A home server includes a proxy facility and is provided between a user terminal and an electronic market server for executing authentication and encryption to the electronic market server, instead of the user terminal, in an electronic commercial transaction. The proxy facility includes: an establishing unit for establishing an encrypted communication session between the user terminal and the home server, using public/secret keys of the user terminal and an electronic signature both transmitted from the user terminal; a proxy unit for executing authentication of a certificate and exchanging a common key between the home server and the electronic market server, using public/secret keys of the electronic market server; and an information unit for informing the common key to the user terminal through the encrypted communication session; wherein an encrypted communication is executed between the user terminal and the electronic market server by using the common key that was exchanged between the home server and the electronic market server.