Security Threats in Vehicular Ad Hoc Networks Ahmed Shoeb Al Hasan 1 - - PDF document

Security Threats in Vehicular Ad Hoc Networks

Ahmed Shoeb Al Hasan1, Md. Shohrab Hossain1, and Mohammed Atiquzzaman2

1Department of Computer Science & Engineering, Bangladesh University of Engineering & Technology, Dhaka, Bangladesh 2School of Computer Science, University of Oklahoma, Norman, OK 73019, USA

Email: shoeb.al.hasan@gmail.com, mshohrabhossain@cse.buet.ac.bd, atiq@ou.edu

Abstract— A new type of Mobile Ad Hoc Network (MANET) is Vehicular Ad Hoc Network (VANET) that allows smart transport system to provide road security and reduce traffic jam through automobile to automobile and automobile to roadside

• communication. However, security issues for VANETs have

become a major concern for researchers. VANET is different from other ad hoc networks due to its dynamic topology and mixed structural design. Hence, designing security schemes to authenticate broadcasted messages and discard malicious messages are crucial in VANETs. Here, at first we identify various security issues for VANET and discuss possible defense mechanisms to mitigate those threats. We then classify the defense mechanisms into major categories and critically analyze them based on different performance criteria. Finally, we list several open research issues related to VANET security to inspire researchers to work on these open problems and propose solutions towards efficient trust organization in VANET. Keywords—Vehicular Ad Hoc Network, VANET, Mobile Ad Hoc Network, MANET, Cryptography, V2V communication, Security Threat.

• I. INTRODUCTION

VANETs are a subgroup

• f

MANETs where communicating nodes are mainly vehicles and roadside infrastructures. At present, VANETs have many implementations focusing different aspects of transport systems, like, driving assistance, public security, roadside facility locator, toll collection, road traffic control, freeway internet connection and increasing security and efficacy of freeway systems. Through the use of Dedicated Short-Range Communication (DSRC)[2], VANETs support Intelligent Transportation System (ITS) [1]. Wireless Access in Vehicular Environment (WAVE) [3] is one of the standards to implement VANET. Fig. 1 illustrates the basic topology of VANET. Two types of communication technologies are implemented for VANET. One is Vehicle to Vehicle (V2V) and another is Vehicle to Infrastructure (V2I). Vehicles consist of GPS, processors, sensors and antennas which are known as On Board Unit (OBUs) to correspond with other vehicles. Vehicles also communicate with infrastructures at the roadside at a static distance from each other known as Road Side Units (RSUs). RSUs can be mobile and they use wired or wireless medium to communicate with each other and the Internet. Vehicles can be connected to Internet through V2I since RSUs are connected to the Internet. Real time and emergency messages can be transmitted using V2V communications to avoid accidents and traffic congestions.

• Fig. 1: Vehicular Ad Hoc Network (VANET).

VANETs are required to implement security measures, for instance, secrecy, reliability and approval to offer protection against invaders and mischievous nodes since VANETs transmit emergency, life critical real-time information. Wormhole attack [4-5], Purposeful attack [6], Illusion attack [7], Denial of Service (DoS) [8], Sybil attack [9-11] are some of the security attacks which can hamper the privacy of the person driving the vehicle as well as the vehicle. Eventually, these attacks may cause death of human lives by reducing traffic safety. Hence, many researchers are extensively working on the security of VANETs. The primary reason of providing security in VANET is necessary so that the original identity of the drivers cannot be disclosed at any time in VANET since malicious nodes can launch attacks using this information as false identity. During V2I communication safety and privacy is very important since drivers and vehicles have to disclose their identity to communicate with RSUs. Vehicles need to ensure the authenticity of the received information before reacting to the received information. There are several surveys on the security threats of VANET [12-14]. La et al. [12] presented some security threats and differentiated them, but no defense mechanism has been discussed. Tangade et al. [13] discussed some trust models to eliminate the threats in VANET networks. Al- Kahtani [14] proposed some approaches to defend security

• threats. However, there exists no work that presents a

complete comparative study among the defense mechanisms. In our earlier works [30-31], we have presented security

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issues for mobility management protocols in space networks [30], and presented a comparative study on the defense mechanism for mobility management protocols in such networks [31]. The contributions of this paper are (i) identifying and illustrating the threats for VANET networks, (ii) outlining the defense mechanisms that can be applied to the respective threats, and (iii) critical analysis and comparison among different defense mechanisms based on performance criteria. The rest of the paper is organized as follows. Section II presents the basics of VANET and its applications. In Section III, we discuss the some of VANET security threats and their mitigation approaches. In Section IV, we classify the defense mechanisms and critically analyze and compare them. In Section V, several open research issues related to VANET security have been discussed. Finally, concluding remarks are discussed in the Section VI.

• II. VANET

VANETs are special type of MANETs where all the communicating nodes are vehicles. But many features of VANET are different from MANET such as cost of VANET is higher than MANET. Due to the higher speed of vehicles

• ver mobile nodes, VANET’s network topology changes

rapidly in contrast to MANET. The nodes move in pre-defined paths in VANET but in MANET nodes move randomly. VANET requires more bandwidth than MANET to manage mobility signaling. Table I illustrates the key differences between VANET and MANET. Table I: Differences between VANET and MANET.

Category VANET MANET Cost Expensive Inexpensive Change of network topology Frequent Slow Mobility High Low Bandwidth Thousand Kbps Hundred Kbps Range Up to 600m Up to 100m Density of nodes Dense Sparse Reliability High Medium Node lifetime Dependent on vehicle lifetime Dependent on power source Moving pattern of nodes Regular Random

VANETs have to deal with high mobility of nodes. In VANET, there are different types of communications. As shown in Fig. 1, a vehicle can contact with another vehicle, known as Vehicle-to-Vehicle (V2V) communication. Also, vehicles need to transmit information with roadside infrastructures, known as Vehicle to Infrastructure (V2I)

• communication. Moreover, road-side unit / infrastructures at

the roadside communicate with one another. Communication in VANET is very challenging due to its high mobility. Basically there are two types of applications in VANET,

• ne is safety related applications and another is comfort

applications.

• A. Safety Applications

These VANET applications aim to save human lives in the

• streets. The feature of these safety applications is to deliver the

safey related data to the actual receiver in time. Safety related applications are listed as follows: 1) Assistance Messages (AM): These messages include lane switching messages, cooperative collision avoidance (CCA), and navigating. Preventing collisions is the main goal

• f CCA. If there is a possibility of a collision among the

vehicles nearby, these applications will trigger automatically to warn the driver to steer the vehicle or reduce the speed, thereby avoiding possible collision(s). Vehicles detecting an accident may start sending messages to other vehicles so that

• thers may take a detour (see Fig. 2).

2) Information Messages (IMs): Examples of such messages are work zone information, in the highway, toll point ahead, and speed limit.. 3) Warning Messages (WMs): Examples of WMs are post-crash, obstacle, stop light (ahead) in a highway, toll point,

• r road condition warnings. Vehicles may start transmiting

WMs to other vehicles in a certain zone after sensing it, thereby helping other subsequent vehicles reducing their speed to avoid accidents [15].

• Fig. 2. Safety application : warning for possible accident.
• B. Comfort Applications

Improving passenger comfort and traffic efficiency is the main objective of comfort applications. These applications can be included in Value Added Services (VASs) which can be used by VANET. Passengers in a vehicle for a long period would be interested to use some applications from vehicular networks. Some of the applications are as follows: 1) Automatic toll collection: Using this service, payment is completed electronically. So the vehicle doesn’t need to stop to pay the fees. 2) Location based aplications: Location of restaurants, gas station, shopping malls, ATMs etc. can be uploaded to the

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• vehicles. Vehicles can exchange these information through

vehicular network to facilatate travelling. 3) Internet Connectivity: Vehicle passengers can access Internet as shown in Fig. 3. They can receive or send emails using internet. Distributing these information using vehicular networks reduces the cost of infrastructure installation along roadside.

• Fig. 3: Comfort applications: Internet connectivity.

4) Entertainment applications: Songs, movies, games etc. can be shared among vehicles using VANET where one or

• re vehicles can store those data
• III. VANET SECURITY THREATS AND DEFENSE MECHANISMS

There exist several security threats for VANET networks. In this section, we identify those security vulnerabilities for

• VANET. Related defense mechanisms [4], [8], [10], [16],

[17], [18] to prevent or mitigate those vulnerabilities are also presented in this section.

• A. False Information

A malicious node can send incorrect or wrong information for its own benefit. For example, an attacker can send wrong traffic information to reduce the road traffic for its easy movement as shown in Fig. 4. Elliptic Curve Digital Signature Algorithm (ECDSA) [6] uses hashing to secure the message and help destination vehicle to authenticate the message. In this approach, transmitting vehicle generates a public key and private key. Each vehicle of VANET has public key. Sender vehicle first uses the public key of the destination node to encrypt the

• message. The message is then encrypted using a hash

algorithm and further encrypted by the private key of the sender vehicle before transmission. The destination vehicle first decrypts the message using sender’s public key, to obtain the hashed message. If the message is altered in the transmission channel, then the hash too will be changed which can be easily detected by the destination vehicle.

• Fig. 4: False information.
• B. Denial of Service (DoS)

A malicious car may send malicious messages repeatedly to jam the network, thereby reducing its efficiency. Fig. 5 shows a malicious car transmits “lane close ahead” message to a valid car as well as to the RSU to block the network.

• Fig. 5: Denial of Service (DoS) attack.

Distributed Denial of Service (DDoS) poses more threat than DoS where multiple vehicles attack one single vehicle. Fig. 6 illustrates a scenario of DDoS. A car C1 is attacked in distributed manner by many vehicles in different timeslots creating a jammed network for C1.

• Fig. 6: Distributed Denial (DDoS) of Service attack.
• C. Deception

A vehicle may pretend to be another one to benefit its

• movement. For example, a private car may pretend itself as an

emergency vehicle (e.g., EMS vehicle) to clear the congestion ahead, thereby making its movement faster.

• D. Black Hole Attack

In this attack, data packets may get lost while travelling through the Black Hole that has no node or some nodes that refuse to transmit data packets to the next destination. Fig. 7 shows such a black hole attack. In the figure, C1 and C2 are transmitting data packets destined to C3 and C4, respectively. But the packets at first reach the black hole with many malicious cars. Data packets are lost in black hole, resulting in C3 and C4 never receiving the packet.

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• Fig. 7: Black hole attack.

To prevent black hole attack, redundant paths between the sender and the destination is kept. However, this adds to the network complexity. Redundancy is more effective for MANETs rather than VANETs as MANETs have more mobile nodes to for possible alternative paths. Use of sequence number in the packet header is another solution to this problem. The destination is then able to figure out the absence of a packet in case of any loss.

• E. Malware and Spam

These attacks are caused by malicious insider nodes of the network rather than outsider. The attack is initiated during the software updating of OBUs and RSUs. The impact of these attacks include increased. These attacks can be mitigated by centralized administration.

• F. Timing Attack

One of the crucial requirements of VANET is to broadcast VANET security messages at the right time. When a malicious car receives an emergency message, it may delay the transmission/forwarding of the message. The neighboring vehicles don’t receive the message at the proper time to avoid a dangerous situation. In Fig. 8 a malicious car receives a message “accident ahead” from C2 but it doesn’t transmit the message immediately.

• Fig. 8: Timing attack.

It adds some timeslots to the message. So this message is received by a car in position C5 (accidental position) instead

• f a safe position C4.
• G. Global Positioning System (GPS) Spoofing

A location table is used by the GPS satellites based to the geographic location and the uniqueness of the vehicle in the network. A malicious vehicle may alter the information in the location table to some other random location. In this case, a vehicle can be deceived to think that it is in a different position by reading the false information, thereby resulting in accidents to the vehicle. An attacker can also use a GPS simulator to produce signals stronger than the

• riginal satellite.
• H. Man in the Middle Attack

A malicious car can overhear communication between two

• vehicles. To launch an attack, a malicious car inserts the

wrong information between communicating vehicles. In Fig. 9, a malicious car C5 listens to the communication between C2 and C4 and transmits wrong information to C3 which C5 receives from C1.

• Fig. 9: Man-in-the-Middle Attack
• I. Sybil Attack

In this attack, a single malicious node may produce different identities [19], [20], thereby, transmits messaging that seem to be from different legitimate vehicles. Other legitimate vehicles think the network has many vehicles which is not the case. This attack can be extremely harmful since at a certain time, a malicious automobile can claim itself to be present in different places. Resource testing [16-17] can be used to detect Sybil

• attack. The computational resources are measured using

computational PUZZLES in the work done in [16]. But this approach is not appropriate for VANET as the attacker vehicle can have more resources than the legitimate vehicle. To

• vercome this problem, radio resource testing is used in [17].

Public Key cryptography [21] can be used to eliminate Sybil attack where all the vehicles will be authenticated using public key. Also, key revocation [22], [23] is another way to reduce Sybil attack. In the proposed method in [10], they have shown that using bi-directional antennas over Omni- directional antennas in receiver’s side can detect Sybil attacks. Timestamp series approach can secure development stage VANET from Sybil attacks [20]. This approach needs a minimum amount of vehicles with communication capabilities and RSU infrastructure. It is assumed that only one vehicle can pass an RSU at a timestamp. RSU issues a digital certificate for the vehicle that passes through. Sybil attack node is detected when a vehicle gets several messages with common timestamp certificate. Fig. 10 shows the working procedure of timestamp series approach.

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• Fig. 10: Timestamp series approach.
• J. Wormhole Attack

A tunnel is created by more than one malicious vehicles to send messages from one part of the network to another part to reach other malicious vehicle. These data packets are disseminated in the network. In this attack, malicious vehicles have the control of the network, stopping the data packet transmission.

• Fig. 11: Wormhole attack
• Fig. 11 shows two attackers at two sides creating a tunnel to

broadcast malicious information. Wormhole attack interrupts broadcast and multicast communication in VANET. A well-known approach to prevent wormhole attack is Packet leash [11]. TESLA with Instant Key disclosure (TIK) is a protocol based on packet leashes that calculates the differences between allowed travel distance and travel distance of the packet to identify an attack. In the AODV routing protocol

• f

VANET, hop-by-hop efficient authentication protocol (HEAP) [5] is an efficient approach to identify wormhole attacks

• K. Illusion Attack

A new threat in VANET which creates illusions to neighboring vehicles when a malicious node broadcasts traffic related warning message based on the current situation of the

• road. Existing authentication methods can’t safeguard

networks from illusion attack because the malicious vehicle controls the sensors to make and transmit wrong traffic information. VANETs can be secured against illusion attack by using Plausibility Validation Network (PVN) [4]. Different cryptology methods along with PVN are used to defend against attacks.

• L. Intentional Attack

It is very hard to defend Intentional attack as this attack is initiated by an authenticated insider. A misbehaving node can hamper a network in many ways such as deny transmitting a message to neighboring nodes, misinterpret message, insert false information or use the bandwidth improperly. A threshold authentication technique is proposed in [7] to defense against misconduct and keeping the privacy of vehicles intact.

• M. Impersonation Attack

A malicious vehicle sends messages using the identity of another vehicle to create traffic jam, chaos, accidents and hides itself. All messages should be signed and authenticated to reduce this problem. A scheme called SPECS [24] detects impersonation attacks and ensures the security related issues of V2V communication.

• IV. CLASSIFICATION OF DEFENSE MECHANISMS

We can classify the privacy and security mechanisms of VANETs into four classes.

• A. Public Key Methods

Each node is equipped with two keys, which are public and secret key. Key organization is handled by Public Key Infrastructure (PKI). Schemes with PKI are proposed when a vehicle has two units of additional hardware: event data recorder and tamper-proof hardware. Event data recorder keeps records of all the events and tamper-proof hardware is used to perform cryptographic approach. Hesham et al. [25] proposed a dynamic key distribution protocol in order to store a minimum number of keys, thereby reducing memory requirements. Secret key for a vehicle is created using vehicle’s unique chassis number, electronic license plate (ELP). This key is known as Vehicle Authentication Code (VAC) which is used as the secret key between a vehicle and certification authority (CA). Gazder et al. [27] proposed a dynamic cluster-based architecture of PKI. Trust value from 0 to 1 is assigned to vehicles where most credible vehicle has trust value 1. 0.1 is the initial value for a new vehicle. A PKI based scheme, Efficient Certificate Management Scheme (ECVM) [28] is that has an effective certificate invalidation scheme which removes an adversary from the network.

• B. Symmetric and Hybrid Methods

In Symmetric and Hybrid methods, vehicles contact each

• ther when both of them share a secret key. Security methods

use either public or symmetric key. But recently a method is proposed which uses both public and symmetric key. This method is known as hybrid system. Two types of communications are used in this approach: pairwise and group

• communication. To avert the use of key pair to reduce
• verhead, symmetric key is used for pairwise communication

in hybrid system.

• C. Certificate Revocation Methods

Certificate revocation means invalidating the association

• f a vehicle. Centralized and decentralized, in these two ways

certification is done. In centralized system certificate authority (CA) initiates revocation. In decentralized approach, revocation decision is taken by the neighboring vehicles. CA

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generates and transmits messages to the RSU when an invalid certificate is detected. When vehicles get the message from RSU, vehicles cancel that certificate and no longer communicate with it.

• D. ID-based Cryptography

In this scheme, computing cost is reduced by implementing ID-based cryptography. For verification purpose, ID-based online/offline signature (IBOOS) scheme is

• used. Offline process is performed first in the vehicles or in

the RSUs. Online phase is performed during V2V communications among the vehicles. IBOOS is more efficient in the verification process than IBS. Using IBS and IBOOS, Lu et al. [29] proposed an ID- based scheme. This scheme does not expose vehicle privacy by not using real-world IDs rather it uses self-constructed

• pseudonyms. In this approach, IBS is used for V2I and

authentication and IBOOS is used during V2V

• authentications. This approach preserves the privacy of

VANET efficiently. Comparison among different defense mechanisms are listed in Table II and are discussed as follows based on several criteria:

• Infrastructure: Public key method and Symmetric

and Hybrid methods do not need to communicate with RSUs. So these methods are infrastructure less. But certificate revocation and ID-Based Cryptography need to communicate with RSUs and hence are infrastructure oriented.

• Key: Public key method uses public and secret key.

Certificate revocation method is part of public key

• infrastructure. So public and secret key is also used in

certificate revocation method. In symmetric and hybrid approach, public key is used for group communication and symmetric key is used for a pair

• f

vehicles. No key is used in ID-Based Cryptography.

• ID: ID or pseudonym is used only in the ID-Based

Cryptography approach. Other methods use different keys instead of using ID.

• Approach: Public key and Symmetric and Hybrid

method communicates based on the certificates generated by a certificate authority (CA). So these approaches are centralized. A malicious vehicle certificate can be revoked by central authority CA or by the neighboring vehicles. So this approach is both centralized and decentralized. ID-Based approach is decentralized as vehicles generate their own IDs and authentication is completed by V2V and V2I communication.

• Purpose: All three methods except certificate

revocation method is used for authentication. Certificate revocation is needed to remove a malicious vehicle from the network.

• Communication: Public key is used to authenticate a

pair of vehicles. A vehicle is communicating with

• ther vehicles using public key. In symmetric and

hybrid approaches, public key is used for group communication and symmetric key is used for pair wise communication. In the certificate revocation method, the certificate authority sends information about a malicious certificate to all the members in the

• network. So this is a group communication. In ID-

Based method a vehicle communicates with others using V2V and with RSU using V2I. So the communication is pairwise.

• V. OPEN VANET RESEARCH PROBLEMS

Some of open research problems related to VANET are listed below:

• Security checks should be performed when a vehicle

switches from one RSU to another because most of the current VANET security schemes do not use this.

• Generally people use Internet on the highway for

urgent communications through email, instant messaging and social network. Therefore, designing protocols to secure the private data and profiles of users from attackers are essential.

• IP addresses change with the pseudonym. However,

MAC addresses do not normally change. An attacker Table II: Comparison among different classes of defense mechanisms.

Criteria Public Key Symmetric and Hybrid Certificate Revocation ID-based Cryptography Infrastructure Infrastructure-less Infrastructure-less Infrastructure-oriented Infrastructure-oriented Key used Public and secret key Symmetric and public key Public and secret key No key used ID No No No ID or Pseudonym Approach Centralized Centralized Centralized or Decentralized Decentralized Purpose Authentication Authentication Disconnecting attacker form a network Authentication Communication Pair wise Pair wise or Group wise Group wise Pair Wise

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can easily find a target vehicle through its MAC address, even if the target vehicle’s IP address is

• changing. Hence, MAC address should change

dynamically to hide the identity of the target vehicle.

• While

developing safe routing protocols for VANETs, more efforts must be given at distributing certificates securely and validating them in a timely manner to avoid any performance bottleneck.

• Another prospective research area might be to find
• ut the motion prototype of vehicles and relate the

motion prototype with the malicious vehicle.

• The number of vehicles in a dense vehicular network

can be large. A defense mechanism which is not designed carefully for a high density situation may fail eventually. Therefore, scalability of defense mechanisms for VANET applications is a major concern and a research problem.

• Robustness of the defense mechanism is a vital issue

as defense mechanism itself can be under attack and be compromised.

• Reliability is a mandatory characteristic for VANET
• applications. Defining and allocating trust values and

settling faith among vehicles is extensively significant to make a VANET application reliable.

• VI. CONCLUSION

VANETs are becoming more popular and useful these days due to its capability to provide safety warnings (to the drivers), thereby reducing accidental losses. However, VANET applications can cause severe threats to the users if the applications are compromised by attackers. It is a difficult task to eliminate malicious vehicles due to the high speed of the vehicles and very frequent topology changes. VANET also impose great challenges to design secured data transmission

• protocols. Hence, ensuring privacy and security in VANETs is

an important research challenge. In this paper, we have illustrated various security threats for VANET and discussed possible defense mechanisms to prevent or mitigate those threats. We then classified the defense mechanisms into major categories and critically analyzed them based on different performance criteria. Finally, we listed several open research issues related to VANET security threats to motivate researchers to work on these open problems and suggest solutions for efficient trust

• rganization in VANET.

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