Secure communication equipment and secure transmission system

A secure transmission system wherein at least first and second communication equipments are connected to one another via a transmission medium;

• wherein said first communication equipment includes:
• first receiving means for receiving a signal supplied from said second communication equipment via said transmission medium;
• converting means for generating an encrypted signal by encrypting an information signal to be transmitted to said second communication equipment, by use f a signal corresponding to said received signal from said second communication equipment, output from said first receiving means;
• and first transmitting means for providing said encrypted signal onto said transmission medium;
• wherein said second communication equipment includes:
• information storage mans for storing, as key information, a signal corresponding to an information signal to be transmitted to said first communication equipment;
• second transmitting means for providing said transmission signal onto said transmission medium;
• second receiving means for receiving said encrypted signal supplied from said first communication equipment via said transmission medium;
• and inverse conversion means for decoding said encrypted signal received by said second receiving means, through utilization of said key information corresponding to the preceding transmitted information signal provided from said information storage means and for outputting said decoded information signal;
• wherein third communication equipment identical in construction with said second communication equipment is provided, said transmission medium is an optical fiber transmission line, and said second and third communication equipments are connected by optical directional splitting means to said optical fiber transmission line;
• wherein said converting means of said first communication equipment includes first and second conversion parts whereby information signals to be transmitted to said second and third communication equipments are encrypted using signals received therefrom, said first transmitting means includes multiplexing means for multiplexing said encrypted signals from said first and second conversion parts and an optical transmitting circuit for providing said multiplexed signal onto said optical fiber transmission line, said first receiving means includes a first optical receiving circuit for receiving a multiplexed signal from said optical fiber transmission line and demultiplexing means for demultiplexing said multiplexed signal received from said first optical receiving circuit into signals received from said second and third communication equipments;
• and
• wherein said second receiving means of each of said second and third communication equipments includes a second optical receiving circuit for receiving a multiplexed signal from said optical directional splitting means and a demultiplexing circuit whereby the received signal destined for the concerned one of said second and third communication equipments is demultiplexed from said received multiplexed signal.

A secure transmission system wherein at least first and second communication equipments are connected to one another via a transmission medium;

• wherein said first communication equipment includes:
• first receiving means for receiving a signal supplied from said second communication equipment via said transmission medium;
• converting means for generating an encrypted signal by encrypting an information signal to be transmitted to said second communication equipment, by use f a signal corresponding to said received signal from said second communication equipment, output from said first receiving means;
• and first transmitting means for providing said encrypted signal onto said transmission medium;
• wherein said second communication equipment includes:
• information storage mans for storing, as key information, a signal corresponding to an information signal to be transmitted to said first communication equipment;
• second transmitting means for providing said transmission signal onto said transmission medium;
• second receiving means for receiving said encrypted signal supplied from said first communication equipment via said transmission medium;
• and inverse conversion means for decoding said encrypted signal received by said second receiving means, through utilization of said key information corresponding to the preceding transmitted information signal provided from said information storage means and for outputting said decoded information signal;
• and
• wherein third communication equipment identical in construction with said second communication equipment is provided and is connected via said transmission medium to said first communication equipment;
• wherein said first receiving means of said first communication equipment includes a first receiving circuit for receiving via said transmission medium a multiplexed signal composed of signals sent out from said second and third communication equipments and multiplexed with each other, demultiplexing means for demultiplexing said multiplexed signal into received signals from said second and third communication equipments, first and second information memories for storing, as pieces of key information, signals corresponding to information signals to be transmitted to said second and third communication equipments, and first and second inverse conversion parts whereby said demultiplexed received signals are decoded using said pieces of key information from said first and second information memories corresponding to said demultiplexed received signals, respectively, to thereby obtain decoded information signals;
• wherein said converting means of said first communication equipment includes first and second conversion parts whereby information signals to be transmitted to said second and third communication equipments are encrypted using said decoded information signals from said first and second inverse conversion parts to thereby obtain encrypted information signals, and said first transmitting means includes multiplexing means for multiplexing said encrypted information signals from said first and second conversion parts and a first transmitting circuit for providing said multiplexed signal onto said transmission line;
• and
• wherein said second receiving means of each of said second and third communication equipments includes a second receiving circuit for receiving said multiplexed signal via said transmission line and a demultiplexing circuit whereby a received signal destined for a particular one of said communication equipments is demultiplexed from said received multiplexed signal and is then provided to said inverse conversion means, and said second transmitting means includes a conversion part whereby an information signal to be transmitted to said first communication equipment is encrypted using a signal corresponding to said decoded information signal from said inverse conversion means and a second transmitting circuit for providing said encrypted information signal onto said transmission medium.

Secure communication equipment comprising:

• receiving means for receiving a signal supplied via a transmission medium;
• converting means for producing an encrypted signal by a logical conversion of a transmission information signal through utilization of at least one part of a signal corresponding to said received signal from said receiving means;
• transmitting means for providing said encrypted signal onto said transmission medium;
• information storage means for storing, as key information, a signal corresponding to said transmission information signal;
• inverse conversion means for obtaining a decoded information signal by decoding said received signal from said receiving means through an inverse logical conversion of said received signal by use of said key information read out of said information storage means;
• said converting means including first random pattern generating means for generating a random pattern through use of at least one part of said signal corresponding to said received signal, and first logical operation means for performing a logical operation of said random pattern from said first random pattern generating means and said transmission information signal and outputting said encrypted signal;
• and
• said inverse conversion means including second random pattern generating means for generating a random pattern through use of at least one part of said key information read out of said information storage means, and second logical operation means for performing a logical operation of said random pattern from said second random pattern generating means and said received signal and outputting said decoded information signal.