Abstract: An encryption/decryption device, system and method for providing secure communication over a communication channel. The encryption device includes a radio interface unit connected to a conventional radio, wherein the interface unit selectively couples a codec, signal processor and modem to the transmit and receive path during secure operation. The codec digitally encodes non-secure analog signals and places them in pulse code modulated format. The signal processor then compresses the pulse code modulated signals into voice coded and then digitally encrypted NRZ signals which are then input into the conventional radio for modulating a carrier frequency on an occupied bandwidth approved for 15 KHz to 25 KHz, or as little as 11.4 KHz, spaced channels. The modem can input the digitally encrypted signals using modified frequency modulation to place the modified digitally encrypted signals substantially within the voice passband of 300 Hz to 3200 Hz.

Abstract: A communication system for providing secured communication over a communication channel. The system includes a DES encryption device and a DES decryption device retrofittable into or within a conventional radio unit. The encryption device receives analog input at the transmitter end of the radio and converts the analog signal to digital signal, then encrypts this digital data, modulates the encrypted digital data using modified frequency modulation (MFM) which is then sent over the communication path. During decryption, the apparatus receives MFM data from the communication path, demodulates this digital data, decrypts the data and then outputs this decrypted digital data to the interface unit. The interface unit contains both a transmitter and a receiver which is capable of half duplex operation. The interface unit also contains a voice coder and a voice decoder which are of the sub-band type.