Data encryption on the physical layer of a data transmission system

A method of encryption of data on the physical layer of a transmission system data comprising the steps of - providing a sequence of key stream {kn], - establish a correspondence of each sequence data blocks with zn symbol QAM - altering each of the symbols zn QAM according to a kn sequence element keystream {kn}, thereby creating symbols vn encrypted, characterized in that - the symbols encrypted vn are assigned to N = 2 distinct sub-carriers a transmission scheme Orthogonal Frequency Division Multiplex OFDM, - in a transmitter, symbols (31) training OFDM periodically inserted, altered according to elements of the sequence keystream (kn) and transmitted - in a receiver, OFDM symbols (31) training are encrypted according to elements of the sequence key stream {kn} and compared with the symbols of encrypted training transmitted (31) received by a synchronizer / evaluator channels (32), and that - there one transfer function hn or synchronization information channel is clear.