Apparatus, system and method for transmitting secure signals over narrow spaced channels

• US 5,305,384 A
• Filed: 09/09/1992
• Issued: 04/19/1994
• Est. Priority Date: 12/04/1990
• Status: Expired due to Fees

• Current Assignee: Chips International Inc.
• Original Assignee: Chips International Inc.
• Inventors: Krause, Lothar A., Ashby, James C., Burkhart, Clark, Vandaveer, Robert L., Favors, Frankie, Tiemann, Roy G.
• Primary Examiner(s): Swann, Tod R.
• Application Number:
  US07/942,661
• Time in Patent Office: 587 Days
• Field of Search: 380/28, 380/29, 380/31, 380/33, 380/34, 380/38, 380/39, 380/40, 380/48, 380/49, 341/72
• US Class Current: 380/29
• CPC Class Codes: H04B 1/667 using a division in frequency subbands for TV signals H04N19/63
• CPC Class Codes: H04K 1/02 by adding a second signal to make the desired signal unintelligible

Abstract

An encryption/decryption device, system and method for providing secure communication over a communication channel. The encryption device includes a radio interface unit connected to a conventional radio, wherein the interface unit selectively couples a codec, signal processor and modem to the transmit and receive path during secure operation. The codec digitally encodes non-secure analog signals and places them in pulse code modulated format. The signal processor then compresses the pulse code modulated signals into voice coded and then digitally encrypted NRZ signals which are then input into the conventional radio for modulating a carrier frequency on an occupied bandwidth approved for 15 KHz to 25 KHz, or as little as 11.4 KHz, spaced channels. The modem can input the digitally encrypted signals using modified frequency modulation to place the modified digitally encrypted signals substantially within the voice passband of 300 Hz to 3200 Hz. The device, system and method incorporates a master prologue sent prior to voice information at a BPS rate different from that of the voice BPS rate. The voice information is sent in blocks with a plurality of resynchronization data frames of bits interlaced between a plurality of voice frames of bits to allow highly reliable late entry and re-entry access. A conventional repeater system can be selectively controlled by a controller device of the present invention for demodulating, error correcting and recompressing the master prologue without descrambling the digitally encoded voice information.

Claims

1. An improved digital encryption device comprising:

a radio interface connected to a conventional radio and adapted to receive a non-secure voice signal;

a codec selectively coupled to said radio interface for receiving said non-secure voice signal and for converting said signal into a pulse code modulated signal;

a signal processor adapted for converting said pulse code modulated signal into a digitally encrypted NRZ signal; and

means for modulating said digitally encrypted NRZ signal on a carrier signal, said modulated carrier signal occupying a necessary bandwidth approved for channels spaced 15 KHz to 25 KHz apart.

2. The improved digital encryption device as recited in claim 1, wherein said modulated carrier signal necessary bandwidth is greater than 11.4 KHz.

3. The improved digital encryption device as recited in claim 1, wherein said modulating means comprises a modem for modified frequency modulating said digitally encrypted NRZ signal to produce a modified digitally encrypted signal having a 300 Hz to 3200 Hz passband.

4. The improved digital encryption device as recited in claim 1, wherein said modulating means comprises a modem for continuous phase modulating said digitally encrypted NRZ signal to produce a modified digitally encrypted signal.

5. The improved digital encryption device as recited in claim 1, wherein said signal processor comprises a voice coder means for compressing said pulse code modulated signal to a rate substantially equal to 4800 bits per second.

6. The improved digital encryption device as recited in claim 1, further comprising a communication channel capable of receiving a modified said digitally encrypted NRZ signal at a rate of at least 2 bits/Hz.

13. The improved digital encryption device as recited in claim 1, further comprising means for transmitting at a rate of at least twice per second a secondary command data block of said modified digitally encrypted signals preceded in each transmission by a master prologue block.

7. An improved digital encryption device comprising:

a radio interface connected within a conventional radio and adapted to receive a non-secure voice signal;

a codec selectively coupled to said radio interface for receiving said non-secure voice signal and for converting said signal into a pulse code modulated signal;

a signal processor adapted for converting said pulse code modulated signal into a digitally encrypted NRZ signal;

a first modem for modified frequency modulating said digitally encrypted NRZ signal to produced a modified digitally encrypted signal occupying a passband between 300 Hz to 3200 Hz; and

a second modem for modulating a carrier signal with said modified digitally encrypted signal, said modulated carrier signal occupying a necessary bandwidth approved for channels spaced 15 KHz to 25 KHz apart.

8. The improved digital encryption device as recited in claim 7, wherein said digitally encrypted NRZ signal comprises a DES-encrypted signal.

9. The improved digital encryption device as recited in claim 7, further comprising a communication channel capable of receiving said modified digitally encrypted signal at a rate of at least 2 bits/Hz.

10. The improved digital encryption device as recited in claim 7, further comprising means for transmitting at a rate of at least twice per second a voice block of said modified digitally encrypted signals preceded in each transmission by a master prologue block.

11. The improved digital encryption device as recited in claim 10, wherein said first modem is selectively capable of transmitting a plurality of bits within said voice block at a faster ate than a plurality of bits within said master prologue.

12. The improved digital encryption device as recited in claim 10, wherein said voice block comprises a plurality of resynchronization data frames of bits interlaced between a plurality of voice date frames of bits.

14. A communication system for providing secure communication over a communication channel comprising:

a conventional radio capable of transmitting and receiving a non-secure voice signal modulated on a carrier signal, said modulated carrier signal occupying a necessary bandwidth approved for channels spaced 15 KHz to 25 KHz apart;

a radio interface unit connected to said radio, said interface comprising;

a codec selectively coupled to receive said non-secure voice signal and convert said non-secure voice signal into a pulse code modulated signal;

a signal processor adapted for compressing said pulse code modulated signal into a transmitted digitally encrypted NRZ signal;

a first modem for modulating said digitally encrypted NRZ signal to produce a transmitted modified digitally encrypted signal;

a second modem for modulating said carrier signal with said transmitted modified digitally encrypted signal to produce said modulated carrier signal;

a communication channel for receiving said modulated carrier signal;

said radio interface unit further comprising;

said second modem for receiving a modulated carrier signal from said communication channel and for converting said modulated carrier signal into a received modified digitally encrypted signal;

said first modem for receiving said received modified digitally encrypted signal and for converting said received modified digitally encrypted signal into a received digitally encrypted NRZ signal;

said signal processor adapted for converting said received digitally encrypted NRZ signal into decrypted pulse code modulated digital signals; and

said codec adapted for converting said decrypted pulse code modulated digital signals to said non-secure voice signals.

15. The communication system as recited in claim 14, wherein said communication channel comprises a telephone line.

16. The communication system as recited in claim 14, further comprises a universal synchronous/asynchronous receiver/transmitter having at least one port for receiving auxiliary data to be transmitted as said transmitted modified digitally encrypted signal over said communication channel.

17. The communication system as recited in claim 14, wherein said first modem comprises means for modifying and for inputting said transmitted digitally encrypted NRZ signal into said second modem in modified frequency modulation format, wherein said transmitted modified digitally encrypted signal comprises a passband of 300 Hz to 3200 Hz.

18. The communication system as recited in claim 14, wherein said first modem comprises means for modifying and inputting said transmitted digitally encrypted NRZ signal into said second modem in continuous phase modulation format.

19. The communication system as recited in claim 14, wherein said transmitted and received digitally encrypted NRZ signal comprises a DES-encrypted signal.

20. The communication system as recited in claim 14, further comprising means for transmitting at a rate of at least twice per second a voice block of said transmitted modified digitally encrypted signal preceded in each transmission by a master prologue block.

21. The communication system as recited in claim 14, further comprising means for transmitting at a plurality of bit rates per second a secondary command data block of said transmitted modified digitally encrypted signal in response to a command word contained with a master prologue block.

22. An improved system for transmitting secure signals through a repeater, the improved system comprising:

a conventional repeater;

a repeater communication controller physically connected to said conventional repeater to selectively control said conventional repeater during reception and retransmission of digitally encrypted signals, said repeater communication controller comprising;

a receive modem for demodulating a received modified digitally encrypted signal to produce a digitally encrypted NRZ signal;

means for error-correcting unencrypted control information within said digitally encrypted NRZ signal; and

a transmit modem for modulating error-corrected said digitally encrypted NRZ signal to produce a transmitted error-corrected modified digitally encrypted signal.

23. The improved system as recited in claim 22, wherein said received modified digitally encrypted signal and said transmitted error-corrected modified digitally encrypted signal each having a 300 to 3200 Hz passband.

24. The improved system as recited in claim 22, wherein said repeater communication controller is connected to a communication channel, said communication channel is adapted to receive a carrier signal modulated by a modified digitally encrypted signal.

25. A method of transmitting and receiving encrypted voice communication signals using a conventional radio, comprising:

encoding, at a bit rate of 4800 BPS and less, a transmitting non-secure voice communication signal into a transmitting digital signal;

encrypting said transmitting digital signal into a transmitting digitally encrypted NRZ signal;

modifying said transmitting digitally encrypted NRZ signal into a modified digitally encrypted signal;

modulating a carrier signal with said modified digitally encrypted signal, said modulated carrier signal occupying a necessary bandwidth approved for channels spaced 15 KHz to 25 KHz apart;

transmitting said modulated carrier signal over a communication channel;

demodulating said modified digitally encrypted signal from said modulated carrier signal;

demodifying said modified digitally encrypted signal into a receiving digitally encrypted NRZ signal;

decrypting said receiving digitally encrypted NRZ signal to produce a receiving digital signal; and

decoding, at a bit rate of 4800 BPS and less, said receiving digital signal to produce a receiving non-secure communication signal.

26. The method as recited in claim 25, wherein said modulating step further comprises modified frequency modulating a digitally encrypted NRZ signal to produce said modified digitally encrypted signal, wherein said modified digitally encrypted signal occupies a 300 Hz to 3200 Hz passband.

27. An improved digital encryption device comprising:

a radio interface connected to a conventional radio and adapted to receive a non-secure voice signal;

a codec selectively coupled to said radio interface for receiving said non-secure voice signal and for converting said signal into a pulse code modulated signal;

a signal processor adapted for converting said pulse code modulated signal into a digitally encrypted NRZ signal; and

means for modulating said digitally encrypted NRZ signal on a carrier signal, said modulated carrier signal is occupying a necessary bandwidth approved for channels spaced greater than 11.4 KHz apart.