Wireless Sensor Nodes are powered by limited batteries and equipped with constrained processor and memory. Therefore, security protocol must be highly efficient to fit WSNs. Meanwhile, considering the large variety of WSN applications and wide deployment, scalability and interoperability are two important concerns of adopting standardized communication protocols. HIP DEX, an IETF Internet draft, provides a generic solution to establish secure connections in WSNs. In this paper, we investigate the security features of HIP DEX based on several practical attack models. We evaluate the performance efficiency of HIP DEX in terms of energy consumption and computing latency on an experimental prototype. Our empirical results show that HIP DEX is applicable for resource constrained sensor nodes to establish hop-by-hop secure connection. In order to reinforce identity protection, we also propose tentative improvements to HIP DEX. Finally, we compare HIP DEX with SSL/TLS to highlight their respective advantages in different WSN architectures.