This invention relates to a method for the transmission of management data to at least one multimedia unit or a group of multimedia units. This method is characterised in that said management data is sent in the form of at least one authorisation message encrypted by means of at least one synchronisation key (SK), the sending of said at least one authorisation message being repeated cyclically and intended for said multimedia unit or said group of multimedia units, and in that the synchronisation key is modified at least during each cycle.