A method for decreasing the risk of unauthorized access to an embedded node in a secure subsystem of a process control system includes receiving a message comprising a message header and a message payload, and determining that the message is an unlock message configured to access one or more protected functions of the embedded node, at least by analyzing a bit sequence of one or more bits in the message header. The method also includes determining whether a manual control mechanism has been placed in a particular state by a human operator, and, based upon those determinations, either causing or not causing the embedded node to enter an unlocked state in which one or more of the protected functions are accessible.