A method of providing a stream of data units with scrambling state identifying data and providing a stream of key messages, synchronized with the stream of data units. The scrambling state identifying data includes an identifier value associated with the first decryption key that associates the data units in a third section. Then separating the first and second sections, with scrambling state identifying data lacking an identifier value associated with the decryption key, and providing in a key message coinciding with first or third sections key information. Thereby enabling an authorized decoder to obtain a value of the first decryption key corresponding with the second value of the first encryption key. Encryption of at least part of the clear data units uses the first encryption key is suspended for each data unit in the sequence included in the third section.