Abstract: A secure supervisory control and data acquisition (SCADA) system includes a SCADA control host system and any number of remote terminal unit (RTU) systems. Each RTU system includes an RTU transceiver, an RTU and a remote security device (RSD) coupling the RTU to the RTU transceiver. The SCADA control host system includes a SCADA control host configured to exchange SCADA information with each of the RTUs in a SCADA format, and a host security device (HSD) coupling the SCADA control host to a host transceiver. The host transceiver is configured to establish communications with each of the plurality of RTU transceivers. The HSD communicates with the RSDs to transparently encrypt the SCADA information using a cryptographic protocol that is independent of the SCADA protocol to thereby secure the communications between the HSD and each of the RSDs.