Abstract: An encryption/decryption unit (EDU) and method for determining a data encryption key used in encrypting and decrypting data transmitted over a non-secure communication link. Each EDU includes a central processing unit (CPU) that controls its operation, random access memory (RAM) in which one or more sets of seed keys are stored, and a data encryption standard (DES) coprocessor that implements a data encryption algorithm developed by the U.S. National Bureau of Standards. The CPU includes special circuitry enabling it to operate in an encrypted mode so that it cannot be interrogated to discover the program or data stored therein. Each EDU randomly generates a pointer, bytes of which determine the number of times that a loop is repeated in which values (initially determined by two of the seed keys) are XORed together and encrypted using one of the seed keys to determine a portion of the data encryption key (DEK).

Abstract: A 911 emergency response system that includes a location identification module, preferably in solid state circuit form, associated with each residence or each extension of a PBX is disclosed. Preferably, the location identification modules are powered by telephone line voltage. A location identification module is enabled when its associated telephone goes off-hook and an emergency code, e.g., 911 is dialed. Thereafter, in response to an inquiry from the emergency response center that receives the emergency call, the location identification module sends the location of the associated telephone to the emergency response center operator where the location is displayed on a dispatcher's console.

Abstract: A polling controller (21) for a polling system in which a central station (11) sequentially contacts a series of remote stations (13) in order to transmit data to or receive data from the remote stations is disclosed. The polling controller (21) is connected between the telco terminals of a central station modem (23) and a telco line (18). When the central station modem (23) goes off-hook, a DTMF transceiver and answer tone detector (45) is connected to the telco line (18). When a dial code that follows the telephone number of the remote station being called by the central station modem is detected, the central station modem is placed on hold. Thereafter, a transfer code, which may be the same as the dial code, is sent to the called remote station (13). In response, a switch (31) at the remote station (13) connects its telco line (18) to a port, determined by the nature of the dial code, and transmits an answer tone to the polling controller (31).

Abstract: A system for exchanging encrypted data between selected devices at stations comprising a network. The system includes an encrypted communications device (ECOM) (12) that selectively encrypts data from one of a plurality of different devices. With the ECOM, a user selectively encrypts voice transmissions from a telephone, facsimile transmissions produced by a facsimile machine, or data transmissions, either from a personal computer (PC) or from a modem connected to a PC for transmission over non-secure telephone lines (18) to another such device connected to an ECOM at the other location. The receiving ECOM initiates secure communications by encrypting a portion of a data encryption key (DEK) that is transmitted back to the first ECOM, which decrypts it and then generates a second portion of the DEK for transmission back to the receiving ECOM. These two portions are then exclusively ORed (XORed) together by each ECOM to determine the DEK for use in encrypting and decrypting data during the current session.

Abstract: An LCD is associated with each phone line. The LCD is powered by the system current in the phone line. When the phone (10) is in an "on-hook" condition, the LCD is energized and it displays a light image of a telephone in an on-hook condition on a solid dark background. When the phone (10) is in an off-hook condition the LCD is turned off causing its liquid crystal compound to become transparent. The LCD working displays a solid light color but an image of a handset appears on this background. This handset image is printed onto the back side of the front glass panel of the LCD in the region that appears as a dark background when the LCD is energized. When a ring is received by the line the LCD flashes back and forth between the two displays at a fast rate. When the line is "on-hold" the LCD flashes between the images at a slower rate.