Analysis and Countermeasures of Security Threats of Wireless Sensor Networks
1 Introduction
WSN (WirelessSensorNetwork) is a self-organizing network, which implements a specific task through a large number of low-cost, resource-constrained sensor node devices working together.
It is a revolution in information perception and collection technology, and one of the most important technologies in the 21st century. It is used in climate monitoring, temperature, light, humidity and other conditions in the surrounding environment, atmospheric pollution monitoring, structural integrity monitoring of buildings, abnormal conditions of the home environment, chemical and biological threat detection and forecast in airports or stadiums In other respects, WSN will be an economic alternative and has a broad application prospect.
Sensor networks bring hope to deploy large-scale networks in complex environments for real-time data collection and processing. But at the same time, WSN is usually deployed in an unmaintained and uncontrollable environment. In addition to the threats of information leakage, information tampering, replay attacks, denial of service, etc. faced by general wireless networks, WSN also faces sensor nodes that are easily vulnerable The attacker physically manipulates and obtains all the information stored in the sensor nodes to control part of the network threat. It is impossible for users to accept and deploy a sensor network that does not solve the security and privacy issues. Therefore, when designing the WSN protocol and software, you must fully consider the security issues that WSN may face and integrate the security mechanism 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 is the ultimate goal of sensor networks-to achieve universal computing and become a part of people's lives This important way is contrary.
A good security mechanism design is based on a deep analysis of the threats and network characteristics it faces, and sensor networks are no exception. This article will deeply analyze the characteristics of wireless sensor networks and the security they may face. Threats, and researched and discussed their corresponding security countermeasures.
2. Analysis of sensor network characteristics
WSN is a large-scale distributed network, which is often deployed in unmaintained and harsh conditions. In most cases, the sensor nodes are one-time use, which determines the low cost and extreme resources of the sensor nodes. Restricted wireless communication equipment [2], its characteristics are mainly reflected in the following aspects: (1) Limited energy: Energy is the most important constraint condition that limits the ability and life of the sensor node. Existing sensor nodes They are powered by standard AAA or AA batteries and cannot be recharged. (2) Limited computing power: the sensor node CPU generally only has 8bit, 4MHz ~ 8MHz processing power. (3) Limited storage capacity: the sensor node generally includes three forms of memory, namely RAM, program memory, and working memory. RAM is used to store temporary data during work, generally not more than 2k bytes; program memory is used to store the operating system, application programs and security functions, etc. Work memory is used to store the acquired sensory information, these two memories 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 also limited to 100m to 1km. (5) Anti-tampering: The sensor node is a low-cost, loosely structured and open network device. Once the attacker obtains the sensor node, it can easily obtain and modify the key information and program code stored in the sensor node Wait.
In addition, most sensor networks have unpredictable network topologies before deployment. At the same time, after deployment, the entire network topology and the role of sensor nodes in the network also change frequently, so unlike wired networks, most wireless networks In that way, the network devices are fully configured, and the range of pre-configuration of the sensor nodes is limited. Many network parameters and keys are formed after the sensor nodes negotiate after deployment.
According to the above analysis of the characteristics of wireless sensors, it can be seen that wireless sensor networks are vulnerable to various threats and attacks such as physical manipulation of sensor nodes, eavesdropping of sensor information, denial of service attacks, and leakage of private information. In the following, based on the characteristics of WSN, the potential security threats faced by WSN will be classified and discussed.
3. Threat analysis and countermeasures
3.1 Physical manipulation of sensor nodes
The future sensor network generally has hundreds or thousands of sensor nodes, and it is difficult to monitor and protect each node. Therefore, each node is a potential attack point and can be physically and logically attacked by attackers. In addition, sensors are usually deployed in unmaintained environments, which makes it easier for attackers to capture sensor nodes. After capturing the sensor node, the attacker can modify or obtain the information or code in the sensor node through the programming interface (JTAG interface). According to the analysis of literature [3], the attacker can use simple tools (computer, UISP Free software) You can transfer all the information in EEPROM, Flash and SRAM to the computer in less than a minute. Through the assembly software, you can easily convert the acquired information into an assembly file format to analyze the transmission. The confidential information such as the program code, routing protocol and key stored in the sensor node can also modify the program code and load it into the sensor node.
Obviously, the current general sensor node has a great security vulnerability. Through this vulnerability, an attacker can easily obtain confidential information in the sensor node and modify the program code in the sensor node. An identity ID, so as to communicate in the sensor network with multiple identities. In addition, the attack can also be carried out by obtaining information such as keys and codes stored in the sensor node, thereby forging or disguising as a legitimate node to join the sensor network in. Once a part of the nodes in the sensor network is controlled, the attacker can launch a variety of attacks, such as listening to the information transmitted in the sensor network, publishing fake routing information or transmitting fake sensor information to the sensor network, and performing a denial of service attack. Wait.
Countermeasure: Because the sensor nodes are easily manipulated by the physical network is an unavoidable security problem of the sensor network, it is necessary to improve the security performance of the sensor network through other technical solutions. For example, node-to-node identity authentication is performed before communication; a new key agreement scheme is designed so that even if a small number of nodes are manipulated, an attacker cannot or is difficult to derive key information of other nodes from the obtained node information Wait. In addition, the security performance of the node itself can also be improved through measures such as authentication of the software of the sensor node.
3.2 Information eavesdropping
According to the characteristics of wireless propagation and network deployment, attackers can easily obtain sensitive or private information through the transmission between nodes. For example, in the scenario of monitoring indoor temperature and light through a wireless sensor network, a wireless receiver deployed outdoors can obtain The temperature and lighting information sent by the indoor sensor; similarly, the attacker can also learn the indoor information by listening to the transmission of information between the indoor and outdoor nodes, thus revealing the living habits of the owner.
Countermeasure: Encrypting the transmitted information can solve the eavesdropping problem, but requires a flexible and robust key exchange and governance scheme. The key governance scheme must be easily deployed and suitable for the characteristics of the sensor node with limited resources. In addition, the key governance scheme must also Ensure that when some nodes are manipulated (in this way, the attacker can obtain the information generated in this node to generate the session key), it will not damage the security of the entire network. Due to the limited memory resources of sensor nodes, it is impractical to implement end-to-end security between most nodes in sensor networks. However, in the sensor network, the information between hops and hops can be encrypted, so that the sensor node only needs to share the key with the neighbor node. In this case, even if an attacker captures a communication node, it only affects the security between adjacent nodes. But when an attacker sends false routing messages by manipulating nodes, it will affect the routing topology of the entire network. The solution to this problem is a robust routing protocol. Another method is multi-path routing, which transmits part of the information through multiple paths and reorganizes at the destination.
3.3 Private issues
The sensor network is used to collect information as the main purpose. The attacker can obtain these sensitive information by eavesdropping and adding fake illegal nodes. If the attacker knows how to obtain limited information from multiple channels of information, then the attacker It is possible to derive effective information from the information obtained in large quantities. The privacy problem of general sensors is not to obtain the information that is unlikely to be collected through the sensor network, but the attacker can monitor the WSN remotely to obtain a large amount of information and analyze the privacy problem according to a specific algorithm. Therefore, the attacker does not need to physically touch the sensor node, which is a low-risk and anonymous way to obtain private information. Remote monitoring can also enable a single attacker to simultaneously obtain information transmitted by multiple nodes.
Countermeasure: Ensuring that sensory information in the network can only be accessed by trusted entities is the best way to ensure privacy issues, which can be achieved through data encryption and access control; another method is to limit the granularity of information sent by the network, Because the more specific the information, the more likely it is to disclose privacy. For example, a cluster node can aggregate the large amounts of information received from neighboring nodes and only transmit the processing results, thereby achieving data anonymization.
3.4 Denial of Service Attack (DOS)
DOS attacks are mainly used to disrupt the availability of the network and reduce or reduce any event that executes the network or system's ability to perform a certain desired function. Such as trying to interrupt, subvert or destroy the sensor network, it also includes hardware failure, software bugs, resource exhaustion, environmental conditions, etc. [4]. Here we mainly consider the loopholes of the protocol and design level. It is very difficult to determine whether an error or a series of errors is caused by an intentional DOS attack, especially in a large-scale network, 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 malicious interference in the network with the transmission of protocols in the network or physical damage to the sensor nodes. The attacker can also launch an attack that quickly consumes the energy of the sensing node. For example, by continuously sending a large amount of useless information to the target node, the target node will consume energy to process the information and transmit the information to other nodes. If the attacker captures the sensor node, he can also forge or disguise as a legitimate node to launch these DOS attacks. For example, it can generate a circular route, thereby exhausting the energy of the node in the cycle. There is no fixed method for defending against DOS attacks, which varies with the attacker's attack method. Some frequency hopping and spread spectrum techniques can be used to alleviate network congestion problems. Proper authentication can prevent the insertion of useless information in the network, however, these protocols must be very effective, otherwise it will also be used as a means of DOS attack. For example, a digital signature based on an asymmetric cryptographic mechanism can be used for information authentication, but creating and verifying a signature is a computationally slow and energy-intensive calculation. An attacker can introduce a large amount of this information into the network. Effectively implement DOS attacks.
4. Summary
Security is a key issue in the design of a good sensor network. Without sufficient measures to protect confidentiality, privacy, integrity, and defense against DOS and other attacks, sensor networks cannot be widely used, and they can only be used in limited Implemented in a controlled, controlled environment, which will seriously affect the application prospects of sensor networks. In addition, when considering the security issues of the sensor network and selecting the corresponding security mechanism, it must be comprehensively designed according to network characteristics and application occasions during the design phase of the protocol and software. Attempting to increase the security function of the system after the fact is usually confirmed as not Successful or weak.
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