A communication system for transmission of at least one message from a first network of a first information system towards a second network of a second information system, where the first network has a higher security classification than the second network, the system comprising: - a system input connectable to the first network and intended for receiving the message, where the message comprises at least one first metadata related to the operation of the first information system; - a system output connectable to the second network; - an information analysis and filtering unit coupled to the system input and intended for generating a filtered message by filtering the message depending on a filtering signal such that at least one sensitive information related to the at least one first metadata is masked; - an information encryption unit coupled with the information analysis and filtering unit, and intended to generate an encrypted message by encrypting the filtered message depending on an encryption signal; - a data diode circuit coupled to the information encryption unit, and comprising a circuit input and a circuit output, where the data diode circuit is intended to unidirectionally transfer the encrypted message between the circuit input and the circuit output, and where the data diode circuit further comprises a command input and activation means for blocking or allowing the passage of the encrypted message between the circuit input and the circuit output depending on a command signal received at the command input; - a message sending unit coupled between the circuit output and the system output and intended to send a call message comprising the encrypted message; and - a processor coupled to the information analysis and filtering unit, the information encryption unit and the circuit, and intended to generate the filtering signal, the encryption signal and the command signal. - a system input connectable to the first network and intended for receiving the message, where the message comprises at least one first metadata related to the operation of the first information system; - a system output connectable to the second network; - an information analysis and filtering unit coupled to the system input and intended for generating a filtered message by filtering the message depending on a filtering signal such that at least one sensitive information related to the at least one first metadata is masked; - an information encryption unit coupled with the information analysis and filtering unit, and intended to generate an encrypted message by encrypting the filtered message depending on an encryption signal; - a data diode circuit coupled to the information encryption unit, and comprising a circuit input and a circuit output, where the data diode circuit is intended to unidirectionally transfer the encrypted message between the circuit input and the circuit output, and where the data diode circuit further comprises a command input and activation means for blocking or allowing the passage of the encrypted message between the circuit input and the circuit output depending on a command signal received at the command input; - a message sending unit coupled between the circuit output and the system output and intended to send a call message comprising the encrypted message; and - a processor coupled to the information analysis and filtering unit, the information encryption unit and the circuit, and intended to generate the filtering signal, the encryption signal and the command signal.