# Enabling Trustworthy Multicast Wireless Services through D2D Communications in 5G Networks
## 2 Related Work  
In the literature, many works deal with the candidate supporting technologies for enabling future 5G networks [11; 12]. D2D communications is considered among these because of its capability to improve network performance in terms of delay, throughput, energy efficiency, and spectral efficiency. The D2D taxonomy presented in [13] distinguishes between inband and outband D2D. Inband D2D communications use the cellular (i.e., licensed) spectrum and can be further categorized as underlay or overlay when the radio resources are shared with cellular users or are dedicated to D2D links. Differently, outband D2D exploits an unlicensed spectrum. To this aim, an extra interface must be used and controlled by the cellular network (i.e., controlled mode) or by the users (i.e., autonomous mode). Usually, the underlay inband D2D is preferred to the other modes because it better utilizes the spectrum and is suitable for all types of devices. As concerns the resource allocation in D2D communications, several solutions can be found in the literature related to D2D [14] or in closely related fields [15]. An interesting usage scenario for the D2D technology is multicasting. Multicast and broadcast services are enabled in 3 GPP Release 8 networks through the evolved Multimedia Broadcast Multicast Service (eMBMS) architecture. According to [16], the group-oriented services will be protagonists in 5G networks, and multicasting will be the effective means to offer these services. Establishing direct communications between devices in proximity has been shown to improve the multicasting performance. In [5], the D2D-enhanced CMS with Single Frequency (D2D-SF) approach was designed to improve the performance of the Conventional Multicast Scheme (CMS), counting on D2D communications occurring simultaneously at the same frequency. This paradigm has shown encouraging results in Long-Term Evolution-Advanced (LTE-A) systems. A further work focusing on content sharing by exploiting both D2D and multicasting technologies can be found in [17]. In this article, the authors present a device-to-device multicast (D2 MD) scheme for content sharing in cellular networks by taking into account social and physical attributes in D2 MD cluster formation, and jointly optimizing power and channel allocation among D2 MD clusters. However, trust and security aspects are still overlooked even if they play a fundamental role when involving social and physical relationships. Another work that addresses a similar topic is presented in [18]. Here, the authors considered a scenario where D2D users may demand multicast data at various rates and, in return, they offer different profits (revenue) to the telecom operator. However, it is shown that satisfying the user requests to maximize the profit is an NP-hard when the resource blocks are limited, and thus they propose a greedy heuristic algorithm to solve this problem. An interesting analysis of content dissemination scenarios is presented in [19], where two game theoretic medium access strategies, based on energy-aware utility functions, are proposed. The impact of cellular network characteristics on D2D communication is analyzed in [20], where the authors also exploit the benefits of network coding (NC) in the design of an adaptive cooperative protocol for the D2D data exchange. No attention has been given so far to security that represents an important aspect for future 5G networks; this is the focus of this paper. According to [21], privacy and security issues must be faced in order to definitely make D2D a successful technology. In [8], a thorough analysis on these problems is conducted. First, the difference between security and privacy concepts is defined. Then, the requirements to be satisfied in order to guarantee both security and privacy in D2D communications are listed, and the possible attacks are identified. Finally, related works and proposed solutions are described. Among these, [PERSON] et al.