# The Security of Big Data in Fog-Enabled IoT Applications Including Blockchain: A Survey
## 5 Fog Computing Security Challenges
### Device Level Security Challenges
#### 5.3.1 Confidentiality  
Confidentiality ensures that data are not exposed to an unauthorized entities. There is a great computation and storage overhead involved in existing security protocols such as SSL/TSL-based communication [127]. For example, it is not effective to apply existing PKI-based systems on all IoT devices due to their heavyweight computation and storage. The PKI and CIA protocols provide strong security in terms of fixed and predefined large sized keys, therefore causing memory and processing overhead. They also do not cater for insider attacks [128]. Cloud architecture does not meet IoT devices requirements such as timing, scalability and location awareness [129]. Therefore, lightweight infrastructure is crucial to provide a timely response. 1. **Authentication:** As fog computing services are offered to an enormous number of end users through front end fog nodes, authentication becomes a critical issue. Fog nodes require authentication at different levels to ensure security in fog computing, as explained by [PERSON] et al. [102]. The existing conventional PKI-based authentication is unable to overcome the security issue being less efficient and with lower scalability options. On the other hand, there exist simple, user-friendly and secure solutions to cater the authentication issues in a location limited channel while depending on physical contact in local ad-hoc wireless network [130]. Moreover, biometric authentication has emerged as an important technology when it comes to authentication in mobile computing, cloud computing and fog computing. Fingerprint authentication, touch-based authentication or face authentication are few examples [98]. 2. **Privacy:** Users are getting more concerned about the breaching to their private and sensitive information such as personal data, location or other information while using the cloud services, IoT or wireless networks. Therefore, it is the most crucial challenge to preserve the privacy in distributed fog environment, as the fog nodes operate at user's end and must gather more sensitive data than the cloud. Several researchers have proposed various techniques to preserve the privacy in different setups such as wireless network, online social network [131], smart grid [132] and cloud [98; 132]. * **Identity privacy:** IoT user's identity must be protected and preserved from public and other IoT user to prevent impersonation attacks. Different pseudonym techniques [133; 134; 135] have been proposed to preserve identity privacy. However, periodic pseudonyms may lead to heavy computation cost in resource constraint IoT domain. Furthermore, group signature [134] and connection anonymization [136; 137; 138] techniques are also proposed for protecting identity privacy [94]. * **Data privacy:** The algorithms to preserve privacy in fog networks run between cloud and fog, but the fact that these algorithms utilize a huge amount of resources at the edge devices cannot be ignored. Fog nodes collect sensitive data that are generated through end devices and sensors [98]. At local gateways, homomorphic encryption can be employed without decryption to permit privacy-preserving collection [139]. Another technique that differential privacy [140] is employed in the case of statistical queries to ensure the privacy of uninformed data entries. * **Usage privacy:** Fog computing comes with another very important concern of users' usage pattern privacy. For instance, the smart meter in smart grids reads and collects a huge amount of data that are private to users, such as at what times user is unavailable at home, the consumption pattern, switching on and off certain appliances, etc. ; such information is a threat to users' privacy. Many researchers addressed privacy preserving techniques in smart metering [141; 142; 143]. It is unfortunate that these techniques cannot be employed in fog computing because of unavailability of a trusted third-party device to cater energy limitations.