Due to application of WSN in mission critical areas, secured message communication is very important. We have attempted to present a methodology that ensures secured communication among nodes in a hierarchical Cluster Based WSN. Our scheme works when member sensor nodes move from one Cluster Head (CH) to another. The proposed scheme is based on Key Redistribution during node mobility and development of an Authentication Model to check whether the new node in a cluster is an intruder. We have carried out extensive simulation experiments, which demonstrate the efficacy of the proposed scheme. The experiments suggest that the number of message transmission in creases linearly with the number of mobile nodes during key-redistribution when a node moves from one CH to another. We have seen that the detection efficiency of the Authentication Model is 0.9 to 1 when tunable threshold value is 0.02 and sensor nodes are sufficiently mobile.