In-vehicle communication system with verification failure holding circuit

An apparatus comprising:

• a processing unit configured to receive a message including a public key certificate having device information specifying a sender, a public key, and data to be used when verification of the public key certificate succeeds;
• and
• a first holding circuit configured to store device information and a public key of a previously received message whose public key certificate has failed verification by the processing unit,
• wherein when the message is received, the processing unit checks whether or not the device information included in the message matches the device information stored in the first holding circuit, and
• wherein when said check indicates a match with stored device information and if the public key and a signature of the public key certificate of the received message are not stored in the first holding circuit, the processing unit is configured to verify a signature of the received message after a verification of the public key certificate of the received message is successful, and
• wherein when said check indicates a match with stored device information and if the public key and signature of the public key certificate stored in the first holding circuit matches the public key and the signature of the public key certificate of the received message, the processing unit is configured to treat verification of the signature of the received message as a failure.