Calculating trust in sensor networks

Figure 6 summarizes some of the most common characteristics of the previous routing
protocols.
Some approaches detailed what should be monitored about other nodes, some did not. The
most common trait to look for was whether the other node forwarded packets. The most
complete list of monitored traits was used in Dynamic Trusted Routing. WSNodeRater
used a shared monitoring mechanism to minimize energy consumption, by sharing the
monitoring load amongst many nodes. Several different ways of detecting and identifying
malicious or suspicious activity have been identified [FGRL07], but the previously detailed
trust management approaches implemented only a subset of these.
Not every approach used indirect trust, these were TGPSR and the Trust-Based Geo-
graphical Routing Scheme. Indirect trust is when nodes share their trust-information
about other nodes. Some approaches used indirect trust, but did not consider whether the
information itself should be trusted. This kind of behavior could be used to spread false
rumors about other nodes. In TLEACH, only the elected cluster-head is allowed to spread
indirect trust-information about other nodes. In CORE, only positive observations about
other nodes is spread as indirect trust-information.
Routing was based on the idea that less trustworthy nodes should be cut off from routing-
duties and thus excluded from the network. In some approaches other services were also
denied from untrustworthy nodes, such as packet forwarding or route discovery. In the
Trust-based Geographical Routing Scheme, a sender could define a minimum trust for
every packet that it sends. The packet is then forwarded to nodes whose trust is atleast
the required minimum trust of the packet.
A clear distinction should be made about trust and reliability. A node should be trusted
when it is seen as friendly. A node should be seen as reliable when it is friendly and
participating in the network. This raises the question, how do we separate the intruders
from the faulty nodes, and should both be handled the same way?
Something that should be taken into consideration is how a potential attack is seen through
trust management. If an attacker manages to insert a malicious node to the network, can
this be detected by these different monitoring schemes? Is it likely that they report false
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