Cryptographic enforcement of access control mechanisms relies on encrypting protected data with the keys stored by authorized users. This approach poses the problem of the distribution of secret keys. In this paper, a key management scheme is presented where each user stores a single key and is capable of efficiently calculating appropriate keys needed to access requested data. The proposed scheme does not require encryption of the same data (key) multiple times with the keys of different users or groups of users. It is designed especially for the purpose of access control. Thanks to that, the space needed for storing public parameters is significantly reduced. Furthermore, the proposed method supports flexible updates when user's access rights change.
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