## 2 Basic Research  
A sensor network randomly detects an object in a limited area and sends this information to a base station. This means a user is exposed to an environment in which the data are highly likely to become redundant or get lost due to the numerous nodes involved. Due to its nature, a sensor network is more vulnerable to cyber attacks than a wired network. In particular, the open environment makes it more difficult to prevent disclosure of information. As a result, one may easily modify data or allow a malicious node to transmit data, destroying the integrity of the entire data or causing excessive load on the network. Particularly, in WSNs, nodes are not controlled once they have been arranged so that a malicious user may destroy, capture, or compromise the nodes [3]. Common attacks using the wireless network include the capture/compromise of nodes, interception, DoS, and router attacks such as HELLO Flood, Sinkhole, Wormhole, and so on. Each type of router attack is defined as below:  
\(\bullet\) Sybil: It causes a node to recognize a single node as a number of identifiers, fatal to geographic routing [4]. \(\bullet\) Hello Flood: A remote attacker sends a HELLO packet with a strong signal so that a packet can be sent to the attacker [5]. \(\bullet\) Wormhole: A node connection, which does not exist, is recognized, used for interception or selective forwarding [6]. \(\bullet\) Sinkholes: It is used along with selective forwarding for interception. The routing data are modified and all the data are induced to pass through the attacker's sinkhole [7]. A cyber attack in the sensor network may develop into the use of one more than one method of attack. That is, one may use a wireless jamming attack for DoS or a battery exhaustion attack. Attack methods in wireless sensor networks are described as follows:  
\(\bullet\) Sniffing (Interception) [8]: A sensing data message or signal message in a wireless channel could be intercepted or exploited to be analyzed for other attacks. \(\bullet\) Battery exhaustion attack [9]: An attacker causes a battery to be used up in a short time so that sensor nodes can not be used anymore. To that end, he may keep requesting data transmission or network connections. A PDoS (Path-based DoS) attack, recently analyzed, shows that a huge number of bug packets are flooded toward the base station in order to induce fast exhaustion of a battery of nodes, reducing the life of the nodes [10]. \(\bullet\) Wireless jamming (signal interference) [11]: An attack of jamming a frequency band or paralyzing a communication channel by continuously sending a signal. \(\bullet\) Physical tampering and side channel attacks [12]: Physical tampering refers to an attack of destroying or dismantling device hardware while a side channel attack means a method of analyzing electric signals from a sensor node or analyzing other signals such as consumption of power. This attack is fatal, for it uses an extracted security key, affecting the entire sensor network. \(\bullet\) Routing attack [13]: False routing data could be provided by a sensor network based on a broadcast network and then routing protocols fabricated. A routing message received could be spoofed, modified, or re-sent, disturbing routing and thus delaying generation or transmission of a routing loop. \(\bullet\) Denial of Service (DoS) in the sensor network [14]: Sensing data services of the sensor network are real-time context-aware services and vulnerable to DoS when an attacker disturbs routing or a message attack delays processing and transmission time, making meaningless real-time services. Common patterns of attacks include launching attacks on a sensor node or BS by means of various methods, blocking transmission of sensing data or causing an error in control signals, which makes services impossible to be offered. \(\bullet\) IP Spoofing [15]: An IP-based sensor node or gateway node is an IP-based network so that an attacker may disguise himself as an authenticated user of sensor services in order to attack a sensor node or network.