A data processing device that is connectable to an information processing device via a first interface that supports hot swapping and is connectable to a peripheral device via a second interface, and that is capable of performing a transferring process including at least a first process for decrypting encrypted data received from the peripheral device and a second process for transferring the decrypted data to the information processing device, the data processing device comprising: an authentication unit configured to perform a process for authenticating the information processing device which is connected via the first interface; a control unit configured to cause, in response to correct performance of authentication by the authentication unit, the data processing device to permit the transferring process, and cause, in response to incorrect performance of authentication by the authentication unit, the data processing device to prohibit the transferring process; a determination unit configured to determine a state of connection of the data processing device to the information processing device via the first interface; characterized in that the determination unit comprises a connection detection circuit which detects a disconnection of the first interface by using a disconnection time of a physical layer communication enable signal or by detecting a change in a connection detection signal provided for the first interface, whereby a physical state of connection of the first interface can be detected, wherein in a case where the determination unit determines that the data processing device is not connected to the information processing device via the first interface after the correct performance of authentication, the control unit cancels a result of the authentication by the authentication unit and causes the data processing device to prohibit the transferring process, and in a case where the data processing device is connected to a device different from the information processing device via the first interface after the transferring process is prohibited, the control unit causes the authentication unit to perform another process for authenticating the information processing device which is connected via the first interface and causes, in response to incorrect performance of authentication by the authentication unit, the data processing device to continue prohibiting the transferring process, and, in a case where the data processing device is connected to the information processing device via the first interface after the transferring process is prohibited, the control unit causes the authentication unit to perform another process for authenticating the information processing device which is connected via the first interface and causes, in response to correct performance of authentication by the authentication unit, the data processing device to change an operation state thereof from a state where the transferring process is prohibited to a state where the transferring process is permitted. an authentication unit configured to perform a process for authenticating the information processing device which is connected via the first interface; a control unit configured to cause, in response to correct performance of authentication by the authentication unit, the data processing device to permit the transferring process, and cause, in response to incorrect performance of authentication by the authentication unit, the data processing device to prohibit the transferring process; a determination unit configured to determine a state of connection of the data processing device to the information processing device via the first interface; characterized in that the determination unit comprises a connection detection circuit which detects a disconnection of the first interface by using a disconnection time of a physical layer communication enable signal or by detecting a change in a connection detection signal provided for the first interface, whereby a physical state of connection of the first interface can be detected, wherein in a case where the determination unit determines that the data processing device is not connected to the information processing device via the first interface after the correct performance of authentication, the control unit cancels a result of the authentication by the authentication unit and causes the data processing device to prohibit the transferring process, and in a case where the data processing device is connected to a device different from the information processing device via the first interface after the transferring process is prohibited, the control unit causes the authentication unit to perform another process for authenticating the information processing device which is connected via the first interface and causes, in response to incorrect performance of authentication by the authentication unit, the data processing device to continue prohibiting the transferring process, and, in a case where the data processing device is connected to the information processing device via the first interface after the transferring process is prohibited, the control unit causes the authentication unit to perform another process for authenticating the information processing device which is connected via the first interface and causes, in response to correct performance of authentication by the authentication unit, the data processing device to change an operation state thereof from a state where the transferring process is prohibited to a state where the transferring process is permitted.