Patent ID: 6920222
Filing Date: 2005-07-19
Classification: H04N

Abstract:
1. A conditional access system comprising: a demultiplexer for demultiplexing a packet stream transmitted from a transmitting site into encrypted coded media data, an ECM (Entitlement Control Message) and an EMM (Entitlement Management Message); an EMM decryption section for retrieving work keys and partial viewing authorization information from the EMM extracted by said demultiplexer; an ECM decryption section for decrypting the ECM using the work keys and for intermittently retrieving scrambling keys from the ECM, based on receiving control information to alternately enable and disable decrypting, when the partial viewing authorization information retrieved by said EMM decryption section permits partial viewing; a media data descrambling section for intermittently descrambling the coded media data using the scrambling keys intermittently retrieved by said ECM decryption section; and a decoding section for decoding the coded media data intermittently descrambled by said media data descrambling section.