A railway safety critical application system substitutes commercial off-the-shelf (COTS) hardware and/or software for railway-domain specific product components, yet is validated to conform to railway safety critical system failure-free standards. The safety critical system uses a pair of tasks executed on a controller of a COTS personal computer or within a virtual environment with asymmetric communications capability. Both tasks receive and verify safety critical systems input message data and security code integrity and separately generate output data responsive to the input message. The first task has sole capability to send complete safety critical system output messages, but only the second task has the capability of generating the output security code. A failure of any of systems hardware, software or processing capability results failure to transmit a safety critical system output message or an output message that cannot be verified by other safety critical systems.