Abstract. Due to limited energy of sensors, existing data integrity protection mechanisms for wireless sensor networks (WSNs) typically use a simple hash function for signing and verification. However, since the computation cost of hash function depends on the length of the input data, this cost may be high for long data streams. In this paper, we present a secure and efficient data integrity protection protocol for WSNs named IPLDS, which only uses hash function for processing a short block of data, and mainly operates on the long data stream using Montgomery modular multiplication, which can reduce the computation costs of long data streams significantly.