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Chen and Chung proposed an improved scheme of hierarchical access control based on the Chinese Remainder theorem and symmetric encryption . In this paper, we point out that the part of their scheme for adding a new class is not correct. Furthermore, we discuss how to fix this problem.
In a user hierarchy we say that a security class is subordinate to another security class if the former has a lower security privilege than the latter. To implement such a hierarchical structure, it is often desirable to allow the user of each security class to derive the keys of its subordinating classes. This problem has been extensively studied but the existing solutions have various drawbacks...
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