Patent ID: 7263188

Claim:
A data delivery system comprising: encrypting means for encrypting data and outputting the resultant encrypted data; transmitting means for transmitting the encrypted data; medium recording means for recording, on a physical storage medium, a key used to decrypt the encrypted data, the physical storage medium being physically transportable; receiving means for receiving the encrypted data transmitted by the transmitting means; medium reading means for reading the key stored on the physical storage medium and physically received by said medium reading means; decrypting means for decrypting the encrypted data received by the receiving means, using the key read by the reading means; reproducing means for reproducing the data decrypted by the decrypting means; control means for controlling the reproduction of the data performed by the reproducing means in accordance with stored information on the storage medium and relating to the permitted use of the data; judgment means for detecting unauthorized use of the data, on the basis of said information stored on the physical storage medium; storage means for storing the received encrypted data; and delete flag recording means for, when the encrypted data stored in the storage means is deleted, recording a delete flag on the physical storage medium, wherein the judgment means detects unauthorized use of the data by judging whether the delete flag is recorded on the physical storage medium.