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We reveal some drawbacks in Ghodosi's scheme and present an improved RSA-based access control scheme for hierarchical groups. The proposed scheme enjoys the following properties: 1. The size of an individual's share sequence is bounded by a small constant times the size of the RSA modulus corresponding to that group. 2. The delegation of information flow from higher-level groups to lower-level groups is completely non-interactive. 3. It doesn't require an online trusted authority to upgrade the system as soon as communication happened. 4. The proposed scheme is resistant to conspiracy.