Abstract: In a communication system, a management node includes: a high-order count value holding unit holding a high-order count value; and a high-order count value distribution unit updating the high-order count value under a high-order update condition and distributing the updated high-order count value to normal nodes. In the communication system, a normal node includes: a count value holding unit holding a count value; a low-order update unit updating a low-order count value held in the count value holding unit under a low-order update condition; and a high-order update unit updating a high-order count value held in the count value holding unit to the high-order count value distributed from the management node together with a reset of the low-order count value.

Abstract: A communication apparatus includes a counter, a reception portion, an update portion, a code generation portion, a determination portion, and a transmission portion. The reception portion receives a communication data from a different one of the communication apparatus. The update portion updates a value of the counter. The code generation portion generates a message authentication code based on the communication data received by the reception portion, the value of the counter, and a common key. The determination portion determines whether the message authentication code generated by the code generation portion matches a message authentication code set in the communication data. The transmission portion transmits a synchronization request when a number of times that the determination portion determines a mismatch between the message authentication codes becomes equal to or more than a predetermined number of mismatches.

Abstract: An abnormality detection device includes: a receiver, a reception predictor, frame information storage, and an abnormality determiner. The receiver receives a communication frame via a communication network. The frame information storage stores information regarding the communication frame. The reception predictor calculates and sets a predicted time range including a scheduled reception time of the communication frame of a target frame type from among a plurality of frame types received by the receiver by referencing the frame information storage and the reception time of the communication frame when the communication frame is received. The abnormality determiner determines the target communication frame is an abnormal frame when the target communication frame is received at a time outside the predicted reception range.

Abstract: A communication apparatus includes a counter, a reception portion, an update portion, a code generation portion, a determination portion, and a transmission portion. The reception portion receives a communication data from a different one of the communication apparatus. The update portion updates a value of the counter. The code generation portion generates a message authentication code based on the communication data received by the reception portion, the value of the counter, and a common key. The determination portion determines whether the message authentication code generated by the code generation portion matches a message authentication code set in the communication data. The transmission portion transmits a synchronization request when a number of times that the determination portion determines a mismatch between the message authentication codes becomes equal to or more than a predetermined number of mismatches.

Abstract: A communication system includes multiple nodes connected with each other. Each of the multiple nodes generates a message authentication code using a count value of a counter. The multiple nodes include a transmission node and a reception node. The count value of the counter is includes a high-order count value and a low-order count value. In the transmission node, a normal message generation portion generates a normal message to include a transmission data, the low-order count value, and the message authentication code, and a synchronization message generation portion generates a synchronization message. In the reception node, a message verification portion verifies the received normal message, a resynchronization request portion transmits a resynchronization request of the counter to the transmission node, and a count value update portion updates the high-order count value stored in the reception count value storage portion when the synchronization message is received.

Abstract: In a communication system, a management node includes: a high-order count value holding unit holding a high-order count value; and a high-order count value distribution unit updating the high-order count value under a high-order update condition and distributing the updated high-order count value to normal nodes. In the communication system, a normal node includes: a count value holding unit holding a count value; a low-order update unit updating a low-order count value held in the count value holding unit under a low-order update condition; and a high-order update unit updating a high-order count value held in the count value holding unit to the high-order count value distributed from the management node together with a reset of the low-order count value.

Abstract: A vehicle communication system includes an onboard apparatus, a mobile device, and a key issuing apparatus provided outside the vehicle for issuing a key for cryptographic communication between the mobile device and the onboard apparatus. The mobile device and the onboard apparatus store the key, and perform the cryptographic communication using the key. The key issuing apparatus issues, to the onboard apparatus, the key and validity information indicating validity of the key. The onboard apparatus includes a determination section determining whether a validity ends, and an update request section transmitting a key update request to request the issuance of a new key. When the key update request has been received, the key issuing apparatus issues a new key to the mobile device, and issues a new key and validity information on the new key to the onboard apparatus.