An information processing method, decrypting method, information processing apparatus, and computer program are provided. An information processing method generates a hierarchical tree used to provide a ciphertext decryptable only by a specific selected device through broadcast encryption. The method includes the steps of generating a unidirectional hierarchical tree including 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 allowing calculation of values of labels associated with a special subset selected from labels of subsets defined based on a subset difference method; generating labels of 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.