Communication apparatus, data communication method, and network system

A communication apparatus, comprising:

• a storage part configured to store a first key generated according to authentication with a transmission source;
• a control part configured to store, on a database, a storage destination of the first key, identification information of the transmission source, and first information remaining unchanged regardless of the initialization of a coupling status and corresponding to the transmission source, with the storage destination of the first key, the identification information and the first information mapped to each other;
• an acquisition part configured to acquire a public key from the transmission source holding the identification information responsive to the first information stored on the storage part if the identification information of the transmission source has changed in response to the initialization of the coupling status;
• and
• a calculation part configured to generate an encryption key for use in encryption and decryption of data transmitted by the transmission source, based on the first key responsive to the first information, and the public key.

A communication method, comprising:

• storing on a storage part a first key generated according to authentication with a transmission source, identification information of the transmission source, and first information remaining unchanged regardless of the initialization of a coupling status and corresponding to the transmission source, with the first key, the identification information and the first information mapped to each other;
• acquiring a public key from the transmission source holding the identification information responsive to the first information stored on the storage part if the identification information of the transmission source has changed in response to the initialization of the coupling status;
• and
• generating an encryption key configured to use in encryption and decryption of data transmitted by the transmission source, based on the first key responsive to the first information, and the public key.

A network system, comprising:

• a first communication apparatus including a first storage part configured to store an authentication key shared according to authentication with a transmission source, identification information of the transmission source, and first information remaining unchanged regardless of the initialization of a coupling status and corresponding to the transmission source, with the authentication key, the identification information and the first information mapped to each other;
• and
• a second communication apparatus including a second storage part configured to store an authentication key shared according to authentication with a transmission destination,
• wherein the first communication apparatus comprises a requesting part configured to send a coupling request to the transmission source if the identification information of the transmission source has changed in response to the initialization of the coupling status, the transmission source holding the identification information responsive to the first information stored on the storage part.