensive technical analysis of QKD's transition from a theoretical quantum optics concept to an actively deployed, carrier-grade infrastructure between 2024 and 2026. It examines underlying physical protocols, hardware vulnerability mitigations, advancements in optical range and network scalability, the commercial integration of hybrid QKD-PQC architectures, and the intensifying geopolitical race to establish global, space-terrestrial quantum communication networks.

A COMPREHENSIVE ANALYSIS OF QUANTUM KEY DISTRIBUTION: THEORETICAL FOUNDATIONS, TECHNOLOGICAL ADVANCEMENTS, AND GLOBAL NETWORK DEPLOYMENTS

SHILPI GUPTA & CHANDAN GUPTA
GUIDE NAME: CHIRAG DEORA
INSTITUTE NAME: CENTRE FOR DISTANCE AND ONLINE EDUCATION – UNIVERSITY OF MUMBAI