System which comprises a tachograph (DTCO) and a toll onboard unit as communication partners for data communication, which each have a data interface which is in the form of a vehicle data bus interface, such that the data communication takes place via a vehicle data bus, to which the communication partners can be coupled, and via which the tachograph and the toll onboard unit are coupled to one another, and - the tachograph (DTCO), as a transmitter of data, is designed to determine a cryptographic check value as a function of payload data, which is intended to be transmitted via the data interface to the respective communication partner, and to transmit the cryptographic check value in addition to the payload data to the respective communication partner, and - the toll onboard unit is in the form of a respective data receiver in order to receive payload data and the cryptographic check value associated with the payload data, via the data interface from the respective communication partner, and to check the received payload data for corruptions, as a function of the received cryptographic check value, wherein - each of the communication partners each has at least one secure memory (SMEM) for storage of at least one cryptographic key, - at least one of the communication partners is designed to produce at least one cryptographic key and for encrypted transmission of the at least one cryptographic key that is produced to at least one of the respective communication partners, - the communication partners are designed to receive and decrypt the at least one encrypted cryptographic key, and for secure storage of the at least one cryptographic key in their respective secure memory (SMEM), and - the communication partners are designed to determine the cryptographic check value as a function of the at least one cryptographic key, wherein the communication partners are designed to determine the cryptographic check value as a message authentication code, as a function of the at least one cryptographic key, wherein the communication partners are designed to determine the cryptographic check value as a shortened message authentication code (RMAC), as a function of the at least one cryptographic key and wherein the communication partners are designed to transmit the cryptographic check value in each case together with the associated payload data in one message. - the tachograph (DTCO), as a transmitter of data, is designed to determine a cryptographic check value as a function of payload data, which is intended to be transmitted via the data interface to the respective communication partner, and to transmit the cryptographic check value in addition to the payload data to the respective communication partner, and - the toll onboard unit is in the form of a respective data receiver in order to receive payload data and the cryptographic check value associated with the payload data, via the data interface from the respective communication partner, and to check the received payload data for corruptions, as a function of the received cryptographic check value, wherein - each of the communication partners each has at least one secure memory (SMEM) for storage of at least one cryptographic key, - at least one of the communication partners is designed to produce at least one cryptographic key and for encrypted transmission of the at least one cryptographic key that is produced to at least one of the respective communication partners, - the communication partners are designed to receive and decrypt the at least one encrypted cryptographic key, and for secure storage of the at least one cryptographic key in their respective secure memory (SMEM), and - the communication partners are designed to determine the cryptographic check value as a function of the at least one cryptographic key,