![](bg7.png)
as a response indicating that it can play the role of a
router/gateway to communicate between requesting
L2 nodes, thus establishing an indirect link.
Owing to the fact that L1 nodes have more keys
deployed in them, this path assures more security.
Counters are set up at each node to keep track of
the number of common key matches obtained. This
phase may be used repetitively to find secure path
between two nodes, which have low Link Strength.
(iii) Path Selection Phase
This phase is responsible for choosing the right path
between a given source and destination node. The
path chosen should have higher Link Strength and
ensure secure communication. Based on this value,
different links in the network are categorized as low,
moderate and high secure paths. Depending on the
requirements, selection of path is done and the data is
routed accordingly. Path Selection Phase allows data
to be routed at different levels of security or at the
same level of security in the network for a given ap-
plication. Path chosen once at a particular threshold
does not imply that selection should always be made
for the same threshold. Switching to different thresh-
olds is also permissible making all nodes participate
in the network. The path selection phase is given in
Table 3.
5.3 An Example
In the proposed scheme, the steps followed to select
the path are as follows:
(i) All the nodes during the direct path establishment
are first identified and the value of Link Strength
is determined.
(ii) Link Strength is calculated for nodes communi-
cating in the indirect path.
In the first stage, direct communication is established
if there exists one or more common keys(nodes are
not communicating via L2). The constraint for es-
tablishing direct communication is atleast 1. At the
last stage, after the direct path phase, we alter the
constraint for direct communication by changing the
common keys to be greater than 1, 2, 3 and so on. The
path is selected by comparing the old and new val-
ues of Link Strength and selecting the one which has
higher value. This process would assure resilience to
the network against node compromise and defend it-
self from the active and passive attacks. The graphs
for Link Strength for a given set of nodes vs the key
matches after the direct phase or threshold keys is
plotted and then analyzed.
Consider a network consisting of an L1 node and
two L2 nodes. If the direct path is established between
two L2 nodes the value of Link Strength depends on
the number of keys deployed in L2. If n keys are de-
ployed in L2 and all the keys are common, the maxi-
mum value of Link Strength is equal to (n/number of
links). Let us consider an indirect path to be estab-
lished inspite of a direct path. If there exists n com-
mon keys between L1 and L2, then Link Strength is
determined to be as [(n1+n2)/2]. Both the direct and
indirect path values are compared, it is observed that
the indirect path is better than a direct path. But, hav-
ing all the keys common is an ideal case.
The communication is open even if there exists a
single key match. The security of open path depends
on the number of common keys. Thus, if the threshold
for the communication increases as 1, 2, . . . so on
(common keys), then the value of Link Strength in-
creases ensuring enhanced security. Owing to the fact
that number of keys deployed in L1 is far greater than
L2, the probability of finding common keys between
L1 and L2 nodes is greater than finding common keys
between two L2 nodes. This is not true for all in-
stances. There may exist an indirect path, whose Link
Strength is low compared to direct path. In such a
case direct path is selected. Thus, based on the above
comparisons, the paths are distinguished as low, mod-
erate and high secure paths and the data is routed.
Successful active attacks allow the intruder to dis-
rupt the functioning of the network. Attackers can
masquerade the network by overhearing the messages
and cause malfunctioning in the network. If an at-
tacker compromises the node, then he can spy the
network and gains full control over it. Such cases
must be avoided and the network must ensure confi-
dentiality and security. The analysis against secure
threats is dependent on Link Strength which is de-
fined as a function of number of common keys. It
becomes more difficult for the intruder to decrypt all
the keys that is open for communication with trusted
neighbors. Moreover,the constraint for the number of
common keys is again not disclosed. Therefore, the
intruder is not aware as to how many common keys
he needs to decrypt and the actual keys for communi-
cation. This ensures a double protected mechanism.
Therefore, security is ensured in both the ways and
proves to be more stable.
6 PERFORMANCE ANALYSIS
In order to implement the proposed Keymatches Con-
strained Secure Routing (KCSR) algorithm three mes-
sages are considered: Send message, Send Path mes-
sage and U pdate message. These messages are de-
KCSR: KEYMATCHES CONSTRAINED SECURE ROUTING IN HETEROGENEOUS WIRELESS SENSOR
NETWORKS
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