US 4,736,422 AGranted

Encrypted broadcast television system

AssigneeIndependent Broadcasting Authority

InventorArthur G. Mason

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Abstract

A conditional access system for transmitting and receiving scrambled television signals over-air includes means for addressing each of the receiving apparatus with an over-air signal whereby to permit reception and descrambling of the signal. The transmitter is provided with means for assembling a cipher block of information including a first key for use in descrambling the television signal and information relating to a plurality of users, and means for encyphering the cipher block with a second key which is common to the plurality of users. On reception a receiver applies the second, common keys to the received cipher block, recovers the first key for use in descrambling the signal and the information relating to the respective user and descrambles the television signal. Further, it is proposed to transmit a further key in encrypted form and to use the first key to decrypt the further key which is then used to descramble the television signal. This provides a three level key system which is very secure but by using a common second key for a plurality of users, the time to access each user is short.

Claims23

Dependent claims

Apparatus for transmitting a scrambled information signal, togther with a key required at a receiver to enable descrambling of the scrambled information signal to occur, to entitled receivers, comprising:

means for scrambling an input information signal A to produce a scrambled information signal S(A);
means for generating a first encryption key P required at a receiver to enable descrambling of the scrambled information signal S(A) to occur;
means for defining groups of entitled receivers;
means for generating a plurality of distribution keys D, each distribution key being generated for a particular group of entitled receivers;
means for generating a plurality of receiver entitlement signals T.sub.C, each receiver entitlement signal being representative of the level of entitlement of a respective receiver to descramble scrambled information signals;
means for assembling data blocks, adapted to assemble for each group of entitled receivers a data block comprising the first encryption key P appended to the receiver entitlement signals T.sub.C for the receivers in the respective group, the receiver entitlement signal T.sub.C for a particular receiver in a group being included in the respective data block at a predetermined location therein;
first encryption means for encrypting each data block using one of the distribution keys, the first encryption means being adapted to encrypt a data block relating to a given group of entitled receivers using a particular distribution key to enable the receivers in a group to use the same particular distribution key to recover the first encryption key P;
and
means for transmitting the scrambled information signal S(A) and the encrypted data blocks.

6 more elements

Receiving apparatus, comprising:

means for receiving a scrambled information signal S(A);
means for storing a distribution key D;
means for receiving a further signal comprising a data block encrypted by the distribution key D, the data block containing the first encryption key P appended to a plurality of receiver entitlement signals T.sub.C each representative of the level of entitlement of a respective receiver to descramble scrambled information signals;
first decryption means for decrypting the received further signal using the distribution key D stored in the storing means;
means operative on the output from the first decryption means for extracting a receiver entitlement signal from a predetermined location in the decrypted data block;
and
descrambling means for descrambling the received scrambled information signal S(A) in response to the correct recovery of the first encryption key P from the output of the first decryption means.

4 more elements

Dependencies are inferred from the claim text.