for encryption a content key Kco by an individual key Ki (e.g., a data encryption section 203 of FIG. 85), means for verifying signature data generated with respect to various kinds of data (e.g., a signature verification section 222 of FIG. 85) held by a user purchasing contents (e.g., a content receiving apparatus 210 of FIG. 85), and means for saving a delivery key (e.g., a tamper resistant 22