Data encryption technique for subscription television system
First Claim
1. A subscription television system comprising:
- head-end means including means for transmitting selected fields of a television signal in a scrambled form, means for inserting a plurality of system control data bits in each of a plurality of horizontal lines of the vertical blanking intervals of said transmitted television signal, said system control data bits being variable from horizontal line to horizontal line and from field to field of said transmitted television signal, and means for inserting a plurality of mode control data bits forming a mode control code in a selected horizontal line of the vertical blanking intervals of said transmitted television signal, said mode control data bits being adapted for processing with selected ones of said system data bits according to a selected function for yielding a non-transmitted predetermined control code when the immediately following field of said television signal is transmitted in said scrambled form and for yielding another code when the immediately following field of said television signal is not transmitted in said scrambled form; and
decoding means including means for receiving said transmitted television signal, logic means for processing the received mode control data bits and the received selected system data bits in accordance with said selected function for deriving said predetermined control code and said other code and means responsive to said derived predetermined control code for enabling unscrambling of the following field of said received television signal.
3 Assignments
0 Petitions
Accused Products
Abstract
A subscription television system includes a head-end for transmitting selected fields of a television signal in a scrambled form, the scrambled fields being identified by an encrypted mode control code inserted in a selected horizontal line of the preceding vertical interval. The mode control code is formed such that a predetermined non-transmitted control code is realized when the mode control code is processed with vertical interval system control data according to a selected function. A decoder processes the received mode control code and system control data according to the selected function to reconstitute the predetermined control code for enabling unscrambling of the following field. The decoder may employ majority voting techniques whereby not all of the bits of the reconstituted control code need be properly recovered to enable the unscrambling function.
120 Citations
8 Claims
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1. A subscription television system comprising:
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head-end means including means for transmitting selected fields of a television signal in a scrambled form, means for inserting a plurality of system control data bits in each of a plurality of horizontal lines of the vertical blanking intervals of said transmitted television signal, said system control data bits being variable from horizontal line to horizontal line and from field to field of said transmitted television signal, and means for inserting a plurality of mode control data bits forming a mode control code in a selected horizontal line of the vertical blanking intervals of said transmitted television signal, said mode control data bits being adapted for processing with selected ones of said system data bits according to a selected function for yielding a non-transmitted predetermined control code when the immediately following field of said television signal is transmitted in said scrambled form and for yielding another code when the immediately following field of said television signal is not transmitted in said scrambled form; and decoding means including means for receiving said transmitted television signal, logic means for processing the received mode control data bits and the received selected system data bits in accordance with said selected function for deriving said predetermined control code and said other code and means responsive to said derived predetermined control code for enabling unscrambling of the following field of said received television signal. - View Dependent Claims (2, 3, 4, 5)
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6. A decoder for use in a subscription television system including head-end means for transmitting selected fields of a television signal in a scrambled form, means for inserting a plurality of system control data bits in each of a plurality of horizontal lines of the vertical blanking intervals of said transmitted television signal, said system control data bits being variable from horizontal line to horizontal line and from field to field of said transmitted television signal, and means for inserting a plurality of mode control data bits forming a mode control code in a selected horizontal line of the vertical blanking intervals of said transmitted television signal, said mode control data bits being adapted for processing with selected ones of said system data bits according to a selected function for yielding a non-transmitted predetermined control code when the immediately following field of said television signal is transmitted in said scrambled form and for yielding another code when the immediately following field of said television signal is not transmitted in said scrambled form said decoder comprising:
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means for receiving said transmitted signal; logic means for processing the received mode control data bits and the received selected system data bits in accordance with said selected function for deriving said predetermined control code and said other code; and means responsive to said derived predetermined control code for enabling unscrambling of the following field of said received television signal. - View Dependent Claims (7, 8)
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Specification