Calculating trust in sensor networks

3 Trust management
Research done in mobile ad hoc networks has shown that network performance is severely
reduced if nodes in the network misbehave [MM02b]. Misbehaving nodes usually refuse to
participate in network activity because of selfish or malicious intents. A selfish node may
refuse to forward packets because it is trying to save energy. A selfish node will use the
network but will not cooperate. A malicious node will go beyond that and do anything to
disrupt the network.
A sensor network organizes and operates very similarly to any ad hoc network. The
network topology is not known beforehand, and nodes may not have complete trust about
their neighbour’s intent. Nodes in a sensor network are often unattended, so gaining
physical access to them would be easy for an attacker. Research has suggested [BBD06]
[FC08] that nodes can be compromised on the field with only a minimal lapse in the
nodes presence. A general assumption about sensors is that they can be captured and
reprogrammed for malicious purposes.
One countermeasure against such an attack would be that each node in a network collects
trust information about its neighbours. This would be called distributed trust manage-
ment.
A node may gather subjective observations about its neighbouring nodes to determine
how much it may trust them. This is called direct trust. This approach would require no
central node or server to determine who should be trusted, and who should not. Such a
distributed trust management system could be more resilient towards attacks where large
parts of the network could be taken over.
Gathering data (or ”evidence”) for trust evaluation can be a cumbersome process. Some
relevant behaviour that a trust management scheme could look for include momentary
absence from the network (see node capture in Chapter 2.4), answering to non-existing
queries, weird or invalid sensor readings or reluctance to co-operate in routing or packet
forwarding [FGRL07].
Nodes may also engage in sharing their trust-information. This sort of behavior could be
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