| 摘要 |
A method and apparatus for providing conditional access to media programs is described. An exemplary method comprising the steps of transmitting media information encrypted according to a control word (CW) to a receiver station, transmitting entitlement management information (EMI) to the receiver station, the EMI comprising a service bitmap, and transmitting entitlement control information (ECI) to the receiver station, the entitlement control information including the control word (CW) encrypted according to a key (K) and an index to an element of the service bitmap, wherein the control word (CW) is decrypted by the receiver stations according to a value of the indexed element of the service bitmap.
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