Wireless sensor network nodes are very tiny in size and their cost is also not very high. During the process of data sensing, data gathering and data transmission, the charge of the power unit associated with any node gets low, after certain time, i.e., each node has its life time. In this paper, a secure symmetric key will be proposed for wireless sensor network. After deployment of nodes, the authors will assign keys manually with hash function which is blowfish. Time synchronization and clustering technique is used.