Secrecy device for wiretapping prevention and detection

• Main Authors: AKAGAWA; MASAKI, KOBAYASHI; OSAMU
• Format: Patent
• Language: English
• Published: 24.03.1992
• Subjects: ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; JAMMING OF COMMUNICATION; SECRET COMMUNICATION; TELEPHONIC COMMUNICATION

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. The detection circuit, in response to reception of a request signal generated at the secrecy device of one of the two communicating party telephone sets, generates pseudorandom data and transmits the pseudorandom data to the secrecy device of the request-signal sender telephone set, and, in response to reception of the pseudorandom data, returns as echo-back data the same data as the pseudorandom data to the secrecy device of the pseudorandom-data sender telephone set, and compares the random data generated at the secrecy device of its own telephone set with the echo-back data and when the both data do not coincide with each other, generates a detection output.