System for providing scrambled content, and system for descrambling scrambled content

摘要

A system for providing scrambled content, comprising a control word generator, each control word including a control word identifier, a scrambler for providing a stream of scrambled data packets, and an encryption device for providing entitlement control messages (ECM's). One or more consecutive packets are scrambled using the same control word (CW). Each packet includes a control word identifier identifying the control word used. The ECM encryption device provides ECM's including a previous control word (CW_P), a current control word (CW_C) and a next control word (CW_N). A system for descrambling scrambled content comprises a descrambler for descrambling the scrambled content and a decryption device for decrypting ECM's to obtain control words. The ECM decryption device delivers control words to the descrambler and the descrambler descrambles the data packets of the scrambled content using a control word having a control word identifier corresponding with the control word identifier of the data packet to be descrambled. The system further comprises a storage device for storing scrambled content and means to control play back of the stored content, going fast forward and going backwards. The system is programmed to extract ECM's and to provide the ECM's to the ECM decryption device for decryption. The system is programmed to request the ECM decryption device to provide at least a next control word (CW_N) at play back or going fast forward, and to provide at least a previous control word (CW_P) and a current control word (CW_C) at going backwards.