# Sensor Network Environments: A Review of the Attacks and Trust Management Models for Securing Them
## 3 Trust Model Concepts
### Security Features  
Conventional security focuses on providing hard security to a system based on the CIA triad (modified)--Confidentiality, Integrity, and Authenticity (as well as availability and access control). The trust model aims to provide most of these security features both internally and externally on the network.  
Conventional security techniques include methods such as encryption, digital signatures, digital certificates and authentication methods (passwords, tokens, biometrics). All these methods mostly assume and are tailored according to the premise that the attacker is an outside entity, as is the case in attacks such as eavesdropping, DDoS or man-in-the-middle (MitM)-type attacks. These methods establish connections between users and assume trust thereafter for the duration of the session. However, in the new network environment types, this is often not good enough, and a new 'zero trust' approach must be taken, as nodes within the network can be compromised or gain access legitimately before launching their attacks, effectively launching them from inside the conventional security barriers.  
Conventional security methods can still be used within the trust models to provide services such as confidentiality, integrity and authentication, although they must often be adapted to suit low-powered nodes. This is conducted through lightweight or edge cryptography [36, 37] and key management [37] methods.  
Trust models use the concept of zero trust, in which no entity is trusted until verified. The trust is dynamically updated. This is usually achieved through time-triggered updating or event-triggered updating. This dynamic updating aims to prevent nodes or entities that were once trusted but then became malicious from launching attacks internally on the network.  
The main security contribution of a trust model is a form of access control. All trust models should be able to provide and deny access to any node on the network. Depending on the use case scenario, models will decide whether a node can be trusted, whether the data can be trusted and used, or whether the node should be allowed to access some form of resources on the network. Models must be able to discard any untrusted data and eject any untrusted or malicious nodes. This access control provided by the models will successfully mitigate attacks, such as packet modification, bogus data injection or malicious software spreading, which can be carried out through a number of different initial attack methods.  
Trust models can also provide authentication if the situation requires. This can be achieved by means of signatures, as seen in [12], where an intrusion detection service provides a signature-based authentication method. As seen in [9], a hardware approach can be taken for the authentication of nodes with the use of radio frequency distinct native attribute (RF-DNA) fingerprinting. This method analyzes the transmitter signal of the node, comparing it to known samples from previous communications. In [9], these data are classified using an SVM (support vector machine). This method is similar to human biometrics (as if the transmitter of the device is the biometric) and definitely has great potential to be used in static hierarchical or clustered network environments, where there is a cluster head or base station with the capabilities of running the required hardware and software.