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Hierarchical access control is for scenarios where some users have access to more organization data than others. In this paper, we propose an efficient key assignment scheme for dynamic hierarchies that features constant decryption cost and does not require any expensive operations like bilinear pairing. The proposed hierarchical key assignment scheme is secure against strong key distinguishability attacks. It also supports dynamic updates like addition and deletion of classes in the hierarchy with efficient procedures for preserving forward and backward secrecy. Another important highlight of the proposed scheme is that secret keys of none of the users have to be updated to preserve forward and backward secrecy in case of dynamic updates. Proposed is the first dynamic hierarchical key assignment scheme whose key derivation procedure has constant computation cost and is pairing-free with strong key …