Secure coding and decoding system and method for television program signals

• US 4,600,942 A
• Filed: 11/27/1984
• Issued: 07/15/1986
• Est. Priority Date: 07/29/1982
• Status: Expired due to Term

• Current Assignee: Telease Incorporated
• Original Assignee: Telease Incorporated
• Inventors: Gerlach, Ronald R., Field, Robert W., Perr, Clarence D.
• Primary Examiner(s): Buczinski, S. C.
• Application Number:
  US06/675,452
• Time in Patent Office: 595 Days
• Field of Search: 358/119, 358/122, 358/117, 358/123, 178/22.12, 178/22.13, 178/22.14
• US Class Current: 380/215
• CPC Class Codes: H04K 1/06 by transmitting the information or elements thereof at unnatural speeds or in jumbled order or backwards
• CPC Class Codes: H04N 7/167 Systems rendering the television signal unintelligible and subsequently intelligible

Abstract

Parts of a composite video signal, such as segments of each horizontal scan line, are stored in analog storage devices and retrieved therefrom in a cyclic manner to rearrange them and thereby encode the signal. The cyclic retrieval of the information from the storage devices is carried out on a selective basis in accordance with the binary state of a pseudo-random signal that is generated independently at each of the encoding and decoding stations. Synchronization of the two independently generated signals is provided by a control word and an initialization word that are transmitted with the encoded video signal, one of which is encrypted. Decryption of the word is carried out with a master key at each of the encoding and decoding stations.

Claims

1. Apparatus for transmitting an encoded television signal to prevent unauthorized viewing of a television program, comprising:

a program source for generating a composite video signal;

a plurality of delay elements connected in series to receive successive parts of the composite video signal;

a switching device having a plurality of input terminals respectively connected to said delay elements to receive a delayed composite video signal, and an output terminal that is selectively connected to one of said input terminals;

means for controlling said switching device to alternately (a) maintain said output terminal connected to one of said input terminals, and (b) sequentially connect said output terminal to each of said input terminals in a cyclic manner, to thereby generate an encoded video signal; and

means for transmitting the encoded video signal.

2. The apparatus of claim 1 wherein said controlling means includes a pseudo-random binary sequence generator.

3. The apparatus of claim 2 further including means for detecting predetermined portions of the television program and enabling said binary sequence generator to operate during a period related to said predetermined portions.

4. The apparatus of claim 3 further including means for inserting into the composite video signal a state word related to the status of the binary sequence generator at the end of an enabling period.

5. The apparatus of claim 2 further including means for generating a setup signal to periodically change an operating parameter of said binary sequence generator.

6. The apparatus of claim 5 further including means for transmitting said setup signal with the encoded video signal.

7. The apparatus of claim 6 wherein said setup signal is transmitted in an encrypted form.

8. The apparatus of claim 5 wherein said setup signal is generated in an encrypted form and said controlling means includes means for decrypting said setup signal.

9. The apparatus of claim 8 further including means storing a master key for controlling said decrypting means.

10. The apparatus of claim 1 wherein the parts of the video signal in two adjacent delay elements overlap one another.

11. The apparatus of claim 1 wherein each of said delay elements stores a portion of a horizontal scan line of the video signal.

12. The apparatus of claim 1 wherein each of said delay elements stores a plurality of horizontal scan lines of the video signal.

13. Apparatus for decoding an encoded video signal having parts thereof that are rearranged relative to other parts, comprising:

means for receiving the encoded video signal;

a plurality of analog delay elements connected in series to receive successive parts of the received signal;

switching means for selecting a delayed output signal from one of the delay elements;

means for controlling said switching means to select the output signal from a predetermined one of said delay elements in a first mode and to sequentially select the output signal from each of the delay elements in a cyclic fashion in a second mode; and

means for receiving the selected output signals from the switching means as a decoded video signal.

14. The apparatus of claim 13 wherein said controlling means includes a pseudo-random binary sequence generator for generating a control signal that determines the mode of operation of said switching means.

15. The apparatus of claim 14 wherein the received signal includes a status word, and further including means for presetting the state of said binary sequence generator in accordance with the status word.

16. The apparatus of claim 14 wherein the received signal includes a setup word for establishing an operating parameter of the binary sequence generator, and further including means for controlling said operating parameter in accordance with said setup word.

17. The apparatus of claim 16 wherein said setup word is received in an encrypted form, and said controlling means includes means for decrypting the received setup word and applying the decrypted word to said parameter controlling means.

18. A method for enabling only authorized television receivers to display a television program in an intelligible manner, comprising the steps of:

generating a television program signal;

generating a pseudo-random binary signal at an encoding station;

alternately arranging parts of the program signal relative to one another in one of two predetermined orders in accordance with the binary signal, to thereby form an encoded program signal;

transmitting the encoded program signal and a status signal relating to the generation of the binary signal at the encoding station;

storing successive parts of the transmitted signal at an authorized receiver;

independently generating the pseudo-random binary signal at the receiver;

synchronizing the independent generation of the pseudo-random binary signals by initializing the generation of binary signal at the receiver in accordance with the status signal and initiating generation of the binary signal upon receipt of a predetermined portion of the transmitted signal;

sequentially retrieving the stored parts of the signal;

selectively altering the order of retrieval in accordance with the binary state of the pseudo-random binary signal, to thereby form a decoded video signal; and

applying the decoded video signal to the authorized receiver for display.

19. The method of claim 18 further comprising the steps of:

generating a coding control signal at the encoding station;

controlling the generation of the binary signal at the encoding station in accordance with the control signal;

transmitting the control signal; and

controlling the generation of the binary signal at the receiver in accordance with the control signal.

20. The method of claim 19 wherein said control signal is generated in an encrypted form, and further including the steps of decrypting the control signal at each of the encoding station and the receiver.

21. A method for enabling only authorized television receivers to display a television program in an intelligible manner, comprising the steps of:

generating a television program signal;

generating a psuedo-random signal at an encoding station;

encrypting said television program signal in accordance with said psuedo-random signal;

producing a control signal indicative of a parameter in the generation of said psuedo-random signal at a predetermined time;

transmitting the encrypted television program signal to a receiver station;

transmitting said control signal with said program signal;

providing a decode control key to the receiver station;

utilizing said decode control key and said transmitted control signal to generate a psuedo-random signal at said receiver station;

decoding the encrypted television program signal in accordance with the psuedo-random signal generated at said receiver station; and

applying the decoded program signal to a receiver for display.

22. The method of claim 21 wherein said decode control key is provided to the receiver station by transmitting it in an encrypted form, and further including the step of providing a master key to said receiver station for controlling the decryption of the transmitted decode control key.

23. The method of claim 21 further including the step of periodically varying the decode control key.

24. The method of claim 22 wherein said master key is transmitted to said receiver station and varied periodically.

25. The method of claim 21 wherein said control signal is transmitted with said encrypted program signal.

26. The method of claim 25 wherein said control signal is transmitted in the video portion of the television program signal.

27. The method of claim 21 wherein said pseudo-random signal is a binary signal and said step of encrypting said television program signal includes the step of modifying said television program signal in at least one of two alternating modes of operation respectively related to the two different states of said binary signal.

28. The method of claim 21 wherein said control signal is an initialization signal defining a state of said pseudo-random signal.

29. The method of claim 21 further including the step of synchronizing the generation of the pseudo-random signal at said receiver station with the generation of the pseudo-random signal at said encoding station.