Security in wireless ad hoc networks is hard to achieve due to the vulnerability of its links, limited physical protection, and the absence of a centralized management point. Consequently, novel approaches are necessary to address the security problem without sacrificing the essential properties of the wireless ad hoc network. Similar to other distributed systems, security in wireless ad hoc networks usually relies on the use of key management mechanisms. In this paper, we present a distributed public key authentication service to protect the network containing malicious and colluding nodes. Our solution was built on a clusteringbased network model and a trust model. These models allow mobile hosts to monitor and rate each other with an authentication metric. We also propose a new system of public key certification in conjunction with a trust value update algorithm. Our authentication service is able to discover and isolate malicious and colluding nodes in the network. Finally, we perform security evaluation on the proposed solution. We simulate a network containing malicious nodes and measure a number of metrics with various security operations to demonstrate the effectiveness of our scheme.