Patent ID: 7831831

Claim:
An authentication communication system comprising: an authenticating apparatus comprising a microprocessor and a memory; and a responder, wherein the memory stores a public key and a public key certificate, the public key corresponding to a secret key of the responder, and the public key certificate certifying validness of a public key, and the microprocessor of the authenticating apparatus is operable to: obtain a revocation list from a non-transitory recording medium on which content and the revocation list are recorded, the revocation list including first revocation information that corresponds to a revoked apparatus that has been revoked by a time of recording the content on the recording medium; store, in the memory of the authenticating apparatus, second revocation information including a second revoked identifier assigned to an apparatus which has been judged to be revoked by the authenticating apparatus; judge, in a first authentication of the responder, based on the obtained revocation list, whether or not the responder is revoked, the first authentication being performed only once when the responder is judged not to be revoked in a second authentication; judge, in the second authentication of the responder, based on the second revocation information, whether or not the responder has been revoked by the authenticating apparatus; judge, using the public key certificate, whether or not the public key corresponds to the responder; prohibit communication with the responder at least one of when the responder is judged to be revoked in the first authentication, when the responder is judged to be revoked in the second authentication, and when the public key is judged not to correspond to the responder; communicate with the responder when the public key is judged to correspond to the responder and the responder has not been judged to be revoked; and add, to the second revocation information stored in the memory, an apparatus identifier assigned to the responder, only when the responder is not included in the revocation list and the authenticating apparatus judges that the public key does not correspond to the responder.