Time-bound hierarchical key management mechanisms are widely discussed in several environments and applications. Obviously, the collusion attacks are the serious problems in the time-bound hierarchical key management schemes. In the collusion attacks, two or more users assigned to some classes in distinct time periods collude to compute a key to which they are not entitled. Two kinds of countermeasures, such as adopting tamper-resistant devices and utilizing public parameters have been proposed to withstand the collusion attacks. In this paper, we proposed a new time-bound hierarchical key management scheme which can effectively defeat the collusion attacks without adopting a tamper-resistant device. Compared with the previous schemes, our design requires less public parameters.
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