## 5 Conclusions  
To enhance the security of AIS communication, this paper proposes a physical-layer security protocol designed for AISs, based on the ITU-R M.1371-5 standard and AIS application scenarios. The protocol enables the generation of symmetric keys between the sender and receiver in a plug-and-play manner, without relying on any third-party infrastructure, ensuring secure AIS communication. It also dynamically adjusts the detection interval and quantization parameters to accommodate the mobility of ships and the impact of noise. Additionally, the security and performance of the proposed protocol were thoroughly analyzed. The results demonstrate that the protocol is resistant to common passive and active attacks. Under typical SNR and speed conditions, the time required to generate keys of different AES standard lengths does not exceed 4000 ms. Existing solutions primarily address AIS security issues using public key cryptography. A comparison between the proposed solution and existing approaches is provided in Table 5.  
Although implementing a public key cryptography system in the marine communication environment is challenging, it can still provide effective identity authentication through digital certificates or signatures, in addition to offering encryption. Future work will focus on integrating suitable ship identity authentication methods into the PLKG protocol and exploring its application in various scenarios, such as ship-to-ship and ship-to-base-station communications, to further enhance the security of maritime communication systems. Conceptualization, Z.Y. and Z.Z. ; methodology, Z.Y. and Z.Z. ; software, J.S. ; validation, J.S. ; formal analysis, J.S. ; investigation, Z.Y. and Z.Z. ; resources, S.J. ; data curation, J.S. ; writing--original draft preparation, Z.Y., Z.Z. and J.S. ; writing--review and editing, S.J. and J.S. ; \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**SNR/NIST** & **Frequency** & **Block** & **Run** & **Long-Run** & **DFT** & **Autocorrelation** & **Permutation** \\ \hline
10 dB 128-bit & 0.3951 & 0.7161 & 0.3652 & 0.7447 & 0.6701 & 0.6416 & 0.2330 \\
20 dB 128-bit & 0.2520 & 0.8685 & 0.3907 & 0.5872 & 0.7762 & 0.6547 & 0.6911 \\
30 dB 128-bit & 0.7382 & 0.5433 & 0.6364 & 0.1710 & 0.4993 & 0.4353 & 0.8713 \\
10 dB 192-bit & 0.8806 & 0.4745 & 0.6376 & 0.7963 & 0.3955 & 0.4428 & 0.6662 \\
20 dB 192-bit & 0.7270 & 0.5871 & 0.0840 & 0.9007 & 0.0123 & 0.8623 & 0.3431 \\
30 dB 192-bit & 0.5984 & 0.1829 & 0.7364 & 0.2092 & 0.8692 & 0.7975 & 0.8816 \\
10 dB 256-bit & 0.3073 & 0.1363 & 0.0789 & 0.5024 & 0.4156 & 0.8306 & 0.3476 \\
20 dB 256-bit & 0.4780 & 0.2253 & 0.9112 & 1.0000 & 0.8028 & 0.6112 & 0.3476 \\
30 dB 256-bit & 0.8103 & 0.6555 & 0.0600 & 0.3393 & 0.5646 & 0.7521 & 0.8148 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: \(p\)-values of NIST SP 800-22 tests for keys of different lengths under varying SNRs. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristic** & **Public Key Cryptography Schemes** & **The Proposed Scheme** \\ \hline Encryption & Asymmetric encryption & Symmetric encryption \\ Decentralization & No & Yes \\ complexity & High & Low \\ Key management & Complex & Simple \\ Unicast security & Yes & Yes \\ Broadcast security & Yes & No \\ Identity authentication & Certificates provide protection & No protection \\ Non-repudiation & Yes & No \\ Robustness & Strong & Vulnerable to channel environment \\ Deployment & Difficult & Easy \\ Scalability & Strong & Weak \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison of characteristics of public key cryptography schemes and the proposed scheme. * [PERSON] et al. (2020) [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON] SecureAIS-securing pairwise vessels communications. In Proceedings of the 2020 IEEE Conference on Communications and Network Security (CNS), Virtual Conference, 29 June-1 July 2020; pp. 1-9. [CrossRef]
* [PERSON] et al.