A synchronous data-stream generator, suitable for use as a synchronous stream cipher providing copy right protection for audio/video data, generates a stream of output data items in synchronisation with a clock trigger. The data-stream generator comprises at least two parallel arranged subgenerators M.sub.i, i.gtoreq.1, such as linear feedback shift registers. The output of the subgenerators M.sub.i is combined forming the output data items of the data-stream generator. A control subgenerator C is used for generating a stream of control data items. Control means (150) comprises for at least one subgenerator M.sub.i an associated number selector S.sub.i for, in dependence on the control data item of the control subgenerator C, selecting a number n.sub.i,j from a group H.sub.i of different integer numbers. At least two numbers of the group H.sub.i are larger than zero. The control means (150) causes the associated subgenerator M.sub.i to provide at the output the selected n.sub.i,j-th data item successive to a last generated data item (effectively skipping n.sub.i,j-1 data items).