Secure communication system

A method for providing communications between STU-III terminals over narrow bandwidth digital circuits, comprising:

• providing secure and non-secure information carried by analog voiceband signals from a first STU-III terminal;
• receiving the provided information carried by analog voiceband signal(s) from the first STU-III terminal and distinguishing between secure and non-secure information carried by the received analog voiceband signals;
• converting the analog voiceband signals into digital baseband data;
• transmitting the digital baseband data;
• receiving the transmitted digital baseband data;
• converting the received digital baseband data into analog voiceband signals carrying the secure and non-secure information provided by the first STU-III terminal;
• and
• providing the analog voiceband signals to a second STU-III terminal.

A method of establishing secure communication between a first STU-III terminal system and a second STU-III terminal system, each of the first and second STU-III terminal systems includes a digital voice codec for transmitting/receiving telephone signals, and a secure interface unit for transmitting/receiving secure telephone signals, the method comprising:

• transmitting from the first STU-III terminal system a predetermined tone signal;
• receiving by the second STU-III terminal system the predetermined tone signal;
• and
• disconnecting the digital voice codec and connecting the secure interface unit of the second STU-III terminal system in response to receiving the transmitted predetermined tone.

A communication system, comprising:

• a first secure communication terminal for providing analog voiceband data;
• a first processing circuit connected to receive the analog voiceband data from the first secure communication terminal and for converting the received analog voiceband data into secure baseband data, said first processing circuit transmitting the secure baseband data;
• a second processing circuit connected to receive the transmitted secure baseband data from the first processing circuit, and for converting the received secure baseband data into analog voiceband data;
• a second secure communication terminal for receiving the analog voiceband data from said second processing circuit;
• and
• a satellite communication link;
• wherein said secure baseband data is transmitted from said first processing circuit via said satellite communication link, and wherein at least one of said first and second secure communication terminals is a STU-III terminal.

A communication system, comprising:

• a first secure communication terminal for providing interchangeably both secure and non-secure information carried by analog voiceband signal(s);
• a first processing circuit connected to receive the analog voiceband signal(s) from the first communication terminal and for converting the received analog voiceband signal(s) into digital baseband data having a nominal rate of 9.6 kbit/s or less, said first, processing circuit operating interchangeably and automatically on secure and non-secure information carried by analog voiceband signals as a user of the first communication terminal chances between secure and non-secure information, and said first processing circuit providing the digital baseband data for transmission;
• a second processing circuit connected to receive the transmitted digital baseband data, and for converting the received digital baseband data into analog voiceband signal(s), said second processing circuit operating interchangeably and automatically on the received secure and non-secure information corresponding to the secure and non-secure information, respectively, provided to the first processing circuit;
• and
• a second secure communication terminal for receiving the analog voiceband signal(s) from said second processing circuit;
• wherein said first processing circuit includes a signal discriminator for distinguishing between secure and non-secure information carried by analog voiceband signal(s) received from said first secure communication terminal.

A communication system, comprising:

• a first secure communication terminal for providing interchangeably both secure and non-secure information carried by analog voiceband signal(s);
• a first processing circuit connected to receive the analog voiceband signal(s) from the first secure communication terminal and for converting the received analog voiceband signal(s) into digital baseband data, said first processing circuit operating interchangeably and automatically on secure and non-secure information carried by analog voiceband signals as a user of the first communication terminal changes between secure and non-secure information, and said first processing circuit providing the digital baseband data for transmission;
• a satellite communication link;
• a second processing circuit connected to receive the transmitted digital baseband data, and for converting the received digital baseband data into analog voiceband signal(s), said second processing circuit operating interchanqeably and automatically on the received secure and non-secure information corresponding to the secure and non-secure information, respectively, provided to the first processing circuit;
• and
• a second secure communication terminal for receiving the analog voiceband signal(s) from said second processing circuit;
• wherein said first processing circuit includes a signal discriminator for distinguishing between secure and non-secure information carried by analog voiceband signal(s) received from said first secure communication terminal, and
• wherein said digital baseband data is provided from said first processing circuit to said second processing circuit via said satellite communication link.

A communication unit comprising:

• a secure communication terminal operable to perform at least one of (1) providing secure information carried by analog voiceband signal(s);
• (2) receiving secure information carried by analog voiceband signals(s);
• (3) providing non-secure information carried by analog voicebind signals(s);
• and (4) receiving non-secure information carried by analog voiceband signal(s);
• and
• a processing circuit operable to perform interchangeably and automatically a first, second, third and fourth function,
• wherein said first function comprises:
• receiving secure information carried by analog voiceband signal(s) output by the secure communication terminal, converting the received voiceband signal(s) carrying the secure information into digital baseband data having a nominal rate of 9.6 kbit/s or less, and providing the digital baseband data for transmission,
• wherein said second function comprises:
• receiving transmitted secure information carried by digital baseband data having a nominal rate of 9.6 kbit/s or less and converting the received digital baseband data into analog voiceband signal(s) carrying secure information to be output to the secure communication terminal,
• wherein said third function comprises receiving transmitted digital baseband data containing non-secure information and having a nominal rate of 9.6 kbit/s or less and converting the received digital baseband data into analog voiceband signal(s) carrying non-secure information to be output to the secure communication terminal;
• and
• wherein said fourth function comprises receiving non-secure analog voiceband signal(s) carrying non-secure information output by the secure communication terminal and converting the received voiceband signal(s) carrying non-secure information into digital baseband data having a nominal rate of 9.6 kbit/s or less, and providing the digital baseband data for transmission.

A communication method from a STU-III terminal over narrowband digital circuits, comprising:

• providing, from said STU-III terminal, secure and non-secure information carried by analog voiceband signals;
• distinguishing between the provided secure and non-secure information carried by analog voiceband signals automatically and interchangeably;
• receiving the analog voiceband signal(s) and converting the received analog voiceband signal(s) into digital baseband data;
• and
• transmitting the digital baseband data.