When the base station is long way from the sensor nodes the security strength is reduced. To overcome this problem the concept of Mobile Sink (MS) is introduced. Still there is a chance of major attack called as Mobile Sink replication attack. One method to eliminate this attack is using pool keys. Normally there are two common types of pool keys are available they are: polynomial pool keys and tame pool keys. In this paper, the authors study the three layer security using tame pool of keys and polynomial pool of keys.