Patent ID: 7245720

Claim:
A system comprising: a number of receivers, at least some of the receivers having a storage medium to store program signals, wherein the program signals comprise content signals of a first and a second type, wherein the second type of content signals is inserted in time slots in the first type of content signals, wherein at least the first type of content signals is scrambled using control words serving as first keys for scrambling to obtain a scrambled program signal and wherein the scrambled program signal is provided together with entitlement control messages (ECMs) containing the control words in an encrypted manner using a second key, a decryptor provided at each receiver for retrieving the control words from the ECMs by decrypting the ECMs, and wherein the control words are delivered by the decryptor for descrambling the program signal, and wherein at least a plurality of said ECMs containing the control words in an encrypted manner further comprises control information to control the decryptor in such a manner that the decryptor processes ECMs to deliver decrypted control words for descrambling at least the first type of content signals so as to maintain at least the time slots for second type of content signals in the first type of content signals during playback of the program signal.