VANETs were identified as a key technology to increase safety for road users. In this paper, we design a security solution that ensures a secure and confident V2V communication between participating vehicles. We present a new group-based trust management and revocation system that evaluates the trustworthiness of participating vehicles based on their behaviors within their groups. Based on trust evaluation, misbehavior detection algorithms within vehicles, group leaders and infrastructure incidentally trigger a hierarchical revocation for excluding malicious entities within a specific area. This results in a lightweight solution for trust evaluation and certificate revocation within a modular, clustered and secure infrastructure based on Public Key Infrastructure (PKI)