## 3 Countermeasures
### Cryptographic-Based Countermeasures  
Cryptographic techniques encompass the majority of primary conventional as well as unconventional measures to achieve a reliable level of security architecture in emerging mobile communication scenarios. Cryptography contains classical concepts of symmetry as well as asymmetry [60]. Several techniques are structured on Public Key Infrastructure (PKI) for identification of Access Points (AP) or Base Stations (BS) in the 6G mobile networks [61]. In [41], the authors suggested the Paillier cryptosystem composed of three algorithms: generation of keys, encryption and decryption. A traditional approach of two large independent and random prime numbers is used in this technique. Although the proposed scheme is targeting 6G communication, it requires extended analysis for estimation of the processing power requirement and MitM vulnerability related to quantum computing-based factorization. A group signature scheme is suitable for incorporating conditional anonymity. Likewise, a short group signature scheme is ideal for group RSA-based strong signatures. Therefore, applications for 6G-based IoTs networks are researched iteratively for group-based signature architecture efficacy in quantum computing [57]. However, RSA implementation in low processing sensors communication will be a challenging problem for attaining resistance to quantum computing-based attacks. There are several symmetric key-based schemes for privacy preservation in the 6G network. Cybertwin is a novel unconventional network architecture in 6G [62]. This unusual framework establishes itself as a network assistant, communication behavior logger, caching mechanism, resource coordinator, support localization and embedded security architecture for the 6G mobile communication system. Cryptographic-centric reference security architecture is considered appropriate for the Cybertwin-driven 6G environment [37]. Similarly, the authors in [63] discussed several challenges, methods, applications and security issues related to Cybertwin-driven 6G architecture. Moreover, the authors in [64] presented a post-quantum secure ring signature based on chameleon hash function to enhance security and privacy in the Cybertwin-driven 6G network. However, limited scalability in commercial applications is major drawback of the ring signature due to linear growth of signature size [65]. Moreover, the chameleon hash algorithm may create compatibility issues in 6G, where the domain including eMBB, UCDC, SURLLC, 3 DCom and BigCom requires a holistic integration with a broad range of modern user elements. In [37], the authors proposed reference architecture for security of a Cybertwin-driven 6G vehicle-to-everything network. The proposed scheme includes a handover authentication between vehicle and edge server with a proxy ring signature technique. Proxy ring signature overcomes scalability issues due to decentralization. However, the concept has major challenges for handling the insecure data at the edge server, processing cost at the edge server and historical data migration problems. The elliptic curve-based non-conventional cryptographic technique is capable of recovering RSA's prime factors [66]. Cybertwin-based  
Figure 4: Number of papers vs. countermeasures. cloud-centric network architecture incorporates an enhanced and compatible always-on connection in 6G communications; however, this brings several cloud-specific vulnerabilities. In [67], the authors suggested the use of a digital signature-based authentication key exchange protocol with provable reliance against several attacks in 6G Cybertwin network architecture. However, the proposed strategy requires typical evaluation related to typical 6G challenges of processing issues in IoT devices, MEC exploitation with quantum computing and authentication delay. Advanced Encryption Standard (AES)-based schemes are widely suggested for privacy-preserving and authentication protocols in 6G networks. In combination with AI-based QoS, AES encryption provides joint network optimization in 6G.