| 摘要 |
A method of decrypting a scrambled digital data item at a client, comprising receiving (1205/1511) actual control messages at said client, wherein each actual control message comprises control word generating information for generating a control word associated with the actual control message; storing (1207/1513) said actual control messages at said client; receiving (1211/1519) a portion of said scrambled digital data item at said client independently of said actual control messages; decrypting (1215/1523) said portion of said scrambled digital data item using said plurality of actual control messages without storing said scrambled digital data item at said client; stopping the receiving (1307) of said portion of said scrambled digital data item whilst continuing to receive actual control messages associated with a subsequent portion of said scrambled digital data item; receiving (1315), via a unicast, said subsequent portion of said scrambled digital data item; and decrypting (1319) said subsequent portion of said scrambled digital data item using said actual control messages. The scrambled digital data item comprises a plurality of segments of scrambled digital data, each segment of scrambled digital data being associated with one of said actual control messages and being scrambled with the control word associated with said one of said actual control messages, and wherein said scrambled digital data item further comprises a plurality of reference control messages, each segment of scrambled digital data comprising one of said reference control messages, each of said reference control messages comprising a control message reference value identifying the actual control message associated with the segment of scrambled digital data. |
