Method to control access to enciphered data

摘要

The method involves sending data e.g. e.g. audio/video content, to a multimedia unit, and sending a control message (ECM1) to the multimedia unit. The control message containing two control words (CW1, CW2) is sent to the multimedia unit after sending the data encrypted by the word (CW1) and before sending the data decrypted by the word (CW2). The time shift between sending the data encrypted by the word (CW1) to the multimedia unit and sending the message is more than 10 percentage and less than 100 percentage of a cryptoperiod.