## 3 Man-In-The-Middle Attacks  
The term \"_Man-In-The-Middle_\" has been derived from basketball scenario where a player in the middle tries to intercept the ball while other two players try to pass it [34]. The same concept is derived in VANET, where MITM attacker jeopardize communication and modify messages among legitimate vehicles. Such attacks leave severe consequences on the network, especially, if content of message contains safety related information. In VANET, the attacker must satisfy following two conditions in order to implement MITM attack, i.e., (1) Firstly, the message containing significant information must be received by the attacker node, and (2) Secondly, the attacker must be able to interpret the content of message [35]. MITM attacks in VANET can be launched under following two modes as depicted in Figure 2.  
1. _Passive Mode:_ Passively, attacker can eavesdrop on the communication channel between legitimate vehicles, e.g., police vehicles or ambulances. 2. _Active Mode:_ Actively, attacker can drop, delay or change the content of received information in the network. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Studies**} & \multicolumn{3}{c}{**Man-In-The-Middle Attacks**} & \multicolumn{3}{c}{**Attacker Pattern**} \\ \cline{2-6}  & **Message** & **Tampered** & **Message Delayed** & **Message Dropped** & **Distributed Attackers** & **Fleet of Attackers** \\ \hline \hline \multirow{2}{*}{
\begin{tabular}{c} [PERSON] et al. [25] \\ [PERSON] et al. [26] \\ [PERSON] et al. [27] \\ [PERSON] et al. [28] \\ [PERSON] et al. [29] \\ [PERSON] et al. [30] \\ [PERSON] et al. [31] \\ [PERSON] et al. [32] \\ [PERSON] et al. [33] \\ Proposed Study \\ \end{tabular} } & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of Different Studies on MITM Attacks in VANET. When an event occurs in VANET, the transmitted packet (\(M_{G}\)) from message generated vehicle contains at least following three important information, i.e., data regarding the event, location of the event generation, and time of the event occurrence along with extra information such as protocol versions, message IDs etc. [36; 37]. For the sake of clarity and relevance, the message generated from the vehicle will contain following three information in our study, i.e., data, location and time. \[M_{G}=\{data,location,time\} \tag{1}\]  
where, data contains the information generated by the vehicle which can be either related to safety or non-safety application. Location contains the coordinates of the event generation vehicle in terms of \(x\), \(y\), \(z\), which can be achieved via GPS of the vehicle. Further time represents the message generation time (\(t_{send}\)). Therefore, above equation can be further expended as:  
\[M_{G}=\{safety\ data,non\ safety\ data,loc_{x},loc_{y},loc_{z},t_{send}\} \tag{2}\]  
In presence of malicious nodes in the network performing MITM attack, the attacker can compromise the content of the Equation (1) in terms of data, location or time. Compromising the data containing safety information can create disaster in the network. Similarly, tampering the location of the message sender can confuse the legitimate vehicle about the message receiver. Further, changing the time of the message can also have impact on the network as the receiver might ignore the message which is out-dated or very old. In light of these characteristics, we consider an attacker, which can tamper the \"legitimate data\" and propagates the \"compromised data\" throughout the network. Actively, attacker can launch MITM in following three manners. 1. Delay the legitimate message
2. Drop the legitimate message
3. Tamper the legitimate message  
Figure 3 depicts the illustration of both passive and active MITM attacks in VANET. It can be seen that passively, MITM attacker can eavesdrop on the communication between legitimate vehicles and actively, the MITM attacker can drop, delay or alter the authentic messages which are propagated throughout the network. Figure 2: Man-In-The-Middle Attacks in VANET.