A data processing and storage apparatus has a hardware security module and a data storage medium storing encrypted data objects and a hierarchical data maintenance structure of encrypted partition tables and hash-nodes forming a rooted tree, where a given partition table comprises a first reference to a given encrypted data object and a first cryptographic key for decryption thereof, where a given hash-node comprises a second reference to a partition tables or hash-node and a second cryptographic key being suitable for decryption thereof, and where the root node is decipherable using a master cryptographic key stored in the hardware security module, the given data object being assigned to the root node via the first and second references of the given partition table and the given hash-nodes forming a set of successive nodes in the rooted tree.