Information transmission method and apparatus for combining multiplexing and encryption

An information transmission system (100) transmits an encrypted information (It) comprised of a plurality of information units (Iu) each hierarchically encrypted and multiplexed to each other is communicated between at least two parties. The information transmission system (100) is constructed by a transmitting unit (110) and a receiving unit (130). The transmitting unit (110) is provided with an information unit generator (111) which produces the information unit (Iu); a scrambler (112) which encrypts the information unit (Iu) to produce an encrypted information unit (Iue), and multiplexer (113) which multiplexes at least one of those information unit (Iu) and said encrypted information unit (Iue) to produce a multiplexed information unit (Im). The receiving unit (130) is provided with a lower layer descrambler (132) which decrypts the encrypted information (It) to produce a multiplexed information unit (Im), demultiplexer (133) which demultiplexes the multiplexed information unit (Im) into any of encrypted information unit (Iue), multiplexed information unit (Iue) and information unit (Iu), and information unit descrambler (134) which decrypts the encrypted information unit (Iue) .