1. An information processing method for generating a hierarchical tree that is used to provide a ciphertext that is decryptable only by a specific selected device through broadcast encryption based on a hierarchical-tree structure, the information processing method comprising: generating a unidirectional hierarchical tree including nodes forming a hierarchical tree, the nodes having respective node associated values, the node associated value of each of the nodes being calculatable by a function using the node associated value and a node attached variable of at least one lower node; setting an intermediate label as a node associated value, the intermediate label allowing calculation of values of labels associated with a special subset selected from labels respectively associated with subsets that are defined based on a subset difference method based on a hierarchical tree; generating labels associated with the special subset by a calculation based on the intermediate label, and generating labels not associated with the special subset by a calculation based on the labels generated; and determining labels to be provided to a receiver associated with a terminal node of the hierarchical tree, so that special-subset non-associated labels that are not associated with the special subset are selected, and as information to be provided to the receiver associated with the terminal node of the unidirectional tree, a node associated value and a node attached variable are selected as a minimum intermediate label for calculating node associated values of nodes included in a path from the node associated with the receiver to a root as an uppermost node.