https://doi.org/10.1140/epjqt/s40507-026-00493-z
Research
BB84 a new hope enhanced QKD for secure email communication with additional quantum gates
Computer Science and Engineering, Rajalakshmi Engineering College, Anna University, Chennai, India
a
This email address is being protected from spambots. You need JavaScript enabled to view it.
Received:
3
January
2026
Accepted:
5
March
2026
Published online:
24
March
2026
Abstract
The imminent realization of fault-tolerant quantum computing presents an existential threat to the cryptographic foundations of the modern digital economy. Algorithms such as Shor’s and Grover’s are poised to dismantle classical public-key encryption schemes like RSA (Shor in SIAM Rev. 41:303–332, 1999) and Elliptic Curve Cryptography (ECC) by solving integer factorization and discrete logarithm problems in polynomial time (Grover in A fast quantum mechanical algorithm for database search, 1996, arXiv [quant-ph]). This vulnerability endangers critical infrastructures, particularly secure email correspondence, which remains a primary vector for sensitive data exchange. Traditional defenses are proving inadequate against the “harvest now, decrypt later” strategies employed by sophisticated adversaries who stockpile encrypted traffic in anticipation of Q-Day (Venkatesh et al. in J. Sci. Eng. Technol. Manag. Sci. 2:567–577, 2025). Against this backdrop, this research introduces BB8-4, an enhanced Quantum Key Distribution (QKD) protocol specifically designed for secure email environments. The protocol advances the standard BB84 paradigm through two distinct innovations: the integration of a Hyper-Entropic 7-Gate State Preparation mechanism and an AI-Driven Dynamic Basis Selection engine.
Unlike traditional implementations that rely on a limited two-basis set, BB8-4 incorporates an expanded library of quantum gates - specifically Identity (I), Hadamard (H), Pauli-X, Pauli-Y, Pauli-Z, Phase (S), and the non-Clifford 
gate (T) - to fundamentally augment the indistinguishability and Von Neumann entropy of the transmitted quantum states. This “7-gate” approach forces an eavesdropper into a higher-dimensional guessing space, significantly degrading the information gain from intercept-resend attacks and raising the disturbance threshold required for detection. Furthermore, the protocol addresses the inherent 50% sifting inefficiency of standard QKD by employing a synchronized Deep Reinforcement Learning (DRL) agent to predict and align measurement bases between Alice and Bob without public disclosure (Kaldari et al. in Quantum reinforcement learning: Recent advances and future directions, 2025, arXiv [quant-ph]).
Key words: Quantum Key Distribution (QKD) / BB84 protocol / Post-quantum cryptography / AI-driven security / Deep reinforcement learning / Hyper-entropic states / Secure email communication / Quantum gates / Eavesdropping detection
© The Author(s) 2026
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
