# Mdpj _sciences_
### Related Works  
The 5G primary authentication standards include two key protocols: the 5G Authentication and Key Agreement (5G-AKA)--which supports 3 GPP devices--and the Extensible Authentication Protocol (EAP)-AKA'--which is used for non-3 GPP devices. A significant improvement over previous generations is the encryption of the SUPI (Subscription Permanent Identifier), addressing the issue of unencrypted IMSI (International Mobile Subscriber Identity) transmission by using an ECIES (Elliptic Curve Integrated Encryption Scheme)to compute and transmit the SUCI (Subscription Concealed Identifier). However, despite these advancements, both protocols remain vulnerable to various attacks, prompting the ongoing development of enhanced protocols to address these security challenges, as shown in Figure 1 [9, 10, 11]. **The 5G-AKA\({}^{\prime}\)**[12] aimed to counteract linkability attacks by reusing the \(K_{HN}\) key, which is negotiated between a User Equipment (UE) device and its corresponding Home Network (HN) through an ECIES, to encrypt the SUPI in the initial phase. In more detail, this protocol lets the HN replace its random number within the authentication token (AUTN) with the value encrypted from that random number with the \(K_{HN}\). Based on the trust in the freshness of the \(K_{HN}\), the UE can use the encrypted result to mitigate replay attacks, as well as linkability attacks. Nevertheless, the protocol remains vulnerable to active attacks from a malicious Serving Network (SN), as it allows the transmission of the anchor key \(K_{SEAF}\) to the SN without authenticating the UE with the HN. Additionally, the protocol does not fully support security for PFS. **The SUCI-AKA** protocol [13] was proposed to achieve PFS for the anchor key \(K_{SEAF}\) and to prevent linkability attacks. It reuses the \(K_{HN}\) key, which was originally generated through an ECIES to encrypt the SUPI for the calculation of the master session key \(K_{AUSF}\). To explain further, because the \(K_{HN}\) is trusted to be fresh by both the UE and the HN, it substitutes the sequence number, thereby defending against the linkability attacks. However, if the long-term key \(K\) and the HN's private key \(sk_{HN}\) are compromised, an attacker can recover the anchor key \(K_{SEAF}\), thereby undermining the protocol's PFS. **The 5G-IPAKA**[14] was proposed to support mutual authentication between the UE and SN, secure key exchange, and PFS. It tried to provide PFS by computing the anchor key using the ECIES secret \(K_{HN}\). This protocol allows the HN to send the anchor key \(K_{SEAF}\) to the SN before finally authenticating the UE. In this way, both the UE and the SN are able to authenticate each other using the Message Authentication Code (MAC) generated and transmitted by the corresponding party with \(K_{SEAF}\), thereby achieving mutual authentication between the two parties. However, if the long-term key \(K\) and the HN's private key \(sk_{HN}\) were to be compromised, the protocol would face issues with PFS. Additionally, since the HN can transmit the anchor key \(K_{SEAF}\) to the SN without authenticating the UE, there is a threat of active attacks from malicious SNs. Furthermore, compatibility issues arise due to the protocol's deviation from the standard procedure. **The 5 GAKA-LCCO**[15] focused on addressing the high communication and computation overhead and SUCI replay attacks. In this protocol, the SN first begins by sending the UE the current timestamp and randomly generated nonce values. Then, the UE applies the values to calculate the key block with the long-term key \(K\) and the ECIES secret key \(k_{HN}\). Based on the generated key block, the protocol optimizes the communication and  
Figure 1: The 5G authentication protocols. computation overhead. In addition, the timestamp can prevent the resource exhaustion attacks and SUCI replay attacks.