# Post-Quantum Key Exchange and Subscriber Identity Encryption in 5G Using ML-KEM (Kyber) 1
## 1 Introduction  
In telecommunications networking, user privacy is important against tracking the behavior and the location of the mobile user. Before 5G, cellular networking provided no ID confidentiality protection. The ID of the user equipment (UE) was transmitted in plaintext before 5G, including 4G and any of the previous cellular generations. Because cellular connections in wireless rely on an open-air medium, the adversary can access, capture, and track the UE ID, e.g., IMSI catching [1, 2]. UE tracking can result in the breach of the location (where the mobile UE is located) and behavior (how and when it uses the connectivity) of the mobile UE and the human owner using the UE. To address such an issue, 5G introduced authentication and key agreement (AKA), which conceal the actual permanent identity of the user to enable the confidentiality protection of the user ID to protect the user privacy. In contrast, previous generations do not conceal user identities. While enabling othersecurity objectives (confidentiality, integrity, authentication, and non-repudiation), 5G AKA includes key exchange and encryption. More specifically, 5G AKA uses the Elliptic Curve Integrated Encryption Scheme (ECIES) [3]. The ECIES involves public-key key exchange to establish the shared key, which in turn can be used for encryption for the confidentiality protection of the ID. The ciphertext of the user equipment ID is called a Subscriber Concealed Identifier (SUCI). Such 5G user equipment ID encryption, however, is vulnerable against quantum-equipped adversary. Assuming quantum computing, [PERSON]'s algorithm [4] can break the mathematical problem (discrete-logarithm problem in this case) anchoring the cipher security and finding the key. Recent prototypes in quantum computing, e.g., IBM and Google, continue to evolve to support greater qubits to realize such threats in order to break the current ciphers. To defend against future quantum attackers, the National Institute of Standards and Technology (NIST) has solicited post-quantum public-key ciphers since 2016 and standardized CRYSTALS-Kyber for the key encapsulation mechanism or KEM cipher standardization in 2022. After standardization, CRYSTALS-Kyber evolved into ML-KEM [5], which is our \"Kyber\" cipher in this paper. (There are three NIST-standardized post-quantum digital signature ciphers that are less relevant to this paper, as our work focuses on encryption for confidentiality protection.) We incorporate PQC on 5G UE ID and analyze the performance impacts of the post-quantum transition for 5G SUCI, which is important since the cellular UE is constrained in resources (mobile, lightweight, and battery-operating). Our performance analyses are more relevant to such mobile/5G networking than other applications with greater resources and looser performance requirements. In this research work, we study the performance analyses of post-quantum ciphers in the 5G AKA identification and registration. We build our scheme on the 3 rd Generation Partnership Project (3 GPP) standard 5G-AKA protocol [6]. While the current 3 GPP-defined 5G-AKA protocol uses the pre-quantum elliptic curve algorithms that are vulnerable against the quantum-equipped adversary (specifically, secp256r1 and X22519), we replace the pre-quantum ciphers and incorporate the post-quantum Kyber-512 [7] into 5G AKA and analyze the pre-quantum vs. post-quantum 5G AKA. We compare the performances of the existing pre-quantum ciphers (the elliptic curve KEM ciphers of secp256r1 and X22519) with the post-quantum cipher (CRYSTALS-Kyber-512) when implemented in 5G AKA. For fairness, we compare the ciphers with the same security levels and fix the computing platform on which we simulate the 5G AKA. Because the mobile UE is resource-constrained, we compare the performances of the ciphers with the shortest key/parameter lengths. We implement and measure performance in processing time, power, energy, and CPU cycles.