<p>The proliferation of smart technologies and Internet of Things (IoT) applications has introduced challenges in managing huge volumes of data, necessitating efficient operations for battery-powered IoT nodes. Data aggregation is a key technique to eliminate redundancy, improve energy efficiency, extend network lifespan, and reduce network traffic. However, IoT sensors are susceptible to various attacks because of their constrained resources and the unpredictability of wireless transmission. We propose an Energy-Efficient and Secure Data Aggregation (EESDA) protocol for IoT networks that employs a secure aggregation method to overcome these challenges. The protocol operates at two levels: the IoT node level and the cluster head level. At the node level, it caches the maximum value of sensed data, reducing traffic and transmitting the encrypted maximum value to the cluster head. At the cluster head level, aggregated encrypted data is managed and forwarded securely to the edge node. The performance of EESDA is evaluated against protocols including Hierarchical Data Aggregation with Particle Swarm Optimization (HDA-PSO), Lightweight Structure-based Data Aggregation Routing (LSDAR), Cluster-based Energy-aware Data Aggregation Routing (CEDAR), and Hybrid Particle Swarm Optimization with Improved Low-Energy Adaptive Clustering Hierarchy (HPSO-ILEACH). Metrics such as the proportion of live nodes, remaining energy, network lifetime, stability, and packet delivery ratio are analyzed under various scenarios. Simulation results show that EESDA effectively conserves residual energy by minimum 20%, extends network lifetime by at least 25%, improves stability by minimum 10%, maintains a high packet delivery ratio with a minimum improvement of 2%, and ensures at least 20% residual energy.</p>