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 method for initiating secure communications between two stations. In this method, a first portion of a session data encryption key (DEK1) is randomly generated by an EDU in one of the stations. The DEK1 is then encrypted using a key exchange key (KEK) selected from a table as a function of a check value determined by applying the DEK1 to encrypt a predefined zero function. The encrypted DEK1 is transmitted to the other station, along with an encrypted EDU ID number for the station that generated the DEK1 and a cyclic redundancy check (CRC) value of the KEK table. The encrypted table entry value used to define the KEK is decrypted at the other station, and a check is made to determine if the KEK table CRC and the EDU ID are correct. If not, communication is terminated.

Abstract: An encryption/decryption unit (EDU) that handles management of encryption keys used in the secure exchange of data over non-secure communication links. Each EDU includes a central processing unit (CPU) that controls its operation, random access memory (RAM) in which tables of key exchange keys (KEKs) are stored, and a data encryption standard (DES) coprocessor that implements a data encryption algorithm developed by the U.S. National Bureau of Standards--all comprising a module that is embedded in a potting material. Attempts to remove the potting material either by mechanical or solvent means are likely to result in loss of the data and program code stored in the module. The CPU includes special circuitry enabling it to operate in an encrypted mode so that it can not be interrogated to discover the program or data stored therein. This program enables the EDU to establish secure communications with another similar EDU over a non-secure link.

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: A telephone line to equipment interface circuit, characterized by a high degree of input impedance isolation, is provided for coupling supervisory and information signals from the line to signal utilizing equipment, such as a control unit of a key telephone system. The interface circuit incorporates first and second operational amplifier comparators connected in opposed phase relationship to the tip and ring conductors of a telephone line. The inputs of the comparators are biased so as to produce output signals that change in a predetermined and symmetrical fashion, similar to full wave rectification, in response to normal and reverse polarity supervisory signals applied to the telephone line by a Central Office, PBX, ESS or other signal originating equipment. The output signals produced by the first and second comparators are applied to separate inputs of a logic circuit, formed by a third operational amplifier comparator, which is biased to perform an AND logic function.

Abstract: In a key telephone system of the type that uses the tip and ring conductors of a telephone line to transmit a hold condition control signal between stations, interstation signal-generating and detecting circuitry are provided at first and second stations, respectively, for enabling the first station to actuate, during a hold condition on the line, an audible signalling device, such as a buzzer, located at the second station. The interstation signal is generated on command by selective actuation of a hold switch button at the first station, and is transmitted over the line as an altered hold control signal, which is detected at the second station. Upon such signal detection, a buzzer is energized alerting the second station to the presence of a held call on the line.

Abstract: The exclusion circuit disclosed herein provides for line privacy in a key telephone system of the type in which a control unit provided at each of a plurality of stations can be operated to selectively connect one or more telephone lines to the phone set at the corresponding station. Within each control unit, an exclusion circuit is provided for each telephone line that extends to the control unit, and is connected so as to cooperate with a line condition sensing circuit, a line switching relay, a relay latching circuit and a manually operated line selector switch, all of which are associated with the same line as the exclusion circuit.

Abstract: To convert a multiple line, multiple telephone set installation into a key telephone system, a control unit is provided at each telephone set. The control unit includes a regulated power supply, a control circuit, pushbutton line select and hold switches, and indicator lights packaged in a compact assembly which can be readily attached to the base of a standard telephone set or mounted separately. Electrically controlled switching devices within each control circuit respond to the pushbutton line select switches to couple the telephone set to a selected one of the lines and automatically disconnect the set from the line when the call has been completed. An incoming ringing signal on any one of the telephone lines is detected by the control circuit and the ringing signal is automatically applied to the bell of the telephone set.

Abstract: To convert a multiple line, multiple telephone set installation into a key telephone system, a control unit is provided at each telephone set. The control unit includes a regulated power supply, a control circuit, pushbutton line select and hold switches, and indicator lights packaged in a compact assembly which can be readily attached to the base of a standard telephone set or mounted separately. Electrically controlled switching devices within each control circuit respond to the pushbutton line select switches to couple the telephone set to a selected one of the lines and automatically disconnect the set from the line when the call has been completed. An incoming ringing signal on any one of the telephone lines is detected by the control circuit and the ringing signal is automatically applied to the bell of the telephone set.

Abstract: A control unit mounting and interconnecting apparatus for telephone desk sets is disclosed which includes a base member including a first plate portion for receiving a printed circuit board and configured to lie within and be supported by a metallic base of the telephone desk set. The base member also includes a second plate portion for supporting a control unit, such as one having a plurality of control keys, and a plurality of walls interconnecting the first plate portion and the second plate portion and defining a recess which slips over an upturned flange of the metallic base of the telephone desk set to maintain the base member in position when installed. Structure is provided in the base member for receiving a printed circuit interconnecting element, of flexible insulating material, which provides electrical interconnections between the control unit and the printed circuit board.

Abstract: After discussion of prior art electrical terminations for floor ducts in which a plurality of electrical cables are located, a pull-out receptacle for such floor ducts is disclosed which includes a sleeve configured to be received in an aperture extending between a floor surface and the interior of the floor duct, with the sleeve having a circumferential flange adapted to overlie those portions of the floor surface adjacent to the floor aperture. A recess is provided in a top surface of the sleeve, and an aperture extends from that recess through the sleeve. A closure member is provided which includes a core configured to be received within the sleeve aperture with a reciprocative, sliding fit, and an integral cap configured to be received in the recess. A first passageway is provided in the core, and a second passageway in the cap, the second passageway communicating with the first passageway for allowing electrical cables to be pulled therethrough.

Abstract: The assembly includes a dielectric base having molded structural portions for receiving and mounting a manually operated switch, and for receiving and mounting a plurality of electrical connection terminals that serve to connect lead wires to the switch contacts. The switch contacts and electromechanical switching mechanism are mounted in a preassembled switch body, from which a plurality of substantially rigid electrical connection prongs extend. The base includes a honeycomb-like cluster of terminal receiving recesses and a plurality of prong receiving apertures, one for each recess. The prong receiving apertures extend inwardly of the base from a surface thereof defining a recess for seating the body of the switch, with each aperture opening into a separate one of the terminal receiving recesses through an interior recess sidewall.

Abstract: A plate, such as an escutcheon plate designed to overlie and cover a wall-mounted outlet receptacle, is provided with a centrally-located aperture extending therethrough which is aligned with a central cavity in a body member upon assembly. Both the aperture and cavity are configured to receive and retain a standardized male connector such as that disclosed in U.S. Pat. No. 3,761,869, Hardesty et al. A plurality of first grooves are provided in a lower surface of the central cavity of the body member and communicate with a corresponding plurality of bores through the body member, each of which in turn communicates by means of a second groove with one of a plurality of terminal-receiving cavities in the body member. A conductor is located in each one of the plurality of bores and has a first wire spring contact portion located within one of the plurality of first grooves and partially extending into the central cavity for engaging a corresponding contact in the male connector.