## 3 Overview of 3 GPP AKMA
### Tls 1.3 PSK Option  
TLS 1.3's use of the PSK option is highly efficient for secure session establishment and resumption, which is crucial for the 5G AKMA system. The ability to resume sessions quickly using pre-shared keys minimizes latency and computational overhead, enabling faster session setup compared with a full TLS handshake. This reduction in handshake latency is particularly beneficial in mobile and IoT environments, where efficient and swift communication is essential. There are three modes in the TLS 1.3 PSK option:  
* **TLS 1.3 PSK-Only**
* TLS 1.3 PSK-only mode relies solely on pre-shared keys to authenticate the involved parties, client and server, and establish a secure session. In this mode, both parties already possess a shared secret key, which they use to derive the necessary cryptographic keys for the session. This mode does not provide forward secrecy since it does not use ephemeral keys for each session. Therefore, it is suitable for environments where the pre-shared keys are securely managed, and the risk of key compromise is minimal.
* **TLS 1.3 PSK-(EC)DHE**
* TLS 1.3 PSK-(EC)DHE combines pre-shared keys with ephemeral (Elliptic Curve) Diffie-Hellman ((EC)DHE) key exchange. This mode provides both mutual authentication through the pre-shared key and forward secrecy through the (EC)DHE key exchange. Note that the (EC)DHE key exchange is authenticated through the pre-shared key, thereby preventing man-in-the-middle attacks. Forward secrecy ensures that even if the long-term pre-shared key is compromised in the future, past session keys generated through that key remain secure. Such a hybrid approach enhances security by combining the simplicity and efficiency of pre-shared keys with the additional protection of forward secrecy, making it suitable for a wider range of applications.
* **TLS 1.3 0-RTT**
* TLS 1.3 0-RTT (0 Round-Trip Time) mode enables clients to send application data in the first message of the handshake, reducing the latency for session resumption. This mode uses pre-shared keys from a previously established session to quickly authenticate and establish encryption keys. While 0-RTT significantly improves performance by allowing immediate data transmission, it has potential security risks, such as replay attacks and limited support for forward secrecy. Therefore, 0-RTT is typically used in scenarios where low latency is critical, and the risks can be mitigated through additional measures, like including anti-replay protections.  
The PSK option of TLS 1.3 is suitable for AKMA's Usa* protocol because it can be protected with \(K_{AF}\) while also providing efficient, low-latency session establishment and resumption, which are essential for the quick and secure interactions required between the UE and the AF in the 5G environment. This option reduces computational overhead and resource usage, making it ideal for resource-constrained devices like IoT while maintaining strong security. Additionally, the ability to reuse pre-shared keys simplifies key management. It aligns well with AKMA's need for streamlined and secure communi  
\begin{table}
\begin{tabular}{c l} \hline \hline
**Notation** & **Meaning** \\ \hline salt & Optional salt value (a non-secret random value). \\  & if not provided, it is set to a string of HashLen zeros \\ IKM & Input keying material \\ PRK & Pseudorandom key (of HashLen octets) \\ info & Optional context and application specific information (can be a zero-length string) \\ L & Length of output keying material in octet. \\ Secret & Preliminary material used to generate encryption keys \\ Label & String used in the KDF \\ Messages & Data unit exchanged in the TLS protocol \\ TH & Transcript-Hash(Messages) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Cont.  
cation, enhancing the overall performance and security of the \(\text{Ua}^{*}\) protocol within the AKMA framework.