Abstract: A secrecy device connected between a telephone handset and a telephone body, which comprises a secrecy circuit for modulating a voice signal received from the handset on a predetermined modulation system basis to send a modulated voice signal to the telephone body and for demodulating a modulated voice signal received from the telephone body on a predetermined demodulation system basis to send a demodulated voice signal to the handset, and a detection circuit for detecting presence of a connection of a wiretapping telephone set to a line connecting two communicating party telephone sets.

Abstract: Each subscriber unit (108) operating on a communication system (100) selects either encrypted or unencrypted transmission mode as a current transmission mode. Before participating in a communication, each subscriber unit (108) receives a message identifying an authorized transmission mode. Only when the current transmission mode corresponds to the authorized transition mode may each subscriber unit (108) transmit so as to participate in the communication.

Abstract: A passive, all optical communications network is provided in which a single optical source in a central station serves many outstations (e.g., telephones in customers' premises). Time division multiplexed optical signals from a laser source are transmitted along a single optical fibre (14) from a central station (4). The signal is split between several secondary fibres at a first splitter (10) (e.g., an array of passive couplers) and between further sets of fibres at a second set of splitters (12). At this stage there are 120 individual fibres to customers' premises (8). Digital speech or data is sent back to the central station by a laser in the customers' premises operating in a low duty-cycle mode. The 120 data streams are interleaved at the branching points.

Abstract: A low probability of intercept communication system (CCSK)--modulates information signals onto an inverse fast Fourier transformation of a large number of simultaneous frequencies that have been determined to be reasonably `quiet` within a given system bandwidth, so as to produce a time domain pulse waveform. The amplitude of each transmitted frequency is weighted. Within the receiver equipment of each participant in the system, the incoming pulse waveform produced by the inverse fast Fourier transformation mechanism at the source is coupled to a fast Fourier transform operator, so as to separate the time domain signal into a plurality of frequency components that contain the modulated data. These components are then convolved with a replica of the plurality of quiet channels to derive a time domain output waveform from which the data modulation can be identified and recovered.

Abstract: An improved fault tolerant processor arrangement is described. In accordance with this invention, redundant processors are coupled in parallel in a master/slave configuration wherein means are provided for disabling the respective outputs of the processors. The master processor includes means for generating a periodic pulse which is detected by the slave processor. As long as the periodic pulse is detected by the slave processor, the output of the master processor remains enabled and the output of the slave processor is disabled. If the periodic pulse is not detected by the slave processor, the slave processor disables the output of the master processor wherein the output of the slave processor becomes enabled.

Abstract: An improved fault-tolerant arrangement for use in a multichannel data encryption unit is disclosed. In accordance with the teachings of this invention, a data encryption system includes a plurality of data encryption devices and a host computer and display system wherein a data bus which couples the host computer and data encryption devices includes first and second power supply lines. Each of the respective data encryption devices includes means for automatically deriving power from either of the first or second power supply lines based on the presence of power thereon. Accordingly, fault-tolerant operation is provided wherein the respective data encryption devices continue operating even in the event of the failure of the host computer.

Abstract: A stand-alone utility device for perceptible reproduction of signals, for example a radio receiver or a TV receiver, is protected from theft because the reproduction quality of the signals is disturbed in the case of unauthorized use by regular suppression of the signal, by generating bleeps or by a combination of both.

Abstract: A passive, all optical communications network is provided in which a single optical source in a central station serves many outstations (e.g. telephones in customers' premises). Time division multiplexed optical signals from a laser source are transmitted along a single optical fibre (14) from a central station (4). The signal is split between several secondary fibers at a first splitter (10) (e.g. array of passive couplers) and between further sets of fibers at a second set of splitters (12). At this stage there are 120 individual fibres to customers' premises (8). Digital speech or data is sent back to the central station by a laser in the customers' premises operating in a low duty-cycle mode. The 120 data streams are interleaved at the branching points.

Abstract: A system and method are disclosed for preventing intelligible interception of information signals transmitted over a two-direction line. A masking signal is applied through a hybrid circuit at the receiving end of the line, and this masking signal, which appears on the line together with the information signal, prevents intelligible decoding. The masking signal includes a series of frequencies which are sequentially applied. Only at the receiving end of the line, where the hybrid circuit attenuates the masking signal which it receives at its receive port, can intelligible decoding take place. The amplitude of the information signals is sensed at the receiving end and the amplitude of the masking signals on the line is adjusted to be great enough to provide security, by confusing an eavesdropping detector, yet small enough at the receiving end so that the receiving detector is not confused.

Abstract: A soft logic cryptographic circuit that can be reprogrammed with various cipher algorithms. The cryptographic circuit can be manufactured in a non-secure environment because a security sensitive cipher algorithm can be programmed after the manufacturing process.

Abstract: An information encryption method particularly intended for a communication system in which bidirectional multiplexed communications of the point-to-multipoint type are derived between a switching exchange and plural terminal stations. The switching exchange transmits first multiplexed words respectively destined for the terminal stations. The terminal stations supply second words which are multiplexed and transmitted towards the switching exchange. In the switching exchange, informations concerning transmission errors detected in the second words are derived and transmitted towards the terminal stations, and the first words are encrypted as a function of second words previously received free of transmission error in the switching exchange. In each of the terminal stations, the informations concerning the transmission errors are detected, and the second words transmitted from the terminal station and received free of transmission error by the switching exchange are memorized.

Abstract: Debug routine accessing system using special keys in the form of floppy disks for unlocking debug routines embedded in the operating software of a reproduction machine, each debug routine having a key number, with the floppy disks having various key numbers for different ones of the debug routines so that on insertion of a selected disk in the machine floppy disk port, the key number is read from the disk and compared with the key numbers of the various debug routines until a match is found enabling the debug routine represented by the key number to be accessed.

Abstract: Data security is provided using an encryption/decryption algorithm which attaches at the primitive BIOS level of the operating system automatically during the power-on self-test routines. The encryption/decryption process is implemented by intercepting the removable media or floppy diskette interrupt in order to add additional interrupt handling routing instructions which perform the encryption and decryption of data passed between the diskette controller and the data transfer buffer area within system RAM. Bitwise alteration of the data in a predefined relationship is used to encrypt and decrypt. The encryption/decryption system attaches before the computer power-up sequence renders data entry hardward active, hence the user cannot readily override the security system. Data stored on nonremovable media such as hard disk media is not encrypted, thereby preserving the integrity of more permanent data.

Abstract: An encryption key, required to encrypt and decrypt data according to a predefined algorithm is usually retained in a volatile memory device. Detection of loss of the key or corruption of the key is frequently possible only be means of the encryption circuit itself testing the key. Automated and repetitive testing of encryption keys by means of a processor or a control circuit periodically requesting the encryption circuit to test an encryption key minimizes data loss and system down time due to corrupted or lost keys.

Abstract: A technique for avoiding accidental actuation of communications system devices which respond to a predetermined pattern of signals. In accordance with the present invention, data to be transmitted through the communications system is scrambled so as to reduce the likelihood of the customer data mimicking the predetermined pattern of signals. At the receiving end, the scrambled customer data is descrambled to its original condition.

Abstract: In a cable television system in which the individual subscriber's converter/tuner is located outside the subscriber's premises in an external control unit ("ECU") and controlled remotely via a subscriber processing unit ("SPU") connected to the ECU by a drop cable, data transmitted from the SPU to the ECU (e.g., channel selection data) is verified by transmitting similar echo back data from the ECU to the SPU. The SPU compares the original and echo back data to assure that the ECU correctly received the original data.

Abstract: In a system in which data between a master and remote location is encrypted by using the DES algorithm, the status of security devices at the remote location is monitored from a centralized security station. A message indicative of the status of the security devices is used to generate an initializing vector (IV). This IV is then used to encrypt the data from the remote to the master.

Abstract: An error correction code data communication system scrambles and descrambles both non-coded data and coded data by using substantially the same code process at the opposite ends of a transmission path. The frequency of the occurrence of an error correction pulse in a decoder is monitored to set up synchronization for descrambling. The transmitter includes an encoder for adding a correction code to a data signal to be transmitted, and a scrambler for randomizing the data signal. The receiver includes a descrambler for descrambling the data signal which was randomized by the scrambler, and a decoder for correcting a code error responsive to the error correction code. The scrambler modulo 2 adds an output of a random signal generator to both an input data signal and an output data signal. The descrambler modulo 2 adds an output of a second random signal generator to both an input data signal and an output data signal.