Vehicular Ad Hoc Networks (VANETs) are based on network technology where cars act as mobile nodes to form a communication network. In VANETs, routing protocols have a significance regarding the overall network performance since they determine the way of sending and receiving packets between mobile nodes. Most of the protocols proposed for VANETs are adapted from Mobile ad hoc networks (MANETs) routing protocols. However, due to the specific characteristics of VANETs, especially high mobility, and dynamic topology, the routing protocols in ad hoc networks do not adapt immediately to VANETs. Therefore, secure routing of Vehicular ad hoc networks (VANETs) against attacks, which are of various types, is still a challenging issue. This paper is going to present a synthesis of the most relevant protocols that have addressed the secure routing issue in VANETs. It also establishes a comparison regarding the offered features and the studied performance aspects through which it is notified that a security mechanism depends not only on the level of efficiency but also on the network constraints.