Plain text or information which is to be processed at the transmitter end of the system is formed by groups of plain text or information signals which are separated by separation signals. In the absence of plain information signals there are inserted fill signals between the plain information signal groups, these fill signals likewise being separated by separation signals. At the transmitter end there are enciphered, apart from the plain information signals and possibly the fill signals, all or a part of the separation signals. The signal flow which appears at the transmission path no longer is divided in a clearly recognizable manner into individual packets. In order to render possible at the receiver end of the system separation of information signals and fill signals which are insignificant as to their information content, during the course of the transmitter end enciphering the separation signals between the fill signals are provided with an appropriate characteristic or recognition information.