Method and apparatus for transmitting encoded data from a transmitting station to a receiving station wherein the transmitting and receiving data stations contain data terminal equipment, cipher equipment and a transmission unit and wherein the data is transmitted from the cipher equipment in the form of user data (BD) in the form of data blocks (DB) which contain a heading (K) with control information and wherein at least one of the data blocks (DB), the user data (BD) are replaced by the cipher equipment associated data (SD) and wherein the heading (K) remains unchanged. The data block which has been replaced by the cipher associated data is again generated and is subsequently transmitted.