DATA TRANSMITTING APPARATUS AND DATA RECEIVING APPARATUS

摘要

A data communication apparatus wherein the time required for a wiretapper to analyze a cipher text is significantly increased up to an astronomical amount of calculation, thereby achieving a high level of concealment. A very small amplitude modulation based on a random number signal generated at a transmitting end is superimposed on a multi-level signal generated based on data and key information, and thereafter the modulated signal is transmitted. At a receiving end, apart from data identification, two threshold values, between which a sufficiently large interval is established by the modulated amplitude using a random number, are used to perform three types of identifications, "1", "0" and "not identifiable", for the random number signal. The information of the bits for which the identification has been succeeded is transmitted back to the transmitting end, whereby those bits are shared as a new key. In this way, the same transceiver can used to perform a cipher text transmission and a key delivery at the same time.