A wireless sensor network (WSN) is a group of resource-constrained, inexpensive, tiny, and homogeneous or heterogeneous sensor nodes. The inherent nature of WSNs such that it makes them deployable in a variety of circumstances, which increases the interest towards them but at the same time poses tremendous challenges such as resource-constrained nodes, unattended operations, unknown topology and wireless communication links. Security in WSNs can be achieved with the help of various cryptographic operations. The strength of cryptographic system depends on the secrecy of the key it uses. So, a solid strong key management frame work is the prerequisite for the cryptographic primitive upon which other security primitives are built. To improve the energy efficiency and increase the resilience more effectively, an Energy Efficient Hierarchical Key management Protocol (EEHKMP) for hierarchical homogeneous WSN is proposed. In this protocol, a Differentiated random KPD (DKPD) process is employed for randomly deployed distributed WSN. Its main objective is to distribute different number of keys which are chosen randomly to different sensors in order to enhance the resilience of certain links such that the nodes can route through those links with higher resilience. This DKPD process divides the sensor nodes into different classes and pre-distributes the keys according to each class. Nodes with maximum residual energy and minimum distance are elected as cluster heads (CHs). The CH sets up the intra-cluster and inter-cluster routes with nodes having more shared keys. CH generates multiple random key shares to generate pair-wise key and transmits each key share to source and destination on each hop route, which is selected based on the cost function. Key shares are hop-by-hop encrypted / decrypted by a combination of all shared pre-distributed keys on that hop. Finally, a key update mechanism is presented to update the keys.
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