# The Security of Big Data in Fog-Enabled IoT Applications Including Blockchain: A Survey
## 4 Fog-Enabled IoT Applications Security Requirements  
As discussed in the previous section, fog-enabled IoT applications are going to be used in every field of life. These networks of smart devices are expected to be remote in nature and use wireless connection for communicating with other IoT devices or fog nodes [34]. This wireless communication medium is vulnerable to various network attacks, such as eavesdropping, etc. (Table 1 presents a list of different security threats to IoT-enabled applications). Thus, the most crucial security properties regarding data security are confidentiality, integrity, and availability. Confidentiality ensures adversaries do not gain unauthenticated and unauthorized access to data. Integrity refers to the completeness and accuracy of data. While, the availability of data and resources guarantees provisioning of network services and data to authorized users when required. In fog-enabled IoT applications, if these properties become compromised by attackers, the result may be devastating and disastrous. Another important factor in the security of IoT applications is the lack of standardized security. Mostly, IoT devices are manufactured by different vendors and the security of these devices lacks industry-accepted standards. Since many IoT security frameworks exist, there is no single agreed-upon framework. Big companies and industry organizations may have their own precise standards, while certain sectors have proprietary, incompatible standards from industry leaders. The variety of these standards makes it difficult to not only secure systems, but also to ensure interoperability between them. Furthermore, authorized entities may start misbehaving to exploit IoT devices with respect to offensive data manipulation, false data injections and so on. Besides that, IoT applications are largely deployed as Low power and Lossy Networks (LLN), such as wireless sensor networks, smart city, and smart health applications. The LLN are a class of networks where the interconnected devices are highly resource constrained (power, memory, processing, etc. ), and are characterized by high loss rates, low data rates and instability in the communication links [35]. Conventional cryptography and trust-based security protocols consume power, storage and computing resources and may result in message overhead and low trust convergence. In IoT environment, existing solutions do not seem to be effective in the sense of security and protection against internal attacks. Table 2 presents a list of internal attacks on the fog-based IoT applications routing mechanism. Moreover, Existing security mechanisms do not take into account the impact of device mobility, which is essential in scenarios such as smart city, smart health, etc. The interconnecting devices such as gateways or field devices can also easily be targeted by hackers from various network communication interfaces. Therefore, all smart devices, for example in a smart home environment, need to be secured with strict security mechanisms; otherwise, an attack on any individual device may result in the malfunctioning of the whole network [36]. IoT systems can be established by connecting sensors with a distributed data transmission system for remote access, processing and storage. Thus, the biggest threat in this working environment is the data security breach, which is often high due to its complex nature at rest and in transit. For example, [PERSON] et al. [37] discussed the significance of secure data transmission among WLAN-based IoT applications. Moreover, the architecture of IoT devices make it difficult to embed security solutions in every device. Therefore, the need of integrating the fundamental security controls in devices and applications arise while considering the ecosystem where these devices are used. The major challenge is the privacy and security of the data generated by home sensors and detectors.