## 4 Trust Assessment Using Various Approaches
### Decentralized: Blockchain  
Blockchain technology, characterized by its distributed ledger system where information is stored across multiple nodes, each possessing an identical copy of the ledger, offers a secure, traceable, decentralized, and immutable data storage solution [26]. Leveraging these properties, blockchain technology has the potential to enhance trust within network environments by ensuring the legitimacy of trust-related data. For instance, in the proposed B-RAN framework [14], which utilizes blockchain, trust relationships in wireless networks are established through an identity-based consensus mechanism. Smart contracts facilitate swift actions on the blockchain, while a hash puzzle-solving requirement for device access helps mitigate resource abuse, latency issues, and unauthorized network access. By enforcing adherence to predefined rules, this hash access scheme fosters trust between clients and network resources. Similarly, in addressing dynamic spectrum access for IoT systems, a trust evaluation mechanism proposed in [82] leverages blockchain technology to ensure privacy, information transparency, decentralized spectrum access, automatic spectrum management, and flexibility through parameterized smart contracts. Trust-related information stored in the blockchain evolves based on the consistency of cooperative measurements in IoT networks, enhancing trustworthiness.  
Blockchain technology has been shown to enhances trust in 5G and 6G networks by mitigating vulnerabilities, enhancing privacy, and providing distributed trust models. Several studies have offered valuable insights to assess the level of trust in 5G and 6G networks using blockchain technology. [PERSON] et al. highlighted the potential of blockchain in mitigating hazards and vulnerabilities in 5G networks and enhancing privacy, trustworthiness, and dependability. Similarly, they emphasized that blockchains in 5G networks provide distributed trust models that bolster security and safeguards against breaches [83]. In 6G networks, [PERSON] et al. introduced the SIX-Trust framework, which includes sustainable trust, infrastructure trust, and xenogenesis trust layers to ensure a secure and trustworthy network [2]. [PERSON] et al. discussed the integration of blockchain technology in service migration to 6G networks, underlining its role in offering a secure and decentralized platform for managing migration processes [84]. [PERSON] et al. stressed the significance of blockchain in meeting the communication and security requirements of 5G networks, such as reliability, low latency, and secure transmission [85].  
The integration of blockchain technology into 6G networks presents opportunities to improve trust relationships by guaranteeing the authenticity and reliability of trust-related data [26; 86]. Blockchain's inherent features of traceability, immutability, and transparency hold promise for enhancing trustworthiness and resolving data-sharing challenges within 6G networks [14]. However, challenges such as computational overheads, energy-intensive operations, scalability limitations, and potential security vulnerabilities, including threats from quantum computing, may hinder the widespread adoption and long-term dependability of blockchain-based trust assessment in 6G networks [12; 86]. Additionally, regulatory and interoperability issues may need to be addressed for seamless integration [14].  
In conclusion, while blockchain technology offers significant potential to enhance trust and security in 6G communication networks, a thorough evaluation of its limitations and potential challenges is essential to realize its full benefits. Despite its promise to ensure security and transparency, addressing concerns such as computational demands and security vulnerabilities will be crucial for maximizing its effectiveness in bolstering trust within 6G networks.