Cryptographically secure communication system

摘要

This relates to a cryptographically secure communication system employed with an analog input, an analog output and a transmission medium each having a given low frequency pass band with a predetermined bandwidth. The input analog signal is sampled and then quantized to have an amplitude equal to one of a predetermined number of discrete amplitude levels. This quantized signal is applied together with a first sequence of signal representing randomly and with substantially equal probability the discrete amplitude levels to a modulo - M adder to encrypt the sample pulses. These encrypted sample pulses are converted to an encrypted analog signal for propagation through the transmission medium. The encrypted analog signal is received from the medium and then sampled and quantized to provide the encrypted amplitude samples at the receiver. These encrypted samples are applied together with a second sequence of signals identical to and synchronous with the first sequence of signals to a modulo - M subtractor to decrypt the received encrypted samples to recover the original analog signal samples which are then converted to an analog output signal. It is also possible to employ a modulo - M subtractor to encrypt the sample pulses and a modulo - M adder to decrypt the received encrypted samples.