This research introduces a blockchain-based decentralized authentication and access control protocol for fog computing environments. It addresses the limitations of centralized models in IoT networks, such as bottlenecks and single points of failure, by leveraging blockchain's decentralized nature. The protocol integrates advanced cryptographic techniques and scalable architecture, enhancing security, efficiency, and scalability. Simulations using iFogSim and Hyperledger Caliper demonstrate significant improvements in authentication time, transaction throughput, and security. The study offers a robust solution for managing the increasing number of IoT devices, advancing blockchain's role in secure fog computing environments.