A device (40) for generating a watermarked stream (39), comprising: at least one input interface (41) configured to receive encrypted control messages (20) and conditional access streams (30) including a main stream (33) and protected watermarking data streams (35) from which a watermarking information (38) can be embedded in said watermarked stream (39); a security module (43) configured to process said control messages (20) and to control access to said conditional access streams (30); a descrambler (45) configured to remove protection applied on at least some of said conditional access streams (30); a watermarking unit (47) configured to generate the watermarked stream (39) from said conditional access streams (30) by selectively processing said watermarking data streams (35) depending on access data (AC, AR) included in some of said control messages (20).