Protocols for Secure Communication in Wireless Sensor Networks

7.1. Secure Communication in Wireless Sensor Networks 219
ensure the secure transmission of messages by authenticating routers, or ensuring
link security, for example.
An alternative communication scheme that can potentially counter these
problems is multi-path communication. Here, the same message is sent over
multiple paths that only share the same end-points, but use no common communication
links or routers (or neither of them). Here, a threshold scheme can
ensure that an attacker cannot reconstruct or modify without detection a message.
Generally, constructing short disjoint paths is a complex task with a high
computational overhead.
Protocols that work in conventional networks with high-powered nodes do
not necessarily work well in highly resource-constrained environments like
wireless sensor networks. Therefore, alternative approaches have been devised.
We have proposed a scheme for constructing multiple disjoint (node) disjoint
paths that is suited for wireless sensor networks. The basic concept are
routing trees that can be set up very easily by selecting a root for each tree
and a single wave of broadcast messages for tree construction. A message is
then routed along the links that are contained in a tree. This increases the path
length by a manageable amount, but also provides for a high degree of disjointness
for pairs of tree paths. This scheme therefore provides a practical trade-off
between additional complexity and security.
7.1.3 Interleaved Authentication
One of the main goals of a secure communication protocol is to provide a means
for remote nodes to exchange messages that are protected against manipulations
that may happen while the messages are in transit. In a wireless sensor
network, nodes act as routers, relaying messages on behalf of other nodes. Secure
communication between two nodes thus depends on the collaboration of
all intermediate nodes. Especially, intermediate nodes are expected to relay
messages with their contents unaltered. An integrity-protecting communication
scheme ensures that manipulations would be detectable.
In a conventional approach, an end-to-end message authentication protocol
is being used, which is based on public key cryptography or pairwise shared
keys. Public key cryptography introduces a relatively large overhead regarding
computational effort for creating and verifying signatures, and requires the
transmission of authentication data of significant size. On these grounds, public
key cryptography is often dismissed for use in resource-constrained environments.
An alternative are fully pairwise shared keys, which allow the use
of more efficient symmetric key cryptography. However, the storage require-