Duplex analog scrambler

• US 4,827,507 A
• Filed: 06/19/1987
• Issued: 05/02/1989
• Est. Priority Date: 06/19/1987
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Marry, Patrick J., Houghton, Michael W., Wilson, Gregory P.
• Primary Examiner(s): Cangialosi, Salvatore
• Application Number:
  US07/065,220
• Time in Patent Office: 683 Days
• Field of Search: 380/9, 380/34, 380/38, 380/44, 380/47, 380/48
• US Class Current: 380/38
• CPC Class Codes: H04K 1/04 by frequency scrambling, i.e. by transposing or inverting parts of the frequency band or by inverting the whole band

Abstract

An analog frequency inversion scrambler employing an exchange of random number seeds between an originating scrambler and an answering scrambler to create two pseudo-random frequency hopping rolling codes has been disclosed. The rolling code used in one direction of a duplex channel is different than the rolling code in the opposite direction and each code is synchronized by periodic synchronization signals.

Claims

1. An analog audio frequency band scrambler which provides security of communications over a communications channel by sequentially frequency inverting an unsecure first message for transmission as a secure first message on the channel to a second analog audio frequency band scrambler and by sequentially frequency reinverting a secure second message received from the second scrambler on the channel, the scrambler comprising:

means for exchanging a first seed number for a second seed number with the second scrambler;

means for generating from said exchanged first and second seed numbers a first code, at least part of which starts the sequential frequency inverting of the unsecure first message and a second code, at least part of which starts the sequential frequency reinverting of the secure second message; and

means for transmitting a first code synchronization signal on the channel and for receiving a second code synchronization signal from the channel whereby frequency reinverting of the secure first message at the second scrambler may be synchronized to said first code synchronization signal and said second code may be synchronized to said second code synchronization signal.

2. An analog audio frequency band scrambler in accordance with claim 1 wherein said means for exchanging further comprises means for generating said first seed number and for transmitting said first seed number in a first message burst on the channel.

3. An analog audio frequency band scrambler in accordance with claim 1 wherein said means for exchanging further comprises means for receiving said second seed number from the channel.

4. An analog audio frequency band scrambler in accordance with claim 3 wherein said means for generating further comprises means for arithmetically combining said first seed number, said second seed number, at least one additive number, and at least one predetermined multiplication factor to generate said first code.

5. An analog audio frequency band scrambler in accordance with claim 4 wherein said means for generating further comprises means for reading predetermined digits of said first code and shifting said code at intervals of time whereby a rolling code is created to further sequence the sequential frequency inversion.

6. An analog audio frequency band scrambler in accordance with claim 3 wherein said means for generating further comprises means for arithmetically combining said first seed number, said second seed number, at least one additive number, and at least one predetermined multiplication factor to generate said second code.

7. An analog audio frequency band scrambler in accordance with claim 6 wherein said means for generating further comprises means for reading predetermined digits of said second code and shifting said code at intervals of time whereby a rolling code is created to further sequence the sequential frequency reinversion.

8. An analog audio frequency band scrambler in accordance with claim 2 wherein said means for transmitting a first code synchronization signal further comprises means for confirming reception of said second seed number and means for transmitting said first seed number in a second message burst prior to transmission of said first code synchronization signal.

9. An analog audio frequency band scrambler in accordance with claim 1 further comprising means for synchronizing said second code to an internal clock signal if said second code synchronization signal is not received from the channel.

10. An analog audio frequency band scrambler in accordance with claim 1 further comprising means for coordinating said first code synchronization signal and said second code synchronization signal whereby said first code synchronization signal and said second code synchronization signal occur essentially simultaneously.

11. An analog audio frequency band scrambler in accordance with claim 1 further comprising means for muting said secure first message during said transmission of said first code synchronization signal.

12. An analog audio frequency band scrambler in accordance with claim 1 further comprising means for indicating said means for transmitting a first code synchronization signal and for receiving a second code synchronization signal have commenced operation.

13. An analog audio frequency band scrambler in accordance with claim 5 further comprising means for determining whether sequential rolling code numbers are equal and for ignoring a second code number equal to an adjacent first code number.

14. An analog audio frequency band scrambler in accordance with claim 1 further comprising means at the second scrambler for receiving said first code synchronization signal and for transmitting a synchronization request signal if said first code synchronization signal is not received.

15. An analog audio frequency band scrambler in accordance with claim 14 further comprising means at the scrambler for detecting said synchronization request signal and for transmitting a third code synchronization signal on the channel in response to said synchronization request signal detection.

16. An analog audio frequency band scrambler in accordance with claim 15 further comprising means at the second scrambler for receiving said third code synchronization signal and for transmitting a synchronization lost signal if said third code synchronization signal is not received, thereby terminating the frequency inverting of the unsecure first message.

17. An analog frequency scrambler in accordance with claim 16 further comprising means at said second scrambler for transmitting a third seed number whereby the frequency inverting of the unsecure first message may be started.

18. An analog frequency scrambler in accordance with claim 14 wherein the communications channel is a duplex radio channel over which the scrambler may transmit in a first direction said first seed number, said first code synchronization signal, and the secure first message and from which the scrambler may receive from a second direction said second seed number, said second code synchronization signal, and the secure second message.

19. A method of providing security of communications over a narrow bandwidth channel by sequentially frequency inverting an unsecure first message for transmission as a secure first message on the channel to a second analog audio frequency band scrambler and by sequentially frequency reinverting a secure second message received from the second scrambler on the channel, the method comprising the steps of:

exchanging a first seed number for a second seed number with the second scrambler;

generating from said exchanged first and second seed numbers a first code, at least part of which starts the sequential frequency inverting of the unsecure first message and a second code, at least part of which starts the sequential frequency reinverting of the secure second message; and

transmitting a first code synchronization signal on the channel and receiving a second code synchronization signal from the channel whereby frequency reinverting of the secure first message at the second scrambler may be synchronized to said first code synchronization signal and said second code may be synchronized to said second code synchronization signal.

20. A method in accordance with the method of claim 19 wherein said step of exchanging further comprises the steps of generating said first seed number and transmitting said first seed number in a first message burst on the channel

21. A method in accordance with the method of claim 19 wherein said step of exchanging further comprises the step of receiving said second seed number from the channel.

22. A method in accordance with the method of claim 21 wherein said step of generating further comprises the step of arithmetically combining said first seed number, said second seed number, at least one additive number, and at least one predetermined multiplication factor to generate said first code.

23. A method in accordance with the method of claim 22 wherein said step of generating further comprises the step of reading predetermined digits of said first code and shifting said code at intervals of time whereby a rolling code is created to further sequence the sequential frequency inversion.

24. A method in accordance with the method of claim 21 wherein said step of generating further comprises the step of arithmetically combining said first seed number, said second seed number, at least one additive number, and at least one predetermined multiplication factor to generate said second code.

25. A method in accordance with the method of claim 24 wherein said step of generating further comprises the steps of reading predetermined digits of said second code and shifting said code at intervals of time whereby a rolling code is created to further sequence the sequential frequency reinversion.

26. A method in accordance with the method of claim 20 wherein said step of transmitting a first code synchronization signal further comprises the steps of confirming reception of said second seed number and transmitting said first seed number in a second message burst prior to transmission of said first code synchronization signal.

27. A method in accordance with the method of claim 19 further comprising the step of synchronizing said second code to an internal clock signal if said second code synchronization signal is not received from the channel.

28. A method in accordance with the method of claim 19 further comprising the step of coordinating said first code synchronization signal and said second code synchronization signal whereby said first code synchronization signal and said second code synchronization signal occur essentially simultaneously.

29. A method in accordance with the method of claim 19 further comprising the step of muting said secure first message during said transmission of said first code synchronization signal.

30. A method in accordance with the method of claim 19 further comprising the step of indicating said steps of transmitting a first code synchronization signal and receiving a second code synchronization signal have commenced.

31. A method in accordance with the method of claim 23 further comprising the steps of determining whether sequential rolling code numbers are equal and for ignoring a second code number equal to an adjacent first code number.

32. A method in accordance with the method of claim 19 further comprising the steps of receiving said first code synchronization signal at the second scrambler and transmitting a synchronization request signal if said first code synchronization signal is not received.

33. A method in accordance with the method of claim 32 further comprising the step of detecting said synchronization request signal at the scrambler and transmitting a third code synchronization signal on the channel in response to said synchronization request signal detection.

34. A method in accordance with the method of claim 33 further comprising the steps of receiving said third code synchronization signal at the second scrambler and transmitting a synchronization lost signal if said third code synchronization signal is not received, thereby terminating the frequency inverting of the unsecure first message.

35. A method in accordance with the method of claim 34 further comprising the step of transmitting from the second scrambler a third seed number whereby the frequency inverting of the unsecure first message may be started.

36. An analog audio frequency band scrambling system which provides security of communications over a duplex interruptible band-limited channel by sequentially frequency inverting an unsecure first message with a sequence of inversion frequency signals at an originating station before transmission as a secure first message on a first half of the duplex channel and by synchronously frequency reinverting the secure message with a like sequence of inversion frequency signals to recover the unsecure first message at an answering station and similarly inverting, transmitting, and reinverting an unsecure second message from the answering station to the originating station on a second half of the duplex channel, the system further comprising:

(a) initialization means comprising,

means at the originating station for generating a first seed number;

means at the originating station for transmitting said first seed number in a first message burst on the first half of the duplex channel;

means at the answering station for generating a second seed number;

means at the answering station for receiving said first seed number from said first half of the duplex channel and for transmitting said second seed number on the second half of the duplex channel in response to said receiving of said fist seed number;

means at the originating station for receiving said second seed number and generating a first rolling code number and a second rolling code number wherein said first and second rolling code numbers each comprise an arithmetic combination of said first seed number, said second seed number, at least one predetermined additive number, and at least one predetermined multiplication factor;

means at the answering station for generating said first and second rolling code numbers;

(b) synchronization means comprising,

means at the originating station for confirming reception of said second seed number;

means at the originating station for transmitting said first seed number in a second message burst and for subsequently transmitting a first synchronizing signal at periodic intervals on the first half of the duplex channel;

means at the answering station for receiving said transmitted first seed number second burst on the first half of the duplex channel and for transmitting a first seed number reception confirmation message and subsequently transmitting a second synchronizing signal at periodic intervals on the second half of the duplex channel;

means at the originating station for synchronizing said second rolling code number to said second synchronizing signal;

means at the answering station for synchronizing said first rolling code number to said first synchronizing signal;

(c) encoding means comprising,

means at the originating station for sequentially sampling said first rolling code number and for utilizing said originating station first rolling code number samples to generate the sequence of inversion frequency signals at the originating station;

means at the answering station for sequentially sampling said first rolling code number and for utilizing said answering station first rolling code number samples to generate the sequence of reinverting frequency signals;

means at the answering station for sequentially sampling said second rolling code number and for utilizing said answering station second rolling code number samples to generate the sequence of inversion frequency signals at the answering station; and

means at the originating station for sequentially sampling said second rolling code number and for utilizing said originating station second rolling code number samples to generate the sequence of reinverting frequency samples.

37. An analog audio frequency band scrambling system in accordance with claim 36 further comprising means at the answering station for synchronizing said first rolling code number to an internal clock if said first synchronizing signal is not received a first time after said periodic interval.

38. An analog audio frequency band scrambling system in accordance with claim 37 further comprising means at the answering station for ceasing to transmit a secure second message over said second half of the duplex channel if said first synchronizing signal is not received a second time in said periodic interval.

39. An analog audio frequency band scrambling system in accordance with claim 36 further comprising means, responsive to said means for ceasing at the originating station, for generating a third seed number and transmitting said third seed number on the second half of the duplex channel whereby secure communications may again be resumed.

40. An analog audio frequency band scrambling system in accordance with claim 36 further comprising means at the originating station and a-t the answering station for coordinating said first and second synchronizing signals whereby said first and second synchronizing signals occur essentially simultaneously.

41. An analog audio frequency band scrambling system in accordance with claim 36 further comprising means at the originating station for muting said first secure message during transmission of said first synchronizing signal.

42. An analog audio frequency band scrambling system in accordance with claim 36 wherein said means at the originating station for generating a first seed number further comprises means for continuously generating a plurality of random numbers and for seizing one of said plurality of random numbers as said first seed number.

43. An analog audio frequency band scrambling system in accordance with claim 36 wherein said means at the answering station for generating a second seed number further comprises means for continuously generating a plurality of random numbers and or seizing one of said plurality of random numbers as said second seed number.

44. An analog audio frequency band scrambling system in accordance with claim 36 further comprising means at the originating station further comprising means for determining whether sequential rolling code numbers are equal and for ignoring a second code number equal to an adjacent first code number.

45. A cellular radiotelephone analog audio frequency band scrambler which provides security of communications over a duplex radiotelephone communications channel by sequentially frequency inverting an unsecure first message for transmission as a secure first message on the channel to a second analog audio frequency band scrambler and by sequentially frequency reinverting a secure second message received from the second scrambler on the channel, the scrambler comprising:

means for establishing a cellular radiotelephone call between said cellular radiotelephone analog scrambler and the second scrambler;

means for exchanging a first seed number for a second seed number with the second scrambler;

means for generating from said exchanged first and second seed numbers a first code to sequence the frequency inverting of the unsecure first message and a second code to sequence the frequency reinverting of the secure second message; and

means for transmitting a first code synchronization signal on the channel and for receiving a second code synchronization signal from the channel whereby frequency reinverting of the secure first message at the second scrambler may be synchronized to said first code synchronization signal and said second code may be synchronized to said second code synchronization signal.

46. A cellular radiotelephone analog audio frequency land scrambler in accordance with claim 45 further comprising means at the second scrambler for transmitting a synchronization request signal if said first code synchronization signal is not received due to handoff.

47. A cellular radiotelephone analog audio frequency band scrambler in accordance with claim 45 further comprising means at the second scrambler for transmitting a second seed number when said cellular radiotelephone call is established.