## 4 Attack Resistance
### Confidentiality Attacks  
Confidentiality attacks attempt to access to the information stored in the sensor network. They can be further classified attending to the target of the attack:  
* Attacks on the confidentiality of communications.
* Attacks on the confidentiality of node information (data generated in the sensor waiting to be sent to a server, service information stored in the network, and server information).  
In a closed system with high-resources devices, information can be protected using cipher algorithm and physical access control. However, sensor networks are more vulnerable due to their characteristics:  
1. Nodes have very limited resources.
2. Potential intruders may physically access to them.  
3 Wireless communications.  
The network can use well-suited cipher algorithms [32] to provide security against attacks to communications. Due to conditions 1 and 2, nodes are more vulnerable to the attacks than communications. Some approaches suggest ciphering stored data [33]. Nevertheless, a combination of logical (cryptography weakness and Trojan horses), and physical (DPA, SPA, micro-probing, reverse engineering) attacks could break the ciphering and access the information.  
Due to the characteristics of the sensor nodes, it is not possible to secure its data against attacks. Even if we cipher the information in the devices, an attacker could use an approach based on logical and physical attacks that could break the ciphering. Since attackers have physical access to the nodes and nodes have limited resources, confidentiality should be based in the main characteristics of sensor networks: distribution and redundancy.  
Attack on the confidentiality of node information  
_Sensor agents_. In this kind of attack, the intruder accesses to the information stored in a sensor. If the attack succeeds, the attacker will obtain the information stored in it, but it is only raw data, not significant by itself. In addition, mapping that information with a concrete user is impossible because mapping information is stored in servers or distributed among a very large number of nodes. While the number of nodes holding some particular information remains much higher than the number of attacked nodes, attackers will not be able to obtain meaningful information.  
_Actuator agents_. These agents do not store other information than the status of the physical device they control and the trust table for its routers.  
_Aggregation agents_. By attacking an aggregation agent or a node that runs an aggregation agent, an intruder may gain access to redundant local raw data, but anything else. Redundant data is useful to discard bad data, but it gives no extra information.  
_Decision-making agents_. They run in servers, which are not physically accessible, and have enough resources to keep the information secure.  
Attack on the confidentiality of communications  
In this attack, an intruder listens to the channel trying to obtain some information. Due to sensor redundancy and information distribution, the attacker should break all communications between sensors and routers to obtain some significant information. The use of some ciphering algorithms will help protecting the system. Since the network is big enough, an attacker that listens to the channel will obtain only a set of \(d_{vi}(t)\). By definition, that set will not represent any meaningful information, so the attack will fail.