Abstract: A data communication apparatus, performing a secret communication, is provided to reduce a random number generation speed using a plurality of random number generators. The data communication apparatus includes random number generation sections generating random numbers, which are each a multi-level pseudo random number, using predetermined key information includes a multi-level signal modulation section selecting a level, from among multi-levels previously prepared, selected level corresponding to information data and a multi-level sequence, which is composed of a combination of values of the random numbers and generating a multi-level modulated signal including a noise having a predetermined noise level using the selected level. Levels of a multi-level signal are in a range of the noise level, and a signal point allocation is set such that all values which are possibly taken by each of the random numbers are allocated to the plurality of levels of the multi-level signal.

Abstract: A data transmitting apparatus has improved security against eavesdropping for secret communication using Y-00 protocol. The multi-level code generation section generates, based on key information, a multi-level code sequence in which a signal level changes so as to be approximately random numbers. The multi-level processing section generates a multi-level signal having a level which corresponds to a combination between information data and the multi-level code sequence. The error signal generation section generates an error signal which changes randomly. The accumulation section accumulates the error signal, and outputs an accumulated error signal. The adding section adds the accumulated error signal to the multi-level signal, and outputs a variable multi-level signal. The modulator section modulates the variable multi-level signal, and outputs a modulated signal.

Abstract: To provide a receiving apparatus which is capable of demodulating information data from a multi-level modulated signal, which is generated by using a Y-00 protocol, without using high-performance component parts. In the receiving apparatus, the soft decision section 211 performs soft decision on the multi-level signal 22, in which a fixed decision level is used. A converted data identification section 214 performs logical decision on a value of the converted information data 25 in accordance with a highest-order bit of a multi-level code sequence 23 and a decision result 24 of the soft decision. A data reproduction section 215 performs an XOR operation between the converted information data 25 and a lowest-order bit of the multi-level code sequence 23, and outputs a resultant thereof as information data 23.

Abstract: A data transmitting apparatus generates, by using predetermined first key information and information data, a multi-level signal in which a signal level changes so as to be approximately random numbers, and converts the multi-level signal into a modulated signal, in a predetermined modulation method and transfer the same. A data receiving apparatus demodulates the modulated signal so as to be converted into a multi-level signal, and reproduces information data from the multi-level signal, using second key information which has the same content as first key information used by the data transmitting apparatus.

Abstract: A data communication system that enhances concealment by significantly increasing the time required for a wiretapper to decrypt a cipher text. The data communication system is constituted by connecting a data transmitting apparatus (13105) to a data receiving apparatus (11201) via a transmission path (110). In the data transmitting apparatus (13105), a multilevel encoding part (111) receives a predetermined first initial value (key information) and information data and generates a multilevel signal that varies in level substantially in a random number manner. A dummy signal superimposing part (118) superimposes a dummy signal on the multilevel signal. A modulating part (112) converts the multilevel signal to a modulated signal of a predetermined modulation form and transmits the modulated signal.

Abstract: A data communication apparatus which improves security against eavesdropping is provided for secret communication using Y-00 protocol. In a data transmitting apparatus 101, a multi-level code generation section 111 generates, based on key information 11, a multi-level code sequence 12 in which a signal level changes so as to be approximately random numbers. A multi-level processing section 112 generates a multi-level signal 13 having a plurality of levels each corresponding to a combination between information data 10 and the multi-level code sequence 12. A level conversion section 113 divides the plurality of levels of the multi-level signal 13 into several groups, and allocates one level of a converted multi-level signal 21 to a plurality of levels included in each of the several groups in an overlapped manner. The level conversion section 113 then converts the multi-level signal 13 into the converted multi-level signal 21.

Abstract: A data communication apparatus wherein the stealthiness has been enhanced by significantly increasing the time required for a wiretapper to decrypt an encrypted text. The data communication apparatus is constituted by connecting a data transmitting apparatus and a data receiving apparatus via a transmission path. The data transmitting apparatus receives a first predetermined initial value (key information) and information data, generates a multi-valued signal the level of which varies substantially like a random number, and converts the multi-valued signal to a modulated signal of a predetermined modulation format for transmission. The data receiving apparatus demodulates the modulated signal to output the multi-valued signal, and then reproduces the information data from the multi-valued signal and a second predetermined initial value (key information) that is received.

Abstract: A data communication apparatus improves security against eavesdropping for secret communication by using Y-00 protocol. A multi-level code generation section generates, based on key information, a multi-level code sequence in which a signal level changes so as to be approximately random numbers. A level conversion section irreversibly converts the multi-level code sequence such that a converted multi-level code sequence does not constitute a mapping of the multi-level code sequence. A multi-level processing section generates a multi-level signal having a plurality of levels each corresponding to a combination between the information data and the multi-level code sequence. A modulator section modulates a multi-level signal in a predetermined modulation method and outputs a modulated signal.

Abstract: A highly concealable data communication apparatus based on an astronomical complexity and causing an eavesdropper to take a significantly increased time to analyze a cipher text, is provided. In a multi-level code generation section 111a, a random number sequence generation section 141 generates, based on predetermined key information 11, a plurality of modulation pseudo-random number sequences. The plurality of modulation pseudo-random number sequences is inputted to a multi-level conversion section 142 as a part of an input bit sequence which is converted into a multi-level code sequence 12. A multi-level processing section 111b combines the multi-level code sequence 12 and information data 10, and generates a multi-level signal 13 having a plurality of levels corresponding to a combination of the multi-level code sequence 12 and the information data 10.

Abstract: A data communication apparatus wherein the stealthiness has been enhanced by significantly increasing the time required for a wiretapper to decrypt an encrypted text. The data communication apparatus is constituted by connecting a data transmitting apparatus and a data receiving apparatus via a transmission path. The data transmitting apparatus receives a first predetermined initial value (key information) and information data, generates a multi-valued signal the level of which varies substantially like a random number, and converts the multi-valued signal to a modulated signal of a predetermined modulation format for transmission. The data receiving apparatus demodulates the modulated signal to output the multi-valued signal, and then reproduces the information data from the multi-valued signal and a second predetermined initial value (key information) that is received.

Abstract: A data communication apparatus which causes the eavesdropper to take a significantly increased time to analyze a cipher text and provides high concealability is provided. A multi-level code generation section 111a generates, based on predetermined key information 11, a multi-level code sequence 12 in which a signal level changes so as to be approximately random numbers. A multi-level processing section 111b combines the multi-level code sequence 12 and information data 10, and generates a multi-level signal 13 having a plurality of levels corresponding to the combination of the multi-level code sequence 12 and the information data 10. A modulator section 112 treats the multi-level signal a predetermined modulating processing and generates a modulated signal.

Abstract: Provided is a data communication apparatus which significantly increases time necessary for an eavesdropper to analyze cipher text and which is superior in concealability based on astronomical computational complexity. A multi-level signal, which is generated by using data and key information, has a minor amplitude modulation, which is based on a random number signal generated on a transmission side, overlapped thereon, and is then transmitted. On a receiving side, instead of data decision, three types of decision, i.e., “1”, “0” and “decision impossible”, are performed on a random number signal by using two threshold values whose interval is significantly wider than a modulation amplitude based on random numbers. Information of a bit whose decision is performed successively is returned to the transmission side, and the bit is used commonly as a new key. Accordingly, in a single transmitting/receiving apparatus, cipher text transmission and key distribution can be realized simultaneously.

Abstract: To provide a receiving apparatus which is capable of demodulating information data from a multi-level modulated signal, which is generated by using a Y-00 protocol, without using high-performance component parts. In the receiving apparatus, the soft decision section 211 performs soft decision on the multi-level signal 22, in which a fixed decision level is used. A converted data identification section 214 performs logical decision on a value of the converted information data 25 in accordance with a highest-order bit of a multi-level code sequence 23 and a decision result 24 of the soft decision. A data reproduction section 215 performs an XOR operation between the converted information data 25 and a lowest-order bit of the multi-level code sequence 23, and outputs a resultant thereof as information data 23.

Abstract: In secret communication using a Y-00 protocol, provided is a data communication apparatus which realizes reduction in a random number generation speed by using a plurality of random number generators, and which also ensures security. The data communication apparatus includes: a plurality of random number generation sections 111a to 111f for generating random numbers, which are each a multi-level pseudo random number, by using predetermined key information; and a multi-level signal modulation section 112 for selecting a level, from among multi-levels previously prepared, the level corresponding to information data and a multi-level sequence, which is composed of a combination of values of the random numbers outputted from the plurality of random number generation sections, and for generating a multi-level modulated signal including a noise having a predetermined noise level by using the selected level.

Abstract: In an optical transmission system in which a pulse signal is converted into an optical signal before transmission, a pulse signal demodulation device capable of correctly demodulating the pulse signal is provided. An optical-to-electrical conversion section (31) converts a received optical signal into an electrical signal, and outputs the electrical signal as a received signal. A reception waveform information calculating section (33) outputs, as reception waveform information, information about a shape of a waveform of a short-pulse signal on which a distortion occurring during the time when a short-pulse signal is converted into an optical signal to when the optical signal is converted into a received signal by the optical-to-electrical conversion section (31), is reflected.

Abstract: In an optical transmission system in which a pulse signal is converted into an optical signal before transmission, a pulse signal demodulation device capable of correctly demodulating the pulse signal is provided. An optical-to-electrical conversion section (31) converts a received optical signal into an electrical signal, and outputs the electrical signal as a received signal. A reception waveform information calculating section (33) outputs, as reception waveform information, information about a shape of a waveform of a short-pulse signal on which a distortion occurring during the time when a short-pulse signal is converted into an optical signal to when the optical signal is converted into a received signal by the optical-to-electrical conversion section (31), is reflected.

Abstract: Provided is a data communication apparatus which is highly concealable and significantly increases time necessary for an eavesdropper to analyze cipher text. A multi-level code generation section (156a) generates, by using predetermined key information, a multi-level code sequence in which a signal level changes so as to be random numbers. The multi-level processing section (111b) combines a multi-level code sequence and information data, and generates a multi-level signal having a level corresponding to a combination of the multi-level code sequence and the information data. In the multi-level code generation section (156a), a random number sequence generation section (157) generates a binary random number sequence by using the predetermined key information. A multi-level conversion section (158) generates a multi-level code sequence from the binary random number sequence in accordance with a predetermined encoding rule.

Abstract: A data communication apparatus which improves security against eavesdropping is provided for secret communication using Y-00 protocol. In a data transmitting apparatus 101, a multi-level code generation section 111 generates, based on key information 11, a multi-level code sequence 12 in which a signal level changes so as to be approximately random numbers. A multi-level processing section 112 generates a multi-level signal 13 having a plurality of levels each corresponding to a combination between information data 10 and the multi-level code sequence 12. A level conversion section 113 divides the plurality of levels of the multi-level signal 13 into several groups, and allocates one level of a converted multi-level signal 21 to a plurality of levels included in each of the several groups in an overlapped manner. The level conversion section 113 then converts the multi-level signal 13 into the converted multi-level signal 21.

Abstract: Provided are a data transmitting apparatus and a data receiving apparatus which use a Y-00 protocol and are capable of preventing an eavesdropper's decryption based on a transition pattern of a multi-level signal level. The data transmitting apparatus 101,103 of the present invention includes: a multi-level code generation section 111 for generating, by using predetermined key information 11, a multi-level code sequence 12 in which a value changes so as to be approximately random numbers; and a multi-level signal modulator section 112,125 for generating a converted multi-level signal 23 in accordance with information shared with the receiving apparatus 201,203, the multi-level code sequence 12 and information data 10, modulating the converted multi-level signal 23 in a predetermined modulation method, and outputting a resultant modulated signal 14. The converted multi-level signal 23 is a signal having a plurality of signal point allocations which are different from one another.

Abstract: A data communication apparatus which improves security against eavesdropping is provided for secret communication using Y-00 protocol. A multi-level code generation section 111 generates, based on key information 11, a multi-level code sequence 12 in which signal in which a signal level changes so as to be approximately random numbers. A multi-level processing section 112 combines information data 10 and the multi-level code sequence 12, and generates a multi-level signal 13 having a plurality of levels each corresponding to the combination of the information data 10 and the multi-level code sequence 12. A delayed wave generation section 113 generates, based on a delay profile 19, a delayed wave of the multi-level signal 13, combines the generated delayed wave and the multi-level signal 13, and outputs a multipath signal 20. A modulator section 114 modulates the multipath signal 20 in a predetermined modulation method, and outputs a modulated signal 14.