This study establishes a statistically rigorous and fully reproducible Monte Carlo bench- mark for the BB84 quantum key distribution (QKD) protocol under symmetric depolarizing channel noise. We implement a transparent, parameterized simulator to conduct extensive noise sweeps from p = 0% to p = 26% depolarizing probability. Through large-scale trials, each processing 104 signals with 10 independent repetitions, we generate statistically robust mean Quantum Bit Error Rate (QBER) and Shor-Preskill secure key rates, complete with 95% confidence intervals. Our results validate the fundamental Q p/2 relationship with a maximum deviation from theory of 0.27% and quantify the sharp security threshold collapse. At p = 10% (QBER ≈ 5%), we achieve an ideal asymptotic key rate of RQKD ≈ 0.427 per sifted bit, while the secure fraction becomes negligible beyond p = 22% (QBER ≈ 11%). The empirically determined threshold, where the secure key rate vanishes at pth 0.22, aligns closely with theoretical predictions. This work’s primary contribution is a validated computational framework that serves as an essential benchmark and a computational null hypothesis against which to quantify performance deviations in practical QKD systems aris- ing from reconciliation inefficiency, finite-key effects, and device imperfections, thus bridging a critical gap between asymptotic security theory and the engineering of real-world quantum networks.
This study establishes a statistically rigorous and fully reproducible Monte Carlo bench- mark for the BB84 quantum key distribution (QKD) protocol under symmetric depolarizing channel noise. We implement a transparent, parameterized simulator to conduct extensive noise sweeps from p = 0% to p = 26% depolarizing probability. Through large-scale trials, each processing 104 signals with 10 independent repetitions, we generate statistically robust mean Quantum Bit Error Rate (QBER) and Shor-Preskill secure key rates, complete with 95% confidence intervals. Our results validate the fundamental Q p/2 relationship with a maximum deviation from theory of 0.27% and quantify the sharp security threshold collapse. At p = 10% (QBER ≈ 5%), we achieve an ideal asymptotic key rate of RQKD ≈ 0.427 per sifted bit, while the secure fraction becomes negligible beyond p = 22% (QBER ≈ 11%). The empirically determined threshold, where the secure key rate vanishes at pth 0.22, aligns closely with theoretical predictions. This work’s primary contribution is a validated computational framework that serves as an essential benchmark and a computational null hypothesis against which to quantify performance deviations in practical QKD systems aris- ing from reconciliation inefficiency, finite-key effects, and device imperfections, thus bridging a critical gap between asymptotic security theory and the engineering of real-world quantum networks.
Quantum Key Distribution (QKD) is increasingly recognized as a robust solution to the vulnerabilities posed by quantum computing to classical encryption systems. This paper presents a comprehensive investigation of the BB84 protocol, the foundational QKD scheme, through simulated quantum communication using IBM’s Qiskit framework. The study models quantum key exchange under both ideal and adversarial conditions, including channel noise and intercept-resend attacks. The Quantum Bit Error Rate (QBER) was measured as a function of noise intensity and eavesdropping, confirming that QBER increases predictably in compromised channels. A threshold of 11% QBER was used to determine the viability of secure key generation. Final key retention rates were analyzed across multiple channel scenarios, revealing BB84’s sensitivity to both photon loss and adversarial interference.\n\nSecurity vulnerabilities such as photon-number-splitting and detector blinding were assessed, and countermeasures including decoy-state protocols and authenticated classical channels were proposed. Four key performance graphs were generated to visualize system behavior under realistic operational conditions. The results support BB84’s theoretical advantage in ensuring information-theoretic security while acknowledging real-world limitations in transmission range and hardware reliability. The paper concludes by addressing future improvements in QKD systems, including satellite-based distribution, quantum repeaters, and device-independent implementations. Through simulation-driven analysis, this study validates BB84 as a practical defense against quantum-enabled attacks and underscores the need for continued development and standardization in post-quantum cryptographic infrastructure.
Quantum Key Distribution (QKD) provides information-theoretic security by exploiting the principles of quantum mechanics. Among QKD protocols, the BB84 scheme remains the most widely adopted for both theoretical research and practical implementation. A critical parameter determining the reliability and security of BB84 is the Quantum Bit Error Rate (QBER), which quantifies errors in the sifted key arising from channel noise or potential eavesdropping. This paper presents a systematic review and analysis of QBER within the BB84 protocol, examining its calculation, statistical estimation methods, and role in detecting eavesdropping activity. Simulation results, corroborated by reported experimental observations, reveal a near-linear relationship between eavesdropping intensity and QBER, with values approaching 25% under full intercept-resend attacks. Four confidence interval estimation methods, Wald, Wilson, Clopper-Pearson, and Hoeffding's inequality, are compared for robust QBER analysis in finite-key scenarios. Protocol enhancements, including decoy-state methods, hybrid cryptographic models, and quantum-resistant authentication, are discussed as mechanisms to mitigate errors and strengthen resilience across fiber, free-space, underwater, and satellite QKD systems. Open challenges in distinguishing noise-induced errors from malicious eavesdropping, and the role of adaptive error correction and machine-learning-assisted QBER estimation in future quantum networks, are identified as key directions for further research.
This paper presents a detailed theoretical and simulation-based comparison between the BB84 quantum key distribution (QKD) protocol and a proof-of-concept contextuality-based QKD protocol (CTX-QKD) under depolarizing noise. We begin by contrasting classical cryptography’s computational security with quantum cryptography’s information-theoretic guarantees. The physics of quantum cryptography, including superposition, entanglement, and the no-cloning theorem, is explored, followed by a mathematical analysis of BB84 and a proposed CTX-QKD framework. Performance metrics include the quantum bit error rate (QBER) for BB84 and contextuality violation measures for CTX-QKD, with confidence intervals derived from proper statistical bounds. A comprehensive simulation methodology using QuTiP, NumPy, and SciPy is described. Simulation results demonstrate that while BB84 shows expected noise tolerance up to 11% QBER, the CTX-QKD protocol maintains strong contextuality violations of the fundamental security condition under high noise conditions where BB84 fails. This study highlights the potential of contextuality as a resource for quantum cryptography and demonstrates a proof-of-concept for physics-based cryptographic security beyond traditional approaches.
Quantum key distribution (QKD) enables secure communication using the principles of quantum physics. The BB84 protocol is not only effective for secure key sharing but also for detecting eavesdropping. This study simulates a computational model of QKD and analyzes error rates under varying numbers of bits. Using Python-based simulations with n = 10, n = 100, and n = 1000 bits, and a fixed noise probability of 0.02, we evaluated scenarios both with and without eavesdropping over 1000 trials. The results show an average error rate of 2% without eavesdropping and over 26% with eavesdropping. Standard deviation increases with lower n, indicating higher variability. This study validates BB84’s robustness under noise and demonstrates its sensitivity to third-party interference.
Practical quantum key distribution (QKD) systems operate under noise, but security of most protocols have been analyzed under ideal noiseless scenarios. In this work, we investigated security performance of BB84 protocol under effect of collective rotation noise. Using theoretical quantum information frameworks, we analyzed key security parameters including quantum bit error rate (QBER), mutual information and secret key rate (SKR). Security of protocol is studied under various eavesdropping scenarios based on intercept and resend attacks. Our results show that collective rotation noise has a significant impact on the information shared between the two parties. Particularly, we extended prior treatments by suggesting a noise engineering strategy where we identified a non-zero noise range where information accessed by Eve is minimized while corresponding SKR degradation remains relatively small. This analysis provide insights into robustness of BB84 protocol under realistic noisy channels and may contribute towards development of more resilient QKD systems.
The absence of real single-photon sources is a significant limitation to the experimental implementation of the BB84 quantum key distribution (QKD) protocol. When substantially attenuated laser pulses are substituted for ideal sources in practical systems, the outcome is weak coherent states where each pulse has a nonzero probability of having multiple photons rather than pure single-photon emission. To evaluate quantum bit error rate (QBER), key generation rate and overall system security it is essential to describe the exact impact of the optical and physical system on such pulses. This practical tradeoff presents additional issues. It is crucial to understand how QBER is impacted by attenuation, loss, dispersion, depolarisation and detector properties particularly in adversarial scenarios such as photon number splitting (PNS) and beam-splitting attacks. Although a significant amount of research has been conducted on algorithmic simulations of BB84, there are few complete frameworks that can physically explain these effects and their impact on QBER. This work models the BB84 protocol at the physical level by developing a Python-based simulation platform that takes into account all significant channel impairments and system inefficiencies. The framework supports both theoretical and practical optimisation of QKD systems by further isolating the effects of different optical losses and eavesdropping techniques on QBER and secure key generation.