# QESIF: A Lightweight Quantum-Enhanced IoT Security Framework for Smart Cities
###### Abstract  
Smart cities necessitate ultra-secure and scalable communication frameworks to manage billions of interconnected IoT devices, particularly in the face of the emerging quantum computing threats. This paper proposes the QESIF, a novel Quantum-Enhanced Secure IoT Framework that integrates Quantum Key Distribution (QKD) with classical IoT infrastructures via a hybrid protocol stack and a quantum-aware intrusion detection system (Q-IDS). The QESIF achieves high resilience against eavesdropping by monitoring quantum bit error rate (QBER) and leveraging entropy-weighted key generation. The simulation results, conducted using datasets TON IoT, Edge-ItoTset, and Bot-IoT, demonstrate the effectiveness of the QESIF. The framework records an average QBER of 0.0103 under clean channels and discards over 95% of the compromised keys in adversarial settings. It achieves Attack Detection Rates (ADRs) of 98.1%, 98.7%, and 98.3% across the three datasets, outperforming the baselines by 4-9%. Moreover, the QESIF delivers the lowest average latency of 20.3 ms and the highest throughput of 868 kbit/s in clean scenarios while maintaining energy efficiency with 13.4 mJ per session. QESIF: A Lightweight Quantum-Enhanced IoT Security Framework for Smart Cities 2025804016  
16 May 2025  
Revised: 2 July 2025  
Accepted: 6 July 2025  
Published: 10 July 2025  
**Citation:** [PERSON]; [PERSON] QESIF: A Lightweight Quantum-Enhanced IoT Security Framework for Smart Cities. _Smart Cities_**. _Smart Cities_**. exchange, and processing of data across various city domains, including energy, transportation, healthcare, and security [4]. However, the rapid deployment of IoT devices has exposed smart city infrastructures to critical cybersecurity risks, including data interception, unauthorized access, and large-scale coordinated attacks. As conventional encryption mechanisms struggle to keep pace with the emerging threats--especially those posed by quantum computing--there is a growing need for next-generation security frameworks [5]. The recent advancements in quantum cryptography, particularly Quantum Key Distribution (QKD), have demonstrated the potential to provide theoretically unbreakable encryption [6]. Integrating QKD with lightweight and resource-constrained IoT systems within smart cities remains largely unexplored [7]. Regarding the advancements in smart city technologies, the underlying security of IoT communication remains a persistent challenge. Although widely adopted, traditional cryptographic schemes are vulnerable to both classical and quantum attacks, particularly in urban environments with high device density and real-time data flow requirements [8; 9]. These vulnerabilities pose severe risks to critical smart city services, from transportation coordination to emergency response systems. Therefore, there is a pressing need to explore quantum-resilient solutions that are scalable and adaptable to smart city architectures. The primary research question addressed in this work is how QKD can be integrated into lightweight IoT frameworks to ensure quantum-resilient and energy-efficient smart city security. Motivated by this question, this research proposes a framework that unifies quantum cryptographic methods with traditional IoT security layers, enhancing both confidentiality and intrusion resilience across a city-wide network. The proposed QESIF is a novel framework that combines QKD with smart city IoT infrastructures through a hybrid security protocol stack. The QESIF introduces a lightweight QKD layer compatible with constrained devices, a middleware layer for key management, and a Q-IDS capable of leveraging quantum error indicators such as QBER to detect eavesdropping. A hybrid protocol stack dynamically shifts between classical and quantum-secured communication based on device capability and criticality of data. This framework is designed to work with existing IoT protocols such as MQTT and CoAP while injecting QKD-generated keys at the transport or session layer.