Method and arrangement for the secure transmission of a message from a transmitter to a receiver

A method for transmitting a message from a transmitter to a receiver, the method comprising the steps of:

• transferring a telegram generated by the transmitter to a transmitter-side access protection device, the telegram containing the message and check data formed with the message, the check data including a security code formed with the message by the transmitter;
• modifying the telegram via the transmitter-side access protection device, the transmitter-side access protection device modifying the telegram by encrypting the check data as a whole or at least a part of the check data containing the security code, the transmitter-side access protection device using a secret key for forming coded data, and in the telegram the coded data replaces the check data which has been encrypted by the coded data resulting in a modified telegram in which the check data is encrypted and the message remains unencrypted in the modified telegram;
• transmitting the modified telegram over a connection being potentially insecure or a potentially vulnerable transmission medium, to a receiver-side access protection device;
• processing, via the receiver-side access protection device, the modified telegram and forwarding a processed telegram to the receiver, wherein the receiver-side access protection device forms the processed telegram by decrypting the coded data using a key complementary to the secret key and replacing the coded data in the modified telegram with decrypted coded data;
• verifying, via the receiver, the processed telegram on a basis of the message contained therein and the check data contained therein, the receiver forming its own check data with the message and comparing the receiver formed check data with the check data contained in the processed telegram;
• and
• rejecting the message, via the receiver, if the receiver formed check data does not correlate with the check data contained in the processed telegram.