DATA TRANSMITTING APPARATUS

摘要

A time required for a wiretapper to decrypt an encrypted text is significantly increased to provide a data transmitting apparatus having a high concealing characteristic. In a data transmitting apparatus (17105), a multilevel encoding part (111) switches a plurality of key information to generate a multilevel code sequence in which the average values of signal levels are different, and then combines the generated multilevel code sequence with information data to generate a multilevel signal having a level corresponding to the combination of the two signal levels. A light modulating part (125) converts the multilevel signal to a modulated signal of a predetermined modulation scheme for transmission. In a data receiving apparatus (17205), a light demodulating part (219) demodulates the modulated signal received thereby to the multilevel signal. A multilevel demodulating part (212) switches a plurality of key information to generate a multilevel code sequence in which the average values of signal levels are different, and then identifies the multilevel signal based on this generated multilevel code sequence to reproduce the information data.