Secure TV scrambling system using framing code switching
First Claim
1. In a television system having encoding filters A, B and C for selectively scrambling a television signal:
- a plurality of subscriber terminals each including means for receiving said scrambled television signal, three complementary decoding filters and means for operating said decoding filters for descrambling said scrambled television signal;
means for selectively inserting first and second relatively noise immune framing code signals in the vertical blanking interval of said television signal;
memory means for storing mode definition information;
means for transmitting mode definition data for changing said mode definition information stored in said memory means; and
means coupled to said operating means for selectively enabling operation of pairs of said descrambling filters in accordance with said stored mode definition information and said framing code signals and for changing among said pairs of descrambling filters only in response to a change in said framing code signals.
3 Assignments
0 Petitions
Accused Products
Abstract
A television signal scrambling system scrambles by suppressing horizontal syncs and changing the phase of the video carrier during the horizontal intervals. Data is transmitted by using two different widths for the horizontal intervals. Framing code information is sent by means of long pulses of two different durations during the vertical blanking interval. Three filters are utilized for dynamic scrambling, with filters A and B defining one scrambling mode and A and C defining a second scrambling mode. Corresponding descrambling filters are included in subscriber terminals and the subscriber microprocessor controllers have information downloaded as to the filter pairs to be used for descrambling based upon the receipt of the first or second framing code and a mode definition. The mode definitions are in the form of encrypted data and are dynamically changed by downloading to the subscriber terminals.
19 Citations
13 Claims
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1. In a television system having encoding filters A, B and C for selectively scrambling a television signal:
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a plurality of subscriber terminals each including means for receiving said scrambled television signal, three complementary decoding filters and means for operating said decoding filters for descrambling said scrambled television signal; means for selectively inserting first and second relatively noise immune framing code signals in the vertical blanking interval of said television signal; memory means for storing mode definition information; means for transmitting mode definition data for changing said mode definition information stored in said memory means; and means coupled to said operating means for selectively enabling operation of pairs of said descrambling filters in accordance with said stored mode definition information and said framing code signals and for changing among said pairs of descrambling filters only in response to a change in said framing code signals. - View Dependent Claims (2)
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3. The method of operating a television signal scrambling system comprising the steps of:
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scrambling a television signal in either a first or a second scrambling mode; storing a plurality of mode definitions at subscriber terminals; conveying relatively noise immune mode switching signals to subscriber terminals; operating the subscriber terminals for switching between corresponding descrambling modes in accordance with the stored mode definition and the conveyed mode switching signals, wherein said descrambling modes are redefined to preclude a change in descrambling modes except in response to mode switching signals; and conveying mode definition data for changing said stored mode definitions. - View Dependent Claims (4, 5)
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6. In a television signal decoder:
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memory means for storing a plurality of mode definitions that define a plurality of television signal descrambling modes; means for receiving mode definition data for storage in said memory means for redefining said plurality of descrambling modes; means responsive to receipt of a framing code signal for operating said decoder according to a selected one of the descrambling modes defined by said stored mode definitions; and wherein said descrambling modes are redefined to preclude a change in descrambling modes except in response to a framing code signal.
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7. A television decoder comprising:
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means responsive to a first relatively noise immune framing code signal for selecting a first descrambling mode and to a second relatively noise immune framing code signal for selecting a second descrambling mode; memory means for storing mode definitions defining said first and said second descrambling modes; means responsive to a data signal for selectively changing the definitions of said descrambling modes in said memory means; and wherein said descrambling modes are redefined to preclude a change in descrambling mode except in response to a framing code signal. - View Dependent Claims (8)
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9. In a television system having:
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encoding means for selectively scrambling a television signal in first and second scrambling modes; means for transmitting a first relatively noise immune framing code signal and a second relatively noise immune framing code signal; means for transmitting a data signal; a plurality of subscriber terminals including; means for receiving said scrambled television signal; descrambling means; means responsive to said framing code signals for operating said descrambling means to descramble television signals scrambled in said first and said second scrambling modes; memory means for storing mode definitions defining said first and said second descrambling modes; means responsive to said data signal for selectively changing the definitions of said descrambling modes stored in said memory means; and wherein a change in said descrambling modes is not permitted except in response to a change in said framing code signals. - View Dependent Claims (10, 11, 12)
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13. A television decoder comprising:
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means responsive to a first relatively noise immune framing code signal for selecting a first descrambling mode and to a second relatively noise immune framing code signal for selecting a second descrambling mode; memory means for storing mode definitions defining said first and said second descrambling modes; means responsive to an encrypted data signal for selectively changing the definitions of said descrambling modes in said memory means; and wherein an actual change in descrambling modes is only permitted in response to a change in said framing code signals.
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Specification