Patent ID: 8724135

Claim:
A printing device comprising: at least one mount section on which a cartridge storing a plurality of secret keys is configured to be detachably mounted; a printing section configured to perform printing on a recording medium with developer accommodated in the cartridge; a first memory section configured to store a plurality of secret keys that is identical to the plurality of secret keys stored in the cartridge; a second memory section configured to store history information relating to a history of usage of the printing device; a secret-key selecting section configured to perform a secret-key selecting operation of selecting, based on the history information, a specific secret key from among the plurality of secret keys stored in the first memory section; a first-authentication-information generating section configured to encrypt a random number based on the selected specific secret key, thereby generating first authentication information; a third memory section configured to store the first authentication information; a transmitting section configured to transmit first identification information and the random number to the cartridge, the first identification information comprising particular information that identifies the specific secret key, the specific secret key being selected by the secret-key selecting section based on the history information; a receiving section configured to receive second authentication information from the cartridge, the second authentication information being generated at the cartridge by encrypting the random number transmitted by the transmitting section based on a secret key identified by the first identification information; and an authenticating section configured to compare the first authentication information stored in the third memory section with the second authentication information received by the receiving section, and to authenticate the cartridge if the first authentication information matches the second authentication information.