# Leveraging Blockchain Technology for Secure 5G Offloading Processes +
## 2 State-of-the-Art
### Authentication in 5G Networks  
Security for 5G networks is a critical concern and has raised considerable interest in the literature [58; 59; 30]. Fifth-generation networks have higher security requirements compared to previous generations due to new business applications, network architectures, air interfaces, and user privacy concerns. The integration of new technologies and services in 5G networks has inevitably introduced higher privacy risks [58], necessitating robust security measures. Authentication emerges as a powerful tool in this context, as it can effectively prevent unauthorized access by verifying the legitimacy of devices and users. In this way, authentication helps to mitigate several risks such as breaching data integrity and privacy by avoiding spoofing or Man-in-the-Middle attacks; or Denial of Service (DoS) attacks, particularly from compromized IoT devices, which can flood the network with malicious traffic [60]. Focusing on authentication, the Authentication and Key Agreement (AKA) protocol is used for the key exchange process between the user equipment, the serving network and the service provider. In particular, the 5G-AKA protocol was outlined in third Generation Partnership Project (3 GPP) specification number 33.501 [61] and is the primary authentication mechanism in 5G networks, designed to enhance security features compared to its predecessors. It introduces subscriber identity protection through the use of Subscription Concealed Identifier (SUCI) for improved privacy. However, research has identified several vulnerabilities in the 5G-AKA protocol [62; 63; 64], such as (i) lack of forward secrecy, (ii) vulnerability to linkability attacks, (iii) potential for active attacks by malicious Serving Networks (SNs); therefore, making this protocol not fully secure [31]. To address these issues, researchers have proposed various improvements and alternative protocols, which are enhanced versions of the 5G-AKA protocol. Some examples are as follows:  
* 5G-AKA-FS [62]: This protocol aims to provide both forward secrecy and unlinkability. It introduces modifications to the key generation process and implements additional security measures to prevent active attacks. * 5G-IPAKA [65]: This improved protocol focuses on mutual authentication between the User Equipment (UE) and the Serving Network (SN), as well as enhanced security for the anchor key and authentication vector. * SUCI-AKA [66]: This variant reuses the Elliptic Curve Integrated Encryption Scheme (ECIES) secret to address linkability attacks. It is important to know that the 5G authentication framework is unified by the same methods and can be used for 3 GPP access and non-3 GPP (such as Wi-Fi) access, and extensible, as the use of Extensible Authentication Protocol (EAP) means that new authentication methods can be added in the future [67]. For this reason, researchers have already explored several alternative authentication methods for 5G networks. One of them is Physical Unclonable Function (PUF)-based Authentication. A two-way identity authentication method (2 WIAM) using PUF has been proposed to enhance security and privacy in 5G networks. This approach combines user-provided authentication and geolocation data to detect module clones [68]. Another one is based on the use of machine learning techniques for authentication in 5G networks to address challenges faced by conventional authentication methods [69].The delegated authentication concept, related to federated identity management, has also been investigated as a potential solution for secure and effective authentication in 5G networks [70]. Additionally, Public Key Infrastructures (PKIs) have already been also considered [71; 72] to improve trust and security. Finally, a secure and effective authentication scheme using Blockchain technology has also been proposed which highly satisfies the 5G frequent authentication requirement [73]. Despite the advancements in 5G authentication, several challenges remain, and more secure solutions are still required.