An enabling key block (EKB) used in an encrypted key distributing tree structure is generated by forming a simplified 2-branch or multi-branch type tree with a terminal node or leaf which is capable of decrypting on the basis of a key corresponding to a node or a leaf of the simplified tree. Further, the EKB includes a tag for indicating a position of an encrypted key in the tree. The tag not only discriminates position but also stores data for judging the presence of encrypted key data within the EKB. As such, a considerable reduction in data quantity is realized, and the decrypting process in a device is also simplified.