An encrypted stream of video information (20) contains first video frames (22) and second video frames which are accessible and not accessible during trick play respectively. From a source stream encrypted that is for decryption with repeatedly changing control words sections of the stream are identified where respective first ones of the frames occur in the stream. Control words for decryption (24) are included in the stream. At least part of the control words are included in the stream at positions selected synchronized to the identified sections.