A controller area network bus based security communications system includes a gateway electronic control unit (ECU) and at least one control area network (CAN) bus ECU. The gateway ECU generates a random number, and sends the random number to the at least one CAN bus ECU. A first CAN bus ECU obtains the random number sent by the gateway ECU, and generates a first information authentication code based on a key of a first CAN identifier, the random number sent by the gateway ECU, a count value of the first CAN identifier, and data of a first CAN packet.