A data processing device transmits specific information through a network, receives a public key transmitted based on the specific information through the network, and stores the received public key. Further, the data processing device receives print data and encrypted data corresponding to the print data, decrypts the received encrypted data by using the stored public key, and prints the received print data if the data after it was decrypted is specific data. Meanwhile, the data processing device does not print the received print data if the data after it was decrypted is not the specific data.