Communication over mobile Wireless Sensor Networks is becoming extremely popular. Handover over multiple access points is highly desirable to mobile nodes, but ensuring security and efficiency of this process is challenging. A novel handover authentication protocol named Pair-Hand is implemented in the present work. Pair-Hand uses pairing-based cryptography to secure handover process and to achieve high efficiency. An efficient batch signature verification scheme is incorporated into PairHand. The congestion problem in Wireless Sensor Networks (WSNs) during handover process is quite different from that in traditional networks. A traffic-aware dynamic routing (TADR) algorithm is proposed to route packets around the congestion areas and scatter the excessive packets along multiple paths consisting of idle or underloaded nodes. TADR improves overall throughput in WSNs. Experiments using our implementation on laptop PCs show that Pair-Hand is feasible in real applications