Target device, method and system for managing device, and external device

An image reading device, comprising:

• a plurality of functional units including at least a mechanical unit, a control unit, and an optical unit, each of the functional units further comprising:
• a tamper-resistant chip including:
• a first device-information storing part that stores device information of the functional unit;
• and
• a confidential-key storing part that stores a confidential key;
• a second device-information storing part that stores device information of other functional units within the image reading device;
• an encrypting part configured to encrypt the device information stored in the first device-information storing part using the confidential key stored in the confidential-key storing part and output encrypted device information;
• a transmitting part configured to transmit the encrypted device information to another functional unit within the image reading device;
• a receiving part configured to receive encrypted device information from other functional units within the image reading device;
• a decrypting part configured to decrypt the received encrypted device information using the confidential key stored in the confidential-key storing part and output decrypted device information;
• an authentication part configured to authenticate whether the decrypted device information corresponds to the device information of other functional units stored in the second device-information storing part, wherein
• the functional units are configured to mutually perform authentications of the decrypted device information with one another to determine whether the functional units are usable,
• the image reading device is configured to switch to an operable state when it is determined that all the functional units are usable, and
• the image reading device is configured to generate an alarm or an error signal when it is determined that at least one of the functional units is unusable.