# Device-To-Device Communication in 5G Environment: Issues, Solutions, and Challenges
## 4 Security and Privacy in D2D Communications  
To date, many of the standardization efforts and research studies are mainly focused on resource management, interference management and the architecture in D2D communication. Both industry and academia largely ignored the security aspect of the D2D communication environment. D2D communications offers a hybrid framework where the centralized and the distributed approaches are paired together. That is why it is risky to some of the privacy and security threats that are being identified by both the ad-hoc wireless and the cellular networks. Some of the security threats faced by D2D communications can affect the confidentiality, authenticity, availability, and also integrity of the network. Furthermore, the need for efficient security solutions to allow private, secure, and also trusted data exchange among cellular network and devices including direct proximity-based communication without any help from the cellular network. Table 4 shows the overview of security issues and, recently, solutions proposed by the researchers in D2D communications. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ref.** & **Problem** & **Algorithm** &
\begin{tabular}{c} **Attack** \\ **Addressed** \\ \end{tabular} & **Findings** & **Limitations** \\ \hline \multirow{6}{*}{[49]} & Interference among & & & & \\  & LTE-U network, & & & & \\  & D2D users, and the & User-Subchannel & & & \\  & opportunistic & Matching & Address & & \\  & feature of & Algorithm for LTE & Spoofing & & \\  & unlicensed channel & and D2D users. & & & \\  & access in existing & & & & \\  & Wi-Fi systems. & & & & \\ \hline \multirow{6}{*}{[50]} & Lack of protection & Optimization-Based & & & \\  & for cellular users & Access Assignment & & & \\  & against & Scheme for & & & \\  & eavesdropping. & D2D users. & & & \\  & & & & \\  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Overview of security issues and recently proposed solutions. [PERSON] et al. (2018) [15] investigate the effect of recent advances of content-centric networking, device-to-device (D2D) communication, and mobile edge computing on Mobile Social Networks (MSNs). The authors found that in order to improve the sharing, efficiency and the security of data exchange, and delivery in the MSN, the knowledge of social relationships among users are ignored. The authors proposed a social trust scheme that enhances the security of the MSN by applying a novel deep reinforcement learning approach to automatically make the decision to optimally allocate the network resources. The solutions begin with an agent receiving a set of observations including the value of trust for each node, the cache contents, the conditions of wireless channel, and the capacity of vacant computation from the integrated network. Then, the agent transmits the parameters to the deep neural network and produces the optimal actions. The revenue of resulting operators is then observed and retransmitted as a reward to the agent. Based on the obtained reward, the agent trains and updates the deep neural network model. The step is repeated until the optimal actions are delivered. The authors use uncertain reasoning to derive trust values due to the uncertainty in trust evaluation. The trust evaluation from direct observations and indirect observations is derived by using the Bayesian inference approach and Dempster-Shafer theory. [PERSON] et al. (2017), in [55], examine various existing authentication and privacy-preserving schemes for 4G and 5G cellular networks to present a comprehensive survey regarding that topic. The issue that the authors identify in the 4G and 5G environment is the lack of restriction in the network and the fast-vertical handover, which leads the devices likely to vulnerabilities like privacy, data confidentiality, communication security, access control, and availability. The reason for this is that the devices will be exposed to all the vulnerabilities that are IP-specific since the environment of 5G cellular networks is IP-based.