Abstract: In a method for converting n data input bits to n data output bits, groups of m data input bits from an input data buffer (10) are used as address input for a plurality of identical substitution look-up tables (20 to 27). Each look-up table (20 to 27) has a plurality of groups of m data output bits stored at a plurality of locations in the table. The output bits held at each location within the look-up tables (20 to 27) are dependent on a control word taken from a control word register (11).

Abstract: A television receiver for receiving scrambled television signals has an arrangement (3) which provides scrambled video components (V) and packet arranged sound/data components (D) some of which are also scrambled. The components (D) are applied to a packet demultiplexer (4) where the packets are assembled from the data in several lines in the signal to provide at a first output (P), the respective packets carrying sound/data information and, at a second output (E), encrypted control data which is applied to a sub-system (6) to produce a video scrambling control word (VS) for each line of the video components. The sub-system (6) during each line produces further bits which are applied to a descrambling control word generator (7) which assembles these further bits from three lines to form a packet scrambling control word.