# Towards a Provably Secure Authentication Protocol for Fog-Driven IoT-Based Systems
## 1 Introduction  
In this modern era, the healthcare system has proved to be an influential industrial IoT (IIoT) application in which IoT devices are deployed either at enormous healthcare centers or small private clinics. Moreover, the increasing popularity of the several wearable smart IoT devices has significantly transformed the typical healthcare system from an originally hospital-centric to a patient-centric system. Such a patient-centric approach bridges the gap between practitioners and patients by offering reliable and seamless delivery of sensitive information. It allows citizens to contact practitioners remotely and be availed of medical advice and prescriptions at their doorstep. For instance, wearable smart IoT devices (i.e., heart rate monitors, Electrocardiograms (ECG) monitoring instruments, etc.) are proficient enough to sense, inspect and stream information to various healthcare professionals without any requirement of a physical visit to the hospital [1, 2]. The healthcare system is considered a particular industry that requires minimized latency. For instance, a delay of only a minute can cause damage to the life of an individual who is suffering from a heart attack. Therefore, in this context, a remarkable fog-driven solution is considered. A fog-driven healthcare system based on IoT is illustrated in Figure 1. It is obvious from Figure 1 that the fog-driven healthcare system based on IoT comprises three layers including (i) the cloud layer of IoT healthcare, (ii) the fog layer of IoT healthcare and (iii) the device layer of IoT healthcare [3,4]. Conventionally, fog computing exhibits classified infrastructure which consists of the fog-nodes and cloud data centers. The sequential architecture of fog computing is depicted in Figure 2, where the sensors and connected IoT devices are utilized to manage unique tasks such as physical objects monitoring, the collection of data related to objects, and communication of data towards the fog-nodes. All the involved devices are further connected to the nearest fog-nodes via numerous communication protocols. The fog-nodes installed at suitable sites are responsible for storing, processing and transmitting the collected data of different objects. The fog-nodes command the data from both cloud and user. Further, they are responsible for refining the collected data and transmitting this accumulated data towards the cloud for interpretation or storage. However, the cloud data center comprises storage devices and high-performance servers. It offers networking, computing and storage facilities for large scale data. Furthermore, the core network and edge network ensure two-way communication for the smooth transmission of data among IoT devices, fog-nodes and the cloud data center. Figure 1: IoT based fog-driven health monitoring system. Figure 2: Hierarchical Infrastructure of the Fog Computing. Contrary to the concept of cloud computing, which is purely considered a centralized system, the deployment of fog-nodes is performed without any suitable safety scope. Simply, fog-nodes and end devices have a high chance of being compromised. This situation could lead to privacy violation through leakage of users' information, such as location, identity, medical records and health status, etc. Table 1 gives an in-depth summary of contemporary existing key agreement protocols with respect to the techniques employed by each protocol, and their limitations against various attacks, in chronological order. Moreover, it is noticeable that no work in the existing literature supports user revocation to the best of our knowledge. In summary, the secure, robust and practical design of an authentication protocol for a fog-based environment is still a challenging job. Keeping this in mind, this paper introduces a three-party identity-based authenticated key agreement protocol for a fog-driven IoT healthcare framework by focusing on the security and privacy challenges faced during the communication.