Method and apparatus for scrambling/descrambling a video signal

An apparatus for descrambling a video signal comprising;

• an A/D converter for receiving a scrambled composite video signal and for converting the composite video signal into a digital signal for descrambling;
• a multiplexing means for receiving the digital signal from said A/D converter and for multiplexing the digital signal in response to an external select signal;
• a D/A converter for receiving the multiplexed digital signal from said multiplexing means and for converting the multiplexed digital signal into an analog signal;
• a synchronous divider for receiving said composite video signal and for dividing the composite video signal into a vertical synchronizing signal and a horizontal synchronizing signal;
• a clock generator for receiving the horizontal synchronizing signal from said synchronous divider to generate a clock signal and for supplying the clock signal to said A/D converter and said D/A converter;
• an initial data generating means for receiving said composite video signal, for extracting from said composite video signal initial data coded during a vertical blanking interval thereof for each field thereof, and for decoding the extracted coded initial data;
• a horizontal blanking interval detector for receiving the horizontal synchronizing signal from said synchronous divider, for detecting a horizontal blanking interval from said horizontal synchronizing signal, and for outputting a low signal during the detected horizontal blanking interval;
• a random number generator for generating pseudorandom numbers of a predetermined number of bits, upon receiving the vertical synchronizing signal from said synchronous divider and the decoded initial data from said initial data generating means;
• a 2'S complement converter for complementing each bit signal from said random number generator;
• and
• an AND logic operating means including a plurality of AND gates where each gate has a first input terminal for receiving each complemented bit signal from said 2'S complement converter, a second input terminal for receiving an output signal from said horizontal blanking interval detector and an output terminal coupled in common to said multiplexing means for applying said external select signal.

A method of scrambling, transmitting and descrambling a video signal comprising the steps of:

• converting a composite video signal into digital signals of a predetermined number of bits and multiplying the digital signals by a transform matrix of a predetermined format to bit-scramble them;
• converting said bit-scrambled digital signals to an analog signal and transmitting the analog-converted signal to a user station;
• re-converting said analog-converted signal into digital signals of said predetermined number of bits and multiplying the digital signals by an alternative transform matrix of the reverse of said predetermined format to descramble them;
• and
• converting said descrambled digital signals to an original composite video signal.