SECURE FRONT END COMMUNICATIONS SYSTEM AND METHOD FOR PROCESS CONTROL COMPUTERS

摘要

A secure front-end communication system which couples a plu- rality of actively redundant process control computers to a computer network. The system includes a front end computer which is capable of establishing time limited communication contracts with one or more computer entity on the computer network. Each time limited communication contract is based upon an acceptable response to the transmission of an unpredicable signal from the front end computer, such as an encrypted transformation of a pseudo-random number gen- erated by the front end computer. A security table is used to identify the network entities that are permitted to send write command mes- sages to the process control computers to which the front end compu- ter is connected. The front end computer also includes at least one per- missive table which is used to determine whether a write command message from the network entity should be transmitted to the process control computer for which the message was intended.