# ML-AKA: An Authentication Protocol for Non-Standalone 5G-Based C-IoT Networks
###### Abstract  
When it comes to the development of 4G and 5G technologies, long-range IoT or machine-to-machine (M2M) communication can be achieved with the help of cellular infrastructure. In non-standalone (NSA) 5G infrastructure, cellular-IoT (C-IoT) devices are attached and authenticated by a 4G core network even if it is connected to a 5G base station. In an NSA-based 5G network, the presence of dual connectivity sometimes raises interoperability and authentication issues due to technological differences between LTE and 5G. An attacker explores these technological differences, introduces the threats, and performs various types of attacks like session hijacking at the interfaces and Man-in-the-Middle (MITM) attacks. With the introduction of these attacks, the attackers exploit the network resources and pinch out various critical information sources. To resolve this issue, the NSA-based C-IoT network must incorporate robust and seamless authentication and authorization mechanisms. This article presents the ML-AKA protocol that is used to enhance interoperability and trust between 4G and 5G networks by using a uniform key-sharing (UKS) mechanism. The proposed ML-AKA protocol is analyzed with the help of the AVISPA tool and validated with the use of Proverif. Further, the proposed protocol is compared with other existing protocols like EPS-AKA and UAKA-D2D, and the outcome shows that the proposed protocol significantly reduces the chances of MITM, DDOS and Spoofing attacks during the interoperability in the NSA-C-IoT network. cellular IoT; LTE; NSA-5G; ML-AKA Article  
10 November 2024 21 November 2024 3 December 2024 10  
50 billion by 2025 [2]. NSA-based C-IoT architecture has multiple purposes that can be easily switched to the next-generation platform from the current LTE network with minimal changes at the base station platforms. Furthermore, NSA-5G can help to reduce the capital cost (CAPEX) and base station capacity. Thus, we can say that NSA-5G-based C-IoT is currently the fastest-developing wireless communication technology that can be used as a backbone for the IoT network. However, the integration of multiple technologies leads to many challenges in terms of the operator and service provider perspectives. Below, we have highlighted some of the network challenges and their probable solutions to support interoperability and dual connectivity in the NSA-based 5G C-IoT network. * _Issue:_ Associations between 5G and 4G lead to increases in network complexity and operational complexity. * _Solution:_ In the proposed NSA-based C-IoT architecture, entities in the LTE core network handle all the control and management functionalities. This will help to smooth the transition of C-IoT devices from 4G to 5G networks. * _Issue:_ The key generation and key management strategies of 4G and 5G are slightly different. * _Solution:_ The proposed architecture uses a multi-layer authentication mechanism to reduce computational complexity within the network elements and user devices. * _Issue:_ An increase in the heterogeneity among IoT devices requires a variety of security keys and key management strategies. * _Solution:_ In the proposed work, uniform key sharing (UKS) uses some encrypted keys that can be used at various levels of the C-IoT network. To partially overcome the above challenges, some of the standard protocols such as UAKA-D2D and EPS-AKA have been employed in traditional LTE networks. But all these standard protocols provide limited data security and integrity [3], so to provide end-to-end security for 5G-NSA-based C-IoT architecture, we have introduced a novel multi-level security protocol. To highlight the applicability of the proposed protocol, we have considered three end-to-end C-IoT communication scenarios. Communications scenarios involve a personal area network (PAN), a global area network (GAN) and a wide area network (WAN). In addition, the proposed protocol is validated through simulation and mathematical analysis.