Receiver, cryptographic key delivery system, receiver control method, and control program

Abstract

To provide a receiver capable of creating a cryptographic key without increasing a processing load.SOLUTION: A receiver comprises: a first modulation section for performing phase modulation on reference light using reception bases randomly assigned correspondingly to transmission bases randomly assigned with a plurality of pieces of weak light, respectively, transmitted from a transmitter and received via a quantum communication path; a detection section that makes the plurality of pieces of weak light and the reference light on which the phase modulation is performed by the first modulation section interfere with each other to detect a plurality of pieces of bit information from each of a plurality of pieces of weak light interfered with reference light of a reception base whose base value agrees with that of a transmission base; an extraction section for extracting a plurality of pieces of bit information having an amplitude component equal to or larger than a threshold out of the detected plurality of pieces of bit information; an acquisition section for acquiring information on weather forecasting; a prediction section for predicting a load situation of the receiver from the information on the weather forecasting; and an adjustment section for adjusting the threshold depending on the predicted load situation of the receiver.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a receiver, an encryption key distribution system, a control method for the receiver, and a control program. [Background technology]

[0002] In cryptographic communication of a message from a sending server to a receiving server, the message is encrypted at the sending server and decrypted at the receiving server using an encryption key that is shared in advance between the sending server and the receiving server. In particular, cryptographic communication in which a new encryption key is generated for each message communication is called one-time pad cryptographic communication.

[0003] Furthermore, in recent years, the development of quantum cryptography communication has been progressing. Quantum cryptography communication is a type of cryptography communication using a one-time pad method, and enables more secure cryptography communication by transmitting an encryption key generated by a transmitter on the sending server side from the transmitter to a receiver on the receiving server side on a photon (particle of light), which is the smallest unit of light, or on weak light. Technology related to quantum cryptography communication is disclosed in Patent Document 1, for example.

[0004] Patent Document 1 discloses a quantum cryptography communication system that detects anomalies based on at least one of the overhead line information of a QKD link connected to a quantum cryptography device to be inspected, weather information for the site where the quantum cryptography device to be inspected is installed, and quantum cryptography device information. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2022-186077 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the system disclosed in Patent Document 1, a receiving device (photon receiver) receives a fixed amount of photons transmitted from a transmitting device regardless of the load status of the receiving device. Therefore, the system disclosed in Patent Document 1 has a problem that the processing load of the receiving device increases when the receiving device receives a fixed amount of photons transmitted from a transmitting device even when the processing load is high.

[0007] An object of the present disclosure is to provide a receiver, an encryption key distribution system, a receiver control method, and a control program that solve the above-mentioned problems. [Means for solving the problem]

[0008] A receiver according to one embodiment of the present disclosure is provided in a cryptographic key distribution system and includes: a first modulation unit that phase-modulates a reference light using a reception basis randomly assigned to a transmission basis randomly assigned to each of a plurality of weak lights transmitted from a transmitter and received via a quantum communication channel; a detection unit that detects a plurality of bit information from each of a plurality of weak lights interfered by the reference light of a reception basis whose basis value matches a transmission basis, among the plurality of weak lights, by interfering between the plurality of weak lights and the reference light phase-modulated by the first modulation unit; an extraction unit that extracts a plurality of bit information having amplitude components equal to or greater than a threshold, from the plurality of bit information detected by the detection unit; an acquisition unit that acquires information regarding a weather forecast for an installation area of ​​a quantum communication channel installed on the ground, among the quantum communication channels; a prediction unit that predicts a load condition of the receiver itself from the information regarding the weather forecast; and an adjustment unit that adjusts the threshold in accordance with the load condition of the receiver predicted by the prediction unit.

[0009] A control method for a receiver according to one aspect of the present disclosure includes phase-modulating a reference light using a randomly assigned reception basis corresponding to a transmission basis randomly assigned to each of a plurality of weak lights transmitted from a transmitter and received via a quantum communication channel, and interfering the plurality of weak lights with the phase-modulated reference light, thereby detecting a plurality of bits of information from each of the plurality of weak lights interfered with by the reference light of a reception basis whose basis value matches the transmission basis, extracting a plurality of bits of information having amplitude components equal to or greater than a threshold from the detected plurality of bits of information, obtaining information regarding a weather forecast for an installation area of ​​a quantum communication channel installed on the ground among the quantum communication channels, predicting a load condition of the receiver itself from the information regarding the weather forecast, and adjusting the threshold according to the predicted load condition of the receiver.

[0010] A control program according to one aspect of the present disclosure causes a computer to execute the following processes: phase-modulating a reference light using a randomly assigned reception basis corresponding to a transmission basis randomly assigned to each of a plurality of weak lights transmitted from a transmitter and received via a quantum communication channel; detecting a plurality of bit information from each of a plurality of weak lights interfered by the reference light of a reception basis whose basis value matches the transmission basis among the plurality of weak lights by interfering with the plurality of weak lights and the phase-modulated reference light; extracting a plurality of bit information having amplitude components equal to or greater than a threshold from the detected plurality of bit information; acquiring information regarding a weather forecast for an installation area of ​​a quantum communication channel installed on the ground among the quantum communication channels; predicting a load condition of a receiver, which is the device itself, from the information regarding the weather forecast; and adjusting the threshold depending on the predicted load condition of the receiver. Effect of the Invention

[0011] The present disclosure can provide a receiver, an encryption key distribution system, a receiver control method, and a control program capable of generating an encryption key without increasing the processing load. [Brief description of the drawings]

[0012] [Figure 1] 1 is a block diagram showing an overview of a receiver provided in a first encryption key distribution system according to the present disclosure. FIG. [Diagram 2] FIG. 1 is a block diagram showing an overview of a first encryption key distribution system according to the present disclosure. [Diagram 3] FIG. 2 is a block diagram showing details of a first encryption key distribution system according to the present disclosure. [Figure 4] 4 is a diagram showing the distribution of a plurality of bit values ​​after basis matching in a receiver provided in the encryption key distribution system shown in FIG. 3. FIG. [Diagram 5] 4 is a diagram showing details of the distribution of a plurality of bit values ​​after basis matching in a receiver provided in the encryption key distribution system shown in FIG. 3. FIG. [Figure 6] 4 is a diagram for explaining a method of extracting a bit value by an extraction unit in a receiver provided in the encryption key distribution system shown in FIG. [Figure 7] 4 is a diagram for explaining a method of extracting a bit value by an extraction unit in a receiver provided in the encryption key distribution system shown in FIG. [Figure 8] 4 is a diagram for explaining a method of extracting a bit value by an extraction unit in a receiver provided in the encryption key distribution system shown in FIG. [Figure 9] FIG. 2 is a block diagram showing a configuration example of a second encryption key distribution system according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments will be described with reference to the drawings. Note that the drawings are simplified, and the technical scope of the embodiments should not be interpreted narrowly based on the description in the drawings. Also, the same elements are given the same reference numerals, and duplicated explanations will be omitted.

[0014] In the following embodiments, when necessary for convenience, the description will be divided into multiple sections or embodiments. However, unless otherwise specified, they are not unrelated to each other, and one is a partial or complete modification, application example, detailed explanation, supplementary explanation, etc. of the other. Furthermore, in the following embodiments, when the number of elements (including the number, numerical value, amount, range, etc.) is mentioned, it is not limited to the specific number, and may be more or less than the specific number, unless otherwise specified or when it is clearly limited to a specific number in principle.

[0015] Furthermore, in the following embodiments, the components (including operation steps, etc.) are not necessarily essential unless otherwise specified or considered to be clearly essential in principle. Similarly, in the following embodiments, when referring to the shape, positional relationship, etc. of the components, etc., it is intended to include those that are substantially similar or similar to the shape, etc., unless otherwise specified or considered to be clearly not essential in principle. The same applies to the above numbers, etc. (including numbers, values, amounts, ranges, etc.).

[0016] <Embodiment 1> <Overview of the receiver provided in the first encryption key distribution system according to the present disclosure> FIG. 1 is a block diagram showing an overview of a receiver 12 provided in a first encryption key distribution system 1 according to the present disclosure.

[0017] The encryption key distribution system 1 is used, for example, in quantum cryptographic communication using an encryption key distribution method called CV-QKD. In cryptographic communication of a message from a sending server to a receiving server, the message is encrypted at the sending server and decrypted at the receiving server using an encryption key shared in advance by the sending server and the receiving server. In particular, cryptographic communication in which a new encryption key is generated for each message communication is called one-time pad cryptographic communication.

[0018] Quantum cryptography communication is a type of cryptography using a one-time pad method, and the cryptographic key distribution system 1 enables more secure cryptography communication by transmitting a cryptographic key generated by a transmitter on the sending server side from the transmitter to a receiver on the receiving server side using weak light. Note that the weak light is light (quantum light) that can detect quantum mechanical state changes by, for example, making the typical intensity about one photon.

[0019] 1, in the encryption key distribution system 1, the receiver 12 includes a modulation unit 121, a detection unit 122, an extraction unit 123, an acquisition unit 124, a prediction unit 125, and an adjustment unit 126. Note that the modulation unit 121, the detection unit 122, the extraction unit 123, the acquisition unit 124, the prediction unit 125, and the adjustment unit 126 are realized by a hardware configuration (for example, a circuit), but as will be described later, this is not limiting, and all or part of them may be realized by causing a CPU (Central Processing Unit) to execute a computer program.

[0020] The receiver 12 receives the multiple weak light beams transmitted from the transmitter 11 via a quantum communication channel 13. The quantum communication channel 13 is, for example, an optical fiber capable of transmitting light waves.

[0021] Each of the plurality of weak lights transmitted from the transmitter 11 includes information on a transmission bit and a transmission basis randomly assigned by the transmitter 11. In other words, each of the plurality of weak lights transmitted from the transmitter 11 is phase modulated using the transmission bit and the transmission basis randomly assigned by the transmitter 11.

[0022] For example, when the bit value of the transmission bit is "0", a phase modulation amount of 0 degrees is assigned, and when the bit value of the transmission bit is "1", a phase modulation amount of 180 degrees is assigned. When the base value of the transmission base is "X", a phase modulation amount of 0 degrees is assigned, and when the base value of the transmission base is "Y", a phase modulation amount of 90 degrees is assigned. Each weak light is phase-modulated with a phase modulation amount obtained by adding together the phase modulation amount according to the bit value and the phase modulation amount according to the base value. Therefore, weak light phase-modulated using a transmission base with a base value of "X" ideally appears on the real axis, and weak light phase-modulated using a transmission base with a base value of "Y" ideally appears on the imaginary axis.

[0023] In the receiver 12, the modulation section 121 phase-modulates the reference light using a randomly assigned reception basis in correspondence with a randomly assigned transmission basis for each of the plurality of weak light beams.

[0024] The detection unit 122 is, for example, a homodyne detector, and performs basis matching for the plurality of weak light beams received. Specifically, the detection unit 122 causes interference between the plurality of weak light beams and the reference light phase-modulated by the modulation unit 121, thereby detecting information of a plurality of bit values ​​(bit information) from each of the plurality of weak light beams that are interfered with by the reference light of the reception basis whose basis value coincides with the transmission basis among the plurality of weak light beams. The bit information includes a phase component representing the bit value, an amplitude component representing the intensity of the bit value, and the like.

[0025] For example, when the basis value of the reception basis is "X", a phase modulation amount of 0 degrees is assigned, and when the basis value of the reception basis is "Y", a phase modulation amount of 90 degrees is assigned. Therefore, the desired bit information can be detected only when interference occurs between weak light and reference light whose transmission basis and reception basis match each other.

[0026] After the base matching by the detection unit 122, the extraction unit 123 performs post-selection. Specifically, the extraction unit 123 extracts a plurality of pieces of bit information having an amplitude component equal to or greater than the threshold value P from among the plurality of pieces of bit information detected by the detection unit 122. Here, the amplitude component of each piece of bit information refers to the amplitude (magnitude) of a difference signal, which is the intensity difference between the light obtained by superposing the reference light and the weak light and the light of the opposite phase. Therefore, the threshold value P is set, for example, in units of the light intensity difference or the potential difference corresponding to the light intensity difference. For example, when the phase modulation amount is 0 degrees corresponding to the bit value "0", the probability distribution of the difference signal is a Gaussian distribution whose average value indicates a positive value. For such a difference signal, a positive threshold value P+ is set. Also, when the phase modulation amount is 180 degrees corresponding to the bit value "1", the probability distribution of the difference signal is a Gaussian distribution whose average value indicates a negative value. For such a difference signal, a negative threshold value P- is set. The absolute values ​​of the threshold values ​​P+ and P- are both the threshold value P. Finally, in the receiver 12, only a part of the bit values ​​(bit strings) extracted by the extractor 123 is used to generate an encryption key.

[0027] The acquisition unit 124 acquires information about the weather forecast of the installation area of ​​the quantum communication channel 13 that is installed on the ground. The information about the weather forecast is information obtained by estimating future conditions such as wind speed and temperature in a specific area based on past or current conditions such as wind speed and temperature in the specific area. In addition, the quantum communication channel installed on the ground among the quantum communication channels 13 is a quantum communication channel that is erected high above the ground, for example, by a steel tower. Hereinafter, the quantum communication channel installed on the ground among the quantum communication channels 13 is referred to as the quantum communication channel 13a. For example, the acquisition unit 124 acquires information about the weather forecast of the installation area of ​​the quantum communication channel 13a from an external device (not shown) such as a weather satellite, or from the announcements made by the Japan Meteorological Agency, etc.

[0028] Here, the quantum communication channel 13a installed on the ground is easily affected by wind and temperature. For example, the higher the wind speed, the greater the fluctuation of the polarization in the quantum communication channel 13a, and therefore the higher the error rate. On the other hand, the lower the wind speed, the smaller the fluctuation of the polarization in the quantum communication channel 13a, and therefore the lower the error rate. Also, the greater the change in temperature per given period (e.g., one day), the greater the expansion / contraction rate of the quantum communication channel 13a, and therefore the higher the error rate. On the other hand, the smaller the change in temperature per given period, the smaller the expansion / contraction rate of the quantum communication channel 13a, and therefore the lower the error rate.

[0029] The prediction unit 125 predicts the load status of the receiver 12 from the information on the weather forecast acquired by the acquisition unit 124. For example, if the information on the weather forecast includes information indicating that the wind speed will increase, the prediction unit 125 predicts that the processing load of the receiver 12 will increase. On the other hand, if the information on the weather forecast includes information indicating that the wind speed will decrease, the prediction unit 125 predicts that the processing load of the receiver 12 will decrease. Also, for example, if the information on the weather forecast includes information indicating that the change in temperature per predetermined period (e.g., one day) will increase, the prediction unit 125 predicts that the processing load of the receiver 12 will increase. On the other hand, if the information on the weather forecast includes information indicating that the change in temperature per predetermined period will decrease, the prediction unit 125 predicts that the processing load of the receiver 12 will decrease.

[0030] The prediction unit 125 may have a function of using information about the weather forecast for the installation area of ​​the quantum communication path 13a and the corresponding actual load status of the receiver 12 to perform machine learning of a model that represents the relationship between the information about the weather forecast for the installation area of ​​the quantum communication path 13a and the predicted value of the load status of the receiver 12. In this case, the prediction unit 125 predicts the load status of the receiver 12 from the information about the weather forecast for the installation area of ​​the quantum communication path 13a using the trained model.

[0031] The adjustment unit 126 adjusts the threshold P according to the load state of the receiver 12 predicted by the prediction unit 125 (future load state of the receiver 12). More specifically, the adjustment unit 126 adjusts the threshold P according to the load state of a processor that performs a predetermined process in the receiver 12 predicted by the prediction unit 125.

[0032] For example, the adjustment unit 126 increases the threshold P as the processing load of the receiver 12 predicted by the prediction unit 125 increases. This limits the bit values ​​extracted by the extraction unit 123 to more reliable bit values, thereby reducing the error rate between the transmitted bits and the received bits, and as a result, the processing load of the receiver 12 is reduced. Also, the adjustment unit 126 decreases the threshold P as the processing load of the receiver 12 predicted by the prediction unit 125 decreases. This increases the bit values ​​extracted by the extraction unit 123, and therefore increases the number of bit values ​​used to generate an encryption key, resulting in a larger amount of keys to be generated.

[0033] Thereafter, error correction processing is performed in the transmitter 11 and the receiver 12. Specifically, when the error rate between the bit string extracted in the transmitter 11 and the bit string extracted in the receiver 12 is less than a predetermined rate, the transmitter 11 and the receiver 12 perform processing to make the mismatched parts of these bit strings match. Note that when the error rate is equal to or greater than the predetermined rate, the bit strings are not suitable for generating an encryption key, and the processing returns to the generation of weak light by the transmitter 11.

[0034] Thereafter, the transmitter 11 and the receiver 12 perform privacy amplification processing on the error-corrected bit string, and as a result, encryption keys having matching bit strings (that is, shared encryption keys) are individually generated.

[0035] In this manner, the receiver 12 provided in the encryption key distribution system 1 according to the present disclosure adjusts the threshold P, which is the minimum value of the amplitude component of the bit information extracted by the extraction unit 123, in accordance with the load condition of the receiver 12 predicted from a weather forecast or the like. This enables the receiver 12 to generate an encryption key to be shared with the transmitter 11 without increasing the processing load.

[0036] <Overview of the first encryption key distribution system according to the present disclosure> FIG. 2 is a block diagram showing an overview of a first encryption key distribution system 1 according to the present disclosure. As shown in FIG. 2, the encryption key distribution system 1 includes a transmitter 11, a receiver 12, and a quantum communication channel 13.

[0037] The transmitter 11 has a light generating unit 111 and a modulating unit 112. The light generating unit 111 generates a plurality of weak lights. The modulating unit 112 phase-modulates the plurality of weak lights generated by the light generating unit 111 one by one using a transmission bit and a transmission basis randomly selected in the transmitter 11. For example, a random number generated by a random number generating unit (not shown) is used as the bit value of the transmission bit. The plurality of weak lights phase-modulated by the modulating unit 112 are transmitted to the receiver 12 via the quantum communication channel 13. The configuration and operation of the receiver 12 are as described above, and therefore will not be described here.

[0038] In the encryption key distribution system 1 according to the present disclosure, the receiver 12 adjusts the threshold P, which is the minimum value of the amplitude component of the bit information extracted by the extraction unit 123, in accordance with the load condition of the receiver 12 predicted from a weather forecast or the like. This allows the encryption key distribution system 1 to generate encryption keys shared by the transmitter 11 and the receiver 12, without increasing the processing load of the receiver 12.

[0039] <Details of the first encryption key distribution system according to the present disclosure> 3 is a block diagram showing details of the first encryption key distribution system 1 according to the present disclosure as an encryption key distribution system 2. The encryption key distribution system 2 includes a transmitter 21, a receiver 22, a quantum communication channel 13, and a classical communication channel 24. The transmitter 21 and the receiver 22 correspond to the transmitter 11 and the receiver 12 in the encryption key distribution system 1.

[0040] Compared to the transmitter 11, the transmitter 21 further includes a control unit 213 in addition to the light generation unit 111 and the modulation unit 112. Compared to the receiver 12, the receiver 22 further includes a control unit 227 in addition to the modulation unit 121, the detection unit 122, the extraction unit 123, the acquisition unit 124, the prediction unit 125, and the adjustment unit 126. The control unit 213 and the control unit 227 are configured to be able to communicate with each other via a classical communication channel 24. The following mainly describes the differences between the encryption key distribution system 2 and the encryption key distribution system 1.

[0041] Fig. 4 is a diagram showing the distribution of a plurality of pieces of bit information detected by the detection unit 122. That is, Fig. 4 is a diagram showing the distribution of a plurality of pieces of bit information after basis matching by the receiver 22. In the example of Fig. 4, the horizontal axis indicates the real axis, and the vertical axis indicates the imaginary axis. In Fig. 4, the more the bit information is distributed, the darker the color becomes, and the less the bit information is distributed, the lighter the color becomes.

[0042] Moreover, Fig. 5 is a diagram showing the details of the distribution of the bit information with a basis value of "X", that is, around the real axis, among the multiple bit information after basis matching of the receiver 22. In the example of the upper diagram of Fig. 5, the horizontal axis indicates the real axis, and the vertical axis indicates the imaginary axis. In the upper diagram of Fig. 5, the more the bit information is distributed, the darker the color becomes, and the less the bit information is distributed, the lighter the color becomes. In the example of the lower diagram of Fig. 5, the horizontal axis indicates the value of the amplitude component of the bit information (the amplitude of the difference signal described above) on the real axis, and the vertical axis indicates the probability that the bit information is detected.

[0043] In the following, we will only explain the distribution of bit information with a base value of "X", i.e., around the real axis, among the multiple bit information detected by the detection unit 122, but basically the same phenomenon occurs with the distribution of bit information with a base value of "Y", i.e., around the imaginary axis.

[0044] As shown in Fig. 5, weak light (bit information) that has been phase modulated based on a transmission bit with a bit value of "0" has a phase modulation amount of 0 degrees, and is therefore distributed so that its average value is located on the positive side of the real axis. Also, weak light (bit information) that has been phase modulated based on a transmission bit with a bit value of "1" has a phase modulation amount of 180 degrees, and is therefore distributed so that its average value is located on the negative side of the real axis. Here, with weak light of low intensity, particularly weak light that is so weak that it overlaps with weak light that has a phase difference of 180 degrees, quantum fluctuations may prevent the correct bit value from being detected.

[0045] Therefore, in the encryption key distribution system 2, as shown in FIG. 6, a threshold P is set in the receiver 22 as the minimum value of the amplitude component of the bit information extracted by the extraction unit 123. More specifically, when the phase modulation amount is 0 degrees corresponding to the bit value "0", the probability distribution of the bit information is a Gaussian distribution with a positive average value. For such a distribution of bit information, a positive threshold P+ is set. Also, when the phase modulation amount is 180 degrees corresponding to the bit value "1", the probability distribution of the bit information is a Gaussian distribution with a negative average value. For such a distribution of bit information, a negative threshold P- is set. The absolute values ​​of the thresholds P+ and P- are both the threshold P. Then, the extraction unit 123 extracts bit information whose amplitude component is equal to or greater than the threshold P from among the multiple pieces of bit information detected by the detection unit 122 (i.e., the bit information after the basis matching), and discards the bit information whose amplitude component is less than the threshold P.

[0046] Furthermore, in the encryption key distribution system 2, as shown in Figs. 7 and 8, the receiver 22 adjusts the threshold P according to the load condition of the receiver 22 predicted from a weather forecast or the like (future load condition of the receiver 22).

[0047] For example, the adjustment unit 126 increases the threshold P as the processing load of the receiver 22 predicted by the prediction unit 125 increases (see FIG. 7). This limits the bit values ​​extracted by the extraction unit 123 to more reliable bit values, thereby reducing the error rate between the transmitted bits and the received bits, and as a result, the processing load of the receiver 22 is reduced. Also, the adjustment unit 126 decreases the threshold P as the processing load of the receiver 22 predicted by the prediction unit 125 decreases (see FIG. 8). This increases the bit values ​​extracted by the extraction unit 123, and therefore increases the number of bit values ​​used to generate encryption keys, resulting in a larger amount of keys to be generated.

[0048] The control unit 213 and the control unit 227 exchange information required to generate an encryption key via the classical communication channel 24. For example, the control unit 213 and the control unit 227 exchange a synchronization signal for synchronously operating the transmitter 21 and the receiver 22. In addition, the control unit 213 and the control unit 227 exchange identification information for associating a plurality of weak light beams transmitted from the transmitter 21 with a plurality of weak light beams received by the receiver 22.

[0049] Furthermore, the control unit 213 and the control unit 227 perform an error correction process after the basis matching and post-selection. Specifically, when the error rate between the bit string (key information) extracted in the transmitter 21 and the bit string (key information) extracted in the receiver 22 is less than a predetermined rate, the control unit 213 and the control unit 227 perform a process of matching the mismatched parts between the bit string extracted in the transmitter 21 side and the bit string extracted in the receiver 22. Note that when the error rate is equal to or greater than the predetermined rate, the bit string is not suitable for generating an encryption key, and the process returns to the generation of photons by the transmitter 21.

[0050] Thereafter, the control unit 213 and the control unit 227 each perform privacy amplification processing on the error-corrected bit string, and individually generate encryption keys (that is, shared encryption keys) having matching bit strings.

[0051] In this manner, in the encryption key distribution system 2 according to the present disclosure, the receiver 22 adjusts the threshold P, which is the minimum value of the amplitude component of the bit information extracted by the extraction unit 123, in accordance with the load condition of the receiver 22 predicted from a weather forecast or the like. This allows the encryption key distribution system 2 to generate encryption keys shared by the transmitter 21 and the receiver 22, respectively, without increasing the processing load of the receiver 22.

[0052] <Embodiment 2> 9 is a block diagram showing a configuration example of a second encryption key distribution system 3 according to the present disclosure. Compared to the encryption key distribution system 2, the encryption key distribution system 3 includes a receiver 32 instead of the receiver 22. Compared to the receiver 22, the receiver 32 further includes a monitoring unit 328. The other configuration of the encryption key distribution system 3 is similar to that of the encryption key distribution system 2, and therefore description thereof will be omitted.

[0053] In the receiver 32, the monitoring unit 328 monitors the current load status of the receiver 32. The adjustment unit 126 adjusts the threshold P based on the monitoring result by the monitoring unit 328 and the prediction result by the prediction unit 125. For example, the adjustment unit 126 increases the threshold P as the processing load of the current receiver 32 monitored by the monitoring unit 328 increases, and decreases the threshold P as the processing load of the current receiver 32 monitored by the monitoring unit 328 decreases. Then, the adjustment unit 126 adjusts the threshold P based on the prediction result by the prediction unit 125, as already described.

[0054] The monitoring unit 328 is not limited to directly monitoring the load status of the receiver 32, and may indirectly or auxiliarily monitor the load status of the receiver 32. For example, the adjustment unit 126 may adjust the threshold P according to the temperature or vibration of the quantum communication path 13, which is an optical fiber, monitored by the monitoring unit 328. The temperature or vibration of the quantum communication path 13 is detected by, for example, a temperature sensor or a vibration sensor. The monitoring by the monitoring unit 328 may be to monitor whether the load status is within a certain range, and in this case, the adjustment of the threshold P by the adjustment unit 126 may be to adjust the threshold P to an appropriate threshold P calculated in advance for the load status.

[0055] For example, the adjustment unit 126 may determine that the processing load of the receiver 32 is greater as the temperature of the quantum communication path 13 increases, and may increase the threshold P, and may determine that the processing load of the receiver 32 is smaller as the temperature of the quantum communication path 13 decreases, and may decrease the threshold P. The adjustment unit 126 may also determine that the processing load of the receiver 32 is greater as the vibration of the quantum communication path 13 increases, and may increase the threshold P, and may determine that the processing load of the receiver 32 is smaller as the vibration of the quantum communication path 13 decreases, and may decrease the threshold P.

[0056] In this way, in the encryption key distribution system 3 according to the present disclosure, the receiver 32 adjusts the threshold P, which is the minimum value of the amplitude component of the bit information extracted by the extraction unit 123, in accordance with the current load condition of the receiver 32 and the future load condition of the receiver 32 predicted from a weather forecast or the like. This allows the encryption key distribution system 3 to generate encryption keys shared by the transmitter 21 and the receiver 32, respectively, without increasing the processing load of the receiver 32.

[0057] Note that the present disclosure can be realized by causing a CPU to execute a computer program, in whole or in part, a cryptographic key distribution system or a receiver provided therein.

[0058] Specifically, the above-mentioned program includes a set of instructions (or software code) for making the computer perform one or more functions described in the embodiment when the program is loaded into the computer. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, the computer-readable medium or tangible storage medium includes a random-access memory (RAM), a read-only memory (ROM), a flash memory, a solid-state drive (SSD) or other memory technology. Also, by way of example and not limitation, the computer-readable medium or tangible storage medium includes a CD-ROM, a digital versatile disc (DVD), a Blu-ray (registered trademark) disc or other optical disk storage. Also, by way of example and not limitation, the computer-readable medium or tangible storage medium includes a magnetic cassette, a magnetic tape, a magnetic disk storage or other magnetic storage device. The program may be transmitted on a transitory computer-readable medium or a communication medium. By way of example and not limitation, the transitory computer-readable medium or the communication medium includes an electrical, optical, acoustic, or other form of propagating signal.

[0059] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-mentioned embodiments. Various modifications that can be understood by a person skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be appropriately combined with other embodiments.

[0060] Furthermore, some or all of the above-described embodiments can be described as, but are not limited to, the following supplementary notes.

[0061] (Appendix 1) Installed in the encryption key distribution system, A first modulation unit that phase-modulates a reference light by using a randomly assigned reception basis in response to a randomly assigned transmission basis for each of a plurality of weak light beams transmitted from a transmitter and received via a quantum communication channel; a detection unit that detects a plurality of bits of information from each of a plurality of weak lights that are interfered with by the reference light of a reception basis having a basis value that coincides with a transmission basis, by interfering the plurality of weak lights with the reference light that has been phase-modulated by the first modulation unit; an extracting unit that extracts a plurality of pieces of bit information having amplitude components equal to or greater than a threshold from the plurality of pieces of bit information detected by the detecting unit; an acquisition unit that acquires information regarding a weather forecast for an installation area of ​​a quantum communication channel installed on the ground among the quantum communication channels; a prediction unit for predicting a load condition of the receiver itself based on information about the weather forecast; an adjustment unit that adjusts the threshold value in accordance with the load status of the receiver predicted by the prediction unit; A receiver comprising:

[0062] (Appendix 2) the adjustment unit increases the threshold as the processing load of the receiver predicted by the prediction unit increases, and decreases the threshold as the processing load of the receiver predicted by the prediction unit decreases. 2. A receiver as defined in claim 1.

[0063] (Appendix 3) the prediction unit predicts that the processing load of the receiver will be large when the information on the weather forecast includes information indicating that the amount of change in temperature in a specified period will be large, and predicts that the processing load of the receiver will be small when the information on the weather forecast includes information indicating that the amount of change in temperature in a specified period will be small; 2. A receiver as defined in claim 1.

[0064] (Appendix 4) the prediction unit predicts that the processing load of the receiver will increase when the information on the weather forecast includes information indicating an increase in wind speed, and predicts that the processing load of the receiver will decrease when the information on the weather forecast includes information indicating a decrease in wind speed. 2. A receiver as defined in claim 1.

[0065] (Appendix 5) A monitoring unit for monitoring a load status of the receiver is further provided, the adjustment unit adjusts the threshold value in accordance with a load status of the receiver monitored by the monitoring unit and a load status of the receiver predicted by the prediction unit. 2. A receiver as defined in claim 1.

[0066] (Appendix 6) The transmitter; A receiver as set forth in Appendix 1; a quantum communication channel provided between the transmitter and the receiver; Equipped with The transmitter includes: A light generating unit that generates the plurality of weak lights; A second modulation unit that phase-modulates the plurality of weak lights one by one using bit information and a transmission basis randomly selected in the transmitter and transmits the phase-modulated light to the receiver via the quantum communication channel; having Cryptographic key distribution system.

[0067] (Appendix 7) The transmitter includes: a first control unit that generates a first encryption key by using at least a part of a plurality of pieces of bit information, the plurality of pieces of bit information being included in each of the plurality of weak light beams phase-modulated by the second modulation unit, the plurality of pieces of bit information being assigned a transmission basis having a basis value matching a reception basis assigned in the receiver; The receiver includes: The method further includes the step of: generating a second encryption key by using at least a part of the plurality of pieces of bit information extracted by the extraction unit; 6. An encryption key distribution system as described in claim 6.

[0068] (Appendix 8) The quantum communication channel is an optical fiber. 6. An encryption key distribution system as described in claim 6.

[0069] (Appendix 9) A reference light is phase-modulated using a randomly assigned reception basis in correspondence with a randomly assigned transmission basis for each of a plurality of weak light beams transmitted from a transmitter and received via a quantum communication channel; By interfering the plurality of weak lights with the phase-modulated reference light, a plurality of bits of information are detected from each of the plurality of weak lights interfered with by the reference light of a reception basis having a basis value that coincides with a transmission basis, among the plurality of weak lights; extracting a plurality of pieces of bit information having amplitude components equal to or greater than a threshold value from the detected plurality of pieces of bit information; Obtaining information regarding a weather forecast for an installation area of ​​a quantum communication channel installed on the ground among the quantum communication channels; A load status of the receiver itself is predicted based on the information on the weather forecast; adjusting the threshold value according to the predicted load status of the receiver; How to control the receiver.

[0070] (Appendix 10) A process of phase-modulating a reference light using a randomly assigned reception basis in correspondence with a randomly assigned transmission basis for each of a plurality of weak light beams transmitted from a transmitter and received via a quantum communication channel; A process of detecting a plurality of bits of information from each of a plurality of weak lights interfered by the reference light of a reception basis having a basis value that coincides with a transmission basis, by interfering the plurality of weak lights with the phase-modulated reference light; A process of extracting a plurality of pieces of bit information having amplitude components equal to or greater than a threshold value from the detected plurality of pieces of bit information; A process of acquiring information about a weather forecast for an installation area of ​​a quantum communication channel installed on the ground among the quantum communication channels; A process of predicting a load condition of the receiver itself based on information about the weather forecast; adjusting the threshold value according to the predicted load status of the receiver; A control program that causes a computer to execute the above.

[0071] (Appendix 11) A transmitter; A receiver; a quantum communication channel provided between the transmitter and the receiver; Equipped with The transmitter includes: A light generating unit that generates a plurality of weak lights; a first modulation unit that phase-modulates the plurality of weak lights one by one using bit information and a transmission basis randomly selected in the transmitter and transmits the phase-modulated light to the receiver via the quantum communication channel; having The receiver includes: A second modulation unit that phase-modulates a reference light by using a reception basis randomly assigned in the receiver in response to a transmission basis randomly assigned to each of the plurality of weak light beams transmitted from the transmitter and received via the quantum communication channel; a detection unit that detects a plurality of bits of information from each of a plurality of weak lights that are interfered with by the reference light of a reception basis having a basis value that coincides with a transmission basis, by interfering the plurality of weak lights with the reference light that has been phase-modulated by the second modulation unit; an extracting unit that extracts a plurality of pieces of bit information having amplitude components equal to or greater than a threshold from the plurality of pieces of bit information detected by the detecting unit; an acquisition unit that acquires information regarding a weather forecast for an installation area of ​​a quantum communication channel installed on the ground among the quantum communication channels; a prediction unit for predicting a load condition of the receiver itself based on information about the weather forecast; an adjustment unit that adjusts the threshold value in accordance with the load status of the receiver predicted by the prediction unit; having Cryptographic key distribution system.

[0072] (Appendix 12) the adjustment unit increases the threshold as the predicted processing load of the receiver increases, and decreases the threshold as the predicted processing load of the receiver decreases. 12. An encryption key distribution system as described in claim 11.

[0073] (Appendix 13) the prediction unit predicts that the processing load of the receiver will be large when the information on the weather forecast includes information indicating that the amount of change in temperature in a specified period will be large, and predicts that the processing load of the receiver will be small when the information on the weather forecast includes information indicating that the amount of change in temperature in a specified period will be small; 12. An encryption key distribution system as described in claim 11.

[0074] (Appendix 14) the prediction unit predicts that the processing load of the receiver will increase when the information on the weather forecast includes information indicating an increase in wind speed, and predicts that the processing load of the receiver will decrease when the information on the weather forecast includes information indicating a decrease in wind speed. 12. An encryption key distribution system as described in claim 11.

[0075] (Appendix 15) A monitoring unit for monitoring a load status of the receiver is further provided, the adjustment unit adjusts the threshold value in accordance with a load status of the receiver monitored by the monitoring unit and a load status of the receiver predicted by the prediction unit. 12. An encryption key distribution system as described in claim 11.

[0076] (Appendix 16) The transmitter includes: a first control unit that generates a first encryption key by using at least a part of a plurality of pieces of bit information, the plurality of pieces of bit information being included in each of the plurality of weak light beams phase-modulated by the first modulation unit, the plurality of pieces of bit information being assigned a transmission basis having a basis value matching a reception basis assigned in the receiver; The receiver includes: The method further includes the step of: generating a second encryption key by using at least a part of the plurality of pieces of bit information extracted by the extraction unit; 12. An encryption key distribution system as described in claim 11.

[0077] (Appendix 17) The quantum communication channel is an optical fiber. 12. An encryption key distribution system as described in claim 11. [Explanation of symbols]

[0078] 1. Encryption key distribution system 2. Encryption Key Distribution System 3. Encryption Key Distribution System 11 Transmitter 12 Receiver 13 Quantum Communication Channels 21 Transmitter 22 Receiver 24 Classical Communication Channels 32 Receiver 111 Light generation part 112 Modulation section 121 Modulation section 122 Detection unit 123 Extraction part 124 Acquisition Department 125 Prediction Department 126 Adjustment section 213 Control Unit 227 Control Unit 328 Monitoring Department

Claims

1. Installed in the encryption key distribution system, a first modulation unit that phase-modulates a reference light by using a randomly assigned reception basis in response to a randomly assigned transmission basis for each of a plurality of weak light beams transmitted from a transmitter and received via a quantum communication channel; a detection unit that detects a plurality of bits of information from each of a plurality of weak lights that are interfered with by the reference light of a reception basis having a basis value that coincides with a transmission basis, by interfering the plurality of weak lights with the reference light that has been phase-modulated by the first modulation unit; an extracting unit that extracts a plurality of pieces of bit information having amplitude components equal to or greater than a threshold from the plurality of pieces of bit information detected by the detecting unit; an acquisition unit that acquires information regarding a weather forecast for an installation area of ​​a quantum communication channel installed on the ground among the quantum communication channels; a prediction unit for predicting a load condition of the receiver itself based on information about the weather forecast; an adjustment unit that adjusts the threshold value in accordance with the load status of the receiver predicted by the prediction unit; A receiver comprising:

2. the adjustment unit increases the threshold as the processing load of the receiver predicted by the prediction unit increases, and decreases the threshold as the processing load of the receiver predicted by the prediction unit decreases.

2. The receiver of claim 1.

3. the prediction unit predicts that the processing load of the receiver will be large when the information on the weather forecast includes information indicating that the amount of change in temperature in a specified period will be large, and predicts that the processing load of the receiver will be small when the information on the weather forecast includes information indicating that the amount of change in temperature in a specified period will be small; 2. The receiver of claim 1.

4. the prediction unit predicts that the processing load of the receiver will increase when the information on the weather forecast includes information indicating an increase in wind speed, and predicts that the processing load of the receiver will decrease when the information on the weather forecast includes information indicating a decrease in wind speed.

2. The receiver of claim 1.

5. A monitoring unit for monitoring a load status of the receiver is further provided, the adjustment unit adjusts the threshold value in accordance with a load status of the receiver monitored by the monitoring unit and a load status of the receiver predicted by the prediction unit.

2. The receiver of claim 1.

6. The transmitter; A receiver according to claim 1; a quantum communication channel provided between the transmitter and the receiver; Equipped with The transmitter includes: A light generating unit that generates the plurality of weak lights; A second modulation unit that phase-modulates the plurality of weak lights one by one using bit information and a transmission basis randomly selected in the transmitter and transmits the phase-modulated light to the receiver via the quantum communication channel; having Cryptographic key distribution system.

7. The transmitter includes: a first control unit that generates a first encryption key by using at least a part of a plurality of pieces of bit information, the plurality of pieces of bit information being included in each of the plurality of weak light beams phase-modulated by the second modulation unit, the plurality of pieces of bit information being assigned a transmission basis having a basis value matching a reception basis assigned in the receiver; The receiver includes: The method further includes the step of: generating a second encryption key by using at least a part of the plurality of pieces of bit information extracted by the extraction unit; 7. The encryption key distribution system according to claim 6.

8. The quantum communication channel is an optical fiber.

7. The encryption key distribution system according to claim 6.

9. A reference light is phase-modulated using a randomly assigned reception basis in correspondence with a randomly assigned transmission basis for each of a plurality of weak light beams transmitted from a transmitter and received via a quantum communication channel; By interfering the plurality of weak lights with the phase-modulated reference light, a plurality of bits of information are detected from each of the plurality of weak lights interfered with by the reference light of a reception basis having a basis value that coincides with a transmission basis, among the plurality of weak lights; extracting a plurality of pieces of bit information having amplitude components equal to or greater than a threshold value from the detected plurality of pieces of bit information; Obtaining information regarding a weather forecast for an installation area of ​​a quantum communication channel installed on the ground among the quantum communication channels; A load status of the receiver itself is predicted based on the information on the weather forecast; adjusting the threshold value according to the predicted load status of the receiver; How to control the receiver.

10. A process of phase-modulating a reference light using a randomly assigned reception basis in correspondence with a randomly assigned transmission basis for each of a plurality of weak light beams transmitted from a transmitter and received via a quantum communication channel; A process of detecting a plurality of bits of information from each of a plurality of weak lights interfered by the reference light of a reception basis having a basis value that coincides with a transmission basis, by interfering the plurality of weak lights with the phase-modulated reference light; A process of extracting a plurality of pieces of bit information having amplitude components equal to or greater than a threshold value from the detected plurality of pieces of bit information; A process of acquiring information about a weather forecast for an installation area of ​​a quantum communication channel installed on the ground among the quantum communication channels; A process of predicting a load condition of the receiver itself based on information about the weather forecast; adjusting the threshold value according to the predicted load status of the receiver; A control program that causes a computer to execute the above.

11. A transmitter; A receiver; a quantum communication channel provided between the transmitter and the receiver; Equipped with The transmitter includes: A light generating unit that generates a plurality of weak lights; a first modulation unit that phase-modulates the plurality of weak lights one by one using bit information and a transmission basis randomly selected in the transmitter and transmits the phase-modulated light to the receiver via the quantum communication channel; having The receiver includes: A second modulation unit that phase-modulates a reference light by using a reception basis randomly assigned in the receiver in response to a transmission basis randomly assigned to each of the plurality of weak light beams transmitted from the transmitter and received via the quantum communication channel; a detection unit that detects a plurality of bits of information from each of the plurality of weak lights that are interfered with by the reference light of a reception basis having a basis value that coincides with a transmission basis, by interfering between the plurality of weak lights and the reference light that has been phase-modulated by the second modulation unit; an extracting unit that extracts a plurality of pieces of bit information having amplitude components equal to or greater than a threshold from the plurality of pieces of bit information detected by the detecting unit; an acquisition unit that acquires information regarding a weather forecast for an installation area of ​​a quantum communication channel installed on the ground among the quantum communication channels; a prediction unit for predicting a load condition of the receiver itself based on information about the weather forecast; an adjustment unit that adjusts the threshold value in accordance with the load status of the receiver predicted by the prediction unit; having Cryptographic key distribution system.

12. the adjustment unit increases the threshold as the predicted processing load of the receiver increases, and decreases the threshold as the predicted processing load of the receiver decreases. The encryption key distribution system according to claim 11.

13. the prediction unit predicts that the processing load of the receiver will be large when the information on the weather forecast includes information indicating that the amount of change in temperature in a specified period will be large, and predicts that the processing load of the receiver will be small when the information on the weather forecast includes information indicating that the amount of change in temperature in a specified period will be small; The encryption key distribution system according to claim 11.

14. the prediction unit predicts that the processing load of the receiver will increase when the information on the weather forecast includes information indicating an increase in wind speed, and predicts that the processing load of the receiver will decrease when the information on the weather forecast includes information indicating a decrease in wind speed. The encryption key distribution system according to claim 11.

15. A monitoring unit for monitoring a load status of the receiver is further provided, the adjustment unit adjusts the threshold value in accordance with a load status of the receiver monitored by the monitoring unit and a load status of the receiver predicted by the prediction unit. The encryption key distribution system according to claim 11.

16. The transmitter includes: a first control unit that generates a first encryption key by using at least a part of a plurality of pieces of bit information, the plurality of pieces of bit information being included in each of the plurality of weak light beams phase-modulated by the first modulation unit, the plurality of pieces of bit information being assigned a transmission basis having a basis value matching a reception basis assigned in the receiver; The receiver includes: The method further includes the step of: generating a second encryption key by using at least a part of the plurality of pieces of bit information extracted by the extraction unit; The encryption key distribution system according to claim 11.

17. The quantum communication channel is an optical fiber. The encryption key distribution system according to claim 11.

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