# Sensor Network Environments: A Review of the Attacks and Trust Management Models for Securing Them
## 5 Trust Data Gathering
### Trust Parameters
This method is similar and overlaps with the communication method discussed above, which analyzes the ratio of successful to unsuccessful/total packets sent to a node, which is also using information about past interactions to help to measure trust. **Resource consumption** can be a clear indicator of a DoS, routing, payload or other type of attack. If a node is consuming an abnormal amount of energy, CPU power or bandwidth, then it is most likely doing something it should not be, such as running CPU intensive processes, downloading programs or running far more communications than usual. These are all telltale signs of many of the attacks discussed in Section 4. Numerous models in the aforementioned communications section can detect increased bandwidth usage by monitoring the communications. CPU power is monitored in [20] using a watchdog mechanism that allows nodes to observe their neighbors' processing consumption. CPU, network and storage trust is used to help to define trust for service composition in mobile cloud environments in [18] and in the IoT domain in [10]. The authors of [23, 25, 27, 28] all use an energy trust value based on the energy consumption rate of the node. It is important to note that, in these networks (WSNs and underwater WSNs), energy consumption is very important, as the sensors are in difficult-to-access, remote locations with limited battery life, and excessive energy usage due to attacks or malfunction can cause the sensors to be out of action for a prolonged period of time. Therefore,it makes sense for networks such as these to use energy usage as a trust-measuring metric, as energy is such a valuable resource for them. Device behavior is examined in [10]. The behavior concerns the device resource usage metrics and whether they are within a predetermined range for the device. This information is obtained from MUD (manufacturer usage description) files. MUD files consist of an MUD URL, where the network can find information about the device connecting to it from the MUD file server [51]. This information notifies the network about what this physical device does, and the network can take appropriate access control measures and can get an accurate idea of its normal resource usage for anomaly detection. **Device status** encompasses information regarding device integrity and device resilience [10]. The integrity of the device is defined in [10] as the extent to which the device is known to run legitimate firmware/OS/software in valid configurations. The resilience of the device is defined as the known security of its firmware/OS/software versions. The authors of [10] apply this metric to the trust calculation of the device. The device most likely will not change its firmware/OS very frequently. Therefore, this metric may be more useful in helping to calculate an initial trust value for a new node joining a network when there are little to no other available data on the node. **Associated risk** is not commonly used in trust models. It is used in [10], where the risk associated with a device is classed as a fuzzy level. The risk is calculated based on the device's probability of being compromised and the damage it could do to the network (based on its access rights and perceived value and also its neighbor's criticality and perceived value in the network). This method involves a great deal of work in classifying the nodes' associated risk accurately, and it may not be useful in many network types (e.g., homogeneous networks). However, in more complex networks, it may be useful for implementing different classes of trust for devices with different priorities and capabilities within the network in order to increase productivity. A similar concept is used in [30], where a role-orientated trust system is used. In the VANET, different weights are given to the information received from normal vehicles, high-authority vehicles (emergency vehicles), public transport, professional vehicles and traditional vehicles (vehicles with little to no travel history, which are assigned a lower weight).