This standard defines a cryptographic protocol to provide integrity with optional confidentiality for cyber security of substation serial links. It does not address specific applications or hardware implementations and is independent of the underlying communications protocol. The elevated concern of cyber security throughout the power industry has created a need to protect communications to and from substations. This standard defines a cryptographic protocol known as Secure SCADA Communications Protocol (SSCP) that protects the integrity and, optionally, the confidentiality of asynchronous serial communications typically used by control system equipment. SSCP is primarily intended to protect serial SCADA communications, but can be applied to other serial communications, such as the maintenance ports of intelligent electronic devices. SSCP is independent of the underlying communications link and protocol (e.g., Modbus, DNP3), and is appropriate for serial communications over leased lines, dial-up lines, multi-drop links, radio, power line carrier, fiber optic, etc. SSCP is suitable for implementation in new equipment or for deployment in bump-in-the-wire devices retrofitting protection to existing systems.