Wireless sensor networks are designed for outdoor environment surveillance and require benign coverage, steady working status and long lifetime, moreover, they require efficient security services for rigorous applications. Most security schemes are designed to work efficiently only when bidirectional links exist. So do most key establishment protocols for WSNs. Traditional key establishment schemes delete all the unidirectional links from the network. Hence, the sensors covered only by unidirectional links are excluded from the collaborating network, even if they are stable and energetic. These schemes shorten the lifetime and decrease the connectivity of the whole network. To improve the network connectivity and increase the number of available sensors in the network, a security mechanism is proposed for wireless sensor networks exploiting unidirectional links. By searching local connection components in a small area, this mechanism helps negotiate shared secrets among nodes that may covered by unidirectional links. It obtains identity authentication and perfect resilience against node compromise.The simulation reveals that, our scheme can greatly increase the proportion of available sensor nodes and network connectivity, which will efficiently prolong the network lifetime.
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