| 摘要 |
A video-on-demand service is facilitated by encrypting, before purchase requests by subscribers, content such as a movie in accordance with one or a series of control words protected by a program key. The transport mechanism for delivery is an MPEG compliant transport mechanism, and the program key is encrypted and contained in an entitlement control message (ECM). The ECMs are transmitted to the set-top terminal associated with the subscriber for a limited time defining a service acquisition window. Thereafter, transmission of some or all ECMs are suppressed. This reduces the likelihood that an unauthorized terminal will intercept the ECM containing the program key, which is needed to descramble the content.
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