# Blockchain for Future Wireless Networks: A Decade Survey
## 3 The Proposed Taxonomy for Security Attacks and Countermeasures
### Passive Attacks  
In passive attacks, malicious users intercept and eavesdrop on the wireless communication channel to obtain unauthorized access. There are various passive attacks in WNs, which are discussed layer-wise as follows. \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Layer** & **Attacks** & **Countermeasures** & **Ref** \\ \hline \multirow{6}{*}{Physical layer} & \multirow{3}{*}{Eavesdropping attack} & \(\bullet\) & Limiting resources by network segmentation \\  & & \(\bullet\) & Avoid untrusted links \\  & & \(\bullet\) & Blocking unintended radiation in a computer using shielding \\ \cline{2-4}  & \multirow{3}{*}{Jamming} & \(\bullet\) & Anti-jamming systems \\  & & \(\bullet\) & Cryptographic \\  & & \(\bullet\) & Steganography \\ \hline \multirow{6}{*}{MAC layer} & \multirow{3}{*}{Device tampering} & \(\bullet\) & Firewalls \\  & & \(\bullet\) & Encryption technique-Hash based message authentication code \\  & & (HMAC) & [97; 98] \\  & & \(\bullet\) & Access restriction \\  & & \(\bullet\) & File integrity monitoring \\ \hline \multirow{6}{*}{MAC layer} & \multirow{3}{*}{MAC Spoofing} & \(\bullet\) & Encrypted protocols \\  & & \(\bullet\) & Alert-enabled traffic monitoring \\  & & \(\bullet\) & Reverse address resolution protocol \\ \cline{2-4}  & \multirow{3}{*}{MiTM attack} & \(\bullet\) & Public-key authentication \\  & & \(\bullet\) & Strong WEP/WAP encryption on AP \\  & & \(\bullet\) & Use of a virtual private network (VPN) and Wi-Fi networks \\ \hline \multirow{6}{*}{Network layer} & \multirow{3}{*}{Wormhole attack} & \(\bullet\) & Packet leashes \\  & & \(\bullet\) & Separate route algorithm \\ \cline{2-4}  & \multirow{3}{*}{Blackhole attack} & \(\bullet\) & Redundant route method \\  & & \(\bullet\) & Time-based baited approach \\ \cline{2-4}  & \multirow{3}{*}{DoS attacks} & \(\bullet\) & Limiting broadcasting \\  & & \(\bullet\) & Protecting endpoints \\  & & \(\bullet\) & Rejecting fake traffic using firewalls and routers \\ \hline \multirow{6}{*}{Transport layer} & \multirow{3}{*}{Flooding attacks} & \(\bullet\) & Configuring the firewall \\  & & \(\bullet\) & Installing an intrusion prevention system (IPS) that identify network traffic patterns \\ \cline{2-4}  & \multirow{3}{*}{Session Hijack} & \(\bullet\) & Encrypt session id \\  & & \(\bullet\) & User authentications \\  & & \(\bullet\) & Secure cookies \\  & & \(\bullet\) & Ciphering the packets \\  & & \(\bullet\) & IPSec, and SSL approaches \\ \hline \multirow{6}{*}{Application layer} & \multirow{3}{*}{SMLP attack} & \(\bullet\) & SSL and TLS \\  & & \(\bullet\) & Inserting a security layer into the SMTP server prevent this attack \\ \cline{2-4}  & \multirow{3}{*}{SQL injection} & \(\bullet\) & Make more than one database user account \\  & & \(\bullet\) & Web applications firewall \\ \cline{1-1}  & & \(\bullet\) & Limit privileges \\ \cline{1-1}  & & \(\bullet\) & Adding input validation prevents SQL injection \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Countermeasures for passive security attacks in different layers of WNs. Physical layer attacks--This layer consists of data transmission, signal detection, encoding, modulation, and frequency selection tasks in the wireless medium [124; 125]. A detailed description of each passive attack on the physical layer is given as follows. * Eavesdropping attack--It is also referred to as wireless sniffing, where an attacker eavesdrops over ongoing communications between sender and receiver [126]. This attack uses an eavesdropping device that monitors network activity, a listening port that records phone conversations, and a tapping transmission link. It silently impacts the performance of the WN in terms of privacy loss and identity theft [127]. Various methods are available to show the eavesdropper from the authentic communication line, such as limiting the resources of the eavesdropper by network segmentation, avoiding opening untrusted links, and applying jammers or beamforming techniques to minimize the signal power of an eavesdropper.