© ICST Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2024.In this paper, we discuss the issue of secure communication among devices with limited resources. We introduce a key agreement protocol that utilizes implicit certificates with elliptic curves specifically designed for devices with limited capacity. We establish a certification chain within a finite graph to depict the connection among nodes within the identical group and propose a workload distribution strategy across all cluster nodes. Additionally, we present a trust scheme that enables nodes to generate implicit certificates on an elliptic curve and securely create keys with their counterparts. The group leader acts as the root CA and constructs a hierarchical structure within the finite graph, establishing a certification chain in an organized manner with an intermediate certificate authority (ICA) at every level. This chain is utilized by nodes for generating and sharing implicit certificates, from which symmetric keys for communication between nodes are derived. We then implement the solution using TelosB sensors in the TOSSIM simulator with an AVL Tree. We evaluate the security and resilience of our proposed scheme through informal analysis and a formal model. The informal analysis demonstrates the robustness of our scheme in achieving key security objectives, while the formal analysis using the extended Canetti-Krawczyk (eCK) model confirms its security and efficiency. Furthermore, we compare the performance of our scheme with other related schemes, highlighting its effectiveness for resource-constrained devices.