Student Seminar
Name: Mr. Shubham Kumar Debadatta
Title: The Classical to Quantum Transition in Secure Communication
Date & Time: Thursday, 18th September 2025 at 4.00 p.m.
Venue: Rajarshi Bhattacharyya Memorial Lecture Hall, Chemical Sciences Building
Abstract:
Secure communication has long been achieved using classical cryptographic techniques, where encryption converts data into ciphertext and decryption restores it using a key. Cryptography provides the theoretical foundation behind this process, while encryption serves as the practical tool. A fundamental issue in this paradigm is the key distribution problem: symmetric encryption requires both parties to share the same secret key, whereas asymmetric systems such as RSA exploit mathematical trapdoor functions.1 The security of RSA is based on the difficulty of factoring large integers, which remains sub-exponential in complexity for classical algorithms. However, quantum computation introduces a major vulnerability—Shor’s algorithm can factor such numbers in polynomial time, rendering RSA insecure if large-scale quantum computers with millions of qubits become available.2 This looming threat calls for alternatives that are fundamentally resistant to quantum attacks.
Quantum key distribution (QKD) provides such a solution by harnessing quantum-mechanical principles to enable secure key exchange, independent of computational assumptions. Among QKD protocols, twin-field QKD (TF-QKD) has emerged as a breakthrough because it surpasses the repeaterless secret key capacity bound. A recent experimental demonstration achieved TF-QKD over 254 km of deployed telecom fibre, distributing secret keys at practical rates using scalable techniques such as off-band phase stabilization and semiconductor avalanche detectors.3 This result not only shows the feasibility of long-distance quantum communication without cryogenic cooling but also illustrates how QKD can be integrated into existing telecommunication infrastructure, offering a realistic pathway toward secure, large-scale quantum networks.
References:
1. Rivest, R. L.; Shamir, A.; Adleman, L. Communications of the ACM 1978, 21 (2), 120–126.
2. Shor, P. W. Proceedings 35th Annual Symposium on Foundations of Computer Science (1994), 124–134.
3. Pittaluga, M.; Lo, Y. S.; Brzosko, A.; Woodward, R. I.; Scalcon, D.; Winnel, M. S.; Roger, T.; Dynes, J. F.; Owen, K. A.; Juárez, S.; et al. Nature 2025, 640, 911–917.