Fog computing is an efficient way of handling IoT data near devices. It minimizes latency and makes things operate more effectively than cloud computing. However, its distributed environment brings important security challenges. The challenges are trust management, node authentication, and data integrity in edge-fog networks. In this paper, a new security system based on blockchain is suggested to improve the security of fog computing networks. By combining PBFT consensus with a strict process to validate nodes, our solution secures and optimizes data processing. The system can process 50 edge devices and 10 fog nodes that work on different types of data, such as sensor data, image data, and control signals. Multiple validator signatures are utilized to validate the nodes, with five signatures required to guard against unauthorized access. Performance tests show steady system performance with an average processing time of 48.3 ms and CPU usage between 0.1 and 0.5, which is indicative of proper load balancing. Data transfer testing shows the system handling 100-to-1000-byte payloads with ease. PBFT mechanism demonstrates Byzantine fault tolerance with no effect on performance, and blockchain provides tamper-proofing for records. Results confirm the scalability, security, and readiness of the framework for real-world fog computing deployments, addressing fundamental challenges in node management and secure data processing.