CSM_155On a high level, secure communication between a vehicle unit and a tachograph card shall be based on the following steps:U.K.
First, each party shall demonstrate to the other that it owns a valid public key certificate, signed by a Member State Certificate Authority. In turn, the MSCA public key certificate must be signed by the European root certificate authority. This step is called certificate chain verification and is specified in detail in section 10.2
Second, the vehicle unit shall demonstrate to the card that it is in possession of the private key corresponding to the public key in the presented certificate. It does so by signing a random number sent by the card. The card verifies the signature over the random number. If this verification is successful, the VU is authenticated. This step is called VU Authentication and is specified in detail in section 10.3.
Third, both parties independently calculate two AES session keys using an asymmetric key agreement algorithm. Using one of these session keys, the card creates a message authentication code (MAC) over some data sent by the VU. The VU verifies the MAC. If this verification is successful, the card is authenticated. This step is called Card Authentication and is specified in detail in section 10.4.
Fourth, the VU and the card shall use the agreed session keys to ensure the confidentiality, integrity and authenticity of all exchanged messages. This is called Secure Messaging and is specified in detail in section 10.5.