Recently, Wireless Sensor Network (WSN) is gaining attention as one of a base station systems that represents the ubiquitous network. WSN is composed of a server and a lot of low-cost wireless sensors. It is used in many applications such as collecting data from agricultural farms, vehicles, home appliances, etc. A sensor node has low operational performances due to very limited power supply capacity and constrained resources for computations. Therefore, advanced security technologies like a public key cryptosystem cannot be simply used for WSN. Instead, a common key is often used in general in a WSN system where it is important to renew the common key regularly to maintain the security. However, the key cannot be renewed when the power supply is disrupted or due to other interruptions for which a sensor cannot participate in the communication. The technique for improving the stubbornness of the system is to add a self recovery capability of the key which is called self-healing. Moreover, when the sensor renews the key, it is necessary to consider the backward secrecy, which guarantees that a passive adversary who knows a contiguous subset of group keys cannot discover the future group keys.

Our research plans to provide the "Backward Secrecy" and the collusion resistance along with proposing a method of key update with low storage and communication overhead for WSN.