Time window key system for video scrambling

• US 4,464,678 A
• Filed: 01/21/1982
• Issued: 08/07/1984
• Est. Priority Date: 01/21/1982
• Status: Expired due to Fees

• Current Assignee: RCA Corporation
• Original Assignee: RCA Corporation
• Inventors: Schiff, Leonard N., Freeman, Smith
• Primary Examiner(s): BUCZINSKI, STEPHEN C
• Application Number:
  US06/341,499
• Time in Patent Office: 929 Days
• Field of Search: 358/117, 358/122, 358/123, 358/124, 340/825.34
• US Class Current: 380/239
• CPC Class Codes: H04N 7/1675 Providing digital key or authorisation information for generation or regeneration of the scrambling sequence pseudo-random number generators in general G06F7/58

Abstract

A video scrambling device requires that a key signal be periodically inserted into a subscribers box, e.g. once a month. The key signal is a function of both the box number and the time, and thus once received must be inserted relatively quickly, e.g. an hour or two. If it is not inserted quickly, a new key signal must be obtained. This makes it extremely difficult for a pirate to distribute a key signal to his customers in time for it to be effective. The scrambling method can be pseudorandom line inversion and also audio scrambling.

Claims

1. Apparatus for decoding a scrambled television signal in which scrambling is accomplished by distorting the television signal at a first rate in synchronism with a television synchronizing rate and in a manner determined by a sequential logic signal derived from a sequential logic circuit, the feedback connections of which are established by a command word and which first feedback connections control the sequence of said sequential logic generator, but which television signal, in order to prevent unauthorized keyless decoding, does not include at said first rate any signal representative of the state of said distortion;

said apparatus comprising;

controllable distortion correction means adapted to receive said scrambled television signal;

3. Apparatus according to claim 1 wherein said scrambled television signal includes periodic decoder synchronizing signal, and wherein said code-controlled sequential logic signal generating means is reset to a standard condition upon each occurrence of said decoder synchronizing signals.

2. code-controlled sequential logic signal generating means coupled to said controllable distortion correction means and including second combinational logic circuit means for generating a sequential control signal at said first rate corresponding with said sequential logic signal and having a sequence established by controllable feedback connections of said combinational logic circuit corresponding with said first feedback connections;

time-of-day clock signal generating means;

distinguishing serial-number memory means for storing a serial-number signal uniquely distinguishing said apparatus from other similar apparatus;

code signal decoding means coupled to said time-of-day clock signal generating means, to said serial-number memory means, to a key word source and to said code-controlled sequential logic means for generating said code word from said time-of-day clock signal, said serial-number signal and from said key word so that said code word is identical to said command word only if said key word and said time of day are related.

4. Apparatus according to claim 2 wherein said periodic decoder synchronizing signals are represented by periodic non-occurrence of horizontal synchronizing signals.

5. A method for decoding a scrambled television signal in which scrambling is accomplished by distorting the television signal at a first rate in synchronism with a television synchronizing rate and in a manner determined by a sequential logic signal derived from a sequential logic circuit, the feedback connections of which are established by a command word and which first feedback connections control the sequence of said sequential logic generator, but which television signal, in order to prevent unauthorized keyless decoding, does not include at said first rate any signal representative of the state of said distortion;

said method comprising the steps of;

generating a time-of-day signal;

generating a serial-number signal;

generating a code word from said time-of-day signal, said serial-number signal, and from a key word so that said code word is identical to said command word only if said key word and said time of day are related;

generating a sequential logic signal from second combinational logic circuit means, said sequential logic signal being generated at said first rate and having a sequence established by controllable feedback connections of said second combinational logic circuit which connections are controlled by said code word; and

correcting said distortion under the control of said sequential control signal.