A method for transmitting information to a first application and/or a second application from a third application, the first application being executed in a first subnetwork of red type and the second application in a second subnetwork of red type, the third application being executed in a network of black type, each subnetwork of red type having a security level higher than the network of black type, the first and second subnetworks of red type being interconnected via the network of black type by a secure tunnel between a first security gateway of the first subnetwork of red type and a second security gateway of the second subnetwork of red type which apply ciphering and deciphering operations such that each first packet with a smaller size than a second packet results after ciphering in a first ciphered packet with a size less than or equal to the size of the packet resulting from the ciphering of the second packet, characterised in that: - the first application transmits to the second application a nominal sequence of packets, the packets in said normal sequence being ordered in a predefined order according to their respective sizes, and said nominal sequence being such that it is possible to determine unambiguously on reception the size of each packet that would have been removed from said sequence; - network equipment of the network of black type on a mandatory path of said secure tunnel routes to the third application each packet in said nominal sequence after ciphering by the first gateway; - when the third application wishes to transmit said information to the first application and/or the second application, the third application makes modifications to said nominal sequence after ciphering by the first gateway, by deleting at least one packet, each deleted packet being dependent on said information, and propagates the packets of said sequence after ciphering by the first gateway that have not been deleted; - when the third application does not wish to transmit information to the first application and/or the second application, the third application propagates the packets of said nominal sequence after ciphering by the first gateway; - on reception of a sequence of packets supposed to be the nominal sequence of packets, the second application checks whether at least one packet has been deleted by the third application; and - when the second application detects that at least one packet has been deleted by the third application, the second application retrieves said information from the size of each thus deleted packet of said nominal sequence of packets. - the first application transmits to the second application a nominal sequence of packets, the packets in said normal sequence being ordered in a predefined order according to their respective sizes, and said nominal sequence being such that it is possible to determine unambiguously on reception the size of each packet that would have been removed from said sequence; - network equipment of the network of black type on a mandatory path of said secure tunnel routes to the third application each packet in said nominal sequence after ciphering by the first gateway; - when the third application wishes to transmit said information to the first application and/or the second application, the third application makes modifications to said nominal sequence after ciphering by the first gateway, by deleting at least one packet, each deleted packet being dependent on said information, and propagates the packets of said sequence after ciphering by the first gateway that have not been deleted; - when the third application does not wish to transmit information to the first application and/or the second application, the third application propagates the packets of said nominal sequence after ciphering by the first gateway; - on reception of a sequence of packets supposed to be the nominal sequence of packets, the second application checks whether at least one packet has been deleted by the third application; and - when the second application detects that at least one packet has been deleted by the third application, the second application retrieves said information from the size of each thus deleted packet of said nominal sequence of packets.