In a two-tiered wireless sensor network, storage nodes act as an intermediate tier between sensors and the sink for storing data and processing queries. This architecture has been widely adopted because of the benefits of power and storage saving for sensors as well as the efficiency of query processing. On the other hand, the importance of storage nodes also makes them attractive targets for compromise. A compromised storage node may leak sensitive information and breach data privacy. In this paper, the authors propose a privacy-preserving protocol specializing for top-k queries that prevents attackers from gaining sensitive information from sensor collected data.