JP6471903B2 - Optical communication system - Google Patents

Description

  The present invention relates to an optical secret communication that transmits information to be transmitted to a receiver without being known by an eavesdropper, and relates to a highly secure and high-speed optical secret communication system.

  In recent years, businesses utilizing the Internet have rapidly developed, and optical communication networks have been used for transmitting personal information and confidential information. Under such circumstances, it has become important to ensure the safety of information as the optical communication network increases in speed and capacity. Quantum key distribution (QKD) and stream cipher using optical quantum noise (hereinafter referred to as QNSC: Quantum Noise Stream Cipher) are well known as quantum ciphers used for optically secret communication. . The former is said to be able to deliver a key unconditionally and safely by transmitting a common key used in stream cipher transmission with a single photon or weak coherent light (for example, Non-Patent Documents 1 and 2). reference). However, it is necessary to deliver a disposable common key having the same length as the original communication text to the recipient, and there is a problem that the speed of cryptographic communication is limited by the speed of key delivery (several hundred kbps).

  On the other hand, QNSC is expected as a secure common key quantum cipher that can be put into practical use on the current optical network and cannot be decrypted even with infinite calculation capability (for example, Non-Patent Documents 3 to 6, Patent Documents 1 and 2). reference). In QNSC, the phase and / or amplitude of an optical signal is subjected to multi-level modulation using a pseudo-random number generated based on a common key, and data information is included in the phase or amplitude fluctuation of the light (this is called quantum noise). By embedding, the eavesdropper cannot receive the optical signal correctly. Although this scheme does not provide complete secrecy, it is given at the time of light detection by increasing the modulation level multilevel and reducing the amplitude and / or phase of the modulated optical signal. High safety can be achieved by setting the quantum noise to be larger than the interval.

JP 2006-303927 A JP 2014-93764 A

C. H. Bennett and G. Brassard, “Quantum cryptography: Public key distribution and coin tossing”, Proc. IEEE Int. Conf. Computers, Systems and Signal Processing, 1984, pp.175-179 T. Hirano, H. Yamanaka, M. Ashikaga, T. Konishi, and R. Namiki, “Quantum cryptography using pulsed homodyne detection”, Phys. Rev. A 68, 2003, 042331 G. A. Barbosa, E. Corndorf, P. Kumar, H. P. Yuen, “Secure communication using mesoscopic coherent state”, Phys. Rev. Lett., 2003, vol. 90, 227901 O. Hirota, K. Kato, M. Sohma, T. Usuda, K. Harasawa, “Quantum stream cipher based on optical communication”, SPIE Proc. On Quantum Communications and Quantum Imaging, 2004, vol-5551 Osamu Hirota, "Optical communication network and quantum cryptography", IEICE Transactions B, 2004, vol. J87-B, pp. 478-486 M. Nakazawa, M. Yoshida, T. Hirooka, and K. Kasai, “QAM quantum stream cipher using digital coherent optical transmission”, Opt. Express, 2014, vol. 22, pp. 4098-4107

  The QNSCs reported so far have the ability to make it difficult to determine the signal level of the stream cipher generated using the common key due to the quantum noise added to the signal, but the security against eavesdropping of the common key itself It was not guaranteed. Therefore, possessing a common key in advance without eavesdropping between the transmission and reception units is a precondition for ensuring safety, and there is a problem in its practicality.

  An object of the present invention is to newly propose a fusion technology of QNSC and QKD technology, and to provide an optically secret communication system capable of safe and high-speed transmission.

  In order to achieve this object, the optical secret communication system according to the present invention uses quantum noise (white light noise having no amplitude or phase correlation) to mask at least one of the phase and amplitude level of an optical signal. An optical concealment communication system using a stream cipher (QNSC) transmission system, wherein a QNSC signal generated by a transmission unit is encrypted by the transmission unit when transmitted to a reception unit via an optical fiber transmission line. A common key to be used is distributed to the receiving unit together with the QNSC signal using a quantum key distribution technique, and the received QNSC is received using the common key that is unconditionally safely shared between the transmitting and receiving units. The signal is configured to be decoded.

  Here, for the distribution of the common key, for example, a homodyne quantum key distribution technique that can use a commercially available semiconductor laser light source or photodiode is used, and QNSC transmission and quantum key distribution are performed using the same optical fiber transmission line system. Are preferably realized simultaneously.

  In addition, the optical secret communication system according to the present invention uses quantum noise (QNSC) transmission that masks at least one of the phase and amplitude level of an optical signal using quantum noise (white light noise having no amplitude or phase correlation). In the optically secret communication system using the system, a common key used for encryption in the transmission unit is distributed to the reception unit of the QNSC transmission system using quantum key distribution technology via an independent optical fiber transmission line, The reception unit may be configured to decrypt the received QNSC signal using the common key shared unconditionally between the transmission and reception units.

  In this case, the common key may be distributed through a multi-stage relay using a quantum key distribution system of an arbitrary method, and thereby the key distribution distance, that is, the transmission distance of the QNSC signal may be expanded.

  The optical secret communication system according to the present invention preferably uses light intensity modulation, optical phase modulation, or quadrature amplitude modulation as a modulation method used in the above-described QNSC transmission system.

  In the QNSC transmission system, the multilevel value of the data signal to be encrypted may be arbitrarily changed with respect to time, thereby preventing the eavesdropping of the encryption pattern.

  According to the present invention, by combining a QNSC transmission system that excels in high-speed transmission and a QKD system characterized by unconditional safety, it is possible to provide an optically secret communication system that combines high safety and high speed. it can.

It is a block diagram which shows the optical secrecy communication system which concerns on 1st Embodiment of this invention. FIG. 2 is a block diagram illustrating (a) a QNSC transmission unit and (b) a QNSC reception unit of the optically secret communication system illustrated in FIG. 1. It is a block diagram which shows the modification of (a) QNSC transmission part of the optical secrecy communication system shown in FIG. 1, and (b) QNSC reception part. FIG. 2 is a block diagram illustrating (a) a QKD transmission unit and (b) a QKD reception unit of the optically secret communication system illustrated in FIG. 1. It is a block diagram which shows the optical secrecy communication system which concerns on 2nd Embodiment of this invention.

FIG. 1 shows the configuration of the optically secret communication system according to the first embodiment of the present invention. The optically secret communication system illustrated in FIG. 1 includes a QNSC transmission unit 2 that encrypts a data signal using the common key 1 as a seed key, a QKD transmission unit 3 that distributes the common key 1 with a quantum key, and a QNSC transmission unit 2. Two WDM couplers 4 for multiplexing and demultiplexing the QNSC signal (wavelength λ ₁ ) and the QKD signal (wavelength λ ₂ ) respectively output from the QKD transmission unit 3, and the combined QNSC signal and QKD signal Are transmitted from the optical fiber transmission line 5 to the receiving unit, the QNSC receiving unit 6 for decoding the QNSC signal transmitted through the optical fiber transmission line 5, and the quantum key distributed through the optical fiber transmission line 5. QKD receiver 7 for generating 1 and classical channel 8 are provided.

High-speed optical secrecy communication of several 10 to 100 Gbit / s is realized between the QNSC transmission unit 2 and the QNSC reception unit 6 via the optical fiber transmission line 5. On the other hand, a common key used for encryption / decryption of QNSC transmission is distributed between the QKD transmission unit 3 and the QKD reception unit 7 via the optical fiber transmission line 5 and the classical channel 8. The common key may be distributed unconditionally and safely at a speed of, for example, several 10 to 100 kbit / s. Using this common key as a seed key (key length: 50 to 100 bits), a new random number sequence of ²⁵⁰ to ¹⁰⁰ bits is generated by a linear feedback shift register (LFSR) inside the QKD transmission system. Encryption / decryption is performed using For example, 10 QNSC signal Gsymbol / s to generate only one symbol, when the random number sequence and to 20 bits used, the time taken to use up the random number sequence generated by 50-stage LFSR (2 ⁵⁰ bits) T Can be calculated as T = 100 ps × 2 ⁵⁰ /20=5.6×10 ³ seconds. If the seed key is updated in a time sufficiently shorter than one period T of this random number sequence, the random number sequence can be safely used for encryption / decryption without the eavesdropper deciphering the generation pattern of the random number sequence. You can continue. That is, it is sufficient if the seed key of about 50 bits can be updated once per second. Therefore, it can be said that the key distribution speed (several 10 to 100 kbit / s) of the QKD system is sufficient for ensuring the safety of the QNSC transmission system over a long period of time. As described above, by integrating the QKD technology into the QNSC transmission system, an extremely secure common key is used for the QNSC transmission, and as a result, an optical secret communication system having both safety and high speed is realized.

  Furthermore, the QKD system has the ability to detect “spoofing attacks” in which an eavesdropper steals a signal and delivers a copy of the eavesdropped signal as the sender. Therefore, by integrating the QKD technology into the QNSC transmission system, it is possible to newly provide a function for monitoring wiretapping in real time.

  A configuration example of the QNSC transmission unit 2 is shown in FIG. The QNSC transmission unit 2 uses a common key 1 to generate an encrypted digital signal, a QNSC transmission digital signal processing circuit 20, a high-speed D / A conversion circuit 21 that converts the generated encrypted digital signal into an analog signal, A CW (Continuous Wave) light source 11 used as a carrier wave when optically distributing the encrypted analog signal, an optical modulator 12 for optical modulation, a noise source 13 applied to the optically modulated optical signal, and an optical signal And an optical multiplexer 14 for multiplexing the noise signal.

  The QNSC transmission digital signal processing circuit 20 includes a key distribution circuit 22 that distributes the common key 1, a data signal generation circuit 24 that generates binary data, and a random number sequence generation circuit 25 that generates a random number sequence based on the distributed keys. An exclusive-OR circuit 26 and an adder circuit 27 that are used when the n-bit binary data output from the data signal generation circuit 24 is encrypted with the m-bit random number sequence output from the random number sequence generation circuit 25; And an encoder 28 for converting the n + m-bit encrypted binary signal generated by these arithmetic circuits into a modulation signal of a desired format.

  For example, when quadrature amplitude modulation (QAM) is used as the modulation format of the encrypted signal, an encryption circuit 23 including a data signal generation circuit 24, a random number sequence generation circuit 25, an exclusive OR circuit 26, and an addition circuit 27. May be provided for each of the I (in-phase) and Q (quadrature) signal generation. In accordance with this, two high-speed D / A conversion circuits 21 are provided, and a QAM modulator may be used as the optical modulator 12. On the other hand, when optical phase modulation or optical intensity (amplitude) modulation is used as the modulation format of the encrypted signal, only one set of each of the encryption circuit 23 and the high-speed D / A circuit 21 is required. Or a light intensity modulator may be used.

  As the CW light source 11, for example, a narrow line width fiber laser or semiconductor laser may be used. Examples of the noise source 13 include spontaneous emission light output from an erbium-doped optical fiber amplifier or Raman optical amplifier, or an irregular pattern optical signal.

  A configuration example of the QNSC receiver 6 corresponding to the QNSC transmitter 2 of FIG. 2A is shown in FIG. The QNSC transmission unit 6 includes a local light source 29 and a coherent reception circuit 30 for performing homodyne or heterodyne detection on the received QNSC signal, a high-speed A / D conversion circuit 31 for converting the detected analog signal into a digital signal, A QNSC reception digital signal processing circuit 32 is provided for restoring binary data from the received digital signal using the same common key 1 as the QNSC transmission unit 2.

  The QNSC reception digital signal processing circuit 32 performs a reverse operation on the decoder 33 that converts the signal level received by the high-speed A / D conversion circuit 31 from a decimal number to a binary number and the encryption circuit 23 in the transmission unit. And a decoding circuit 34 for restoring the data. The configuration of the decryption circuit 34 is the same as that of the encryption circuit 23 except that a subtraction circuit 35 is used instead of the addition circuit 27.

  For example, when a QNSC signal using QAM as the modulation format of the encrypted signal is subjected to homodyne detection using the local light source 29, the coherent reception circuit 30 may be a 90-degree hybrid and two balanced PDs. Two high-speed A / D conversion circuits 31 and two decoding circuits 34 may be provided for demodulating I and Q signals. On the other hand, when optical phase modulation or optical amplitude modulation is used as the modulation format of the encrypted signal, one balance PD is used for the coherent reception circuit 30, and the high-speed A / D conversion circuit 31 and the decryption circuit 34 are each set. You just have to do it. Further, when using light intensity modulation without code information as the modulation format of the encrypted signal, the local light source 29 is not necessary, and the coherent receiving circuit 30 may be a normal photodiode.

  An example of a method for synchronizing the optical phase of the local light source 29 with the optical phase of the transmitted QNSC signal is a phase control method using an optical phase locked loop circuit or an optical injection locking circuit. Further, when generating a QNSC signal in the QNSC transmission unit 2, a tone signal that is phase-synchronized with the CW light source 1 is set to the polarization orthogonal to the signal, and the tone signal is polarization-separated in the QNSC reception unit 6. It is also possible to employ a self-delayed homodyne detection system that extracts and uses it instead of the local light source 29.

  The QNSC transmission unit 2 and the QNSC reception unit 6 are each provided with a wavelength multiplexing circuit and a wavelength separation circuit, and wavelength division multiplexing transmission using a multi-wavelength light source is performed, thereby increasing the transmission capacity of the optical secret communication system. it can.

  The QNSC transmission unit 2 and the QNSC reception unit 6 may be respectively provided with a polarization multiplexing circuit and a polarization separation circuit, and the transmission capacity of the optically secret communication system can be doubled by using the polarization multiplexing transmission method.

  Another configuration example of the QNSC transmission unit 2 is shown in FIG. The difference from the QNSC transmission unit 2 shown in FIG. 2A is that the number of bits of data to be encrypted (n bits) and the number of bits of a random number sequence used for encryption (m bits) with respect to time. A multi-level switching signal 36, a multi-level switching circuit 37, a plurality of different combinations of n and m bits, and an encoder 38 are newly provided so as to be arbitrarily switched. . Other operations are the same as those of the QNSC transmission unit 2 shown in FIG.

  In the digital signal processing circuit 20 ′ for QNSC transmission, an encryption circuit 23 and an encoder 28 with a plurality of different combinations of n and m bits are prepared in advance, and the multilevel switching circuit 37 has one of them. The selection is made in correspondence with the multi-value switching signal 36. As a result, the encryption algorithm can be arbitrarily switched with respect to time, and the decryption by the eavesdropper can be made more difficult. It should be noted that the higher the bit number n of data, the higher the S / N of the signal necessary for the authorized receiver to correctly determine the threshold value of the data. Therefore, it is important to adjust the amount of noise added to the QNSC signal by the noise source 13 according to the number of bits n of data.

  Further, in order to synchronize between the encryption and decryption circuits in the QNSC transmission unit 2 and the QNSC reception unit 6, for example, the information of the multilevel switching signal 36 is added to the header of the encrypted signal, and the information is encrypted. What is necessary is just to transmit to the QNSC receiving part 6 with a digitization signal. The header information added at this time is controlled by the multilevel switching circuit 37.

  FIG. 3B shows the configuration of the QNSC receiver 6 corresponding to the QNSC transmitter 2 of FIG. The difference from the QNSC receiving unit 6 shown in FIG. 2B is that a multi-value switching signal extraction circuit 39 that extracts a multi-value switching signal 36 from a received signal, and a multi-value switching circuit 37. In this case, a decoding circuit and a decoder 40 having a plurality of different combinations of n and m bits are newly provided. Other operations are the same as those of the QNSC receiving unit 6 shown in FIG.

  In the QNSC reception digital signal processing circuit 32 ′, a plurality of different decoding circuits 34 and decoders 33 having different combinations of n and m bits are prepared in advance, and the multilevel switching circuit 37 selects one of them. A selection is made in correspondence with the extracted multilevel switching signal 36. Thereby, the decryption process by the same combination of n and m bits as the encryption circuit of a transmission part can be implemented.

  A configuration example of the QKD transmission unit 3 is shown in FIG. The QKD transmission unit 3 includes a QKD transmission digital signal processing circuit 43 that generates a secure common key from various information shared with the QKD reception unit 7 via the optical fiber transmission line 5 and the classical channel 8, and a digital signal processing circuit 43. A low-speed D / A conversion circuit 44 for outputting various information in analog, a low-speed A / D conversion circuit 45 for inputting an analog signal to the digital signal processing circuit 43, and a key generated in the digital signal processing circuit 43 A QKD transmission light source 41 and an optical modulator 42 that are used for optically distributing data via the optical fiber transmission line 5 are provided.

  The QKD transmission digital signal processing circuit 43 includes a key data generation circuit 46 that generates key information that is a source of a common key, a base signal generation circuit 47 that defines a ground state of an optical phase used for distribution of the key data, Based on these information, an encoder 48 that converts key data into optical modulation information, key data and base information generated by the transmitter, and information on the reception status at the receiver delivered from the receiver via the classical channel 8 A determination circuit (transmission unit) 49 that determines a key that can be securely distributed based on the common key storage circuit 50 that stores a key determined to be safe as a common key. As the light modulation information converted by the encoder 48, for example, quaternary phase modulation of 0, π / 2, π, 3π / 2 can be used.

  Examples of processing performed by the determination circuit 49 include base collation, error correction, and confidentiality enhancement processing that are generally widely used as quantum key distribution techniques. Various types of information used in these processes are shared between the QKD transmission unit 3 and the QKD reception unit 7 via the classical channel 8.

  On the other hand, it is necessary to consider consistency with the QNSC transmission system when optical distribution of key data using the optical fiber transmission line 5 is performed. In order to integrate with the QNSC transmission system, it is very important to construct a QKD system using optical components that are generally commercially available without using a special light source or photodetector. Therefore, a commercially available semiconductor laser using direct modulation is used as the transmission light source 41, and the information of the key data is distributed on the phase of the optical pulse signal output from the laser. At that time, by distributing the optical pulse signal with the average number of photons weakened to about 1 photon / pulse, safe coherent optical transmission that operates at the quantum noise limit is realized. On the other hand, the receiving unit employs a homodyne detection method that excels in high-sensitivity light detection, and enables light detection using a commercially available photodiode operating at room temperature. As described above, by adopting the quantum key distribution technique based on the homodyne method, it is possible to realize a QKD system excellent in consistency with the QNSC transmission system.

  FIG. 4B shows the configuration of the QKD receiver 7 corresponding to the QKD transmitter 3 in FIG. The QKD receiver 7 includes a QKD reception local light source 51 and a balance PD 52 for homodyne detection of a QKD signal, and an optical modulator for adding observation base information to the output light from the QKD reception local light source 51 42, a low-speed A / D conversion circuit 45 that converts various signals distributed from the QKD transmission unit 3 to the QKD reception unit 7 through homodyne detection signals and classical channels into digital signals, and based on these input signals A QKD reception digital processing circuit 53 that generates a common key and a low-speed D / A conversion circuit 44 that is used when various signals are output from the digital processing circuit are provided.

  The QKD reception digital processing circuit 53 uses an observation base signal used to select a base (one of 0 or π / 2) to be observed when determining the ground state from the phase information of the received QKD signal. The generation circuit 54, the observation base information, the key data information detected by the balance PD 52, and various types of information distributed from the transmission unit via the classical channel 8 (information on each processing of base verification, error correction, and confidentiality enhancement) And a common key accumulating circuit 50 for accumulating a key determined to be safe as a common key.

  As an example of a method for synchronizing the optical phase of the local light source 51 for QKD reception with the optical phase of the transmitted QKD signal, there is a phase control method using an optical phase locked loop circuit or an optical injection locking circuit. Further, when generating a QKD signal in the QKD transmission unit 3, a tone signal that is phase-synchronized with the QKD transmission light source 41 is set to a polarization orthogonal to the signal, and in the QKD reception unit 7, this tone signal is polarized. It is also possible to employ a self-delayed homodyne detection system that separates and extracts and uses it instead of the local light source 51 for QKD reception.

  In order to synchronize the operations of the QKD transmission unit 3 and the QKD reception unit 7, when a weak QKD signal is distributed to the optical fiber transmission line 5, a synchronization trigger signal may be distributed along with it.

  FIG. 5 shows the configuration of the optically secret communication system according to the second embodiment of the present invention. The optically secret communication system illustrated in FIG. 5 includes a QNSC transmission unit 2 that encrypts a data signal using the common key 1 as a seed key, a QKD transmission unit 3 that distributes the common key 1 with a quantum key, and the two transmission units. Optical fiber transmission line 5 and other optical fiber transmission lines 10 for independently transmitting output signals from the optical fiber, optical amplifier 9 for multi-relay transmission of the optical QNSC signal, and QNSC for decoding the transmitted QNSC signal A receiving unit 6, a QKD receiving unit 7 for generating a secure common key 1 from a quantum key distributed through another optical fiber transmission line 10, and a classical channel 8, and a plurality of units for distributing the common key 1 in multiple relays And a QKD system of stages (QKD transmission unit 3, other optical fiber transmission line 10, QKD reception unit 7, classical channel 8).

  In the second embodiment, since the QNSC signal and the QKD signal are transmitted through independent optical fiber transmission lines, the QNSC signal is transmitted to the optical fiber transmission line 5 and the optical amplifier without being restricted by the distributable distance of the QKD system. Long-distance transmission of several hundred km or more can be performed by multi-relay transmission using 9. The operations of the QNSC transmission unit 2 and the QNSC reception unit 6 are the same as in the first embodiment.

  On the other hand, in the distribution of QKD signals, the distance that can be transmitted by one QKD system is limited to about 50 km, but by connecting QKD systems in multiple stages, the common key 1 can be extended over several hundred km or more. Can be delivered. The multi-relay distribution is realized as follows. First, in each stage of the QKD system, a common key is shared by quantum key distribution technology. Here, a key shared by the QKD system at the first stage is a common key 1, and a key shared by the QKD system at the N stage is a common key N. Next, the common key 1 is passed from the first-stage QKD receiver 7 to the second-stage QKD transmitter 3. The received common key 1 is encrypted by the one-time pad method using the common key 2 shared by the second-stage QKD system, and the common key 1 is transferred from the second-stage QKD transmission unit 3 to the QKD reception unit 7. Information is encrypted. Then, the encrypted signal received by the second-stage QKD receiving unit 7 is decrypted using the common key 2, and the information of the common key 1 is restored. By repeatedly performing the one-time pad encryption transmission of the common key 1 information from the third stage onward, the information on the common key 1 can be securely transmitted to the QKD receiving unit 7 at the Nth stage.

  Here, in the QKD system of the second embodiment, a special light source or a photodetector can be used by distributing using another optical fiber transmission line 10 different from QNSC transmission. In addition to the homodyne method using the optical phase of the carrier wave signal as a quantum key distribution method, four types of quantum states are assigned to the information on the polarization state of the signal and the optical phase difference from the previous bit. Conventional techniques such as a distribution method may be used.

  As described above, in the second embodiment, the transmission distance of the optical secret communication system is reduced by using the multi-relay transmission of the QNSC signal using the optical amplifier and the multi-relay distribution of the common key using the multistage QKD system. Can be expanded to over 100 km.

  In the first or second embodiment, light intensity modulation, optical phase modulation, or quadrature amplitude modulation may be used as the modulation method used in the QNSC transmission system.

  In the first or second embodiment, the multilevel value of the data signal to be encrypted in the QNSC transmission system is arbitrarily changed with respect to time, thereby making it difficult to eavesdrop on the encrypted pattern. May be.

  By using the present invention, it is possible to realize optically secret communication capable of transmitting information to be transmitted to a receiver at high speed without being known to an eavesdropper, and its industrial applicability is high.

DESCRIPTION OF SYMBOLS 1 Common key 2 QNSC transmission part 3 QKD transmission part 4 WDM coupler 5 Optical fiber transmission line 6 QNSC reception part 7 QKD reception part 8 Classical channel 9 Optical amplifier 10 Other optical fiber transmission line 11 CW light source 12 Optical modulator 13 Noise source DESCRIPTION OF SYMBOLS 14 Optical multiplexer 20, 20 'QNSC transmission digital signal processing circuit 21 High-speed D / A conversion circuit 22 Key distribution circuit 23 Encryption circuit 24 Data signal generation circuit 25 Random number sequence generation circuit 26 Exclusive OR circuit 27 Addition circuit 28 Encoder 29 Local light source 30 Coherent reception circuit 31 High-speed A / D conversion circuit 32, 32 'QNSC reception digital signal processing circuit 33 Decoder 34 Decoding circuit 35 Subtraction circuit 36 Multilevel switching signal 37 Multilevel switching circuit 38 Multiple Encryption circuit with different combinations of n and m bits, and 39 Encoder 39 Multi-level switching signal extraction circuit 40 Decoding circuit and decoder using different combinations of n and m bits 41 QKD transmission light source 42 Optical modulator 43 QKD transmission digital signal processing circuit 44 Low-speed D / A conversion Circuit 45 Low-speed A / D conversion circuit 46 Key data generation circuit 47 Base signal generation circuit 48 Encoder 49 Determination circuit (transmission unit)
50 Common key saving circuit 51 Local light source for QKD reception 52 Balance PD
53 Digital signal processing circuit for QKD reception 54 Observation base signal generation circuit 55 Judgment circuit (reception unit)

Claims (6)

An optically secret communication system using a quantum noise stream cipher (QNSC) transmission system that masks at least one of a phase and an amplitude level of an optical signal using quantum noise,
When transmitting the QNSC signal generated by the transmission unit to the reception unit via the optical fiber transmission line, the common key used for encryption in the transmission unit is combined with the QNSC signal using a quantum key distribution technique. Delivered to the receiver,
The optically secret communication system, wherein the reception unit is configured to decrypt the received QNSC signal using the common key that is unconditionally and safely shared between the transmission and reception units. In the distribution of the common key, a quantum key distribution technology by a homodyne method that can use a semiconductor laser light source or a photodiode is used,
2. The optically secret communication system according to claim 1, wherein QNSC transmission and quantum key distribution are realized simultaneously using the same optical fiber transmission line system. An optically secret communication system using a quantum noise stream cipher (QNSC) transmission system that masks at least one of a phase and an amplitude level of an optical signal using quantum noise,
The common key used for encryption in the transmitter is distributed to the receiver using quantum key distribution technology via an independent optical fiber transmission line.
The optically secret communication system, wherein the reception unit is configured to decrypt the received QNSC signal using the common key shared unconditionally between the transmission and reception units.   The said common key is distributed via the multistage relay of the quantum key distribution system of arbitrary systems, Thereby, the transmission distance of the said QNSC signal which is a key distribution distance is expanded. Optical secret communication system.   5. The optically secret communication system according to claim 1, wherein light intensity modulation, light phase modulation, or quadrature amplitude modulation is used as a modulation method used in the QNSC transmission system. 6. 6. The multilevel value of a data signal to be encrypted is arbitrarily changed with respect to time in the QNSC transmission system, thereby preventing an eavesdropping of an encryption pattern. The optically secret communication system according to any one of the above.