PURPOSE: To establish initial synchronism in two-way secret communication using a telephone line, by returning a confirmation synchronizing signal from the 2nd terminal when a synchronizing signal sent from the 1st terminal is detected.
CONSTITUTION: A sound transmission signal transmitted from transmitter 3 is inputted to secrecy device 11, which performs secrecy processing according to prescribed rules to make the input into a secrecy signal. This processing is performed by digitizing the sound signal and then by performing arithmetic using a binary random-number string. Sound detecting circuit 12 detects the output of device 11 to open gate switch circuit 13 and also permits gate switch circuit 14 to cut off the sound input from hybrid circuit 2. On arrival of a dial signal at this communication terminal from another communication terminal, transmission-reception control circuit 17 operates to set device 11 in initial sunchronizm mode, and initial synchronizing signal SYNC1, transmitted at intervals of a prescribed period, is received and confirmed by another terminal, which returns synchronizing signal SYNC2 to establish synchronism at the timing of its reception.
SUGIYAMA FUMIO
NAKAMURA MAKOTO
