An intermediary third-party receives, from a master device, a batch of pre-generated secure commands; plays it so as to send sequentially, to a slave device, the commands. The batch includes an initial command indicating the establishment of a channel secured with a session key dependent on a sequence counter, and second commands protected by a MAC code that is a function of the session key. An update of the sequence counter in non-volatile memory of the slave on each new establishment of a secure channel renders the pre-generated batch obsolete by virtue of a new session key. In order to allow the batch to be replayed, the invention provides for each update value of the counter to be temporarily stored in volatile memory, and for the current value to be overwritten in non-volatile memory on predefined events, including a test counter reaching a maximum number of replays.