| 摘要 |
A data transmitting apparatus 1101 generates, by using predetermined first key information 11; and information data 10, a multi-level signal 13 in which a signal level changes so as to be approximately random numbers, and converts the multi-level signal 13 into a modulated signal 14, in a predetermined modulation method and transfer the same. A data receiving apparatus 1201 demodulates the modulated signal 14 so as to be converted into a multi-level signal 15, and reproduces information data 18 from the multi-level signal 15, using second key information 16 which has the same content as first key information 11 used by the data transmitting apparatus 1101.
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