Abstract— With the Internet of Things (IoT), the number of connected devices on the internet has increased to billions, and this number is expected to grow exponentially in the coming years. Services and applications based on the IoT are expected to expand to cover more areas in the near future. Performance, connectivity and security are very important aspects of such an expansive environment. In order to enhance the performance and security of the IoT, a secure and cost-effective model for IoT applications that is based on Message Queue Telemetry Transport (MQTT) is proposed. This model addresses the IoT security challenges primarily by moving access control and data management from the MQTT broker to a fog server. The performance of the proposed model is validated by multiple metrics; and the obtained results show that it can be deployed successfully in the implementation of IoT applications to enhance both the IoT’s security and performance.