the present invention relates to the incorporation in the removable cartridge c , as an interface between the usual storage stk and the outside of the aforementioned cartridge , of an encrypting - decrypting module mcd devoid of any non - volatile memory and capable of supporting an encoding key 10 which is assigned prior to each recording session so that all the stored data is encrypted and here is no trace of the aforementioned encoding key left the moment the first power supply cut - off to the module occurs , as a result of a general power supply cut - off , for example via connection 30 , or as a result of the disengagement of the cartridge from the recorder .