In the last decade, there has been growing interest in Vehicular Ad Hoc NETworks (VANETs). Today car manufacturers have already started to equip vehicles with sophisticated sensors that can provide many assistive features such as front collision avoidance, automatic lane tracking, partial autonomous driving, suggestive lane changing, and so on. Such technological advancements are enabling the adoption of VANETs not only to provide safer and more comfortable driving experience but also provide many other useful services to the driver as well as passengers of a vehicle. However, privacy, authentication and secure message dissemination are some of the main issues that need to be thoroughly addressed and solved for the widespread adoption/deployment of VANETs. Given the importance of these issues, researchers have spent a lot of effort in these areas over the last decade. We present an overview of the following issues that arise in VANETs: privacy, authentication, and secure message dissemination. Then we present a comprehensive review of various solutions proposed in the last 10 years which address these issues. Our survey sheds light on some open issues that need to be addressed in the future.

Introduction

Several applications such as early warning systems which can warn about road construction, collisions, weather-related hazards, merging lanes, speed limits for curves, and pedestrian crossing warnings, are ready for the widespread deployment in Vehicular Ad-hoc NETworks (VANETs). Apart from assisting drivers to drive safely, VANETs can also provide infotainment to drivers/passengers for a more enjoyable driving as well as riding experience. Furthermore, VANETs can also assist in paying for parking and tolls, finding parking places, updating inbuilt vehicle navigation systems with real-time traffic situation, and downloading music, video and software updates [1–۳]. VANETs can also assist law enforcement agencies in reconstructing accidents as well as reaching the location of the accidents faster. The general model of VANETs proposed in the literature consists of two major components: On Board Units (OBUs), installed on vehicles, and Road Side Units (RSUs) installed on roadside to support the infrastructure needed for the deployment of VANETs. Each vehicle is assumed to be equipped with a set of sensors to collect phenomena surrounding the vehicle; the OBU processes the information collected by the sensors and sends/receives them to/from other relevant vehicles directly or through nearby RSUs [4]. The RSUs may also connect to the Internet to provide the necessary services to vehicles. A broad range of applications can be enabled by two main types of communication: (i) infrastructurebased communication (Vehicle to Infrastructure (V2I) communication) and (ii) direct communication between vehicles (Vehicle to Vehicle (V2V) communication) [5] as shown in Fig. 1. Major efforts for standardizing VANETs communication protocols have been carried out by the IEEE 802.11 Task Group by defining enhancements to IEEE 802.11 required to support Intelligent Transportation Systems (ITS) applications. This amendment is currently known as IEEE 802.11p.