Abstract: A method and apparatus for providing secure electronic communications over a communications medium between first and second locations is disclosed. A data device for generating and/or receiving data is located at each of the locations. A composite modem is coupled to each data device. Each composite modem comprises a microprocessor controller operating under program control for determining the configuration of the message to be transmitted from one data device to the other. The controller is coupled to a switching circuit which selects, in dependence on a configuration message generated by the controller, the configuration of the message to be transmitted. A plurality of characteristic controllers are coupled to the switching circuit.