  In-network data aggregation in Wireless Sensor Networks (WSNs) provides
efficient bandwidth utilization and energy-efficient computing.Supporting
efficient in-network data aggregation while preserving the privacy of the data
of individual sensor nodes has emerged as an important requirement in numerous
WSN applications. For privacy-preserving data aggregation in WSNs, He et al.
(INFOCOM 2007) have proposed a Cluster-based Private Data Aggregation (CPDA)
that uses a clustering protocol and a well-known key distribution scheme for
computing an additive aggregation function in a privacy-preserving manner. In
spite of the wide popularity of CPDA, it has been observed that the protocol is
not secure and it is also possible to enhance its efficiency. In this paper, we
first identify a security vulnerability in the existing CPDA scheme, wherein we
show how a malicious participant node can launch an attack on the privacy
protocol so as to get access to the private data of its neighboring sensor
nodes. Next it is shown how the existing CPDA scheme can be made more efficient
by suitable modification of the protocol. Further, suitable modifications in
the existing protocol have been proposed so as to plug the vulnerability of the
protocol.
