Security system for television signal encryption
First Claim
1. Apparatus for securely transmitting a scrambled information signal to a receiver, comprising:
- means for scrambling an input information signal;
means for transmitting the scrambled information signal;
means for generating a first encryption key required at said receiver to enable descrambling of said transmitted scrambled information signal;
means for generating a second encryption key indicative of an authorized receiver;
means for forming a first block of information including the first encryption key;
first encryption means for encrypting the first block of information using the second encryption key to provide a first encrypted signal;
means for forming a second block of information including the first encryption key;
2 Assignments
0 Petitions
Accused Products
Abstract
A conditional access system for over-air transmission and reception of scrambled television signals improves the reliability of the reception by transmitting a key signal for use in descrambling the television signal in a block of information which is itself encyphered by the key signal. On reception, the receiver after decyphering of the block of information compares the key signal recovered from the block with the key signal provided at the receiver for decyphering the block. Descrambling will only be allowed if comparison shows the two key signals to be the same. The system also provides for information relating to the credit status of each user to be transmitted over-air. In order to ensure rapid operation, the credit status signal is sent repeatedly and a further signal is appended which is used at the receiver to prevent repeated accumulation of credit. An alternative arrangement is for the transmitter to transmit a signal indicative of the total sum of credit ever purchased by a user and for the user'"'"'s receiver to include a counter for accumulating all charges for programs viewed. A simple comparison between the two signals is sufficient to establish whether or not the viewer may view a program.
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Citations
22 Claims
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1. Apparatus for securely transmitting a scrambled information signal to a receiver, comprising:
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means for scrambling an input information signal; means for transmitting the scrambled information signal; means for generating a first encryption key required at said receiver to enable descrambling of said transmitted scrambled information signal; means for generating a second encryption key indicative of an authorized receiver; means for forming a first block of information including the first encryption key; first encryption means for encrypting the first block of information using the second encryption key to provide a first encrypted signal; means for forming a second block of information including the first encryption key; - View Dependent Claims (3, 6, 8, 11, 12, 13, 15, 16, 18, 22)
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2. second encryption means for encrypting the second block of information using the first encryption key to provide a second encrypted signal;
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means for transmitting the first and second encrypted signals with the transmitted scrambled information signal to enable detection in said receiver of transmission errors in the keys. - View Dependent Claims (4, 5, 7, 9, 10)
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14. Apparatus for receiving a scrambled information signal and for descrambling the scrambled information signal in response to detection that a first encryption key required to enable descrambling has been correctly received, comprising:
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means for receiving a scrambled information signal; storage means for storing a second encryption key; means for receiving a second signal comprising a first block of information, including a first encryption key, encrypted by the second encryption key; first decryption means for decrypting the second signal using the stored second encryption key to recover the first encryption key from the first block of information; means for receiving a third signal comprising a second block of information, including the first encryption key, encrypted by the first encryption key; second decryption means for decrypting the third signal using the first encryption key recovered from the first block of information to recover the first encryption key from the second block of information; comparison means for comparing the first encryption key recovered from the first block of information with the first encryption key recovered from the second block of information to detect transmission errors; and means for descrambling the received scrambled information signal enabled by correct reception of a first encryption key. - View Dependent Claims (17, 19, 20, 21)
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Specification