A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> The notion of on-line/off-line signature schemes was introduced in 1990 by Even, Goldreich and Micali. They presented a general method for converting any signature scheme into an on-line/off-line signature scheme, but their method is not very practical as it increases the length of each signature by a quadratic factor. In this paper we use the recently introduced notion of a trapdoor hash function to develop a new paradigm called hash-sign-switch, which can convert any signature scheme into a highly efficient on-line/off-line signature scheme: In its recommended implementation, the on-line complexity is equivalent to about 0.1 modular multiplications, and the size of each signature increases only by a factor of two. In addition, the new paradigm enhances the security of the original signature scheme since it is only used to sign random strings chosen off-line by the signer. This makes the converted scheme secure against adaptive chosen message attacks even if the original scheme is secure only against generic chosen message attacks or against random message attacks. <s> BIB001 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Large-scale peer-to-peer systems face security threats from faulty or hostile remote computing elements. To resist these threats, many such systems employ redundancy. However, if a single faulty entity can present multiple identities, it can control a substantial fraction of the system, thereby undermining this redundancy. One approach to preventing these "Sybil attacks" is to have a trusted agency certify identities. This paper shows that, without a logically centralized authority, Sybil attacks are always possible except under extreme and unrealistic assumptions of resource parity and coordination among entities. <s> BIB002 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> This paper introduces and makes concrete the concept of certificateless public key cryptography (CL-PKC), a model for the use of public key cryptography which avoids the inherent escrow of identity-based cryptography and yet which does not require certificates to guarantee the authenticity of public keys. The lack of certificates and the presence of an adversary who has access to a master key necessitates the careful development of a new security model. We focus on certificateless public key encryption (CL-PKE), showing that a concrete pairing-based CL-PKE scheme is secure provided that an underlying problem closely related to the Bilinear Diffie-Hellman Problem is hard. <s> BIB003 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Intervehicle communication (IVC) networks, a subclass of mobile ad hoc networks (MANETs), have no fixed infrastructure and instead rely on the nodes themselves to provide network functionality. However, due to mobility constraints, driver behavior, and high mobility, IVC networks exhibit characteristics that are dramatically different from many generic MANETs. This paper elicits these differences through simulations and mathematical models and then explores the impact of the differences on the IVC communication architecture, including important security implications. <s> BIB004 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> The proliferation of hotspots based on IEEE 802.11 wireless LANs brings the promise of seamless Internet access from a large number of public locations. However, as the number of users soars, so does the risk of possible misbehavior; to protect themselves, wireless ISPs already make use of a number of security mechanisms, and require mobile stations to authenticate themselves at the Access Points (APs). However, IEEE 802.11 works properly only if the stations also respect the MAC protocol. We show in this paper that a greedy user can substantially increase his share of bandwidth, at the expense of the other users, by slightly modifying the driver of his network adapter. We explain how easily this can be performed, in particular with the new generation of adapters. We then present DOMINO (System for Detection Of greedy behavior in the MAC layer of IEEE 802.11 public NetwOrks), a piece of software to be installed in the Access Point. DOMINO can detect and identify greedy stations, without requiring any modification of the standard protocol at the AP and without revealing its own presence. We illustrate these concepts by simulation results and by the description of our prototype. <s> BIB005 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Inter-Vehicular Communications (IVC) are a cornerstone of the future intelligent transportation systems. A crucial enabling component of IVC is its security and privacy. Indeed, as vehicular computing systems become interconnected, there will be new venues for attackers to exploit system vulnerabilities. In addition, proper security mechanisms can assist in law enforcement and automate payment operations, such as toll collection. Leveraging on experience gained from other networks like the Internet or wireless LANs, system security for vehicular networks has to be introduced in the design phase. In the following sections, we outline several security threats encountered in IVC, then we present the obstacles needed to overcome in order to cope with these threats. Finally, we describe several tools that will be helpful in building secure IVC networks. <s> BIB006 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> The strength of the GPS signal on the earth’s surface averages -160 dBw . While many GPS receivers leave large space for signal dynamics, enough power space is left for the GPS signals to be overridden (spoofed). Spoofing is completely different from jamming. The objective of jamming is to simply interrupt the availability of the signal in space at the receiver. The effect is to cause the signal at the receiver to be corrupted so that no valid GPS signal can be decoded by the receiver. The goal of spoofing, on the other hand, is to provide the receiver with a misleading signal, fooling the receiver to use fake signals in space for positioning calculations. The receiver will produce a misleading position solution. While the GPS P-code is heavily encrypted and thus, is hard to spoof, the civilian GPS signal, the C/A code, is easy to spoof because the signal structure, the spread spectrum codes, and modulation methods are open to the public. The purpose of this paper is to analyze the vulnerability of the satellite signal and GPS system to spoof attacks, propose the anti-spoofing algorithms and illustrate the simulations of spoofing impact and anti-spoofing results. It is believed by the authors of this paper that GPS can be spoofed in theory and producing a spoofing satellite signal is possible. However, practical spoofing that provides misleading navigation results at the receiver is difficult to conduct due to the signal infrastructure, and by applying trivial anti-spoofing algorithms in GPS receivers, spoofing attack can be easily detected. <s> BIB007 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Vehicular Ad hoc Network (VANET), a subclass of mobile Ad Hoc networks (MANETs), is a promising approach for future intelligent transportation system (ITS). These networks have no fixed infrastructure and instead rely on the vehicles themselves to provide network functionality. However, due to mobility constraints, driver behavior, and high mobility, VANETs exhibit characteristics that are dramatically different from many generic MANETs. This article provides a comprehensive study of challenges in these networks, which we concentrate on the problems and proposed solutions. Then we outline current state of the research and future perspectives. With this article, readers can have a more thorough understanding of vehicle ad hoc networking and the research trends in this area. <s> BIB008 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> The paper presents a remote user authentication scheme using the properties of bilinear pairings. In the scheme, the remote system receives user login request and allows login to the remote system if the login request is valid. The scheme prohibits the scenario of many logged in users with the same login-ID, and provides a flexible password change option to the registered users without any assistance from the remote system. <s> BIB009 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> In order to reduce car accidents, provide emergency information, novel applications on vehicular ad hoc networks (VANETs) have drawn a lot of attention in resent years. This paper presents a new security threat on VANET applications called illusion attack. In this attack, based on the current during condition on the road, the adversary broadcasts the scene-aligned traffic warning messages, which produce an illusion to cars at its neighborhood. In consequence, the illusion can largely manipulate other drivers' behaviors on their responses. The illusion attack can easily cause car accident, traffic jam and the decrease of VANET performance in terms of bandwidth utilization. We discuss the reasons why traditional authentication mechanisms cannot resolve this security threat effectively and propose a new model, called plausibility validation network (PVN), to remedy the illusion attack. Finally, we analyze the security properties and potential overhead of proposed model. <s> BIB010 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> In this paper we revisit the security models of certificateless signatures and propose two new constructions which are provably secure in the random oracle model. We divide the potential adversaries according to their attack power, and for the first time, three new kinds of adversaries are introduced into certificateless signatures. They are Normal Adversary, Strong Adversary and Super Adversary (ordered by their attack power). Combined with the known Type I Adversary and Type II Adversary in certificateless system, we then define the security of certificateless signatures in different attack scenarios. Our new models, together with the others in the literature, will enable us to better understand the security of certificateless signatures. Two concrete schemes with different security levels are also proposed in this paper. The first scheme, which is proved secure against Normal Type I and Super Type II Adversary, enjoys the shortest signature length among all the known certificateless signature schemes. The second scheme is secure against Super Type I and Type II adversary. Compared with the scheme in ACNS 2006 which has a similar security level, our second scheme requires lower operation cost but a little longer signature length. <s> BIB011 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Recent advances in wireless communications technology and car industry made it possible to consider wireless Ad-hoc (or mixed Ad-hoc/infrastructure) networks, providing connectivity among vehicles on the road. Such network, often referred to as VANET (Vehicular Ad-hoc Network) is seen to be one of the most valuable concept for improving efficiency and safety of the future transportations, as well as boosting operators' revenue. Thus, several ongoing research projects supported by industry, governments and academia, establishing standards for VANET networks. This paper covers current research challenges and future applications for such networks, discusses possible deployment scenarios and provides some insights to the state-of-the-art of the current standardization of interfaces and protocols on a global scale. <s> BIB012 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> This article presents a comprehensive survey of the state-of-the-art for vehicle ad hoc networks. We start by reviewing the possible applications that can be used in VANETs, namely, safety and user applications, and by identifying their requirements. Then, we classify the solutions proposed in the literature according to their location in the open system interconnection reference model and their relationship to safety or user applications. We analyze their advantages and shortcomings and provide our suggestions for a better approach. We also describe the different methods used to simulate and evaluate the proposed solutions. Finally, we conclude with suggestions for a general architecture that can form the basis for a practical VANET. <s> BIB013 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Vehicular ad hoc networks (VANETs) are important components of Intelligent Transportation Systems. The main benefit of VANET communication is seen in active safety systems that increase passenger safety by exchanging warning messages between vehicles. Other applications and private services are also permitted in order to lower the cost and to encourage VANET deployment and adoption. Security is one of the major challenges that must be addressed before VANETs can be successfully deployed. Another crucial issue is support of different applications and services in VANETs. In this paper we propose a secure and application-oriented network design framework for VANETs. We consider both security requirements of the communications and other requirements of potential VANET applications and services. The proposed framework consists of two basic components: an application-aware control scheme and a unified routing scheme. We also study a number of key enabling technologies that are important to a practical VANET. Our study provides a guideline for the design of a more secure and practical VANET. <s> BIB014 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> In any vehicular adhoc network, there is always a possibility of incorrect messages being transmitted either due to faulty sensors and/or intentional malicious activities. Detecting and evicting sources of such misbehavior is an important problem. We observe that the performance of misbehavior detection schemes will depend on the application under consideration and the mobility dynamics of the detecting vehicle. Further, the underlying tradeoff in any such detection algorithm is the balance between False Positives and False Negatives; one would like to detect as many misbehaviors as possible, while at the same time ensuring that the genuine vehicles are not wrongly accused. ::: ::: In this work we propose and analyze (via simulations) the performance of a Misbehavior Detection Scheme (MDS) for Post Crash Notification (PCN) application. We observe that the performance of this proposed scheme is not very sensitive to the exact dynamics of the vehicle on small scales, so that slight error in estimating the dynamics of the detecting vehicle does not degrade the performance of the MDS. <s> BIB015 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Certificateless public key cryptography is a recently proposed attractive paradigm which combines advantages of both certificate-based and ID-based public key cryptosystems as it avoids usage of certificates and does not suffer from key escrow. In this paper, we present a certificateless signature (CLS) scheme that is proved to be secure in the random oracle model under the hardness assumptions of k-CAA and Inv-CDHP. Our scheme upholds all desirable properties of previously proposed CLS schemes, and requires general cryptographic hash functions instead of the MapToPoint hash function which is inefficient. Furthermore, our scheme is significantly more efficient than all known CLS schemes, and the size of signatures generated by our scheme is approximate 160 bits, which is the shortest certificateless signatures so far. So it can be used widely, especially in low-bandwidth communication environments. <s> BIB016 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> In the modern health services era, data is accessed by the doctors and nurses using small handheld devices like mobile, Personal Digital Assistants and other electronic handheld devices. Individual’s health related information is normally stored in a central health repository. This data can be accessed by authorized doctors. Data is prone to be exposed to a number of mobile attacks while being accessed. Potential attacks like man-in-the-middle attacks can be seen while accessing the information from the central health repositories using handheld devices. This paper proposes an architecture using XACML (eXtensible Access Control Markup Language) policy to control the privacy and data access of health service data accessed through handheld devices. <s> BIB017 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Vehicular ad-hoc networks (VANETs) are a promising communication scenario. Several new applications are envisioned, which will improve traffic management and safety. Nevertheless, those applications have stringent security requirements, as they affect road traffic safety. Moreover, VANETs face several security threats. As VANETs present some unique features (e.g. high mobility of nodes, geographic extension, etc.) traditional security mechanisms are not always suitable. Because of that, a plethora of research contributions have been presented so far. This chapter aims to describe and analyze the most representative VANET security developments. <s> BIB018 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> This paper evaluates and compares mobile ad hoc network (MANET) routing protocols for wireless sensor network (WSN). It focuses and compares the performance analysis based on Quality of Service (QoS) factors on the throughput and delay between Ad Hoc on Demand Distance Vector (AODV) and Temporary Ordered Routing Algorithm (TORA) protocols for mesh network with a single source. Ad Hoc on Demand Distance Vector is a reactive protocol and Temporary Ordered Routing Algorithm is on-demand reactive protocol which is the hybrid protocol. Previous research did shown that AODV is better than TORA for a larger nodes that is more than 30 nodes an some says that TORA is better for smaller nodes environment. In wireless ad hoc network, the nodes must be able to interconnect each other to establish the link or connection from source to the destination. The results show that AODV outperformed TORA in the throughput but AODV had higher delay than TORA. After the analysis has been done, this paper shows that AODV outperforms TORA in the wireless sensor network only with a single source and destination which less than 30 nodes in a network. <s> BIB019 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Certificateless signature scheme is a practical solution to confront the drawback, Key Generation Center (KGC) being able to forge the signature of a user, of an identity based (ID-based) signature scheme. Lots of previous research results have shown the security models and the generic constructions for certificateless signatures. However, most of them did not satisfy Girault’s level-3 security which the conventional public key infrastructure (PKI) can achieve. Until 2007, Hu et al. introduced a generic construction and security model that can fulfill the requirement of Girault’s level-3 security. Recently, Du and Wen proposed a certificateless short signature scheme which is more computation efficient than the previous ones. But a flaw in security proofs and lack of Girault’s level-3 security can be still found in their scheme. In this paper, a cryptanalysis on Du-Wen scheme and an improved scheme will be presented, and we also provide formal proofs to demonstrate the security of the proposed scheme. <s> BIB020 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Recent advances in hardware, software, and communication technologies are enabling the design and implementation of a whole range of different types of networks that are being deployed in various environments. One such network that has received a lot of interest in the last couple of years is the Vehicular Ad-Hoc Network (VANET). VANET has become an active area of research, standardization, and development because it has tremendous potential to improve vehicle and road safety, traffic efficiency, and convenience as well as comfort to both drivers and passengers. Recent research efforts have placed a strong emphasis on novel VANET design architectures and implementations. A lot of VANET research work have focused on specific areas including routing, broadcasting, Quality of Service (QoS), and security. We survey some of the recent research results in these areas. We present a review of wireless access standards for VANETs, and describe some of the recent VANET trials and deployments in the US, Japan, and the European Union. In addition, we also briefly present some of the simulators currently available to VANET researchers for VANET simulations and we assess their benefits and limitations. Finally, we outline some of the VANET research challenges that still need to be addressed to enable the ubiquitous deployment and widespead adoption of scalable, reliable, robust, and secure VANET architectures, protocols, technologies, and services. <s> BIB021 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Vehicular Ad hoc Networks (VANETs) are emerging mobile ad hoc network technologies incorporating mobile routing protocols for inter-vehicle data communications to support intelligent transportation systems. Among others security and privacy are major research concerns in VANETs due to the frequent vehicles movement, time critical response and hybrid architecture of VANETs that make them different than other Ad hoc networks. Thus, designing security mechanisms to authenticate and validate transmitted message among vehicles and remove adversaries from the network are significantly important in VANETs. This paper presents several existing security attacks and approaches to defend against them, and discusses possible future security attacks with critical analysis and future research possibilities. <s> BIB022 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> In Vehicular Ad hoc Networks (VANETs), authentication is a crucial security requirement to avoid attacks to both inter-vehicle and vehicle-roadside communication. Vehicles have to be prevented from the misuse of their private data and the attacks on their privacy. In this paper, we investigate the authentication and privacy issues in VANETs. We propose a novel ID-based authentication framework with adaptive privacy preservation for VANETs. In this framework, adaptive self-generated pseudonyms are used as identifiers instead of real-world IDs. The update of the pseudonyms depends on vehicular demands. The ID-Based Signature (IBS) scheme and the ID-Based Online/Offline Signature (IBOOS) scheme are used, for authentication between the Road Side Units (RSUs) and vehicles, as well as authentication among vehicles, respectively. System evaluation has been executed using efficient IBS and IBOOS schemes. It shows that, the proposed authentication framework with privacy preservation is suitable to the VANET environment. <s> BIB023 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Vehicular ad hoc networks (VANETs) are classified as an application of mobile ad hoc network (MANET) that has the potential in improving road safety and in providing travellers comfort. Recently VANETs have emerged to turn the attention of researchers in the field of wireless and mobile communications, they differ from MANET by their architecture, challenges, characteristics and applications. In this paper we present aspects related to this field to help researchers and developers to understand and distinguish the main features surrounding VANET in one solid document, without the need to go through other relevant papers and articles starting from VANET architecture and ending up with the most appropriate simulation tools to simulate VANET protocols and applications. <s> BIB024 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> In the near future, it is expected that vehicles which increasingly become an intelligent systems will be equipped with radio communications interfaces. Thus, vehicular networks can be formed and they are commonly known as VANETs (Vehicular Ad hoc NETworks), a use case of mobile ad hoc networks where cars are the mobile nodes. As VANETs exhibit several unique features such as the high mobility of nodes, short connection times, etc. conventional security mechanisms are not always effective. Consequently, a wide variety of research contributions have been recently presented to cope with the intrinsic characteristics of vehicular communication. This paper provides a summary of the recent state of the art of VANETs, it presents the communication architecture of VANETs and outlines the privacy and security challenges that need to be overcome to make such networks safety usable in practice. It identifies all existing security problems in VANETs and classifies them from a cryptographic point of view. It regroups, studies and compares also the various cryptographic schemes that have been separately suggested for VANETs, evaluates the efficiency of proposed solutions and explores some future trends that will shape the research in cryptographic protocols for intelligent transportation systems. <s> BIB025 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Abstract Vehicular ad hoc networks (VANETs), a subset of Mobile Ad hoc NETworks (MANETs), refer to a set of smart vehicles used on the road. These vehicles provide communication services among one another or with Road Side Infrastructure (RSU) based on wireless Local Area Network (LAN) technologies. The main benefits of VANETs are that they enhance road safety and vehicle security while protecting drivers’ privacy from attacks perpetrated by adversaries. Security is one of the most critical issues related to VANETs since the information transmitted is distributed in an open access environment. VANETs face many challenges. This paper presents a survey of the security issues and the challenges they generate. The various categories of applications in VANETs are introduced, as well as some security requirements, threats and certain architectures are proposed to solve the security problem. Finally, global security architecture for VANETs is proposed. <s> BIB026 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> In recent years, the VANET has received a greater attention among researchers in academia and industry due to its potential safety application and nonsafety application. Malicious users are one of the types of attackers in VANET and create the security problems. Confidentiality, integrity and availability (CIA) are major components of security goals. The increasing research interest, potential applications, and security problem in VANET lead to the needs to review the attacks on security goals. In this paper, the aim is to present the survey of attacks on security goals and to describe in details the nature of attacks and the behaviour of attackers through different scenarios in the network. The paper also provides a better understanding of security goals and finally it provides an analysis and classifies the attacks on the basis of security goals into different threat levels that can help in the implementation of VANET in real life. <s> BIB027 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> The certificateless signature CLS scheme is a special signature scheme that solves the key escrow problem in identity-based signature schemes. In CLS schemes, the private key is generated cooperatively by the key generator center KGC and signer, such that a malicious KGC cannot masquerade as the signer and sign a message. He et al. in 2011 proposed an efficient CLS scheme without using bilinear pairings. However, we discovered that the CLS scheme by He et al. cannot resist a strong type 2 adversary if this adversary replaces the master public key of the KGC. This work proposes an improved scheme that overcomes this weakness. Copyright © 2012 John Wiley & Sons, Ltd. <s> BIB028 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> During these years, the research field of certificateless signature (CLS) scheme is promptly investigated as the key escrow problem in identity-based cryptography can be solved via CLS concept. However, due to the bandwidth limitation of mobile communication and the resource-constraint property of handheld mobile devices, most CLS schemes cannot fulfill the requirement of computation efficiency for mobile communication architecture. Hence, the design of lightweight CLS protocol refined from traditional cryptosystem technologies for existing mobile communication environment becomes one of the most important research trends. In this paper, we demonstrate a novel CLS scheme which is immune against bilinear pairings. Without the heavy computation of bilinear pairings, our proposed scheme is efficient and practical for mobile communication. Meanwhile, the proposed CLS scheme possesses strong security density owing to the adoption of point addition of elliptic curve cryptography. A formal security analysis is presented to guarantee the security robustness of our CLS protocol under the hardness of breaking elliptic curve discrete logarithm problem. <s> BIB029 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Certificateless public key cryptography was introduced to solve the complicated certificate management problem in traditional public key cryptography and the key escrow problem in identity-based cryptography. The aggregate signature concept is useful in special areas where the signatures on many different messages generated by many different users need to be compressed. This feature is very attractive for authentication in a resource constrained environment because it allows large bandwidth and computation time savings. This paper proposes a new certificateless signature scheme. A new certificateless aggregate signature scheme for vehicle-to-infrastructure communication in vehicular ad hoc networks based on the new certificateless signature scheme is presented. We demonstrate that the proposed certificateless aggregate signature scheme can also achieve conditional privacy preservation, in which each traffic message launched by a vehicle is mapped to a distinct pseudo identity. A legal authority can retrieve the real identity from any pseudo identity for any dispute event. In addition, the proposed scheme is provably secure against existential forgery on adaptively chosen message attack in the random oracle model assuming the computational Diffie-Hellman problem is hard. Furthermore, the proposed scheme presents efficient computational overhead with the existing well-known schemes and is suitable for practical use. <s> BIB030 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Vehicular ad-hoc networks (VANETs) are the most hopeful approach to provide safety information and other infotainment applications to both drivers and passengers. VANETs are formed by intelligent vehicles equipped with On Board Units and wireless communication devices. Hence, VANETs become a key component of the intelligent transport system. Even though VANETs are used in enormous number of applications, there are many security challenges and issues that need to be overcome to make VANETs usable in practice. A great deal of study has been done towards it, but security mechanisms in VANETs are not effective. This study provides a summary about the VANET, characteristics and security challenges. This study also provides a summary of some major security attacks on security services such as availability, confidentiality, authentication, integrity and non-repudiation and the corresponding countermeasures to make VANET communications more secure. <s> BIB031 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> In urban vehicular ad hoc networks (VANETs), the network topology changes rapidly due to high mobility and uneven distribution of vehicles, thus the street connectivity is hard to estimate. Conventional routing protocols consider the street density as a decisive factor of street connectivity; however, they ignore the vehicle gathered phenomenon induced by traffic lights at the intersections. In this letter, we first explore the effect of traffic lights on vehicle distribution in a street, and then calculate street connectivity based on the distribution and density of vehicles in the middle area of a street. Finally, we propose a street-centric protocol called traffic-light-aware routing protocol based on street connectivity. Simulation results have shown that our protocol can improve the delivery ratio and reduce end-to-end delay for urban VANETs. <s> BIB032 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Cooperative Intelligent Transportation Systems, mainly represented by vehicular ad hoc networks (VANETs), are among the key components contributing to the Smart City and Smart World paradigms. Based on the continuous exchange of both periodic and event triggered messages, smart vehicles can enhance road safety, while also providing support for comfort applications. In addition to the different communication protocols, securing such communications and establishing a certain trustiness among vehicles are among the main challenges to address, since the presence of dishonest peers can lead to unwanted situations. To this end, existing security solutions are typically divided into two main categories, cryptography and trust, where trust appeared as a complement to cryptography on some specific adversary models and environments where the latter was not enough to mitigate all possible attacks. In this paper, we provide an adversary-oriented survey of the existing trust models for VANETs. We also show when trust is preferable to cryptography, and the opposite. In addition, we show how trust models are usually evaluated in VANET contexts, and finally, we point out some critical scenarios that existing trust models cannot handle, together with some possible solutions. <s> BIB033 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Existing secure and privacy-preserving schemes for vehicular communications in vehicular ad hoc networks face some challenges, e.g., reducing the dependence on ideal tamper-proof devices, building efficient member revocation mechanisms and avoiding computation and communication bottlenecks. To cope with those challenges, we propose a highly efficient secure and privacy-preserving scheme based on identity-based aggregate signatures. Our scheme enables hierarchical aggregation and batch verification. The individual identity-based signatures generated by different vehicles can be aggregated and verified in a batch. The aggregated signatures can be re-aggregated by a message collector (e.g., traffic management authority). With our hierarchical aggregation technique, we significantly reduce the transmission/storage overhead of the vehicles and other parties. Furthermore, existing batch verification based schemes in vehicular ad hoc networks require vehicles to wait for enough messages to perform a batch verification. In contrast, we assume that vehicles will generate messages (and the corresponding signatures) in certain time spans, so that vehicles only need to wait for a very short period before they can start the batch verification procedure. Simulation shows that a vehicle can verify the received messages with very low latency and fast response. <s> BIB034 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Developing highly efficient routing protocols for vehicular ad hoc networks (VANETs) is a challenging task, mainly due to the special characters of such networks: large-scale sizes, frequent link disconnections, and rapid topology changes. In this paper, we propose an adaptive quality-of-service (QoS)-based routing for VANETs called AQRV. This new routing protocol adaptively chooses the intersections through which data packets pass to reach the destination, and the selected route should satisfy the QoS constraints and fulfil the best QoS in terms of three metrics, namely connectivity probability, packet delivery ratio (PDR), and delay. To achieve the given objectives, we mathematically formulate the routing selection issue as a constrained optimization problem and propose an ant colony optimization (ACO)-based algorithm to solve this problem. In addition, a terminal intersection (TI) concept is presented to decrease routing exploration time and alleviate network congestion. Moreover, to decrease network overhead, we propose local QoS models (LQMs) to estimate real time and complete QoS of urban road segments. Simulation results validate our derived LQM models and show the effectiveness of AQRV. <s> BIB035 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Abstract VANET is an emergent technology with promising future as well as great challenges especially in its security. In this paper, we focus on VANET security frameworks presented in three parts. The first presents an extensive overview of VANET security characteristics and challenges as well as requirements. These requirements should be taken into consideration to enable the implementation of secure VANET infrastructure with efficient communication between parties. We give the details of the recent security architectures and the well-known security standards protocols. The second focuses on a novel classification of the different attacks known in the VANET literature and their related solutions. The third is a comparison between some of these solutions based on well-known security criteria in VANET. Then we draw attention to different open issues and technical challenges related to VANET security, which can help researchers for future use. <s> BIB036 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Existing secure and privacy-preserving vehicular communication protocols in vehicular ad hoc networks face the challenges of being fast and not depending on ideal tamper-proof devices (TPDs) embedded in vehicles. To address these challenges, we propose a vehicular authentication protocol referred to as distributedaggregate privacy-preserving authentication. The proposed protocol is based on our new multiple trusted authority one-time identity-based aggregate signature technique. With this technique a vehicle can verify many messages simultaneously and their signatures can be compressed into a single one that greatly reduces the storage space needed by a vehicle or a data collector (e.g., the traffic management authority). Instead of ideal TPDs, our protocol only requires realistic TPDs and hence is more practical. <s> BIB037 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Location privacy is one of the major challenges in vehicular ad hoc networks. Due to the open and broadcast nature of wireless communication, the safety messages of vehicles can be easily collected by malicious eavesdroppers to continuously track vehicles. Cryptographic mix-zone (CMIX) is a promising tool to enhance vehicle privacy, in which the safety messages of vehicles are encrypted using a group secret key. In that way, any outsider cannot monitor the safety messages broadcasted by the vehicles in the CMIX. Existing CMIX protocols need fully trusted dealers to distribute group secret keys and/or suffer from the problem of efficient key update. This paper proposes a novel method based on a new security tool referred to as one-time identity-based authenticated asymmetric group key agreement to create CMIXes which withstand malicious eavesdroppers. Different from the existing solutions, our proposal does not rely on the existence of fully trusted dealers and deals with efficient key update in CMIX for the first time. In our protocol, any vehicle in a CMIX could be a group secret key distributer. Furthermore, once the group secret key of the CMIX has to be updated, a vehicle in the CMIX just needs to broadcast a short ciphertext, then all the vehicles in the CMIX may refresh the group secret key to the new one efficiently. <s> BIB038 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Vehicular cloud (VC) extends cloud computing to vehicles participating in vehicular ad hoc networks, aiming to provide computing and storage services at low cost to vehicles, improve traffic efficiency and safety, ensure real-time services, etc. Due to the highly dynamic nature of VC, it is challenging to efficiently form a dynamic VC securely and anonymously or to securely deliver messages to the dynamic VC without potentially violating the privacy of cloud users. In this paper, we present a concrete secure and privacy-preserving communication scheme for VC establishment and data dissemination. Our scheme allows a group of vehicles that are geographically close to each other to form a VC securely, anonymously and dynamically. This allows vehicle resources to be integrated and shared securely. Once a VC is formed, any cloud user may deliver messages to be securely and anonymously processed in the VC. <s> BIB039 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Abstract In order to eliminate the complexity associated with managing public key encryption certificates and the drawbacks of identity-based encryption key escrows, the concept of certificateless public key cryptography has been recommended. Further, in specific application areas where the signatures on numerous messages generated by different users need to be compressed, the concept of the aggregate signature is useful. An aggregate signature can not only reduce the cost of verification, but also reduce the length of the signature, which makes it effective in environments constrained by bandwidth and storage. In this paper, we propose a new, efficient, certificateless aggregate signature based on the elliptic curve cryptosystem (ECC), and demonstrate its ability to support conditional privacy preservation. This scheme demonstrates the process of secure communication between vehicles and the infrastructure in vehicular ad hoc networks (VANETs). The proposed scheme not only satisfies privacy requirements (with security analysis), but also achieves lower message overhead than previous schemes. We demonstrate that the performance of our scheme surpasses that of existing authentication schemes for VANETs in terms of computation and communication costs. <s> BIB040 </s> A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) <s> • <s> Vehicular ad hoc networks (VANETs) are becoming the most promising research topic in intelligent transportation systems, because they provide information to deliver comfort and safety to both drivers and passengers. However, unique characteristics of VANETs make security, privacy, and trust management challenging issues in VANETs’ design. This survey article starts with the necessary background of VANETs, followed by a brief treatment of main security services, which have been well studied in other fields. We then focus on an in-depth review of anonymous authentication schemes implemented by five pseudonymity mechanisms. Because of the predictable dynamics of vehicles, anonymity is necessary but not sufficient to thwart tracking an attack that aims at the drivers’ location profiles. Thus, several location privacy protection mechanisms based on pseudonymity are elaborated to further protect the vehicles’ privacy and guarantee the quality of location-based services simultaneously. We also give a comprehensive analysis on various trust management models in VANETs. Finally, considering that current and near-future applications in VANETs are evaluated by simulation, we give a much-needed update on the latest mobility and network simulators as well as the integrated simulation platforms. In sum, this paper is carefully positioned to avoid overlap with existing surveys by filling the gaps and reporting the latest advances in VANETs while keeping it self-explained. <s> BIB041
Roadside Unit: The RSUs are computing devices, which is fixed alongside of the road or in specified location such as: parking area or at the intersection BIB024 . It is used to provide local connectivity to the passing vehicles. The RSUs consists of network devices for dedicated short range communication (DSRC) based on IEEE 802.11p radio technology. Specifically, RSUs can also be used to communicate with other network devices within the other infrastructure networks BIB024 . • Onboard Unit: An OBU is a GPS-based tracking device that is usually equipped in every vehicle to sharing vehicle information to RSUs and other OBUs. OBU consists of many electronics components such as: resource command processor (RCP), sensor devices, the user interface, and read/write storage for retrieving storage information. The main function of OBU is to connects with RSU or other OBUs through wireless link of IEEE 802.11p  , and is responsible to communicate with other OBUs or RSUs in the form of messages. Moreover, OBU take input power from the car battery, and each vehicle consists of a sensor type global positioning system • Roadside Unit: The RSUs are computing devices, which is fixed alongside of the road or in specified location such as: parking area or at the intersection BIB024 . It is used to provide local connectivity to the passing vehicles. The RSUs consists of network devices for dedicated short range communication (DSRC) based on IEEE 802.11p radio technology. Specifically, RSUs can also be used to communicate with other network devices within the other infrastructure networks BIB024 . • Onboard Unit: An OBU is a GPS-based tracking device that is usually equipped in every vehicle to sharing vehicle information to RSUs and other OBUs. OBU consists of many electronics components such as: resource command processor (RCP), sensor devices, the user interface, and read/write storage for retrieving storage information. The main function of OBU is to connects with RSU or other OBUs through wireless link of IEEE 802.11p  , and is responsible to communicate with other OBUs or RSUs in the form of messages. Moreover, OBU take input power from the car battery, and each vehicle consists of a sensor type global positioning system (GPS), an event data recorder (EDR), and forward and backward sensors, which are used to provide input to OBU BIB031 . • Trusted Authority: TA is responsible for managing the entire VANET system such as registering the RSUs, OBUs, and the vehicle users. Moreover, it has the responsibility to ensure the security management of VANETs by verifying the vehicle authentication, user ID and OBU ID in order to avoid harm to any vehicle. The TA utilizes a high amount of power with large memory size and can also reveal OBU ID and details in case of any malicious message or suspicious behavior BIB015 . In additional to these, TA has the mechanism to identify the attackers as well.  Warning Propagation Message: If there is any crucial situation where the message is required to send to a specific vehicle or to a group of vehicles. For example, if there is any accident or collision, then a warning message should be sent to the vehicles that are on the way to avoid traffic jams and increase traffic safety. To deal with this issue, a new routing algorithm is required, which can be used to send the warning messages to the destination BIB018 . • V2V Group Communication: In the V2V communication domain, only vehicles that are sharing some of the same features can take part in this communication BIB018 . This includes vehicles with the same brand or vehicles sharing the same location in the time interval. • Vehicle Beaconing: Periodically sent, the beacon messages all vehicles, which are nearby and RSUs. These messages contain the speed, velocity, and acceleration of the sending vehicle. Infrastructure to Vehicle Warning: To improve the traffic flow and road safety, warning messages are broadcast from the infrastructure via RSUs to all vehicles within its vicinity when a possible accident or collision is detected, especially in the curve route, intersections, or with a narrow road. Dedicated Short Range Communication (DSRC): DSRC is a wireless communication technology tool that permits vehicles to communicate with each other in ITS or other infrastructure such as   . As shown in Figure 2 , the spectrum of 75 MHz DSRC is sectioned into seven channels, and starts from Ch 172 to Ch 184. The Ch 178 is the control channel that can support the safety power applications  . The other six channels such as BIB035 BIB032 176, 180, 182 , and 184 are the service channel (SCH). The Ch 172 and Ch 184 are used for high power and public safety messages  , while other channels can be used to send both as a safety and non-safety messages. • WAVE: According to the IEEE published materials for the latest ITS standards  , the WAVE IEEE 1609 describes an architecture, mechanism, sets of protocols, and interface, which are used to develop communication in the VANET environment, i.e., V2V and V2I communications BIB025 . Figure 3 shows the different standards of the WAVE architecture and its integration with the open system interconnection (OSI) model. • IEEE 802.11p: After introducing the IEEE 1609 standards, the IEEE extended the family of IEEE 802.11 protocols by adding a new member 802.11p, which is used to facilitate the vehicular communication network BIB025 . This is in compliance with the dedicated short range communication (DSRC) band. is used as a communication tool and includes all necessary features of all the layers BIB025 . The dedicated short range (DSRC) communication, WAVE, and IEEE 802.11p are used to designate the full standard of communication protocol to deal with VANETs. • Dedicated Short Range Communication (DSRC): DSRC is a wireless communication technology tool that permits vehicles to communicate with each other in ITS or other infrastructure such as V2V and V2I. In 1999, the Federal communication commission (FCC) allocated the band from 5.850 to 5.925 GHz, with a spectrum of 75 MHz for DSRC   . As shown in Figure 2 , the spectrum of 75 MHz DSRC is sectioned into seven channels, and starts from Ch 172 to Ch 184. The Ch 178 is the control channel that can support the safety power applications  . The other six channels such as BIB035 BIB032 176, 180, 182 , and 184 are the service channel (SCH). The Ch 172 and Ch 184 are used for high power and public safety messages  , while other channels can be used to send both as a safety and non-safety messages. • WAVE: According to the IEEE published materials for the latest ITS standards  , the WAVE IEEE 1609 describes an architecture, mechanism, sets of protocols, and interface, which are used to develop communication in the VANET environment, i.e., V2V and V2I communications BIB025 . Figure 3 shows the different standards of the WAVE architecture and its integration with the open system interconnection (OSI) model. • IEEE 802.11p: After introducing the IEEE 1609 standards, the IEEE extended the family of IEEE 802.11 protocols by adding a new member 802.11p, which is used to facilitate the vehicular communication network BIB025 . This is in compliance with the dedicated short range communication (DSRC) band.  High Mobility: High mobility nodes are the main features of VANETs, which have high mobility as compared to MANETs. VANETs are different from other types of ad hoc networks in which nodes can move in random directions, which makes it difficult to estimate their location and  High Mobility: High mobility nodes are the main features of VANETs, which have high mobility as compared to MANETs. VANETs are different from other types of ad hoc networks in which nodes can move in random directions, which makes it difficult to estimate their location and network topology, because the vehicles are limited to the road direction, traffic lights, and to respond to other nearby vehicles. In the past, several research studies have explored this special feature BIB012 BIB004 BIB013 . According to the references BIB021  , the high mobility of nodes reduces the communication time between the nodes in the network. Wireless Communication: The nodes connection and data communication are exchanged through a wireless medium. Therefore, it is necessary to develop a secure communication during transmission BIB036 . Dynamic Network Topology: The topology of VANETs is not constant and can change rapidly due to the high mobility of vehicles. Therefore, it makes VANETs more vulnerable to attacks and difficult to recognize the suspect vehicles. • Driver Safety: VANETs can improve driver safety, enhances passenger comforts, and improves the traffic flow. The main advantage of VANETs is that vehicles can communicate directly. Therefore, it allows the number of applications, which required directly to communicate between nodes to other networks such as RSUs or OBUs. Limitation of Transmission Power: The transmission power is very constrained in the WAVE, which ranges from 0 to 28.8 dBm and was limited to the distance up to 1 Km. Thus, the limited power transmission resulted in limiting the coverage distance of VANETs [66, BIB017 . • Network Strength: The strength of the network in VANETs depends on the flow of the traffic on the street, in case of traffic jams it can be very high, and low when there is no traffic on the road. Large Network: The network can be larger in downtown areas, highways, and also the entry and exit point of the city BIB013 BIB008 . • Volatility: In VANETs, the connections between two nodes are usually developed due to their mobility. Each vehicle has high mobility, so it is possible that the connection among the vehicles can be lost and may remain active within a few wireless hops BIB041 that makes difficult to ensure the personal security in VANETs. Availability: Availability is the most important part of security services due to its direct relationship with all safety applications. The main responsibility of availability is managing functionality, and its security must ensure that the network and other applications must remain functional in case of faulty or malicious conditions BIB014 . • Confidentiality: Based on certificates and shared public keys, confidentiality ensures that the designated receiver have access to the data while outside nodes may not be able to get access to that data until confidential data was received by the designated user. • Authentication: Authentication plays a vital role in VANET. It prevents the VANET against suspected entities in the network. It is important to have the related information of the transmission mode such as user identification and sender address. Authentication have the right to control the authorization level of vehicles, and it can also prevent Sybil attacks by assigning individual identity to each vehicle BIB026 . • Data Integrity: It ensures that the message content is not altered during the communication process. In VANETs, data integrity can be ensured by using the public key infrastructure and cryptography revocation process BIB033 . • Non-Repudiation: It ensures that, in case of the dispute sender, the receiver of the message does not refuse to engage in transmission and reception  BIB019 . attacks because of its distinctive characteristics. Specifically, security challenges should be addressed properly. Otherwise, it will lead toward creating many constraints for securing communication in VANETs BIB036 . In the VANET security, it is necessary to mention the requirements that the system should be inline with the appropriate network operation. Unable to fulfill these requirements may lead to possible threats or attacks in VANETs. The main security requirements are categorized into five main domains such as availability, confidentiality, authentication, data integrity, and non-repudiation  ,  . Figure 4 shows the security services as well as their threats and attacks. These security services are discussed in this section. Availability: Availability is the most important part of security services due to its direct relationship with all safety applications. The main responsibility of availability is managing functionality, and its security must ensure that the network and other applications must remain functional in case of faulty or malicious conditions BIB014 . • Confidentiality: Based on certificates and shared public keys, confidentiality ensures that the designated receiver have access to the data while outside nodes may not be able to get access to that data until confidential data was received by the designated user. • Authentication: Authentication plays a vital role in VANET. It prevents the VANET against suspected entities in the network. It is important to have the related information of the transmission mode such as user identification and sender address. Authentication have the right to control the authorization level of vehicles, and it can also prevent Sybil attacks by assigning individual identity to each vehicle BIB026 . • Data Integrity: It ensures that the message content is not altered during the communication process. In VANETs, data integrity can be ensured by using the public key infrastructure and cryptography revocation process BIB033 . • Non-Repudiation: It ensures that, in case of the dispute sender, the receiver of the message does not refuse to engage in transmission and reception  BIB019 .  Denial of Service (DOS) Attacks: DOS is one of the most common attacks in VANETs, which occur by the internal or external vehicles performing the attacks in the VANET network BIB021 . The attacker jamming the communication between vehicles and effectively blocking every possible way of action. This attack can be performed by many attackers concurrently in a distributed way, called distributed denial of service (DDoS) BIB027 . • Jamming Attack: In this attack, the attacker disturbs the communication channel in VANETs by using a heavily powered signal with equivalent frequency  . This is the most dangerous attack for safety applications, because it does not follow the valid safety alert. For any successful jamming attack, by performing an action, the jammer can block the useful signal within the same time of the occurrence of an event. Malware Attack: The attack can be penetrated into the system through the software components, which are used to operate the OBUs and RSUs BIB022  . If the malware attack occurred in VANETs, that may lead to malfunctioning of the other components of the VANET system. • Broadcast Tampering Attack: In this attack, untrustworthy vehicles can replicate the same messages by modifying the message or generate and insert a new message information in the VANETs while behaving as a transmit node for inter-vehicle communication BIB033 . Therefore, this may lead to hide the correct safety messages to dedicated users, which may be the reason for dangerous accidents. Blackhole Attack: This is the main attack that targets availability in ad hoc networks, and also exists in VANETs. This attack is usually caused by a registered VANET user. The suspected node receives the packets from the network but it declines the contribution in the networking operation. This may disrupt the routing table and prevents an important message to the recipients due to the malicious node, which pretends to contribute in the non-practical event BIB025 BIB021 BIB022 . Grayhole Attack: It is the variant of the blackhole attack. It occurs when untrustworthy vehicles select some of the data packets to forward and dropping the other packet without being tracked BIB033 . • Greedy Behavior Attack: This attack is normally on the functionality of the message authentication code (MAC), when the malicious vehicle misuses the MAC protocol to increase the large amount of bandwidth, which costs other users. This resulted in overload traffic and causes a collision on the transmission channel, which can produce a delay in the legitimate services of the registered user BIB005 . • Spamming Attack: In this attack, a numerous amount of spam messages are injected by the attacker such as advertisements in the VANET system, which causes collisions by utilizing more bandwidth BIB021  . Eavesdropping Attack: Eavesdropping is very common in wireless communication technology, such as MANETs and VANETs. The aim of this attack is to get the confidential information from the protected data. Therefore, by this attack, secret details can be disclosed with non-registered users, such as stealing user identity and data location, which may be used to track the vehicles. • Traffic Analysis Attack: This is one of the dangerous attacks that threatens confidentiality. In this attack, after listening to a message transmission, the attacker then analyzes its frequency and tries to extract and gather the maximum useful information. Man-in-the-Middle Attack: It can take place in the middle of V2V communication to check closely and alter the messages. The attacker can get the access and control the entire V2V communication, but the communication entities think that they can communicate with each other directly in private BIB009 . • Social Attack: The social attack is used to divert the attention of the driver. The attacker sends out immoral and unethical messages to the drivers. The aim of attackers is to get the reaction of the drivers after they received this type of immoral messages. Therefore, it affects the driving experience and performance of the vehicle in the VANET system BIB006 . Sybil Attack: It is first discussed by Reference BIB002 . This is a most dangerous attack in which the node can produce many fake identities to disrupt the normal mode of operations of the VANETs by broadcasting multiple messages using fake IDs. The attacker can manipulate other vehicle behavior, and receive a vehicle system where the messages are transmitted from the different vehicles. Therefore, they feel there is congestion on the road and they are enforced to alter their paths and leave the road clear. • Tunneling Attack: It is similar to the wormhole attack BIB021 . The attacker uses the same network to initiate the private conversation, and the attackers join two far-away parts in VANETs by utilizing an extra communication channel named a tunnel. Therefore, the nodes, which are very far-away from each other, can communicate as neighbors. • GPS Spoofing: In this attack, the attacker uses the trick to create a false GPS location information and did not reveal the correct position to dodge the vehicles that may think it is available in some other location BIB007 . • Node Impersonation Attack: This attack takes place when an attacker successfully guesses the valid ID of the registered users in the VANETs BIB022 . • Free-Riding Attack: This attack is very common and is initiated by an active malicious user by making false authentication efforts while being associated with a cooperative message authentication. In this attack, the malicious user may take advantage of other user's authentication contributions without having its own. This type of behavior is called a free-riding attack. This attack may raise a serious threat to cooperative message authentication  . • Replay Attack: It is a very common attack, which is also known as a playback attack. This attack occurs when valid data are fraudulently transmitted or cause a delay to produce an unauthorized and malicious effect. In order to tackle this attack, the VANET must require enough of a time source with larger cache memory, which are used to compare the received messages. • Key and/or Certificate Replication Attack: This attack is caused by the utilization of duplicate keys and/or certificates of other vehicles as a proof of authentication to create uncertainty, which makes the situation worse for traffic authorities to identity the vehicle. Specifically, the aim of this attack is to create confusion for trusted authorities (TAs) especially in case of any dispute. Message Tampering: It is a very common attack, in which the attacker can alter the exchanged messages in V2V or V2I communication. Masquerading Attack: The attacker uses false IDs to act as another vehicle. This attack occurs when one user did not show his own identity and pretends to be a different user to legally obtain unauthorized access. Masquerading Attack: The attacker enters in the VANET system by registered user ID and passwords and tried to broadcast false messages, which appeared to come from the registered node [83] . Replay Attack: The attacker aims to repeat or delay transmission fraudulently by having a valid data and inject beacon and messages received before the VANET network continuously, which may cause difficulty for traffic authority to identify the vehicles in case of the emergency [84,85]. • Message Tampering Attack: As the name of the attack indicated, this attack normally occurs when the attacker modifies or alters recent message data to be transmitted  . For instance, if the route is congested then, the attacker alters the data to clear the road. This can influence the users to alter their driving paths. Illusion Attack: This attack receives data from antennas and collects malicious data from sensors, which generate traffic warning messages by using an existing road condition that may create illusion to the vehicles nearby BIB010 . The illusion attack may be caused by vehicle accidents and traffic congestion and also minimizes the performance of the VANET system by utilizing undesirable bandwidth. Repudiation Attack: This attack occurs when an attacker denies to engage in the activity of sending and receiving messages in case of any dispute BIB031 . Computational and Communication Overhead: The number of cryptographic operations performed by a vehicle or trusted authority for verifying an authentication request must be minimized. For example, the time required to process a digital signature in authentication must be controlled. Utilization of Bandwidth: The bandwidth utilization is very important in the authentication and must be utilized properly in bytes per second (bps) to handle a request for an authentication such as exchanging cryptographic secret keys and credentials. • Scalability: The process of the authentication is scalable, which can handle multiple network operations and communications. • Time Response: The time that is needed to respond for an authentication mechanism must be reduced. Powerful Authentication: The authentication schemes must have a good capability to prevent VANETs from attacks. Privacy of User Protection: It is used to prevent the personal information of users from malicious users or attackers. • User Location Protection: Meant to protect user's information such as vehicle location at a certain time and route information. The aim of authentication schemes is to identify the malicious nodes and bogus messages. Thus, it provides security in VANETs. Regarding authentication schemes, several research studies have been proposed, which ensure the secured communication in VANETs. These schemes utilized different cryptography techniques for signing and verifying the messages. In this paper, we discussed the authentication schemes in terms of cryptography and signature in detail, as shown in Figure 5 . Cryptograph-based authentication schemes are categorized into symmetric cryptography (Hash Function and timed efficient stream loss-tolerant authentication (TESLA)), asymmetric cryptography (PKI certificate and ECDSA), and identity-based cryptography. Signature-based authentication schemes are separated into identity-based signature, certificateless signature, and group signature. The classification of authentication schemes in each category are discussed in terms of analysis and their related works. Setup: PKG evaluates the master key and public parameters. Then, PKG discloses these parameters to all vehicles publicly in the VANET. • Key Extraction: PKG uses the vehicles ID and master ID to compute a private key. Then the PKG sends these private keys to communicate with the vehicle through a secure channel. Signing Signature: Signature SIG can be generated by using a private key by assuming a message M, and timestamp T. Verification: This algorithm is used to find out whether signature SIG is valid or not by having these parameters such as identity, signature, and message. To overcome the computational overhead in the IBS scheme for VANETs, Lu et al. BIB023 proposed a novel authentication framework with adaptive privacy using an ID-based online/offline authentication (IBOOS) technique. In Reference BIB034 , Zhang et al. introduced an identity-based technique for signature hierarchical aggregation and batch verification. In this approach, identity-based signatures are generated from different vehicles, which can be aggregated and verified in a batch, and the message collector is used to re-aggregate the aggregated signatures. This scheme significantly reduced the large computational process of certification verification by utilizing the identity-based vehicles and RSUs. In 2001, a new hash-sign-switch method has been proposed based on the trapdoor hash function. In this scheme, the signing process is efficiently divided into the online and offline phases. Due to a good pairing process, the efficiency of this method is better than the IBS scheme. However, the requirement of memory storage space makes IBOOS unsuitable for VANETs BIB001 . In the verification, the IBS eliminates the requirement of certificates, which can be used in the verifications of public keys. Thus, it did not need to be distributed as public keys, which are related to certificates BIB041 . Specifically, only PKG knows the private keys in VANETs because it is generated by PKG in IBS, which may generate an escrow problem. To overcome this problem, in the year of 2017, Zhang et al. BIB037 introduced an efficient technique to authenticate the vehicle protocol named as a distributed aggregate privacy-preserving authentication (DAPPA), which is based on multiple trusted authorities with the IBS technique. In Reference BIB038 , Zhang introduced a novel approach based on a new security tool named as one-time identify-based authenticated asymmetric group key to develop cryptography mix-zone (CMIX) against eavesdropping. In 2018, Zhang et al. BIB039 introduced a secure privacy-preserving communication scheme for establishing vehicle cloud (VC) and data broadcasting in the VC. In this approach, a group of vehicle, which are located near VANETs, are used to develop a secure and dynamic VC. Therefore, it enables all the vehicle resources to be integrated and exchanged data securely, and any cloud user can process their data securely once the VC is formed. Figure 6 illustrates the diagram of DAPPA, in which the RSU consists of a large communication range, as compared with the vehicles. Each RSU consists of an initial key pair and a corresponding certificate, which is issued by the trusted authority BIB041 . Every vehicle contains the secret to develop secure channels with RSUs, and every vehicle generates a request to RSUs when entering into the communication range to share its private key. The vehicle utilizes the shares for each message to generate a one-time private key and a one-time ID-based signature within the authorization period. Then, the other users can utilize the sender's ID to verify the signature. By using a one-time private key, distributed aggregate privacy-preserving authentication (DAPPA) resolves the escrow problem, which is not rooted by the trusted authority. However, it can make the system more complex since the vehicles need to request the shares from an adjacent RSU. Furthermore, the utilization of the one-time private key and ID-based signature can cause the delay and significantly reduces the communication efficiency in the VANET system BIB041 . Then, the other users can utilize the sender's ID to verify the signature. By using a one-time private key, distributed aggregate privacy-preserving authentication (DAPPA) resolves the escrow problem, which is not rooted by the trusted authority. However, it can make the system more complex since the vehicles need to request the shares from an adjacent RSU. Furthermore, the utilization of the onetime private key and ID-based signature can cause the delay and significantly reduces the communication efficiency in the VANET system BIB041 .  Setup: Setup utilizes a security parameter k to produce the master key msk and master public key mpk. Furthermore, it can also produce parameters param, which can be distributed among all nodes BIB041 . • Partial Private Key Extract: It can produce a partial private key DID by having different parameters such as master key, master public key, system parameters, and an identity ID BIB041 . • Set Secret value: The secret value xID is generated by using the master public key and other system parameters param BIB041 .  Setup: Setup utilizes a security parameter k to produce the master key msk and master public key mpk. Furthermore, it can also produce parameters param, which can be distributed among all nodes BIB041 . • Partial Private Key Extract: It can produce a partial private key D ID by having different parameters such as master key, master public key, system parameters, and an identity ID BIB041 . • Set Secret value: The secret value x ID is generated by using the master public key and other system parameters param BIB041 . • Set Private Key: This algorithm utilizes param, partial private key D ID , and secret value x ID as input parameters. The secret value x ID is used to transform D ID into full private key P A . The algorithm returns P A BIB003 . • Set Public Key: It generates the public key PK ID by using different parameters such as the master key, the system function, an identity, and its secret value BIB041 . • Sign: It generates a certificateless signature by using a system parameter, a master public key, and more BIB041 . • Verify: It can verify the signature by using several parameters such as the system parameter, master public key, ID, the ID public key, and more BIB041 . The security models are further classified into two types such as super type I adversary A I and super type II adversary A I I BIB011 . A I solves the real-world adversary who can obtain IDs and some valid signatures, while A I I solve the malicious KGC who contain the master secret key and can initiate the attack such as the eavesdropping attack on signatures and create signing queries. In recent years, there are few research studies that have been proposed regarding certificateless signature referred to as a certificateless short signature (CLSS) BIB016 BIB020 . These schemes proved to be the secure method against A I and A I I in the random oracle model BIB041 . At the end of 2014, several researchers have proposed the CLS scheme without utilizing any pairing to increase the efficiency, but the signature length is very large, which cannot constrain unlimited bandwidth and storage devices in VANETs BIB028 BIB029 . In 2015, a scheme for V2I communication based on a certificateless signature is introduced. In this technique, conditional privacy preservation is obtained by mapping the traffic message transmitted by the vehicle into false identity. In case of dispute, the responsible authority can recover the real identity from the pseudo identities BIB030 . Furthermore, this method produces efficient computational overhead in comparison with other competent techniques. At the beginning of 2018, Cui et al. BIB040 introduced a method for a certificateless aggregate signature based on an elliptic curve cryptosystem (ECC), which can support conditional privacy preservation. It provides secure communication between V2I in VANET. Furthermore, it can satisfy privacy requirements and also achieves lower message overhead, which are advantages over other methods. In-Vehicle Signage: In this application, RSU is fixed on the specific location i.e., hospital area, school zone, and university area to broadcast safety messages to vehicles approaching those locations. • Turning Speed Warning: In this application, RSU is fixed on the road before turning to broadcast the safety messages to vehicles approaching toward turning. The speed of vehicles needs to be discussed with turning in order to safely pass through the turning. Low-Bridge Warning: This application is used to alert the driver for the height of the bridge by broadcasting warning messages to the vehicle through road infrastructure, which is assembled in the vicinity of the bridge. Additionally, an OBU is equipped in the vehicle, which can determine whether or not there is a space to pass through the bridge. In-Vehicle Amber Alert: This application relies on I2V communication and sends (Americas broadcast emergency response) messages to vehicles. This message is only broadcast when the law enforcement authorities confirm that the vehicle is involved in suspected crime, and circulate amber alerts to the vehicle in that area excluding a suspected vehicle. Low-Parking Warning: This application notifies the driver for the minimum car parking height in which the vehicle is trying to enter. This system relies on broadcasting warning messages to the vehicle from an RSU, which is placed near the parking lot, and then OBU can analyze whether or not to enter in the parking area. Cooperative Forward Collision Warning: This application guides vehicles to take the alternate route in order to avoid travel to the accident location. This application uses V2V communication with a multi-hop technique to send warning messages to the driver regarding the incident situation. Warning messages include position, direction, route, speed, etc. so that each vehicle on the road can analyze the severity of an incident and then forward it to other vehicles. • Road Condition Warning: This application relies on V2V communication. In this application, vehicles obtain sufficient information about the road conditions from the electronic sensors equipped in the vehicle. After obtaining the information, the TA process this information to identify the road conditions and send the warning messages to the driver and the other vehicles on the road. • Pre-Crash Sensing: This application aims to predict the situation in which an accident is about to happen. The information can be collected from vehicle sensors, and additional information may be required from other vehicles via V2V communication in order to predict a situation. This application is most helpful for heavy traffic and aims to enhance the safety of passengers and drivers. • V2V Road Feature Notification: This application is used to collect information for the road infrastructure by using V2V communication, and then broadcasting this information to the other vehicles on the road. By sending messages, this application assists and notifies drivers of the road conditions such as potholes, debris, etc. in advance, and then the alerted vehicle sends this notification to other vehicles on the road. This application is most applicable in rural traffic where road surfaces are not smooth. Emergency Electronic Brake light: In case of smog or foggy weather, this application warns the vehicles traveling on the road for sudden hard breaking by using V2V communication that broadcast safety messages to the other vehicles, and notify them for hard breaking in advance. Warning for Violating the Stop Sign: In this application, a warning message is sent to the vehicles to warn the driver about the distance between the vehicle and the stop sign and also the speed necessary to avoid hard breaking. This application reduces the violation of stop signs, which can prevent the vehicle from a fatal accident or hazardous conditions. • Violating Traffic Signal Warning: This application is used to send warning messages to the vehicles and warn them about a hazardous condition, i.e., fatal accident, severe incident, road bottlenecks, etc. that may happen if the vehicle did not stop in front of the sign  . • Intersection Collision Warning: This application gathers the information of the road intersection through the electronics sensors and then analyzes this information. The system will send a warning message to the vehicles in case of probability of an incident occurring is high. In this application, the data collected by the sensors include speed, position, acceleration, traffic flow information, etc. • Pedestrian Crossing Information: This application is used to notify the driver if there is a pedestrian crossing the road. In this application, the information is collected for the pedestrians through sensors installed in the sidewalk, which can significantly reduce accidents by sending alert messages to the vehicles instantaneously in case a potential collision between pedestrians and vehicles is identified.