Fei Chen and Alex X. Liu
July, 2009
The architecture of two-tiered sensor networks, where storage nodes serve as an intermediate tier between sensors and a sink for storing data and processing queries, has been widely adopted because of the benefits of power and storage saving for sensors as well as the efficiency of query processing. However, the importance of storage nodes also makes them attractive to attackers. In this paper, we propose SafeQ, a protocol that prevents attackers from gaining information from both sensor collected data and sink issued queries. SafeQ also allows a sink to detect compromised storage nodes when they misbehave. To preserve privacy, SafeQ uses a novel technique to encode both data and queries such that a storage node can correctly process encoded queries over encoded data without knowing their actual values. To preserve integrity, we propose a new data structure called neighborhood chaining that allows a sink to verify whether the result of a query contains exactly the data items that satisfy the query. To improve performance, we optimize SafeQ using Bloom filters. In addition, we propose a solution to adapt SafeQ for event-driven sensor networks. In comparison with prior art results, SafeQ excels in two aspects. First, SafeQ provides significantly better security and privacy. While prior art allows a compromised storage node to obtain a reasonable estimation on the value of sensor collected data and sink issued queries, SafeQ makes such estimation impossible. Second, SafeQ delivers significantly better performance on both power consumption and storage space. We performed extensive side-by-side comparison with prior art in our experiments. Results show that the power and space savings of SafeQ over prior art grow exponentially with the number of dimensions. Regarding power consumption, for two-dimensional data, our experimental results show that SafeQ consumes one order magnitude less power for sensors and storage nodes, and for three-dimensional data, SafeQ consumes two orders magnitude less power for sensors and storage nodes. Regarding space on storage nodes, for two-dimensional data, our experimental results show that SafeQ uses one order magnitude less space, and for three-dimensional data, SafeQ uses two orders less space.
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