Abstract

When the master or host computer receives an incoming call, a random number is generated that is then encrypted and sent to the remote user station that placed the initiating call. If a response is not returned from the requester within a preselected time period, the master station disconnects the incoming call. When a timely and proper response to the master stations's encrypted random number is received at the master station, the response is decrypted and compared to a stored list that identifies the authorized remote terminals. After a proper remote station identification, the connection between the host computer and the requesting remote station is maintained. An authorized remote station that initiated the call to the master computer, provides the proper response to the master computer's encrypted random number by decrypting the message to determine the random number and then transmitting its identification number to the host computer is encrypted format, using the random number as the encryption key. The mast station decrypts the response to determine the identification number of the remote station which initiated the call. The user terminal identification number and its software for decrypting messages from the host computer are maintained in volatile storage. If the user terminal is removed from its proper location and reinstalled elsewhere, the interruption of electrical power wipes out the data stored in the user terminal. When reconnected the user terminal is incapable of responding to challenges from the host computer.