A data processing device for connection between a storage device and a controlling device that controls the storage device, the data processing device comprising: first receiving means for receiving, from the controlling device, a command that is either: a first command for reading data which is not encrypted and is stored in the storage device; or a second command for reading data which is encrypted and is stored in the storage device; second receiving means for receiving data from the storage device; storing means for storing seed information for generating key information on the basis of the seed information stored in the storing means and unique information from the controlling device; and key generating means for generating the key information and storing the key information in the storing means, the key information being generated each time the data processing device is activated, on the basis of the seed information stored in the storing means and the unique information of the controlling device obtained each time from the controlling device and received at the first receiving means; encryption means for encrypting data received from the controlling device, wherein the data is encrypted using the key information; decryption means for decrypting data which is encrypted and is received from the storage device, wherein the data is decrypted using the key information; a memory storing reference data for determining whether a command is executable by the storage device; determining means for determining that the command received by the first receiving means is to be issued to the storage device in a case where the information corresponding to the received command is stored in the memory and determining that the received command is not to be issued to the storage device in a case where the information corresponding to the received command is not stored in the memory; first controlling means for exercising control so that the command determined to be issued to the storage device by the determining means is issued to the storage device and so that the command determined not to be issued to the storage device by the determining means is not issued to the storage device; and second controlling means for controlling the decryption means not to perform decryption process on data which is not encrypted and is received by the second receiving means from the storage device when the issued command is the first command, and for controlling the decryption means to perform decryption process on the data which is encrypted and is received by the second receiving means from the storage device, when the issued command is the second command, the data being decrypted using the key information. first receiving means for receiving, from the controlling device, a command that is either: a first command for reading data which is not encrypted and is stored in the storage device; or a second command for reading data which is encrypted and is stored in the storage device; a first command for reading data which is not encrypted and is stored in the storage device; or a second command for reading data which is encrypted and is stored in the storage device; second receiving means for receiving data from the storage device; storing means for storing seed information for generating key information on the basis of the seed information stored in the storing means and unique information from the controlling device; and key generating means for generating the key information and storing the key information in the storing means, the key information being generated each time the data processing device is activated, on the basis of the seed information stored in the storing means and the unique information of the controlling device obtained each time from the controlling device and received at the first receiving means; encryption means for encrypting data received from the controlling device, wherein the data is encrypted using the key information; decryption means for decrypting data which is encrypted and is received from the storage device, wherein the data is decrypted using the key information; a memory storing reference data for determining whether a command is executable by the storage device; determining means for determining that the command received by the first receiving means is to be issued to the storage device in a case where the information corresponding to the received command is stored in the memory and determining that the received command is not to be issued to the storage device in a case where the information corresponding to the received command is not stored in the memory; first controlling means for exercising control so that the command determined to be issued to the storage device by the determining means is issued to the storage device and so that the command determined not to be issued to the storage device by the determining means is not issued to the storage device; and second controlling means for controlling the decryption means not to perform decryption process on data which is not encrypted and is received by the second receiving means from the storage device when the issued command is the first command, and for controlling the decryption means to perform decryption process on the data which is encrypted and is received by the second receiving means from the storage device, when the issued command is the second command, the data being decrypted using the key information.