Abstract: Apparatus for coding and decoding of electrical signals within a pre-established frequency band and useful for providing communication secrecy. A transmission and coding circuit and a reception and decoding circuit is provided between means for the generation and reception of electrical signals and means for the exchange of coded signals with at least one other coding and decoding apparatus. Commutation means is utilized for complementarily enabling the circuits. The circuits include first means for temporarily storing consecutively received portions of the electrical signals, second means for enabling the operation of the first means to consecutively store in memory the signal portion and to transmit those signal portions in a different order, and third means for controlling the storage of the electrical signal portions in memory within the first means according to one of a fixed sampling frequency and two or more frequencies variable in a prestablished order.