## 3 Countermeasures
### Cryptographic-Based Countermeasures
In [68], the authors proposed lightweight cryptography with the color image-based scheme for privacy preservation in 6G networks. The authors used the Hybrid Particle Swarm Optimization-based Cuckoo Search Optimization Algorithm scheme for multiple secret sharing. However, this steganographic approach requires evaluation for implementation in non-image related applications of the 6G era, such as dense sensors network, tactical drone swarm, etc. Similarly, further analysis is required for cryptanalysis and threat spectrum coverage of the proposed scheme. Likewise, the authors in [69] suggested random number generation with a single Central Processing Unit (CPU) for 23.8 Tbit per second, which is employable in various security-related implementations in high-speed communication such as 6G. Although the proposed solution targets the eMBB scenario of 6G communication, it will contain trivial vulnerabilities specific to the stream cipher. Moreover, further research is required for secure management of memory and key sharing mechanisms. The authors in [70] proposed a secure, lightweight cryptography-based eHealth system for the 6G network, which also addressed vulnerabilities related to MitM in low-latency D2D communication. The solution focused on the security of Mobile Edge Computing (MEC) integration in 6G architecture for private data management in Internet of Medical Things (IoMT) devices. However, the proposed solution requires elaboration to analyze the role of Certification Authority (CA), key generation and the management process. In [71], the authors proposed a reconfigurable Field Programmable Gate Array (FPGA)-based stream cipher for 6G-based high speed and massive throughput data streaming hardware applications. The scheme is a potential countermeasure for resource constraints related to security challenges in smart devices. However, the scheme has a complex design, therefore, memory management will be a challenge. Moreover, the scheme is vulnerable to cryptanalysis attacks. Similarly, 6G physical layer provisions the implementation of a Delta-Orthogonal Multiple Access (D-OMA)-based security scheme through distributed encryption with a low intercept probability [72]. However, D-OMA-based physical layer encryption will cause challenges related to compatibility with the upper layer and integration issues with non-OAM devices in heterogenous network environments. Visible Light Communication (VLC) arose as an effective option for data communication. Therefore, VLC is considered as a potential medium for handling 6G-based high-throughput applications. In [73], the authors suggested use of asymmetric encryption for optimum error rate in comparison to conventional symmetric encryption in 6G-enabled VLC-based indoor applications. 6G technology is being designed with the aim to achieve a 1 Tbps throughput with less than 100 us latency. Therefore, it is imperative to analyze related challenges and design a corresponding Next Generation Transport-layer Protocol (NGTP). The authors in [74] presented an AI-empowered AES encryption for joint network optimization. The solution employs Kalman filtering to predict future harvesting power and key length switching. However, the proposed solution requires further research to ascertain the vulnerabilities in case of relatively short keys; similarly, the proposed solution requires a compatibility analysis for implementation in a multi-tier heterogeneous network. The authors in [75] discuss the cryptographic limitations in the use of user identifiers, the Subscriber Concealed Identifier (SUCI), during the post-quantum 6G era. They proposed a SUCI for SIM card security based on the post-quantum Key Encapsulation Mechanisms (KEM) standard declared by NIST. Although the solutions have been highlighted as potential countermeasures to quantum attacks, the research work requires further extension for analysis related to processing and delay requirements in 6G domains. Table 3 presents an evaluation of the prevailing security cryptographic countermeasure mechanisms in 6G mobile networks.