# Securing Wireless Sensor Networks Using Machine Learning and Blockchain: A Review
## 4 WSN Design Challenges and Unique Characteristics  
WSN security solution design is highly affected by the unique features of these networks that make them more susceptible to cyberattacks than other technologies. This is primarily due to their challenging underlying infrastructure, which consists of a collection of sensor nodes utilizing scarce resources. The basic building blocks of a sensor node consist of four main units, namely, processing, sensing, communication, and power [31], as shown in Figure 2. The processing unit is the central unit, containing a processor or micro-controller that controls the sensor's activities and executes the communication protocols; however, it has limited storage memory. The processing unit is connected to the sensing unit by an Analog to Digital Converter (ADC). The sensing device captures surrounding data, which are then converted into an electrical signal by the ADC. The communication \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Year** & **Ref.** & \multicolumn{4}{c}{**Direction**} \\ \cline{3-6}  & & **ML** & **BC** & **Attacks** & IDS & **Integration** \\ \hline
2015 & [9] & ✓ & ✓ & ✓ & \\ \hline
2015 & [19] & ✓ & DoS & ✓ & \\ \hline
2017 & [32] & ✓ & & & \\ \hline
2018 & [21] & ✓ & ✓ & ✓ & \\ \hline
2018 & [16] & ✓ & ✓ & & \\ \hline
2020 & [17] & ✓ & & & \\ \hline
2020 & [18] & ✓ & & ✓ & \\ \hline
2021 & [20] & ✓ & & & ✓ & \\ \hline
2022 & [22] & ✓ & & ✓ & ✓ & \\ \hline
2021 & [31] & & ✓ & & \\ \hline
2023 & our work & ✓ & ✓ & ✓ & ✓ & ✓ \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Existing works on applicability of ML and BC for WSN security. * WSNs have many appealing applications, creating a need for different levels of secure functionalities and service requirements, such as secure node selection, data aggregation [36], localization, and routing. * Resource-constrained devices have limited memory, power, and transmitting bandwidth. For example, TelosB [37] is an ultra-low-power sensor with a a 16 bit processor and 8 MHz RISC microcontroller with only 10 Kb RAM, 48 Kb program memory, and 1024 Kb flash storage. The required total space for a typical code, such as TinyOS, which is the de facto standard operating system for wireless sensors, is approximately 4 Kb [38]. Therefore, any implemented security algorithm within the network must not be computationally demanding beyond these limitations. * Security algorithms must be able to manage unsupervised sensors, which could be exposed to physical attack by demolishing the hardware or to attackers equipping sensors with extra hardware to perform hidden or malicious functions prior to their being deployed in the network area. * Determining the adopted broadcast dynamic channel used as a wireless communication medium is challenging, as it is unattended and might be affected by collision and interference issues. WSN communication links are usually based on the 802.15.4 standard, and can be implemented via the use of other technologies as well, such as Bluetooth, ZigBee, PLC, WiFi, 4G, and 5G. * The lack of fixed physical infrastructure is a significant design challenge due to the rapidly changing connectivity between nodes. * A dynamic underlying network topology results from node failure, deployment of new nodes, possible variations in node position (which is especially the case under harsh environmental conditions), node mobility. The resulting flexibility in terms of link connectivity presents a design challenge for security algorithms, which must be able to adapt to network node variations in order to obtain the extra measure of protection provided by monitoring of corrupted nodes. * WSN routing protocols have weaknesses, including malicious routing information injection, alteration, or spoofing, which might lead to network disruptions such as creation of routing loops, broadcasting of fake error messages to partition the network, attracting or repelling network traffic from particular nodes, extending or shortening route paths, and increasing end-to-end latency.