Quantum key distribution system, quantum key distribution device, and quantum key distribution method

Abstract

To make it possible to easily select a transmission path in which encryption key generation speed is higher.SOLUTION: A quantum key distribution system comprises: a transmitter for transmitting photons to be used for generation of an encryption key by quantum key delivery; and a receiver for receiving the photons. The transmitter comprises a quantum signal transmission section for transmitting the photons as a quantum signal. The receiver comprises a quantum signal reception section for receiving the quantum signal. The quantum key distribution system comprises: a first switch section for selecting a transmission path for transmitting the quantum signal from a plurality of transmission paths; and a second switch section for selecting a transmission path for receiving the quantum signal from the plurality of transmission paths.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to a quantum key distribution system, a quantum key distribution device, and a quantum key distribution method. [Background technology]

[0002] Quantum key distribution (QKD) systems have been known for some time, which utilize the quantum mechanical properties of light to theoretically share encryption keys between two remote locations without disclosing information to a third party (eavesdropper) with any computing power. A QKD device on the transmitting side, which outputs the encryption key on photons, is paired with a QKD device on the receiving side, which detects the photons. The transmitting and receiving QKD devices are connected, for example, by two optical transmission paths. Specifically, one optical fiber is assigned to a quantum signal channel that transmits the encryption key on photons, and the other optical fiber is assigned to a classical signal channel that is mainly used for exchanging control information. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5813575 [Non-patent literature]

[0004] [Non-Patent Document 1] ETSI GS QKD 011 V1.1.1(2016-05) Summary of the Invention [Problem to be solved by the invention]

[0005] However, with conventional techniques, it has not been easy to select a transmission path that will increase the encryption key generation speed. [Means for solving the problem]

[0006] A quantum key distribution system according to an embodiment includes a transmitting device that transmits photons used to generate a cryptographic key by quantum key distribution, and a receiving device that receives the photons. The transmitting device includes a quantum signal transmitting unit that transmits the photons as a quantum signal. The receiving device includes a quantum signal receiving unit that receives the quantum signal. The system also includes a first switch unit that selects a transmission path for transmitting the quantum signal from a plurality of transmission paths, and a second switch unit that selects a transmission path for receiving the quantum signal from the plurality of transmission paths. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a quantum key distribution system according to the first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of a default transmission path according to the first embodiment. [Figure 3] FIG. 3 is a diagram illustrating an example of an intersecting transmission line according to the first embodiment. [Figure 4] FIG. 4 is a flowchart showing an example of the quantum key distribution method according to the first embodiment. [Figure 5] FIG. 5 is a diagram illustrating an example of the configuration of a quantum key distribution system according to the second embodiment. [Figure 6] FIG. 6 is a diagram illustrating an example of the configuration of a quantum key distribution system according to the third embodiment. [Figure 7] FIG. 7 is a diagram illustrating an example of the configuration of a quantum key distribution system according to the fourth embodiment. [Figure 8] FIG. 8 is a diagram illustrating an example of the configuration of a quantum key distribution system according to the fifth embodiment. [Figure 9] FIG. 9 is a diagram illustrating an example of the configuration of a quantum key distribution system according to the sixth embodiment. [Figure 10] FIG. 10 is a diagram illustrating an example of the configuration of a quantum key distribution system according to the seventh embodiment. [Figure 11] FIG. 2 is a diagram illustrating an example of the hardware configuration of the QKD device according to the first to seventh embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a quantum key distribution system, a quantum key distribution device, and a quantum key distribution method will be described in detail with reference to the accompanying drawings.

[0009] The encryption key generation speed of a quantum key distribution system is affected by the optical transmission path between the sending QKD device and the receiving QKD device. The encryption key generation speed is indicated by the increase per unit time of the encryption key shared by the sending QKD device and the receiving QKD device. A typical example of an optical transmission path is an optical fiber. Light passing through an optical fiber is affected by crosstalk between optical fibers, bending of the fiber, fiber vibration, optical loss at the fiber connection surface, intrusion of light from outside, temperature, humidity, and stress.

[0010] Because quantum signal channels transmit encryption keys on photons, their optical power is much lower than that of classical signal channels. As a result, quantum signal channels are more susceptible to the intrusion of external light into the optical transmission path than classical signal channels. Even if the external light is weak, the transmitted photons are buried in the external light because their inherent optical power is low, making it difficult for the receiving QKD device to correctly detect them.

[0011] Furthermore, if the optical loss in the optical transmission line increases for some reason, the optical power of the quantum signal channel reaching the receiving QKD device will further decrease, making it more difficult for the receiving QKD device to correctly detect the signal. For these reasons, the quantum signal channel is more susceptible to the effects of the optical transmission line between the sending and receiving QKD devices than the classical signal channel.

[0012] Assume that one of two optical fibers is assigned to a quantum signal channel and the other to a classical signal channel. Assume also that the specifications, characteristics, and external environment of the two optical fibers are the same. Suppose the state of the two optical fibers changes to one where external light enters only the optical fiber assigned to the quantum signal channel. In this case, using the optical fiber that allows external light to enter for transmission of the classical signal channel and the optical fiber that does not allow external light to enter for transmission of the quantum signal channel will improve the detection accuracy of the quantum signal channel at the receiving QKD device, thereby increasing the speed of cryptographic key generation.

[0013] For example, if the optical fiber assigned to the quantum signal channel has a higher optical loss than the optical fiber assigned to the classical signal channel, with other characteristics remaining the same, using the optical fiber with the higher optical loss for transmitting the classical signal channel and the optical fiber with no higher optical loss for transmitting the quantum signal channel will improve the detection accuracy of the quantum signal channel at the receiving QKD device, thereby increasing the speed of cryptographic key generation.

[0014] Previously, to switch optical transmission paths, technicians had to switch optical fibers on both the sending and receiving QKD devices and check whether the encryption key generation speed actually increased. If the encryption key generation speed did not increase after the switch, it was necessary to return to the original optical fiber connection.

[0015] (First embodiment) In the first embodiment, a quantum key distribution system having a function of selecting an optical transmission line will be described.

[0016] [Configuration example] 1 is a diagram showing an example of the configuration of a quantum key distribution system 100 according to the first embodiment. The quantum key distribution system 100 according to the first embodiment includes QKD devices 10 and 20, and optical transmission lines 31a and 31b.

[0017] The transmitting QKD device 10 comprises a control unit 11, a quantum signal transmission unit 12, a classical signal communication unit 13, and a switch unit 14. The receiving QKD device 20 comprises a control unit 21, a quantum signal reception unit 22, a classical signal communication unit 23, and a switch unit 24.

[0018] The QKD device 10 on the transmitting side transmits the encryption key on a photon to the QKD device 20 on the receiving side.

[0019] The control unit 11 controls the quantum signal transmission unit 12, the classical signal communication unit 13, and the switch unit 14. The control unit 11 is realized by at least one control device. This control device may be, for example, a central processing unit (CPU), a microprocessor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof.

[0020] The quantum signal transmission unit 12 transmits the encryption key on a photon. The classical signal communication unit 13 transmits and receives signals on a classical signal channel to and from the classical signal communication unit 23. In the classical signal channel, a control signal for quantum key distribution is transmitted and received as a classical signal.

[0021] The switch unit 14 is a 2x2 optical switch that switches the roles of the optical transmission lines 31a and 31b in response to a command from the control unit 11.

[0022] The receiving-side QKD device 20 receives the encryption key transmitted on photons by the transmitting-side QKD device 10. The control unit 21 controls the quantum signal receiving unit 22, the classical signal communication unit 23, and the switch unit 24. Like the control unit 11 described above, the control unit 21 is realized by at least one control device. The quantum signal receiving unit 22 receives the quantum key transmitted on photons by the quantum signal transmitting unit 12. The classical signal communication unit 23 transmits and receives signals on a classical signal channel to and from the classical signal communication unit 13. The switch unit 24 is a 2x2 optical switch that switches the roles of the optical transmission paths 31a and 31b in response to commands from the control unit 21.

[0023] The optical transmission line 31a is used as a transmission line for a quantum signal channel or a classical signal channel, and the optical transmission line 31b is used as a transmission line for a quantum signal channel or a classical signal channel.

[0024] Hereinafter, when there is no need to distinguish between the optical transmission lines 31a and 31b, they will simply be referred to as the optical transmission line 31.

[0025] Fig. 2 is a diagram showing an example of a default transmission path in the first embodiment. The example in Fig. 2 shows a case where the default transmission path is selected by both switch units 14 and 24. The encryption key transmitted on a photon from the quantum signal transmitter 12 is received by the quantum signal receiver 22 via optical transmission path 31a. The classical signal communication unit 13 and the classical signal communication unit 23 transmit and receive classical signal channel signals to and from each other via optical transmission path 31b.

[0026] Fig. 3 is a diagram showing an example of an intersecting transmission path in the first embodiment. The example in Fig. 3 shows a case where the intersecting transmission path is selected by both switch units 14 and 24. The encryption key transmitted on a photon from the quantum signal transmitting unit 12 is received by the quantum signal receiving unit 22 via optical transmission path 31b. The classical signal communication unit 13 and the classical signal communication unit 23 transmit and receive classical signal channel signals to and from each other via optical transmission path 31a.

[0027] [Example of quantum key distribution method] Fig. 4 is a flowchart showing an example of the quantum key distribution method according to the first embodiment. The example in Fig. 4 shows a flowchart for selecting an optical transmission path that will result in a higher encryption key generation speed in the quantum key distribution system 100 having a function for selecting the optical transmission path 31a or 31b.

[0028] First, the control units 11 and 12 cooperate to stop the generation of the encryption key, thereby stopping the transmission of the quantum signal (step S201).

[0029] Next, the switch unit 14 selects the default transmission path in response to a command from the control unit 11, and the switch unit 24 selects the default transmission path in response to a command from the control unit 21 (step S202).

[0030] Next, the control units 11 and 12 cooperate to start generating an encryption key and measure the encryption key generation speed V1 (step S203).

[0031] Next, the control units 11 and 12 cooperate to stop the generation of the encryption key, thereby stopping the transmission of the quantum signal (step S204).

[0032] Next, the switch unit 14 selects the intersecting transmission path in response to a command from the control unit 11, and the switch unit 24 selects the intersecting transmission path in response to a command from the control unit 21 (step S205).

[0033] Next, the control units 11 and 12 cooperate to start generating an encryption key and measure the encryption key generation speed V2 (step S206).

[0034] Next, the control unit 11 or 12 determines whether the encryption key generation speed V1 is greater than the encryption key generation speed V2 (step S207). If the encryption key generation speed V1 is not greater than the encryption key generation speed V2 (step S207, No), this flow ends.

[0035] If the encryption key generation rate V1 is higher than the encryption key generation rate V2 (Yes at step S207), the control units 11 and 12 cooperate to stop the generation of the encryption key, thereby stopping the transmission of the quantum signal (step S208).

[0036] Next, the switch unit 14 selects the default transmission path in response to a command from the control unit 11, and the switch unit 24 selects the default transmission path in response to a command from the control unit 21 (step S209).

[0037] Next, the control units 11 and 12 cooperate to start generating an encryption key (step S210).

[0038] The encryption key generation speeds V1 and V2 may be measured by the control unit 11, the control unit 21, or the control units 11 and 21 in cooperation with each other.

[0039] As described above, in the quantum key distribution system 100 of the first embodiment, the QKD device 10 (an example of a transmitting device) transmits photons used to generate encryption keys through quantum key distribution. The QKD device 20 (an example of a receiving device) receives the photons. The quantum signal transmitting unit 12 transmits the photons as quantum signals. The quantum signal receiving unit 22 receives the quantum signals. The switch unit 14 on the transmitting side selects a transmission path for transmitting the quantum signal from the two optical transmission paths 31a and 31b. Furthermore, the switch unit 24 on the receiving side selects a transmission path for receiving the quantum signal from the two optical transmission paths 31a and 31b.

[0040] As a result, the quantum key distribution system 100 of the first embodiment can more easily select an optical transmission path 31 that will increase the encryption key generation speed. For example, periodically or at an appropriate time (for example, when encryption key generation starts, or when the encryption key generation speed drops), it can more easily reselect an optical transmission path 31 that will increase the encryption key generation speed.

[0041] As a result, the quantum key distribution system 100 of the first embodiment can maintain a higher encryption key generation speed than conventional systems.

[0042] (Second embodiment) Next, a second embodiment will be described. In the description of the second embodiment, the same description as in the first embodiment will be omitted, and only the differences from the first embodiment will be described.

[0043] [Configuration example] 5 is a diagram showing an example of the configuration of a quantum key distribution system 100-2 according to the second embodiment. The quantum key distribution system 100-2 according to the second embodiment includes QKD devices 10 and 20, and n optical transmission lines 31-1 to 31-n.

[0044] The transmitting QKD device 10 comprises a control unit 11, a quantum signal transmission unit 12, a classical signal communication unit 13, and a switch unit 15. The receiving QKD device 20 comprises a control unit 21, a quantum signal reception unit 22, a classical signal communication unit 23, and a switch unit 25.

[0045] The transmitting-side QKD device 10 transmits the encryption key on a photon to the receiving-side QKD device 20. The operations of the control unit 11, quantum signal transmission unit 12, and classical signal communication unit 13 are the same as those in the first embodiment, and therefore will not be described here.

[0046] The switch unit 15 is a 2×N optical switch that selects, in response to a command from the control unit 11, a transmission line to be used for the quantum signal channel and a transmission line to be used for the classical signal channel from the optical transmission lines 31-1 to 31-n.

[0047] The receiving-side QKD device 20 receives the encryption key transmitted on the photons by the transmitting-side QKD device 10. The operations of the control unit 21, quantum signal receiving unit 22, and classical signal communication unit 23 are the same as those in the first embodiment, and therefore will not be described here.

[0048] The switch unit 25 is a 2xN optical switch that selects, in response to a command from the control unit 21, a transmission line to be used for the quantum signal channel and a transmission line to be used for the classical signal channel from the optical transmission lines 31-1 to 31-n.

[0049] Disturbances to the optical transmission paths 31-1 to 31-n and the characteristics of the optical transmission paths 31-1 to 31-n change over time. In the second embodiment, the control units 11 and 21, for example, test all of the optical transmission paths 31-1 to 31-n and measure the encryption key generation speed for each path. Then, based on the measurement results, the control units 11 and 21 select the optical transmission path 31 that provides the highest encryption key generation speed, thereby maintaining a higher encryption key generation speed than before.

[0050] Specifically, for example, the control units 11 and 21 periodically measure the encryption key generation speed for each of the multiple optical transmission paths 31-1 to 31-n, and determine the transmission path for transmitting the quantum signal based on the encryption key generation speed.

[0051] Furthermore, for example, when starting to generate an encryption key, the control units 11 and 21 measure the encryption key generation speed for each of the multiple optical transmission paths 31-1 to 31-n, and determine the transmission path for transmitting the quantum signal based on the encryption key generation speed.

[0052] Furthermore, for example, when the encryption key generation rate becomes lower than a threshold, the control units 11 and 21 measure the encryption key generation rate for each of the multiple optical transmission paths 31-1 to 31-n, and determine the transmission path for transmitting the quantum signal based on the encryption key generation rate.

[0053] As described above, the control unit 11 controls the switch unit 15, and the control unit 21 controls the switch unit 25, thereby determining the transmission line for the quantum signal channel that will result in the highest encryption key generation speed from among the n optical transmission lines 31-1 to 31-n. Then, the control unit 11 controls the switch unit 15, and the control unit 21 controls the switch unit 25, thereby determining the transmission line for transmitting and receiving the classical signal of the classical signal channel from among the n-1 transmission lines excluding the transmission line used for the quantum signal channel.

[0054] As a result, the quantum key distribution system 100-2 of the second embodiment can achieve the same effects as those of the first embodiment. Compared to the first embodiment, the number of options for the optical transmission line 31 increases from two to n, which may increase the speed of generating encryption keys for the transmission line of the quantum signal channel.

[0055] (Third embodiment) Next, a third embodiment will be described. In the description of the third embodiment, the same description as in the second embodiment will be omitted, and only the differences from the second embodiment will be described.

[0056] [Configuration example] 6 is a diagram showing an example of the configuration of a quantum key distribution system 100-3 according to the third embodiment. The quantum key distribution system 100-3 according to the third embodiment includes QKD devices 10 and 20, n optical transmission lines 31-1 to 31-n, and an optical transmission line 41.

[0057] The transmitting QKD device 10 comprises a control unit 11, a quantum signal transmission unit 12, a classical signal communication unit 13, and a switch unit 16. The receiving QKD device 20 comprises a control unit 21, a quantum signal reception unit 22, a classical signal communication unit 23, and a switch unit 26.

[0058] The transmitting-side QKD device 10 transmits the encryption key on a photon to the receiving-side QKD device 20. The operations of the control unit 11, quantum signal transmission unit 12, and classical signal communication unit 13 are the same as those in the second embodiment, and therefore will not be described here.

[0059] The switch unit 16 is a 2×N optical switch that selects, in response to a command from the control unit 11, a transmission line to be used for the quantum signal channel from among the optical transmission lines 31-1 to 31-n.

[0060] The optical transmission line 41 is used as a transmission line for the classical signal channel.

[0061] The receiving-side QKD device 20 receives the encryption key transmitted on the photons by the transmitting-side QKD device 10. The operations of the control unit 21, quantum signal receiving unit 22, and classical signal communication unit 23 are the same as those in the second embodiment, and therefore will not be described here.

[0062] The switch unit 26 is a 2×N optical switch that selects, in response to a command from the control unit 21, a transmission line to be used for the quantum signal channel from among the optical transmission lines 31-1 to 31-n.

[0063] In the third embodiment, the control unit 11 controls the switch unit 16, and the control unit 21 controls the switch unit 26, thereby making it possible to select a transmission path for a quantum signal channel that will result in a higher encryption key generation speed from among n optical transmission paths 31-1 to 31-n.

[0064] As a result, the quantum key distribution system 100-3 of the third embodiment can achieve the same effects as those of the second embodiment. Compared to the second embodiment, the quantum key distribution system 100-3 has the advantage that the exchange of control information between the transmitting QKD device 10 and the receiving QKD device 20 is not interrupted because the optical transmission path 41 of the classical communication channel is not switched.

[0065] (Fourth embodiment) Next, a fourth embodiment will be described. In the description of the fourth embodiment, the same description as in the first embodiment will be omitted, and only the differences from the first embodiment will be described.

[0066] [Configuration example] 7 is a diagram showing an example of the configuration of a quantum key distribution system 100-4 according to the fourth embodiment. The quantum key distribution system 100-4 according to the fourth embodiment includes QKD devices 10 and 20, optical transmission lines 31a and 31b, and switch devices 61 and 62.

[0067] The transmitting QKD device 10 comprises a control unit 11, a quantum signal transmitting unit 12, and a classical signal communication unit 13. The receiving QKD device 20 comprises a control unit 21, a quantum signal receiving unit 22, and a classical signal communication unit 23.

[0068] The transmitting-side QKD device 10 transmits the encryption key on a photon to the receiving-side QKD device 20. The operations of the control unit 11, quantum signal transmission unit 12, and classical signal communication unit 13 are the same as those in the first embodiment, and therefore will not be described here.

[0069] In the fourth embodiment, the switch unit 14 of the first embodiment is realized as a switch device 61 outside the QKD device 10.

[0070] The receiving-side QKD device 20 receives the encryption key transmitted on the photons by the transmitting-side QKD device 10. The operations of the control unit 21, quantum signal receiving unit 22, and classical signal communication unit 23 are the same as those in the first embodiment, and therefore will not be described here.

[0071] In the fourth embodiment, the switch unit 24 of the first embodiment is realized as a switch device 62 outside the QKD device 10.

[0072] The quantum key distribution system 100-4 of the fourth embodiment can achieve the same effects as those of the first embodiment. Compared to the first embodiment, the quantum key distribution system 100-4 can be realized using existing QKD devices, because the switch devices 61 and 62 are provided outside the QKD devices 10 and 20, making it possible to select the optical transmission path 31 more inexpensively.

[0073] (Fifth embodiment) Next, a fifth embodiment will be described. In the description of the fifth embodiment, the same description as in the second embodiment will be omitted, and only the differences from the second embodiment will be described.

[0074] [Configuration example] 8 is a diagram showing an example of the configuration of a quantum key distribution system 100-5 of the fifth embodiment. The quantum key distribution system 100-5 of the fifth embodiment includes QKD devices 10 and 20, n optical transmission lines 31-1 to 31-n, and switch devices 71 and 72.

[0075] The transmitting QKD device 10 comprises a control unit 11, a quantum signal transmitting unit 12, and a classical signal communication unit 13. The receiving QKD device 20 comprises a control unit 21, a quantum signal receiving unit 22, and a classical signal communication unit 23.

[0076] The transmitting-side QKD device 10 transmits the encryption key on a photon to the receiving-side QKD device 20. The operations of the control unit 11, quantum signal transmission unit 12, and classical signal communication unit 13 are the same as those in the second embodiment, and therefore will not be described here.

[0077] In the fifth embodiment, the switch unit 15 of the second embodiment is realized as a switch device 71 outside the QKD device 10.

[0078] The receiving-side QKD device 20 receives the encryption key transmitted on the photons by the transmitting-side QKD device 10. The operations of the control unit 21, quantum signal receiving unit 22, and classical signal communication unit 23 are the same as those in the second embodiment, and therefore will not be described here.

[0079] In the fifth embodiment, the switch unit 25 of the second embodiment is realized as a switch device 72 outside the QKD device 10.

[0080] The quantum key distribution system 100-5 of the fifth embodiment can achieve the same effects as those of the second embodiment. Compared to the second embodiment, the quantum key distribution system 100-5 can be realized using existing QKD devices, because the switch devices 71 and 72 are provided outside the QKD devices 10 and 20, making it possible to select the optical transmission path 31 more inexpensively.

[0081] (Sixth embodiment) Next, a sixth embodiment will be described. In the description of the sixth embodiment, the same description as in the third embodiment will be omitted, and only the differences from the third embodiment will be described.

[0082] [Configuration example] 9 is a diagram showing an example of the configuration of a quantum key distribution system 100-6 according to the sixth embodiment. The quantum key distribution system 100-6 according to the sixth embodiment includes QKD devices 10 and 20, n optical transmission lines 31-1 to 31-n, an optical transmission line 41, and switch devices 81 and 82.

[0083] The transmitting QKD device 10 comprises a control unit 11, a quantum signal transmitting unit 12, and a classical signal communication unit 13. The receiving QKD device 20 comprises a control unit 21, a quantum signal receiving unit 22, and a classical signal communication unit 23.

[0084] The transmitting-side QKD device 10 transmits the encryption key on a photon to the receiving-side QKD device 20. The operations of the control unit 11, quantum signal transmission unit 12, and classical signal communication unit 13 are the same as those in the third embodiment, and therefore description thereof will be omitted.

[0085] In the sixth embodiment, the switch unit 16 of the third embodiment is realized as a switch device 81 outside the QKD device 10.

[0086] The receiving-side QKD device 20 receives the encryption key transmitted on the photons by the transmitting-side QKD device 10. The operations of the control unit 21, quantum signal receiving unit 22, and classical signal communication unit 23 are the same as those in the third embodiment, and therefore will not be described here.

[0087] In the sixth embodiment, the switch unit 25 of the third embodiment is realized as a switch device 82 outside the QKD device 10.

[0088] The quantum key distribution system 100-6 of the sixth embodiment can provide the same effects as those of the third embodiment. Compared to the third embodiment, the quantum key distribution system 100-6 can be realized using existing QKD devices, because the switch devices 81 and 82 are provided outside the QKD devices 10 and 20, making it possible to select the optical transmission path 31 more inexpensively.

[0089] (Seventh embodiment) Next, a seventh embodiment will be described. In the description of the seventh embodiment, the same description as in the first embodiment will be omitted, and only the differences from the first embodiment will be described. In the seventh embodiment, a case will be described in which the QKD device 10 further has a function of receiving an encryption key, and the QKD device 20 further has a function of transmitting an encryption key.

[0090] [Configuration example] 10 is a diagram showing an example of the configuration of a quantum key distribution system 100-7 according to the seventh embodiment. The quantum key distribution system 100-7 according to the seventh embodiment includes QKD devices 10 and 20, and four optical transmission lines 31a to 31d.

[0091] The QKD device 10 includes control units 11a and 11b, quantum signal transmission units 12a and 12b, classical signal communication units 13a and 13b, and switch units 14a and 14b.

[0092] The operations of the control unit 11a, quantum signal transmission unit 12a, classical signal communication unit 13a, and switch unit 14a are similar to those of the control unit 11, quantum signal transmission unit 12, classical signal communication unit 13, and switch unit 14 of the first embodiment, and therefore will not be described here. That is, the control unit 11a, quantum signal transmission unit 12a, classical signal communication unit 13a, and switch unit 14a are used to transmit an encryption key to the QKD device 20.

[0093] The operations of the control unit 11b, quantum signal transmission unit 12b, classical signal communication unit 13b, and switch unit 14b are similar to those of the control unit 21, quantum signal reception unit 22, classical signal communication unit 23, and switch unit 24 of the first embodiment, and therefore will not be described here. That is, the control unit 11b, quantum signal transmission unit 12b, classical signal communication unit 13b, and switch unit 14b are used to receive an encryption key from the QKD device 20.

[0094] The QKD device 20 includes control units 21a and 21b, quantum signal transmission units 22a and 22b, classical signal communication units 23a and 23b, and switch units 24a and 24b.

[0095] The operations of the control unit 21a, quantum signal transmission unit 22a, classical signal communication unit 23a and switch unit 24a are similar to those of the control unit 11b, quantum signal transmission unit 12b, classical signal communication unit 13b and switch unit 14b of the QKD device 10, so explanations will be omitted.

[0096] The operations of the control unit 21b, quantum signal transmission unit 22b, classical signal communication unit 23b and switch unit 24b are similar to those of the control unit 11a, quantum signal transmission unit 12a, classical signal communication unit 13a and switch unit 14a of the QKD device 10, so explanations will be omitted.

[0097] As shown in Figure 10, QKD devices 10 and 20 may be capable of both transmitting and receiving cryptographic keys.

[0098] Finally, an example of the hardware configuration of the QKD devices 10 to 10-7 and 20 to 20-7 of the first to seventh embodiments will be described.

[0099] [Example of hardware configuration] 11 is a diagram showing an example of the hardware configuration of the QKD devices 10 to 10-7 and 20 to 20-7 of the first to seventh embodiments. The QKD devices 10 to 10-7 and 20 to 20-7 include a processor 301, a main memory device 302, an auxiliary memory device 303, a display device 304, an input device 305, a quantum communication IF 306, and a classical communication IF 307.

[0100] The processor 301 , the main memory device 302 , the auxiliary memory device 303 , the display device 304 , the input device 305 , the quantum communication IF 306 and the classical communication IF 307 are connected via a bus 310 .

[0101] The processor 301 executes a program read from the auxiliary storage device 303 to the main storage device 302. The main storage device 302 is memory such as a ROM and a RAM. The auxiliary storage device 303 is a HDD, a memory card, or the like.

[0102] The display device 304 displays the status of the QKD devices 10 to 10-7 and 20 to 20-7, etc. The input device 305 accepts input from the user. The display device 304 and the input device 305 may be realized by a touch panel or the like having a display function and an input function. Furthermore, the display device 304 and the input device 305 do not have to be provided in the QKD devices 10 to 10-7 and 20 to 20-7. In this case, for example, the display function and input function of an external terminal connected to the QKD devices 10 to 10-7 and 20 to 20-7 are used.

[0103] The quantum communication IF 306 is an interface for connecting to a transmission path of a quantum signal channel through which photons are transmitted. The classical communication IF 307 is an interface for connecting to a transmission path of a classical signal channel through which control signals are transmitted between the opposing QKD device 1.

[0104] The programs executed by QKD devices 10 to 10-7 and 20 to 20-7 are provided as computer program products stored in the form of installable or executable files on computer-readable storage media such as CD-ROMs, memory cards, CD-Rs, and DVDs (Digital Versatile Discs).

[0105] Furthermore, the programs executed by the QKD devices 10 to 10-7 and 20 to 20-7 may be stored on a computer connected to a network such as the Internet, and may be provided by being downloaded via the network.

[0106] Furthermore, the programs executed by the QKD devices 10 to 10-7 and 20 to 20-7 may be configured to be provided via a network such as the Internet without being downloaded.

[0107] Furthermore, the programs executed by the QKD devices 10 to 10-7 and 20 to 20-7 may be provided in advance by being stored in a ROM or the like.

[0108] The programs executed by QKD devices 10 to 10-7 and 20 to 20-7 have a modular configuration that includes functions that can be realized by the programs, among the functional configuration of QKD device 1 of the embodiment. The functions realized by the programs are loaded into main memory device 302 by processor 301 reading and executing the programs from a storage medium such as auxiliary memory device 303. In other words, the functions realized by the programs are generated on main memory device 302.

[0109] It should be noted that some or all of the functions of the QKD devices 10 to 10-7 and 20 to 20-7 may be realized by hardware such as an IC (Integrated Circuit), etc. The IC is, for example, a processor that executes dedicated processing.

[0110] Furthermore, when each function is realized using a plurality of processors, each processor may realize one of the functions, or may realize two or more of the functions.

[0111] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0112] 10 QKD equipment 11 Control section 12 Quantum signal transmission unit 13 Classical Signal and Communication Department 14 Switch section 15 Switch section 16 Switch section 20 QKD equipment 21 Control section 22 Quantum signal receiver 23 Classical Signal and Communication Department 24 Switch section 25 Switch section 26 Switch section 31 Optical transmission line 41 Optical transmission line 61 Switching device 62 Switching Device 71 Switching Device 72 Switching Device 81 Switching Device 82 Switching Device 100, 100-2~100-7 Quantum Key Distribution System 301 processor 302 Main storage 303 Auxiliary storage device 304 Display device 305 Input Device 306 Quantum Communication Interface 307 Classical Communication IF 310 Bus

Claims

1. a transmitter that transmits photons used to generate an encryption key by quantum key distribution; a receiving device for receiving the photons, the transmitting device includes a quantum signal transmitting unit that transmits the photons as a quantum signal; the receiving device includes a quantum signal receiving unit that receives the quantum signal; a first switch unit that selects a transmission path for transmitting the quantum signal from a plurality of transmission paths; a second switch unit that selects a transmission path that receives the quantum signal from the plurality of transmission paths, Quantum key distribution system.

2. The transmitting device a first control unit that determines a transmission path for transmitting the quantum signal based on the encryption key generation speed measured for each of the plurality of transmission paths; the first switch unit selects the transmission path determined by the first control unit from the plurality of transmission paths; The receiving device a second control unit that determines a transmission path for transmitting the quantum signal based on a generation speed of the encryption key; the second switch unit selects the transmission path determined by the second control unit from the plurality of transmission paths. The quantum key distribution system of claim 1 .

3. the plurality of transmission paths are two transmission paths, The transmitting device a first classical signal communication unit that transmits and receives a control signal in quantum key distribution as a classical signal; the first control unit determines, of the two transmission paths, the transmission path having a higher encryption key generation speed as the transmission path for transmitting the quantum signal, and determines, of the two transmission paths, the transmission path having a slower encryption key generation speed as the transmission path for transmitting and receiving the classical signal; The receiving device Further comprising a second classical signal communication unit that transmits and receives the classical signal; the second control unit determines, of the two transmission paths, the transmission path having a higher encryption key generation speed as the transmission path for receiving the quantum signal, and determines, of the two transmission paths, the transmission path having a slower encryption key generation speed as the transmission path for transmitting and receiving the classical signal. The quantum key distribution system according to claim 2 .

4. the plurality of transmission paths are n transmission paths (n is an integer of 3 or more), The transmitting device a first classical signal communication unit that transmits and receives a control signal in quantum key distribution as a classical signal; the first control unit determines, among the n transmission paths, a transmission path having a higher encryption key generation speed as a transmission path for transmitting the quantum signal, and determines, as a transmission path for transmitting and receiving the classical signal, from n-1 transmission paths excluding the transmission path used for transmitting the quantum signal; The receiving device Further comprising a second classical signal communication unit that transmits and receives the classical signal; the second control unit determines, among the n transmission paths, a transmission path having a higher encryption key generation speed as a transmission path for receiving the quantum signal, and determines, as a transmission path for transmitting and receiving the classical signal, from n-1 transmission paths excluding the transmission path used for transmitting the quantum signal; The quantum key distribution system according to claim 2 .

5. the first and second control units periodically measure a generation rate of the encryption key for each of the plurality of transmission paths, and determine a transmission path for transmitting the quantum signal based on the generation rate of the encryption key. The quantum key distribution system according to any one of claims 2 to 4.

6. the first and second control units measure a generation speed of the encryption key for each of the plurality of transmission paths when starting generation of the encryption key, and determine a transmission path for transmitting the quantum signal based on the generation speed of the encryption key. The quantum key distribution system according to any one of claims 2 to 4.

7. the first and second control units measure the encryption key generation rate for each of the plurality of transmission paths when the encryption key generation rate becomes lower than a threshold, and determine a transmission path for transmitting the quantum signal based on the encryption key generation rate. The quantum key distribution system according to any one of claims 2 to 4.

8. the first switch unit is provided in the transmitting device, The second switch unit is provided in the receiving device. The quantum key distribution system according to any one of claims 1 to 4.

9. the first switch unit is a first device connected to the transmitting device, the second switch unit is a second device connected to the receiving device; The quantum key distribution system according to any one of claims 1 to 4.

10. a quantum signal transmitter that transmits, as a first quantum signal, photons used to generate a cryptographic key by quantum key distribution; a quantum signal receiving unit that receives, as a second quantum signal, a photon transmitted from another quantum key distribution device; a first switch unit that selects a transmission path for transmitting the first quantum signal from a plurality of transmission paths; a second switch unit that selects a transmission path from the plurality of transmission paths that receives the second quantum signal; A quantum key distribution device comprising:

11. a transmitting device transmitting, as a quantum signal, photons used to generate an encryption key by quantum key distribution; a step of a first switch unit selecting a transmission path for transmitting the quantum signal from a plurality of transmission paths; a second switch unit selecting a transmission path for receiving the quantum signal from the plurality of transmission paths; receiving the quantum signal by a receiving device; A quantum key distribution method comprising:

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