An AKA protocol for 5G-assisted D2D communication in Out-of-Coverage scenario

5G-assisted Device to Device (D2D) communication can be broadly categorized into three use case scenarios: In Coverage, Relay Coverage, and Out-of Coverage. The main challenge lies in ensuring secure communication in Out-of Coverage scenarios, as in this situation, neither of the two devices is within the 5G network's coverage area. Although several researchers have developed authentication mechanisms for securing D2D communication, most are unsuitable for Out-of Coverage scenarios. Additionally, many of these mechanisms cannot withstand free-riding attacks due to the absence of a trusted entity. In a 5G cellular network, a trust relationship can be established between a registered device and the home network through mutual authentication whenever the former is within the latter's coverage area. Leveraging this trust, this paper proposes a lightweight 5G-assisted authentication protocol for mutual authentication between two communicating devices in Out-of Coverage scenarios. The proposed protocol meets the necessary security goals and mitigates various security attacks, including free-riding attacks. The correctness of the proposed protocol is formally established using the Scyther tool and Random Oracle Model. Furthermore, performance analysis shows that the protocol is efficient in terms of computation overhead, communication overhead and energy consumption compared to similar works in the literature. The computation overhead is found to be 596.12 ms for the Requestor device and 587.26 ms for the Requestee device. The communication overhead is 2720 bits and the total energy consumption for both devices combined is found to be 3016.93 millijoules.