# Sensor Network Environments: A Review of the Attacks and Trust Management Models for Securing Them
## 4 Attack Types
### Routing Attacks  
In most cases reviewed in this paper, the networks are a type of ad hoc network, meaning that there are not typical routers in the network. However, all nodes, or a portion of nodes (depending on the topology), essentially act as routers within the network and can be targeted for such routing attacks. The authors of [41] provide an overview of some common routing protocols and routing attack types in ad hoc networks, and the solutions to these using routing protocols. These attacks can also be thwarted through the use of trust models in many cases, hence they are mentioned here. Ideally, a good routing protocol and trust model would be used to ensure the most secure approach to these attacks; however, routing protocols are beyond the scope of this paper and, therefore, they are not discussed here.  
**Hello flood**. This attack uses Hello packets to announce to many nodes that they are neighbors. A laptop-class adversary can be used to send this packet to all the nodes in a network to convince them that a compromised node is their neighbor [42]. This type of attack can be used to disrupt routing or, in clustered network structures, to fool the cluster head selection process into choosing the compromised node as a cluster head, placing it in an ideal position to launch further attacks.  
**Wormhole**. This attack requires two or more attacker nodes. One attacker receives packets and 'tunnel' them to the other through a private high-speed network. This allows the attackers to deliver packets with better metrics than a normal multi-hop route [45]. This allows the attacking nodes to obtain more traffic, as they provide the fastest route which in turn makes them a threat for launching further routing, payload or DoS attacks on the network. Wormhole attacks can also be used to secretly 'tunnel' information out of a network.  
**Black-hole.**[46] A black-hole attack is one in which the attacker node simply drops all packets sent to it (just like a real black-hole, where things can only fall in but never come back out). This prevents the packets from reaching their target destination and, in situations where routing replies or packet acknowledgments are required, causes errors in the network and becomes very disruptive. The upside to black-hole attacks is that they are relatively easy to detect.  
**Gray-hole.** Gray-hole attacks are similar to black-holes, but instead of discarding all the information sent into it, the gray-hole attack only discards some packets or parts of packets. This allows traffic to continue flowing and replies and acknowledgments to be received, but with a subtle loss of information, making this type of attack much harder to detect than a black hole.  
**Sinkhole.** This is an attack where a compromised node tries to attract all the traffic from neighbor nodes based on the routing metric used in the routing protocol [47]. With almost all the network traffic passing through this node, it can launch further attacks, such as packet modification, or black-hole-, gray-hole- or reputation-type attacks.