There is provided a communication system in which a network device and an information processing device are communicatably connected to each other through a network. The network device comprises a certificate providing unit to transmit an electronic certificate to the information processing device through the network; and a printing unit configured to print an image of a public key corresponding to the electronic certificate. The information processing device comprises: a certificate reception unit to receive the electronic certificate from the certificate providing unit through the network; an image output unit to generate and output an image of the public key described in the received electronic certificate; and an installation unit configured to install the electronic certificate onto the information processing device in response to a fact that the generated image of the public key is output by the image output unit and a command for installation of an electronic certificate is received.