Protocols for Secure Communication in Wireless Sensor Networks

6.4. Security Evaluation 179
Bandwidth overhead (byte)
3500
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2000
1500
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0
0 2 4 6 8 10 12 14 16 18 20
Path length
Figure 6.9: Bandwidth overhead
Canvas, |mac|=7
Canvas, |mac|=20
EC
MACs are truncated, the advantage of Canvas is retained, however.
6.4 Security Evaluation
Before we actually present these results, we give a brief overview of the method
that has been used to retrieve the numerical values for these comparisons.
6.4.1 Analytical Assessment of Resilience
We introduce here the function B(x), which takes the number x of compromised
nodes as input and returns an approximation of the number of compromised
paths. It is obvious that this approximation can be very rough only. The number
of compromised nodes says nothing about the topological position of the nodes
within the network. Each position differs in how many paths it will help to
compromise.
As a network model, we will use a random geometric graph. We loosely
assume it has rectangular shape, and we ignore border effects.
The suffix E for B() describes an approximation if end-to-end authentication
is being used. In this case, only those paths are considered compromised that
have at least one compromised end node. For each compromised node, there
are on average 2(N − 1) paths to other nodes that are considered compromised