Two cluster-based security frameworks without a third-party infrastructure in VANETs are proposed and analyzed in this paper. Utilizing some concepts of PCREF [1] with suitable modification reaches our first proposed framework for serving as a benchmark. By further associating trust values with vehicles and taking key updates into account based on the first proposed framework, our second proposed framework is devised and serves as the most recommended framework. Through a theoretical approach, the security strength (regarding confidentiality, data authenticity, data availability, and the expected filtering position of the bogus report) and the overheads of storage, computation, and communication are thoroughly analyzed for both our proposed frameworks. Illustrated by numerical examples, the security strength and overhead are checked in detail for the two proposed frameworks to reach a constructive recommendation.