Coding system for descrambling video

A decoder system for descrambling a scrambled video signal, the decoder system comprising:

• first key code receiver means for receiving a first key code encoded in the scrambled video signal, said first key code being in scrambled format in the scrambled video signal and having a predetermined relationship with respect thereto;
• second key code receiver means for receiving a second key code encoded in the scrambled video signal;
• first key code descrambling means for descrambling said first key code in response to said first key code identification means and producing a descramble code for descrambling the video signal;
• and
• second key code identification means for identifying said second key code.

A system for sending from a sending station an information signal encrypted in a selected one of a plurality of encryption modes to a plurality of receiving stations, each of the receiving stations having a decoder arrangement respectively associated therewith, predetermined ones of the receiving stations being authorized to decode the encrypted signal to receive the information content therein, the system comprising:

• security code sending means coupled to the sending station for sending with the encrypted signal a first security code which is to be stored in each of the decoders;
• security code change means for changing said first security code in each of said decoders to a second security code over a transitional period of time;
• and
• field code generator means for sending field code information compatible with said first and second security codes during said transitional period of time.

A method of supplying video information contained in a video signal from a sending station exclusively to a preselected one of a plurality of receiving stations, each of the receiving stations having a decoder associated therewith, the method comprising the steps of:

• distorting the video signal at the sending station in accordance with a predetermined one of a plurality of alternative distortion modes;
• encoding an identification code onto the video signal which uniquely identifies one of the decoders;
• encoding a first security key onto the video signal at the sending station, said first security key being encoded in a predetermined scrambled format and in a predetermined relationship with respect to said encoded identification code;
• and
• sending the encoded video signal to the plurality of receiving stations, whereby a selected receiving station having a decoder associated therewith which has stored therein an identification code which corresponds to the identification code encoded onto the video signal will accept the first security key.

A method of unscrambling a scrambled video signal in a predetermined one of a plurality of decoders, the method comprising the steps of:

• receiving at an input of each of the decoders a scrambled security code, each decoder having a respectively associated conversion code installed therein, said scrambled security code being descrambleable by a conversion code respectively associated with the predetermined one of the plurality of decoders;
• receiving at said input of each of the decoders a field code, during a predetermined portion of a signal to be unscrambled;
• combining said field code with an unscrambled version of said security code to produce a mode code;
• and
• unscrambling a field portion of said scrambled video signal corresponding to said field code in response to said mode code.

A system for sending from a sending station an information signal encrypted in a selected one of a plurality of encryption modes to a receiving station, the receiving station having a decoder arrangement respectively associated therewith, the receiving station being authorized to decode the encrypted signal to receive the information content therein, the system comprising:

• security code sending means coupled to the sending station for sending with the encrypted signal a first security code which is to be stored in the decoder;
• security code change means for changing said first security code in said decoder to a second security code over a transitional period of time;
• field code generator means for sending field code information compatible with said first and second security codes during said transitional period of time;
• and
• processing means for providing to the decoder a mode code corresponding to the selected one of the encryption modes in response to a selectable one of said first and second security codes, and said field code.