Key management is at the heart of securing wireless sensor networks. Exclusion Basis Systems (EBS) is a combinatorial framework for group key management. It is secure and efficient for dynamic key management; however it could not resist collusion attack. A novel scheme combining EBS with broadcasting polynomial, LEP was proposed to solve this problem. Compromised nodes can be evicted by rekeying. LEP employs EBS to refresh keys when there is no collusion attack, otherwise broadcasting polynomial is used to rekey the network. Our scheme is secure when there are no more than t compromised nodes in the network. Performance analysis shows that LEP scheme is efficient in both communication cost and storage overhead with desirable scalability.

Cloud computing offers an appealing business model, and it is tempting for companies to delegate their IT services, as well as data, to the cloud. But in cloud environment, lack of practical auditing party always put the users' data in danger. Users may suffer a serious data loss without any compensation for they have lost all their control on their data. We present in this paper a novel way to implement a trusted third party for auditing in cloud environment (TTP-ACE), a trusted and easy-to-use auditor for cloud environment. TTP-ACE enables the cloud service providers' accountability and protects the cloud users' benefits.