Wireless Sensor Networks and Industrial Internet of Things use smart, autonomous and usually limited capacity devices in order to sense and monitor industrial environments. The devices in a wireless sensor network are managed by a controller, which should authenticate them before they join the network. OCARI is a wireless sensor network technology providing optimized protocols in order to reduce the energy consumption. To enhance OCARI security and ensure a robust authentication of devices, we propose a strong authentication method based on the One Time Password algorithm and deployed at the MAC sub-layer. This method is specially designed to be implemented on devices with low storage and computing capacities.