## 1 Introduction  
Internet of Things (IoT) adoption in healthcare has revolutionized the delivery of medical services, enabling real-time monitoring, personalized care, and remote diagnostics. Wearable devices, implantable sensors, and mobile health applications now form a connected ecosystem that continuously generates sensitive health data. These data are transmitted across networks to cloud platforms or healthcare provider dashboards for processing and intervention. However, the inherent resource constraints of IoT devices and the critical sensitivity of health-related data present significant challenges to ensuring security, privacy, and system efficiency.  
Conventional security protocols, such as TLS and IPsec, while robust, are often unsuitable for constrained environments due to their computational and memory overhead [1, 2, 3]. In many IoT deployments, particularly in e-health scenarios, devices operate with limited processing power, battery capacity, and communication bandwidth. As a result, there is a growing demand for lightweight cryptographic techniques that can ensure data confidentiality and integrity without degrading device performance or user experience. For instance, wearable heart rate monitors or portable glucose sensors typically rely on low-power microcontrollers, which lack the resources to efficiently perform full TLS handshakes.  
This research presents a secure, scalable IoT communication framework tailored for e-health environments. The proposed system incorporates multi-layer encryption strategies and a multi-broker MQTT architecture to ensure efficient, end-to-end protection of patient data across distributed hospital settings. At the edge, lightweight encryption schemes are used to minimize latency and preserve device resources. Data is first transmitted to a local broker within the hospital network and then securely forwarded to a centralized cloud MQTT broker, where more computationally intensive security operations are applied. Finally, authorized medical staff access the data through a secure web or mobile application, acting as a subscriber. In this work, we extend our previous evaluation of lightweight encryption schemes presented in [4] by designing a secure, dual-layer MQTT communication architecture tailored for healthcare IoT systems. The proposed framework integrates Salsa20-Blake2b encryption at the edge with AES-256 over TLS 1.3 for secure transmission to the cloud. A custom bridge application is introduced to seamlessly manage the cryptographic transition between edge and cloud environments, ensuring end-to-end data confidentiality while maintaining performance efficiency.  
To evaluate the effectiveness of the proposed approach, the system was implemented using multiple encryption schemes and benchmarked in terms of encryption time, memory usage, CPU cycles, and throughput. The results demonstrate the feasibility of secure, real-time data transmission in healthcare settings using layered encryption without relying solely on heavy TLS-based solutions.  
The paper is organized as follows. Section 2 presents the theoretical foundations of lightweight cryptography and MQTT-based communication. Section 3 reviews related work in the field of IoT encryption and MQTT security. Section 4 introduces the proposed system architecture. Section 5 details the implementation of the publisher and subscriber modules. Section 6 presents experimental results, performance and security analysis. Finally, Section 7 concludes the paper and outlines future work.