JP2013201523A - Quantum encryption key distribution system and quantum encryption key reception device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reception device which can perform consistent security certification regardless of characteristics of a photon detector.SOLUTION: In a quantum encryption key distribution system, a quantum encryption key reception device which receives transmission signal light transmitted from a transmission device, comprises: a reference light source which generates reference light and has corrected characteristics; and quantum state measurement means which measures a quantum state of the transmission signal light by comparing the quantum state of the transmission signal light with the quantum state of the reference light.

Description

  The present invention relates to a quantum cryptography key distribution system and a quantum cryptography key receiver.

  With the explosive spread of the Internet and the commercialization of electronic commerce, the social needs of cryptographic technologies such as confidentiality and tampering prevention of communication and personal authentication are increasing. Quantum cryptographic key distribution technology, which is a technology for sharing a secure secret key, is attracting attention.

  FIG. 8 is a block diagram illustrating a general quantum cryptography key distribution system including an eavesdropping device.

  In the quantum cryptography key distribution system shown in FIG. 8, the transmission device 61 includes a light source 62 that generates photons, a 2-bit random number generator 63, and an encoder 64 that encodes key data and a modulated ground state into photon states based on the light source 62. Consists of.

  On the other hand, the receiving device 68 includes a 1-bit random number generator 69, a decoder 6A that modulates the observation ground state into photons based on the random number generator 69, and a photon detector 6B that generates a signal serving as key data. The transmitter 61 and the receiver 68 are connected by an optical transmission line 66. The eavesdropping device 67 is inserted in the middle of the optical transmission line 66 and can freely access the optical transmission line 66 and any signals propagated thereby.

  The quantum cryptography key distribution protocol has a characteristic that modern cryptography cannot prove to be secure, but in proof of its security, the transmitter / receiver can be trusted and leak key data and encode / decode base information, or It is assumed a priori that there is no side channel to control these from the outside. However, since the quantum key distribution device has a transmission path for key transmission, an input / output channel to the transmission path necessarily exists. This input / output channel to the transmission path can be a security risk.

  The problem is that there may be a side channel that passes through this transmission path. The side channel 65 that leaks key data and encoding / decoding base information is transmitted on the transmission side, and the side channel that externally controls these on the reception side. The channel 6C becomes an important problem for security.

  The theoretical model assumes an ideal component device, whereas a device used in reality has various characteristics different from the ideal and causes security vulnerabilities. Quantum hacking of a quantum cryptography key distribution device that exploits such vulnerability has been proposed.

  A transmission side channel used for quantum hacking is known to be generated by expanding the state space of a photon pulse serving as an information carrier due to non-ideality of a light source. In the standard safety proof, it is assumed that the light source produces only a single photon.

  However, in an actual quantum cryptography key distribution device, a weak laser light source or a pseudo single photon light source is used. These non-ideal light sources include states other than the single photon state (vacuum state and multi-photon state), and the possibility of side channel attack using this opens. Although a photon number split attack has been raised as a specific attack (see Non-Patent Document 1), it is considered that these security holes were closed by using a photon or a single photon light source (Non-Patent Document 1). (See Patent Document 2 and Non-Patent Document 3).

  On the other hand, the receiving side channel used for quantum hacking is known to be caused by inappropriate use of a decoder (see Non-Patent Document 4) or non-ideality of a photon detector. Standard security proofs assume the use of an ideal photon detector, called a threshold detector. The threshold detector is a photon detector that reacts not only to a single photon state but also to a multi-photon state and generates a binary detection signal according to the presence or absence of the photon, and its safety proof does not depend on the number of photons. The use of an ideal photon detector having an equal reaction probability for any number of photon states is assumed (see Non-Patent Document 5 and Non-Patent Document 6).

  However, the reaction probability of an actual photon detector depends on the photon number state. By utilizing the deviation from this assumed characteristic, the possibility of side channel attack opens. Various types of side channel attacks (time-shift attack, blinding attack, etc.) are exemplified as specific attack methods, and some have been demonstrated by experiments (see Non-Patent Document 7 to Non-Patent Document 10).

G. Brassard, N. Lutkenhaus, T. Mor, and B.C. Sanders, Phys. Rev. Lett. 85, 1330 (2000). W.-Y.Hwang, Phys. Rev. Lett. 91, 057901 (2003). Nicolas Sangouard and Hugo Zbinden, "What are single photons go o d for ?," arXiv: 1202.0493. R. Gelles and T. Mor, arXiv: 1110.6573. N. J. Beaudry, T. Moroder, and N. Lutkenhaus, "Squashing Models for Optical Measurements in Quantum Communication," Phys. Rev. Lett. 101, 093601 (2008). T. Tsurumaru and K. Tamaki, "Security proof for quantum-key- distribution systems with threshold detectors," PhysRevA. 78, 032302 (2008). L. Lydersen et.al., "Superlinear threshold detectors in quantum cryptography," Phys. Rev. A 84, 032320 (2011). B. Qi, C.-H. F. Fung, H.-K. Lo, and X. Ma, Quantum Inf. Comput. 7, 73 (2007). L. Lydersen, C. Wiechers, C. Wittmann, D. Elser, J. Skaar, and V. Makarov, Nat. Photonics 4, 686 (2010). I. Gerhardt, Q. Liu, A. Lamas-Linares, J. Skaar, C. Kurtsiefer, and V. Makarov, Nat. Commun. 2, 349 (2011). International Conference on IEEE Computers, Systems, and Signal Processing, by Bennett and Brassard (IEEE Int. Conf. On Computers, Systems, and Signal Processing, Bangalore, India, p. 175 (1984)). E. Biham, B. Huttner, and T. Mor, "Quantum cryptographic network based on quantum memories," Phys. Rev. A, 54, 2651 (1996). D. Gottesman, H.-K.Lo, N. Lutkenhaus and J. Preskill, "Security of quantum key distribution with imperfect devices," Quant. Inf. Comp. 5, pp. 325-360 (2004).

  The point of the side channel problem is that a third party may be able to use the quantum state of the carrier other than the signal quantum state assumed in the quantum key distribution protocol.

  In the use of carriers, it is necessary to eliminate such risks by eliminating the generation, observation, encoding and decoding of such unexpected quantum states, or making their presence detectable.

  In particular, the problem on the receiving side channel seems to be more serious than the problem on the transmitting side. This is because the characteristics of the photon detector used are extremely difficult to quantitatively model and vary from device to device, making it difficult to perform general safety certification. The fact that the security of the receiving device depends on the detector characteristics itself is a major cause of shaking the reliability of a practical quantum cryptography key distribution device.

  Regarding the receiving side channel, a new security hole has been pointed out even if the countermeasures are taken into consideration. Even if a countermeasure against a known attack can be taken, a practical quantum cryptography key distribution device is not proven to be secure. It is important that security holes in the quantum cryptography key distribution device be crushed consistently by improving implementation and modeling improved devices to improve security proofs. This is the only method that can achieve provable security that a practical quantum cryptography key distribution device is superior to modern cryptography, and it has been desired to develop a receiving device capable of performing consistent security proof.

  The present invention has been made in view of the above-described problems of a quantum cryptography key distribution apparatus, and provides a receiving apparatus capable of consistently certifying security regardless of the characteristics of the photon detector.

The quantum cryptographic key distribution receiving device of the present invention is a quantum cryptographic key receiving device of a quantum cryptographic key distribution system that receives transmission signal light transmitted from a transmitting device.
A reference light source that generates reference light and is calibrated in advance.
A quantum state measuring means for measuring the quantum state of the transmission signal light by comparing the transmission signal light with the quantum state of the reference light;
It is characterized by having.

  The quantum key distribution system of the present invention is characterized by using the above quantum key receiver.

  According to the present invention, the greatest problem of the conventional receiving apparatus that the safety of the receiving apparatus depends on the detector characteristics is solved, and the reliability of the reference light source and the random number generator arranged in the receiving apparatus is assumed. Thus, it is possible to realize a quantum key distribution device that can consistently prove security regardless of the characteristics of the photon detector included in the receiving device. Thereby, the security of the secret key distributed by the quantum cryptographic key distribution apparatus can be improved.

It is a block diagram which shows the structure of 1st Embodiment of the quantum encryption key receiver used for the quantum encryption key distribution system by this invention. It is a block diagram which shows the structure of 2nd Embodiment of the quantum encryption key receiver used for the quantum encryption key distribution system by this invention. It is a block diagram which shows the structure of 3rd Embodiment of the quantum encryption key receiver used for the quantum encryption key distribution system by this invention. It is a block diagram which shows the structure of 4th Embodiment of the quantum encryption key receiver used for the quantum encryption key distribution system by this invention. It is a figure which shows one Example of the quantum encryption key receiver by this invention. It is a 1st conceptual diagram for qualitatively explaining the security of distribution key data. It is a 2nd conceptual diagram for qualitatively explaining the security of distribution key data. It is a block diagram which shows the structure of a general quantum encryption key distribution system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of an embodiment of a quantum encryption key receiving apparatus used in a quantum encryption key distribution system according to the present invention.

  This embodiment includes a reference light source 11, an encoder 12, a random number generator 13, a quantum collective state comparison and measurement circuit 14, a photodetector group 15, and a key data analysis device 16.

  The quantum state of the light generated by the calibrated reference light source 11 is either one of two states that are quantum mechanically complementary by an encoder (modulator) 12 based on the 1-bit random number generated by the random number generator 13. It is converted to the state of at random. The quantum collective state comparison measurement circuit 14 has two input ports, and the reference light whose state has been converted by the encoder 12 is incident on one input port.

  The signal light transmitted from the transmitting device (not shown) via the optical transmission path 17 is incident on the other input port of the quantum collective state comparison measurement circuit 14. The quantum collective state comparison measurement circuit 14 controls the quantum entanglement of light input to each input port, thereby measuring cooperative quantum states without measuring individual quantum state variables of light incident from the two input ports. A variable (function value of an individual quantum state variable) is measured, and four signal lights indicating measurement results are output.

  The photodetector group 15 is composed of four photodetectors that detect the four signal lights output from the quantum collective state comparison measurement circuit 14. The photodetector group 15 is obtained by the light detection pattern detected by the photodetector group 15. The collaborative quantum state variable is revealed. The found cooperative quantum state variable value is incident on the key data analyzer 16. The key data analysis device 16 receives random number data used for complementary state conversion synchronized with the cooperative quantum state variable value, and base modulation data (not shown) announced by the sender. The content is analyzed and the security key is extracted.

  The arrangement of the encoder 12, the random number generator 13, the comparison measurement circuit 14, and the photodetector group 15 can be switched between the two incident lights. This reflects that the quantum collective state comparison measurement circuit 14 performs a comparative measurement of the quantum state of light incident from two input ports. FIG. 2 is a block diagram showing the configuration of the second embodiment of the quantum key receiving apparatus according to the present invention, in which this arrangement is replaced.

  The present embodiment includes a reference light source 21, a decoder (demodulator) 22, a random number generator 23, a quantum collective state comparison / measurement circuit 24, a photodetector group 25, and a key data analysis device 26.

  The quantum collective state comparison and measurement circuit 24 has two input ports, and light generated by the calibrated reference light source 21 is incident on one input port. The signal light transmitted from the transmitting device (not shown) via the optical transmission path 27 is converted into two states that are quantum mechanically complementary by the decoder 22 based on the 1-bit random number generated by the random number generator 23. Are randomly converted into one of the states and incident on the other input port of the quantum collective state comparison measurement circuit 24.

  The quantum collective state comparison and measurement circuit 24 controls the quantum entanglement of light input to each input port, thereby measuring cooperative quantum states without measuring individual quantum state variables of light incident from the two input ports. A variable (function value of an individual quantum state variable) is measured, and four signal lights indicating measurement results are output.

  The photodetector group 25 is composed of four photodetectors that detect the four signal lights output from the quantum collective state comparison and measurement circuit 24. The photodetector group 25 is obtained by the light detection pattern detected by the photodetector group 25. The collaborative quantum state variable is revealed. The found cooperative quantum state variable value is incident on the key data analyzer 26. The key data analyzer 26 receives random number data used for complementary state conversion synchronized with cooperative quantum state variable values, and base modulation data (not shown) announced by the sender. The content is analyzed and the security key is extracted.

  In the embodiment shown in FIG. 1, the encoder (modulator) 12 performs complementary state conversion on the reference light, whereas in this embodiment, the decoder (modulator) is used for the signal light. 22 performs complementary state conversion. The variation in the arrangement of the state conversion only affects the analysis logic in the key data analysis device 26, and both are equivalent.

  In the quantum key distribution protocol, the BB84 protocol, which uses single photon or weak laser light of single photon level as signal light and encodes key data in a two-dimensional state modulation space such as polarized light or time bin, is the most reliable. It is known as a protocol (see Non-Patent Document 11).

  FIGS. 3 and 4 respectively show the configurations of a third embodiment and a fourth embodiment of a quantum encryption key receiving device used in the quantum encryption key distribution system according to the present invention, which performs a reception operation using the BB84 protocol. It is a block diagram.

  In the third and fourth embodiments, single photon light sources 31 and 41 are used as reference light sources 11 and 12 in each embodiment shown in FIGS. 1 and 2, and bells are used as quantum collective state comparison measurement circuits 14 and 24, respectively. This is an example using the state measurement circuits 34 and 44.

  The operations of the single photon light source 31, the encoder 32, the random number generator 33, the bell state measurement circuit 34, the photodetector group 35, and the key data analyzer 36 shown in FIG. 3 are the same as those of the reference light source 11 shown in FIG. , Encoder 12, random number generator 13, quantum collective state comparison and measurement circuit 14, photodetector group 15, and key data analyzer 16, and single photon light source 41, decoder 42, shown in FIG. The operations of the random number generator 43, the bell state measurement circuit 44, the photodetector group 45, and the key data analysis device 46 are the same as the reference light source 21, decoder 22, random number generator 23, and quantum collective state comparison measurement circuit shown in FIG. 24, the same as the photodetector group 25 and the key data analyzer 26.

  As an example of the calibrated light source 11, in addition to the single photon light source, a weak coherent light source that is used as a calibrated light source in the transmitter in the fluorescent photon protocol and randomly varies in intensity to several calibrated intensities can be considered ( Non-Patent Documents 2 and 3).

[Description of operation]
Hereinafter, the operation of the receiving device of the quantum cryptography key distribution device according to the present invention will be described with reference to FIG. 3, FIG. 4, and FIG. 5, taking the BB84 protocol as an example.

  In the embodiment shown in FIG. 3, the photons emitted from the single photon light source 31 in synchronization with the photons transmitted from the transmission device are complemented by the encoder 32 based on the 1-bit random number generator 33. The state is converted to one of the non-orthogonal two-signal quantum states. The photons are incident on the bell state measurement circuit 34 together with the transmission photons from the transmitter. Bell state measurement circuit 34 is a cooperative quantum state variable of signal quantum states of two incident photons of four possible outcomes.

Measure the value of. here,

Is the x (y), z component operator corresponding to the complementary non-orthogonal two-signal quantum state,

The value of takes 0 or 1. i = 0 (1) means that transmission / reception data correlates (anti-correlation) with respect to data that matches the selection basis of the transmission / reception device. The measurement result is determined by the photon detection pattern of the photon detector group 35. Based on the announcement of the selection basis of the transmission device and the random number data of the random number generator 33 indicating the selection basis of the reception device, the key data analysis device 36 extracts meaningful key data that matches the selection basis of the transmission / reception device, The bit values of these measurement result data are inverted as necessary to obtain key data candidates. A secure final key is extracted by passing the candidate key data random number bit string to a subsequent process such as error correction or confidentiality enhancement.

  In the embodiment shown in FIG. 4, the only difference is that the state conversion to a complementary non-orthogonal two-signal quantum state is performed by the decoder 42 on the transmitted photons from the transmitter, and the others are the same. The key data analysis device 46 extracts meaningful key data candidates based on the announcement of the transmission device, the random number data of the random number generator 43, and the measurement result found by the bell state measurement circuit 44, and passes them to the subsequent process.

  FIG. 5 is an example corresponding to the embodiment shown in FIG. 3 and shows a quantum key receiving device according to the present invention configured using a probabilistic bell state measurement circuit with a polarization state space as a signal quantum state space. It is a figure which shows one Example.

  This embodiment includes a single photon light source 51, a polarization modulator 52, a random number generator 53, a beam splitter 54, a polarization beam splitter 55, a photon detector 56-59, a simultaneous signal detection analyzer 5A, and a key data analysis device 5B. It is configured.

  The beam splitter 54 and the polarization beam splitter 55 that separates the vertical polarization form a stochastic bell state measurement circuit, the polarization modulator 52 acts as an encoder, the photon detectors 56-59, and the simultaneous signal detection analyzer 5A A photon detector group is configured.

  The photons generated by the single photon light source 51 are converted into vertical or obliquely polarized light by the polarization modulator 52 based on the data generated by the 1-bit random number generator 53, and sent through the transmission path 5C. The light is incident on the beam splitter 54 together with the transmitted photons from the transmitting device (not shown). Two propagating photons from the beam splitter 54 are respectively incident on two polarization beam splitters 55, and are separated and emitted according to the polarization state.

  Propagating photons are detected by the photon detectors 56-59, and only two of the four possible cooperative quantum state variable measurement results are deterministically determined by the simultaneous detection pattern, and the other two results. Cannot be determined.

  Based on the detection pattern, the simultaneous signal detection analyzer 5A sorts data for which a definitive discrimination result is obtained from data that cannot be discriminated, and discards the latter. The key data analysis device 5B is necessary for the basic bit 0 for data that matches the selection basis of the transmission / reception device and obtains a definitive discrimination result based on the announcement of the transmission device and the random number data of the random number generator 53. The key data candidate is obtained after performing bit inversion.

  Next, the security of the distributed key data obtained in this way will be qualitatively described.

  FIG. 6 is a first conceptual diagram for qualitatively explaining the security of distributed key data. The above diagram combines a receiving device according to the present invention with an ideal transmitting device that transmits a single photon. It is a block diagram which shows a structure.

  The single photon light source 71, the random number generator 72, the encoder 73, the bell state measurement circuit 74, and the photon detector group 75 correspond to the receiving device, and the single photon light source 76, the random number generator 77, and the encoder 78 correspond to the transmitting device. To do.

  The apparatus system shown in the upper diagram of FIG. 6 is a time reversal system of the quantum entangled light source-based quantum cryptography key distribution apparatus system shown in the lower diagram of FIG. 6, and is called a time reversal quantum entanglement scheme (Non-Patent Document 12). reference).

  In the quantum cryptography based on the quantum entangled light source, if the reliability of the photon detector group 79 and the random number generator 7A arranged in the territory of the sender / receiver can be guaranteed, the security of the distributed key can be secured without depending on the reliability of the quantum entangled light source 7C. Can prove sex. Similarly, in the time reversal quantum entanglement scheme, if the reliability of the single photon light source 71/76 and the random number generator 72/77 arranged in the territory of the transmitter / receiver can be ensured, the bell state measurement circuit 74 and the photon detection It is shown in Non-Patent Document 12 that the security of the distribution key can be proved without depending on the reliability of the device group 75 as described below.

  FIGS. 7A and 7B are second conceptual diagrams for qualitatively explaining the security of distributed key data shown in Non-Patent Document 12. FIG. FIGS. 7 (a) and 7 (b) both show a scheme of a configuration in which the quantum entanglement is performed by Bell state measurement 82/86 on a half-break of a quantum entangled photon pair generated by two quantum entangled light sources 81/84.

  As shown in FIG. 7B, it is assumed that the observation of the half-break of the quantum entangled photon pair in A and B is performed prior to the bell state measurement 86 in time.

  If the observations at A and B are projection measurements to the four states used in the BB84 protocol called the BB84 state, the quantum state of the other half-cracked system toward the bell state measurement 86 after observation becomes the BB84 state 85, and the time Equivalent to the inverted quantum entanglement scheme.

  On the other hand, as shown in FIG. 7 (a), assuming that the Bell state measurement 82 is performed prior to the observation of the single splitting of the quantum entangled photon pair at A and B, the other half splitting system toward A and B after the observation is obtained. The quantum state becomes the maximum quantum entangled state 83.

  Since the maximum quantum entangled state is isolated from all systems including the quantum system used by the eavesdropper, the eavesdropper cannot obtain any information from this system. Whether the quantum state of the system towards A and B is the maximum quantum entangled state is delivered using a random complementary basis, regardless of the reliability of the two quantum entangled light sources 84 and the bell state measurement 86. It can be experimentally verified from the qubit error of the distributed encryption key.

  If the quantum bit error of the distributed encryption key obtained as described above is sufficiently small, it is proved that the quantum state of the system toward A and B is the maximum quantum entangled state, and the security of the distributed key is proved.

  Here, the observation execution timing is arbitrary, and the configuration shown in FIG. 7A and the configuration shown in FIG. 7B are quantum-mechanically equivalent. As a result, the time-reversed quantum entanglement scheme is used. The security of the distribution key is also proved.

  In the above description, it is assumed that the light source of the transmission device is a reliable single photon light source. However, when a multiphoton component is mixed, it corresponds to the multiphoton component by the method of Non-Patent Document 13. By discarding a part of the key data, security can be ensured and it can be proved that the method of the present invention is safe.

  As described above, the difficulty in proving the safety of the receiving apparatus is caused by the difficulty in quantitatively modeling the characteristics of the photon detector used. Compared to this, it is easy to evaluate the light source characteristics and quantitatively model them. Therefore, in the present invention, it is assumed that the light source characteristics can be evaluated in a safe environment and the characteristics can be known with high reliability. By comparing and observing the quantum state of the transmitted signal light using the known quantum state of the photon generated by this light source as a reference, the quantum state of the transmitted signal light other than the known quantum state is rejected, and the corresponding observation data is It becomes possible to detect a side channel attack on the receiving side as an error increase in transmission key data, or to be excluded later. Since the quantum state of the reference light is known, it is possible to calculate a secure key generation amount when a quantum encryption key distribution protocol with a limited signal quantum state is executed.

  In the above description, the operation principle of the present invention has been described by taking the BB84 protocol using a single-photon light source or a weakly coherent light source and using the polarization state space as the signal state space as an example. The receiving device of the quantum cryptographic key distribution apparatus including the reference light source and the quantum collective state comparison measurement can be applied to an arbitrary light source, an arbitrary signal state space, and an arbitrary quantum cryptographic key distribution protocol.

  For example, the polarization state space may be a time bin state space, and can be applied in principle to a quantum key distribution scheme using coherent light and its phase space.

  Further, the present invention has been described as a receiving device of the quantum cryptography key distribution device. However, the present invention is not limited to the quantum key distribution protocol, and can be used as a reception device when executing a task using any quantum cryptography protocol.

  Furthermore, the present invention is useful as a receiving apparatus for executing any quantum information task, not limited to the quantum cryptography protocol.

11, 21 Reference light source 12, 32, 73, 78, 7B Encoder 13, 23, 33, 43, 53, 72, 77, 7A Random number generator 14, 15 Quantum collective state comparison measurement circuit 15, 25, 35, 45, 75, 79 Photodetector group 16, 26, 36, 46, 5B Key data analyzer 17, 27, 37, 47, 5C Optical transmission line 22, 42 Decoder 31, 41, 51, 71, 76 Single photon light source 34 , 44, 73 Bell state measurement circuit 52 Polarization modulator 54 Beam splitter 55 Polarization beam splitter 56-59 Photon detector 5A Simultaneous signal detection analyzer 7C EPR light source 81, 84 Quantum entangled light source 82, 86 Bell state measurement 83 Maximum quantum entanglement State 85 BB84 state

Claims (9)

In the quantum key receiving device of the quantum key distribution system that receives the transmission signal light transmitted from the transmission device,
A reference light source that generates reference light and is calibrated in advance.
A quantum state measuring means for measuring the quantum state of the transmission signal light by comparing the transmission signal light with the quantum state of the reference light;
A quantum cryptography key receiving device comprising: The quantum cryptography key receiving device according to claim 1,
The quantum measuring means is
A random number generator for generating random numbers;
An encoder that converts the reference light into one of two quantum mechanically complementary states according to the random number generated by the random number generator;
A quantum cryptography key receiving device comprising: a measurement circuit that inputs the transmission signal light and the encoder output and measures cooperative quantum state variables by controlling the quantum entanglement. The quantum cryptography key receiving device according to claim 1,
The quantum measuring means is
A random number generator for generating random numbers;
An encoder for converting the transmission signal light into one of two quantum mechanically complementary states according to the random number generated by the random number generator;
A quantum cryptographic key receiving apparatus comprising: a reference circuit that inputs the reference light and the encoder output and measures a cooperative quantum state variable by controlling the quantum entanglement. In the quantum key receiving device according to claim 2 or 3,
The quantum key receiving apparatus, wherein the measurement circuit is a bell state measurement circuit. In the quantum key receiving device according to any one of claims 2 to 4,
A key data analysis device for extracting a safety key from the cooperative quantum state variable measured by the measurement circuit, the output of the random number generator, and the base modulation data announced by the transmitter that has transmitted the transmission signal light; A quantum cryptography key receiving device comprising: In the quantum key receiving apparatus according to any one of claims 1 to 5,
A quantum cryptography key receiving device, wherein the reference light source is a single photon light source. In the quantum key receiving apparatus according to any one of claims 1 to 5,
A quantum key receiving apparatus, wherein the reference light source is a coherent light source. The quantum cryptography key receiving device according to claim 7, wherein
A quantum cryptography key receiving device, wherein the coherent light source is a coherent light source whose intensity varies with time. A quantum cryptography key distribution system using the quantum cryptography key receiving device according to any one of claims 1 to 8.

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