Wireless sensor networks (WSNs) are often deployed in hostile environments, thus being subjected to great security risks. However, due to the influence of environment and dynamic topology, the communication radiuses of all nodes are no strictly consistent, which may cause different neighbor number and redundant neighbors for one central node. In this paper, we present a key agreement scheme without the trusted third parties by exploiting the special characteristics of Hopfield neural network:

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... e two nodes converge in a steady state from their respective initial states after iterating finite times, while maintaining the confidentiality of the key by quantifying the key to strings. Compared to existing solution, the proposed method requires less memory and has lower communication overhead to key agreement. We take the HNNs with four cells (N=16) as an example to illuminate how one bit shared key is achieved. So each cell exists in possible sixteen different states, the combination state space of four cells is shown as the following formula: