A Hybrid Wireless Sensor network (HWSN) with static and mobile nodes is considered. Static sensors monitor the environment and report events occurring in the sensing field. Mobile sensors are then dispatched to visit these event locations to conduct more advanced analysis. Mobile sensor will collect the information about the event and in turn will send it to the base station. As WSN is vulnerable to attacks, a big challenge is to provide security for the communication that takes place between

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... e base station and mobile sensor. Therefore the goal of the paper is to provide security for the data that is transferred between the base station and mobile sensor. In this paper data security will be provided using Sensor Network Encryption Protocol (SNEP) which is one of the building block of SPINS. This paper contributes in defining a suitable data security mechanism.