A bidirectional gateway with enhanced security level between a high-security communication network and a low-security communication network. The return pathway from the low-security network to the high-security network comprises a low-speed link. The physical layer of the low-speed link differs from the physical layers involved in the high-security network and the low-security network. The low-speed link having a linking layer according to a protocol differing from the protocols used on the linking layers used on the high-security network and the low-security network. The linking layer of the low-speed link has an authentication protocol to guarantee the data's origin.