Attribute based systems enable fine-grained access control among a group of users each identified by a set of attributes. Secure collaborative applications need such flexible attribute based systems for managing and distributing group keys. However, current group key management schemes are not well designed to manage group keys based on the attributes of the group members. In this poster, we propose a novel key management scheme that allows users whose attributes satisfy a certain policy to

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... ve the group key. Our scheme efficiently supports rekeying operations when the group changes due to joins or leaves of group members. During a rekey operation, the private information issued to existing members remains unaffected and only the public information is updated to change the group key. Our scheme is expressive; it is able to support any monotonic policy over a set of attributes. Our scheme is resistant to collusion attacks; group members are unable to pool their attributes and derive the group key which they cannot derive individually.