As the IoT is moving out of its early stages, it is emerging as an area of future internet. The evolving communication paradigm among cloud servers, Fog nodes and IoT devices are establishing a multilevel communication infrastructure. Fog provides a platform for IoT along with other services like networking, storage and computing. With the tremendous expansion of IoT, security threats also arise. These security hazards cannot be addressed by mere dependence on cloud model. In this paper we present an overview of security landscape of Fog computing, challenges, and, existing solutions. We outline major authentication issues in IoT, map their existing solutions and further tabulate Fog and IoT security loopholes. Furthermore this paper presents Blockchain, a decentralized distributed technology as one of the solutions for authentication issues in IoT. We tried to discuss the strength of Blockchain technology, work done in this field, its adoption in COVID-19 fight and tabulate various challenges in Blockchain technology. At last we present the Cell Tree architecture as another solution to address some of the security issues in IoT, outlined its advantages over Blockchain technology and tabulated some future course to stir some attempts in this area.