1. Introduction Wireless Sensor Networks (WSNs) are self-organizing networks that achieve a specific task through the collaborative work of a large number of low-cost, resource-constrained sensor nodes. They represent a revolution in information sensing and acquisition technology and are one of the most important technologies of the 21st century. WSNs offer a wide range of promising applications in areas such as climate monitoring, detecting temperature, light, and humidity in the surrounding environment, monitoring air pollution levels, monitoring the structural integrity of buildings, detecting abnormal situations in the home environment, and detecting and forecasting chemical and biological threats in airports or stadiums. Sensor networks offer hope for deploying large-scale networks in complex environments for real-time data acquisition and processing. However, WSNs are typically deployed in unmaintained and uncontrolled environments. In addition to the threats faced by general wireless networks, such as information leakage, information tampering, replay attacks, and denial-of-service, WSNs also face the threat of sensor nodes being easily physically manipulated by attackers who can then access all the information stored in the sensor nodes and control parts of the network. Users are unlikely to accept and deploy a sensor network that hasn't properly addressed security and privacy issues. Therefore, when designing WSN protocols and software, it's crucial to fully consider the potential security problems WSNs may face and integrate security mechanisms into the system design. Only in this way can the widespread application of sensor networks be promoted. Otherwise, sensor networks can only be deployed in limited, controlled environments, which contradicts the ultimate goal of sensor networks—to achieve universal computing and become an important part of people's lives. A good security mechanism design is based on a deep analysis of the threats it faces and the characteristics of the network. Sensor networks are no exception. This paper will analyze the characteristics of wireless sensor networks and the security threats they may face, and research and discuss corresponding security countermeasures. 2. Analysis of the characteristics of sensor networks WSN is a large-scale distributed network that is often deployed in environments with no maintenance and harsh conditions. In most cases, sensor nodes are used only once, which determines that sensor nodes are low-cost and extremely resource-constrained wireless communication devices [2]. Its characteristics are mainly reflected in the following aspects: (1) Limited energy: Energy is the most important constraint limiting the capability and lifespan of sensor nodes. Existing sensor nodes are powered by standard AAA or AA batteries and cannot be recharged. (2) Limited computing power: The CPU of sensor nodes generally only has 8-bit, 4MHz to 8MHz processing power. (3) Limited storage capacity: Sensor nodes generally include three types of memory, namely RAM, program memory and working memory. RAM is used to store temporary data during operation, which generally does not exceed 2k bytes; program memory is used to store operating system, application program and security functions, etc.; working memory is used to store the acquired sensor information. These two types of memory are generally only tens of kilobytes. (4) Limited communication range: In order to save energy consumption during signal transmission, the transmission energy of the RF module of the sensor node is generally between 10mW and 100mW, and the transmission range is limited to 100 meters to 1 kilometer. (5) Anti-tampering: The sensor node is a low-cost, loosely structured, and open network device. Once an attacker obtains the sensor node, it is easy to obtain and modify the key information and program code stored in the sensor node. In addition, the network topology of most sensor networks is unpredictable before deployment. After deployment, the entire network topology and the role of the sensor node in the network are also frequently changing. Therefore, unlike wired networks and most wireless networks, the network devices are not fully configured. The scope of pre-configuration of sensor nodes is limited. Many network parameters and keys are negotiated by the sensor nodes after deployment. Based on the above analysis of the characteristics of wireless sensors, it can be seen that wireless sensor networks are susceptible to various threats and attacks such as physical manipulation of sensor nodes, eavesdropping on sensor information, denial-of-service attacks, and leakage of private information. The following will classify and describe the potential security threats faced by WSNs and discuss countermeasures based on their characteristics. 3. Threat Analysis and Countermeasures 3.1 Physical Manipulation of Sensor Nodes Future sensor networks generally have hundreds or thousands of sensor nodes, making it difficult to monitor and protect each node. Therefore, each node is a potential attack point and can be attacked physically and logically by attackers. In addition, sensors are usually deployed in unattended environments, which makes it easier for attackers to capture sensor nodes. Once a sensor node is captured, the attacker can modify or obtain information or code in the sensor node through the programming interface (JTAG interface). According to the analysis in the literature [3], the attacker can use simple tools (computer, UISP free software) to transfer all the information in EEPROM, Flash and SRAM to the computer in less than a minute. Through assembly software, the obtained information can be easily converted into assembly file format, thereby analyzing the confidential information such as program code, routing protocol and key stored in the sensor node. At the same time, the attacker can also modify the program code and load it into the sensor node. Clearly, currently used sensor nodes have significant security vulnerabilities. Attackers can easily exploit these vulnerabilities to obtain confidential information from sensor nodes and modify their program code. For example, they can give sensor nodes multiple identity IDs, allowing them to communicate within the sensor network under different identities. Furthermore, attackers can obtain keys and code stored in sensor nodes to impersonate legitimate nodes and join the sensor network. Once an attacker controls a subset of nodes in the sensor network, they can launch various attacks, such as eavesdropping on information transmitted within the sensor network, publishing false routing information or transmitting false sensor data, and launching denial-of-service attacks. Countermeasures: Since the vulnerability of sensor nodes to physical manipulation is an unavoidable security problem for sensor networks, other technical solutions must be implemented to improve their security performance. These include node authentication before communication; designing new key negotiation schemes so that even if a small number of nodes are manipulated, attackers cannot or will find it very difficult to deduce the key information of other nodes from the obtained node information; and further enhancing the security of the nodes themselves by authenticating the legitimacy of the sensor node software. 3.2 Information Eavesdropping Due to the characteristics of wireless propagation and network deployment, attackers can easily obtain sensitive or private information through inter-node transmissions. For example, in scenarios where indoor temperature and lighting are monitored via a wireless sensor network, an outdoor wireless receiver can acquire temperature and lighting information sent by indoor sensors. Similarly, by eavesdropping on the transmission of information between indoor and outdoor nodes, attackers can also obtain indoor information, thereby revealing the homeowner's lifestyle. Countermeasures: Encrypting transmitted information can solve the eavesdropping problem, but a flexible and robust key exchange and management scheme is required. The key management scheme must be easy to deploy and suitable for the limited resources of sensor nodes. Furthermore, the key management scheme must ensure that even if some nodes are manipulated (so that the attacker can obtain the session key information stored in that node), the security of the entire network will not be compromised. Because sensor nodes have limited memory resources, achieving end-to-end security between most nodes in a sensor network is impractical. However, hop-to-hop encryption can be implemented in sensor networks, so sensor nodes only need to share keys with neighboring nodes. In this case, even if an attacker captures a communication node, it only affects the security between adjacent nodes. However, when attackers manipulate nodes to send false routing messages, they can affect the routing topology of the entire network. One solution is a robust routing protocol; another is multi-path routing, which transmits partial information through multiple paths and reassembles it at the destination. 3.3 Privacy Issues Sensor networks are primarily used for information gathering. Attackers can obtain this sensitive information through eavesdropping, adding fake or unauthorized nodes, etc. If an attacker knows the algorithms for extracting limited information from multiple paths, they can derive useful information from the large amount of data acquired. The privacy issue in sensors generally doesn't stem from obtaining information that is unlikely to be collected through the sensor network itself, but rather from attackers remotely monitoring the WSN to obtain a large amount of information and then analyzing it using specific algorithms to identify privacy issues. Therefore, attackers do not need physical contact with sensor nodes, making it a low-risk, anonymous way to obtain private information. Remote monitoring also allows a single attacker to simultaneously obtain information transmitted by multiple nodes. Countermeasures: Ensuring that only trusted entities can access the sensor information in the network is the best way to guarantee privacy. This can be achieved through data encryption and access control. Another method is to limit the granularity of the information sent by the network. The more detailed the information, the more likely it is to leak privacy. For example, a cluster node can aggregate and process a large amount of information received from neighboring nodes and only transmit the processing results to achieve data anonymization. 3.4 Denial-of-Service (DoS) DoS attacks are mainly used to disrupt the availability of the network and reduce or lower the ability of the network or system to perform a certain expected function. Such as attempting to interrupt, subvert or destroy the sensor network, as well as hardware failure, software bugs, resource exhaustion, environmental conditions, etc. [4]. Here we mainly consider vulnerabilities at the protocol and design levels. It is difficult to determine whether an error or a series of errors is caused by an intentional DoS attack, especially in large-scale networks, because the sensor network itself has a relatively high single node failure rate. DoS attacks can occur at the physical layer, such as channel blocking, which may include maliciously interfering with the transmission of protocols in the network or physically damaging sensor nodes. Attackers can also launch attacks that rapidly deplete the energy of sensor nodes. For example, they can continuously send large amounts of useless information to a target node, forcing the target node to consume energy to process this information and then transmit it to other nodes. If an attacker captures a sensor node, they can also forge or impersonate a legitimate node to launch these DoS attacks. For instance, they can create loop routes, thus exhausting the energy of the nodes in the loop. There is no fixed method for defending against DoS attacks; it varies depending on the attacker's methods. Some frequency hopping and spread spectrum techniques can be used to alleviate network congestion. Proper authentication can prevent the insertion of useless information into the network; however, these protocols must be highly effective, otherwise they too can be used as a means of DoS attacks. For example, digital signatures based on asymmetric cryptography can be used for information authentication, but creating and verifying signatures is a slow and energy-intensive computation. Attackers can introduce large amounts of such information into the network, effectively launching a DoS attack. 4. In conclusion, security is a critical issue in good sensor network design. Without sufficient measures to protect confidentiality, privacy, integrity, and defend against DoS and other attacks, sensor networks cannot be widely used and can only be implemented in limited, controlled environments, which will seriously affect their application prospects. Furthermore, when considering sensor network security issues and selecting corresponding security mechanisms, it is essential to comprehensively design the protocol and software based on network characteristics and application scenarios during the design phase. Attempting to add security features after the fact usually proves unsuccessful or inadequate.