# A Hierarchical Blockchain-Based Trust Measurement Method for Drone Cluster Nodes
## 1 Introduction
In terms of trust aggregation, an adaptive fuzzy trust aggregation network is proposed by the literature [14] to compute node trust evaluations. This approach integrates trust factors such as the data packet forwarding rate, trusted interaction degree, and detection packet receiving rate to calculate a node's direct trust degree. It further combines the indirect trust degree of trusted neighboring nodes to formulate a comprehensive trust degree. The literature [15] establishes trust values by comparing a node's message forwarding count with its energy consumption rate and presents a distributed trust management scheme. Nonetheless, this approach incurs a notable communication overhead and poses a considerable trust acquisition cost. In contrast, the literature [16] devises the provenance-based trust model framework, which traces the source to achieve accurate point-to-point trust evaluation within resource-constrained network settings. This framework seeks to optimize correct message delivery to the intended node while minimizing message delay and communication costs. Yet, it faces challenges concerning algorithm efficiency and the precision of trust recognition. The above research has laid a good foundation for the research on the trust evaluation model of UAV nodes, but some of the literature ignores the influence of trust timeliness on trust evaluation in the direct trust degree calculation [12; 13], which can not reflect well on node behavior, which reduces the accuracy of trust calculation. The trust evaluation of UAVs in the other literature still has shortcomings such as the single trust evaluation factor [9; 15], relatively fixed trust evaluation weight [11], high communication overhead [10; 14; 15], unreasonable trust evaluation [16], etc. Furthermore, while much of the current research is centered around assessing the reputation of UAVs, there is a notable lack of attention directed toward establishing robust mechanisms for credible reputation management. Table 1 summarizes the main contributions and limitations of the aforementioned literature. To counter the potential threat of malicious nodes targeting UAVs during data collection and transmission, [PERSON] et al. [17] have proposed a distributed solution using blockchain technology. This approach introduces a novel lightweight blockchain architecture, which  
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reduces computational and storage costs while simultaneously offering advantages in terms of privacy and security. A blockchain-powered trusted drone cluster communication scheme was devised by [18]. This scheme employs attribute-based algorithms for UAV authentication, verifying and adding data to the blockchain based on the attributes of the UAVs. However, this approach faces the challenge of significant underlying blockchain communication latency. The literature [19] employs a hierarchical blockchain approach with main and sub-chains to address the issue of secure identity verification for drone clusters across trust domains and diverse network environments. However, this method's efficiency for authentication is affected to some extent as the number of authentication nodes increases, leading to an increase in data transmission volume. A distributed key management solution tailored for heterogeneous UAVs was introduced by [20], leveraging the capabilities of blockchain technology. With this scheme, UAVs can autonomously distribute cluster keys, update their public-private key pairs, migrate between clusters, and securely revoke malicious UAVs. However, there is a limitation in this approach as it is challenging to detect malicious behavior in the head node of UAVs. Through research on the above literature, there are still some problems and challenges in the combination of blockchain technology and UAVs. The drone cluster network is typically organized into communication clusters based on a hierarchical structure. Data exchange between distinct clusters is facilitated through the cluster head node responsible for forwarding the information.