Calculating trust in sensor networks

7. The distance to the sink node, because nodes closer to the sink will be seen as more
favourable.
The scheme also proposes that a log of previous interactions should be kept to combat
on-off -types of attacks, where malicious nodes may try to confuse other nodes by selec-
tively co-operating with them. This log would contain a history of previous interactions
accounted by whether they were successful or unsuccessful. In addition to this log the over-
all number of interactions with a node will also be recorded. The number of interactions
will be used to define a confidence factor for a node.
Six of these traits are directly calculated as direct trust. Trust of node B by node A
concerning trait i is then calculated as:
T A,B
i
= aiS A,B
i
aiS A,B
i
A,B
− biFi A,B
+ biF
Where ai and bi are the weight given to successful and unsuccessful occurrences of trait i.
S A,B
i
is the number of successful occurrences of trait i and F A,B
i
occurrences of trait i.
i
32
are the number of failed
The confidence factor of a node will be calculated according to the total number of inter-
actions with a node. This factor is defined as:
C A,B = 1 −
1
nB + wc
Where nB is the number of interactions with node B and wc is a baseline factor that is
used to weigh the initial confidence of newly discovered nodes.
Finally a direct trust value will be calculated as:
DT A,B = C A,B 6�
(
i=1
Wi ∗ T A,B
i )
Where Wi is a weighing factor for the six previous trusts concerning trait i.
Indirect trust is used in the scheme when for example a new, previously unknown node is
found or when there is a neutral opinion about a node. In these cases a node will request