Network device and network system

A network device connected via a bus with a plurality of network devices, comprising:

• an authentication unit that executes authentication based upon message authentication information included in data transmitted, via the bus, by one of the plurality of network devices acting as a sender device;
• a processing unit that invalidates the data upon determining that unauthorized data have been transmitted by the sender device impersonating another network device among the plurality of network devices if the authentication fails;
• and
• a first table enabling management with regard to whether or not the data are allowed to be transmitted via the bus;
• a second table enabling management of a key to be used for the authentication for the data by the authentication unit;
• and
• a data format decision-making unit that makes a decision while the data are being transmitted as to whether or not the data correspond with the first table and the second table, wherein:
• the processing unit invalidates the data while the data are being transmitted if the data format decision-making unit decides that the data do not correspond with at least one of the first table and the second table, as well as if the authentication executed by the authentication unit has failed.

A network system, comprising:

• a sender device;
• and
• a network device connected via a bus with the sender device, comprising:
• an authentication unit configured to execute authentication based upon message authentication information included in data transmitted, via the bus, by the sender device;
• and
• a processing unit configured to:
• determine, if the authentication fails, that unauthorized data have been transmitted by the sender device impersonating another network device among a plurality of network devices;
• and
• invalidate, upon the determination, the data by generating a value in the data.