Is 5G Handover Secure and Private? A Survey

The next-generation mobile cellular communication and networking system (5G) is highly flexible and heterogeneous. It integrates different types of networks, such as 4G legacy networks, Internet of Things (IoT), vehicular ad hoc network (VANET), and wireless local access network (WLAN) to form a heterogeneous network. This easily results in continual vertical handovers between different networks. On the other hand, substantial deployment of small/micro base stations (BSs) brings frequent horizontal handovers within a network. The continual handovers among BSs and various networks expose mobile equipment (ME) to the risk of security and privacy threats. So far, many security and privacy mechanisms have been proposed to ensure secure handover either vertically or horizontally in 5G networks. Nevertheless, there still lacks a thorough survey to summarize recent advances and explore open issues although handover security and privacy are crucial to 5G. In this article, we summarize security and privacy requirements in handovers to resist potential attacks. Following these requirements as the evaluation criteria, we review secure and privacy-preserving handover schemes by categorizing them into two scenarios, i.e., vertical handover and horizontal handover. As for the vertical handover, we review related work from three classes, i.e., handovers within Third-Generation Partnership Project (3GPP) networks, between 3GPP and non-3GPP networks, and between non-3GPP networks. Concerning horizontal handovers, we review related work from two classes, i.e., intramobile service controller (MSC) and inter-MSC handover. Meanwhile, we analyze and compare the technical means and performance of these works in order to uncover open issues and inspire future research directions.