Vehicular ad hoc networks (VANETs) have the potential to increase road safety and comfort. Especially because of the road safety functions, there is a strong demand for security in VANETs. After defining three application categories the paper outlines main security and privacy requirements in VANETs. Next, a security architecture for VANETs (SAV) is proposed that strives to satisfy the requirements. To find mechanisms applicable in the architecture a survey of existing mechanisms is given.