Patent ID: 8290155

Claim:
An information processing apparatus for executing cryptogram generating processing, the information processing apparatus comprising: a processor configured to generate a cryptogram block and a key specifying code, the cryptogram block including cryptograms to be sent to user apparatuses, and that can be decoded by a key stored only in at least a selected one of the user apparatuses, wherein the user apparatuses correspond to leaves of lowest rank nodes of a multi-way tree configuration; the key specifying code includes key specifying information describing a key specifying tree as a partial tree of the multi-way tree configuration, the key specifying code identifying configuration nodes associated with subsets of the key specifying tree, the key specifying tree having the selected user apparatus as a leaf, and the key specifying information includes subset division identifying information describing the subsets of the key specifying tree, each cryptogram is associated with one of the subsets of the key specifying tree, and is encoded by a corresponding subset key, the subset identifying information indicating that the cryptograms included in the cryptogram block are encoded by the subset keys, the subsets being divided subsets of a dividable subset, the dividable subset being a set of specific leaves in the configuration nodes of the key specifying tree; and wherein the key specifying information is configured to be coded data indentifying a combination of a key specifying bit (a), a partition bit (b), a division method specifying information bit (c), the division method specifying bit indicating a division mode of the divided subset, and a leaf bit (d); wherein the key specifying bit, the partition bit, the division method specifying information bit, and the leaf bit are separate bits.