In a method for securing the transfer of a data stream from a sender device to at least one receiver device, through a network comprising a plurality of nodes connected to one another by a plurality of links, the sender device is connected to an input node in the network and each receiver device is connected to an output node of the network. The method comprises the following steps: a) the transmission of the data stream to the receiver devices through the associated output nodes; b) the informing of the output nodes by the input node that the transmission or maintaining of transmission of the data stream, in clear (i.e. non-encrypted) form necessitates the authentication of the output nodes; c) the reception by the input node of at least one authentication request sent by at least one of said output nodes; d) the authentication by the input node of the output nodes that are destination nodes of the data streams; e) the transmission of the data stream in clear form to, at most, the authenticated output nodes and the stopping of the transmission of the data stream to the other output nodes.