Abstract: A process for assuring secure communication over a radio link and apparatus to perform the process includes a scrambler-descrambler installed at a multiple line input multiple line output telephone switch. Individuals equipped with compatible scrambler-descramblers can place calls to the switch and automatically transmit unique identity code information which, if recognized, opens an audio circuit and connects an available output telephone line. The individual can then place a telephone call to third party and all audio transmission over the radio link will be scrambled. Scrambled audio signals received at the switch are descrambled and passed to the third party. Audio signals received at the switch from the third party are scrambled and transmitted to the individual whose instrument descrambles the signal.