Receiver, encryption key distribution system, receiver control method, and control program

Abstract

To provide a receiver capable of generating an encryption key without increasing processing load.SOLUTION: A receiver provided in an encryption key delivery system includes: a first modulation unit which phase-modulates reference light, using a reception base allocated randomly, for a transmission base allocated randomly to each of multiple weak light beams transmitted from a transmitter and received through a quantum communication path; a detection unit which causes the multiple weak light beams interfere with the reference light phase-modulated by the first modulation unit, to detect multiple pieces of bit information from each of the weak light beams interfered by the reference light having a reception base which is the same in base value as the transmission base, out of the multiple weak light beams; an extraction unit which extracts multiple pieces of bit information having an amplitude component equal to or higher than a threshold, out of the detected multiple pieces of bit information; a monitoring unit which monitors load status of the receiver; and an adjustment unit which adjusts the threshold, in accordance with the load status of the receiver monitored by the monitoring unit.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In encrypted communication, when message communication is performed between a transmission server and a reception server, encryption of the message at the transmission server and decryption of the message at the reception server are performed using an encryption key pre-shared between the transmission server and the reception server. In particular, encrypted communication in which a new encryption key is generated and used for each single message communication is referred to as one-time pad encrypted communication.

[0003] Furthermore, in recent years, development of quantum encrypted communication has been progressing. Quantum encrypted communication is a type of one-time pad encrypted communication, in which an encryption key generated by a transmitter on the transmission server side is carried on photons (light particles), which are the minimum unit of light, or weak light, and distributed from the transmitter to a receiver on the reception server side, thereby enabling encrypted communication with higher security. A technique related to quantum encrypted communication is disclosed in, for example, Patent Document 1.

[0004] Patent Document 1 discloses a multiple quantum communication system including a first quantum communication system and a second quantum communication system. In this multiple quantum communication system, the first quantum communication system and the second quantum communication system share a quantum communication path. Further, a transmission apparatus of the second quantum communication system includes a generation unit that generates photons, a modulation unit that transmits a quantum signal generated by modulating the photons to a reception apparatus, a control unit that controls the generation unit and the modulation unit, and a change unit that inputs a control signal for changing the operation timing of the generation unit and the operation timing of the modulation unit to the control unit when the error rate of the quantum signal of the first quantum communication system and the error rate of the quantum signal of the second quantum communication system are equal to or greater than a predetermined threshold. Thereby, this multiple quantum communication system stabilizes the distribution speed of encryption key information.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-157405 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in the system disclosed in Patent Document 1, the receiving device (photon receiver) receives a fixed amount of photons transmitted from the transmitting device regardless of the load on the receiving device. Therefore, in the system disclosed in Patent Document 1, if the receiving device receives a fixed amount of photons transmitted from the transmitting device even when the receiving device is under heavy processing load, the processing load on the receiving device increases, which is a problem.

[0007] One of the purposes of this 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 aspect 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 randomly assigned receiving basis corresponding to a randomly assigned transmitting basis for 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 the plurality of weak lights that are interfered with by the reference light of a receiving basis whose basis value matches that of the transmitting basis, by interfering the plurality of weak lights with the reference light phase modulated by the first modulation unit; an extraction unit that extracts a plurality of bit information having amplitude components greater than or equal to a threshold from the plurality of bit information detected by the detection unit; a monitoring unit that monitors the load status of the receiver itself; and an adjustment unit that adjusts the threshold according to the load status of the receiver monitored by the monitoring unit.

[0009] A receiver control method according to one aspect of this disclosure involves phase-modulating a reference light using a randomly assigned receiving basis corresponding to a randomly assigned transmitting basis for each of a plurality of weak lights transmitted from a transmitter and received via a quantum communication channel, interfering the plurality of weak lights with the phase-modulated reference light, thereby detecting a plurality of bit information from each of the plurality of weak lights that are interfered with by the reference light of a receiving basis whose basis value matches that of the transmitting basis, extracting a plurality of bit information from the detected plurality of bit information that has amplitude components above a threshold, monitoring the load status of the receiver, and adjusting the threshold according to the load status of the monitored receiver.

[0010] A control program according to one aspect of this disclosure causes a computer to perform the following processes: phase modulate a reference light using a randomly assigned receiving basis corresponding to a randomly assigned transmitting basis for each of a plurality of weak lights transmitted from a transmitter and received via a quantum communication channel; detect a plurality of bit information from each of the plurality of weak lights that are interfered with by the reference light of a receiving basis whose basis value matches that of the transmitting basis, by interfering the plurality of weak lights with the phase modulated reference light; extract a plurality of bit information from the detected plurality of bit information that has an amplitude component greater than or equal to a threshold; monitor the load status of the receiver, which is the computer itself; and adjust the threshold according to the load status of the receiver being monitored. [Effects of the Invention]

[0011] This disclosure provides a receiver capable of generating cryptographic keys without increasing processing load, a cryptographic key distribution system, a receiver control method, and a control program. [Brief explanation of the drawing]

[0012] [Figure 1] This is a block diagram illustrating the overview of a receiver provided in the encryption key distribution system according to Embodiment 1. [Figure 2] This is a block diagram illustrating an overview of the cryptographic key distribution system according to Embodiment 1. [Figure 3] This is a block diagram showing the details of the cryptographic key distribution system according to Embodiment 1. [Figure 4] This figure shows the distribution of multiple bit values ​​after base verification at the receiver in the cryptographic key distribution system shown in Figure 3. [Figure 5] This figure illustrates the method of extracting bit values ​​by the extraction unit in the receiver of the cryptographic key distribution system shown in Figure 3. [Figure 6] This figure illustrates the method of extracting bit values ​​by the extraction unit in the receiver of the cryptographic key distribution system shown in Figure 3. [Figure 7] This figure illustrates the method of extracting bit values ​​by the extraction unit in the receiver of the cryptographic key distribution system shown in Figure 3. [Modes for carrying out the invention]

[0013] The embodiments will be described below with reference to the drawings. Note that the drawings are simplified, and the technical scope of the embodiments should not be narrowly interpreted based on their depiction. Furthermore, the same elements are denoted by the same reference numerals, and redundant explanations are 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, and one may be a modification, application, detailed explanation, or supplementary explanation of part or all of the other. Furthermore, in the following embodiments, when referring to the number of elements (including number, numerical value, quantity, range, etc.), unless otherwise specified or clearly limited to a specific number in principle, it is not limited to that specific number, and may be greater than or less than that specific number.

[0015] Furthermore, in the following embodiments, the components (including operation steps and the like) are not necessarily essential, except for cases where they are particularly explicitly specified and cases where they are clearly considered to be essential in principle. Similarly, in the following embodiments, when referring to the shapes, positional relationships, and the like of components and the like, unless otherwise explicitly specified or clearly considered otherwise in principle, the shapes and the like shall be construed to include those substantially approximate or similar thereto. This also applies to the aforementioned numbers and the like (including the number of pieces, numerical values, quantities, ranges, and the like).

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

[0017] The encryption key distribution system 1 is used, as an example, for quantum encryption communication of an encryption key distribution scheme called CV-QKD. In encryption communication, when message communication is performed between a transmission server and a reception server, encryption of a message at the transmission server and decryption of the message at the reception server are performed using an encryption key pre-shared between the transmission server and the reception server. In particular, encryption communication in which a new encryption key is generated and used for each single message communication is called one-time pad scheme encryption communication.

[0018] Quantum encryption communication is a type of one-time pad scheme encryption communication, and the encryption key distribution system 1 enables more secure encryption communication by loading the encryption key generated by the transmitter on the transmission server side onto weak light and distributing it from the transmitter to the receiver on the reception server side. The weak light is, for example, light (quantum light) whose typical intensity is about one photon, such that quantum mechanical state changes can be detected.

[0019] As shown in Figure 1, in the encryption key distribution system 1, the receiver 12 includes a modulation unit 121, a detection unit 122, an extraction unit 123, a monitoring unit 124, and an adjustment unit 125. The modulation unit 121, the detection unit 122, the extraction unit 123, the monitoring unit 124, and the adjustment unit 125 are implemented by a hardware configuration (for example, a circuit), but as will be described later, the implementation is not limited thereto, and all or a part of them may be implemented by causing a CPU (Central Processing Unit) to execute a computer program.

[0020] The receiver 12 receives a plurality of weak lights transmitted from the transmitter 11 via the quantum communication path 13. The quantum communication path 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 related to a transmission bit and a transmission basis that are randomly assigned in the transmitter 11. In other words, each of the plurality of weak lights transmitted from the transmitter 11 is phase-modulated using a transmission bit and a transmission basis that are randomly assigned in 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 basis value of the transmission basis is "X", a phase modulation amount of 0 degrees is assigned, and when the basis value of the transmission basis is "Y", a phase modulation amount of 90 degrees is assigned. Each weak light is phase-modulated with a phase modulation amount that is the sum of the phase modulation amount corresponding to the bit value and the phase modulation amount corresponding to the basis value. Therefore, the weak light phase-modulated using the transmission basis with the basis value "X" ideally appears on the real axis, and the weak light phase-modulated using the transmission basis with the basis value "Y" ideally appears on the imaginary axis.

[0023] In the receiver 12, the modulation unit 121 phase-modulates reference light using a randomly assigned reception basis corresponding to the transmission basis randomly assigned to each of the plurality of weak lights.

[0024] The detection unit 122 is, for example, a homodyne detector, and performs base matching for multiple received weak lights. Specifically, the detection unit 122 interferes the multiple weak lights with a reference light phase-modulated by the modulation unit 121, and detects multiple bit values ​​(bit information) from each of the multiple weak lights that are interfered with by the reference light of the received base whose base value matches that of the transmitted base. The bit information includes a phase component representing the bit value and an amplitude component representing the intensity of the bit value.

[0025] For example, if the base value of the receive base is "X", a phase modulation amount of 0 degrees is assigned, and if the base value of the receive base is "Y", a phase modulation amount of 90 degrees is assigned. Therefore, the desired bit information can only be detected when interference occurs between a weak light and a reference light whose respective transmit and receive bases coincide.

[0026] After base matching by the detection unit 122, the extraction unit 123 performs post-selection. Specifically, the extraction unit 123 extracts multiple bit pieces of information from the multiple bit pieces of information detected by the detection unit 122 that have amplitude components greater than or equal to a threshold P. Here, the amplitude component of each bit piece of information is the amplitude (magnitude) of the difference signal, which is the intensity difference between the light obtained by superimposing the reference light and the weak light, and the light with the opposite phase. Therefore, the threshold P is set in units of, for example, the intensity difference of the light, or the potential difference corresponding to the intensity difference of the light. For example, if the phase modulation amount is 0 degrees corresponding to the bit value "0", the probability distribution of the difference signal will be a Gaussian distribution with a positive mean. For such a difference signal, a positive threshold P+ is set. Also, if the phase modulation amount is 180 degrees corresponding to the bit value "1", the probability distribution of the difference signal will be a Gaussian distribution with a negative mean. For such a difference signal, a negative threshold P- is set. The absolute values ​​of thresholds P+ and P- are both the threshold P. Ultimately, the receiver 12 generates the encryption key using only a portion of the bit values ​​(bit sequences) extracted by the extraction unit 123.

[0027] The adjustment unit 125 adjusts the threshold P according to the load status of the receiver 12. More specifically, the adjustment unit 125 adjusts the threshold P according to the load status of the processor that performs predetermined processing in the receiver 12.

[0028] For example, the adjustment unit 125 has a monitoring unit 124 that directly monitors the load status of the receiver 12, and adjusts the threshold P based on the monitoring results from the monitoring unit 124. In this case, the adjustment unit 125 increases the threshold P as the processing load of the receiver 12 increases. As a result, the bit values ​​extracted by the extraction unit 123 are limited to more reliable bit values, the error rate between transmitted bits and received bits decreases, and as a result, the processing load of the receiver 12 is reduced. Also, the adjustment unit 125 decreases the threshold P as the processing load of the receiver 12 decreases. As a result, the number of bit values ​​extracted by the extraction unit 123 increases, the number of bit values ​​used to generate the encryption key increases, and as a result, the amount of key generated increases.

[0029] Subsequently, error correction processing is performed in the transmitter 11 and receiver 12. Specifically, if the error rate between the bit sequence extracted by the transmitter 11 and the bit sequence extracted by the receiver 12 is less than a predetermined rate, the transmitter 11 and receiver 12 perform a process to correct the mismatch between those bit sequences. If the error rate is above the predetermined rate, the process returns to the generation of weak light by the transmitter 11 because it is not suitable for generating an encryption key.

[0030] Subsequently, the transmitter 11 and receiver 12 perform confidentiality enhancement processing on the error-corrected bit sequences, and as a result, cryptographic keys (i.e., shared cryptographic keys) with matching bit sequences are individually generated.

[0031] In this manner, the receiver 12 in the cryptographic key distribution system 1 according to this embodiment adjusts the threshold P, which is the minimum value of the amplitude component of the bit information extracted by the extraction unit 123, according to the load status of the receiver 12. As a result, the receiver 12 can generate a cryptographic key to be shared with the transmitter 11 without increasing the processing load.

[0032] <Overview of the encryption key distribution system according to Embodiment 1> Figure 2 is a block diagram showing an overview of the cryptographic key distribution system 1 according to Embodiment 1. As shown in Figure 2, the cryptographic key distribution system 1 comprises a transmitter 11, a receiver 12, and a quantum communication channel 13.

[0033] The transmitter 11 includes a light generation unit 111 and a modulation unit 112. The light generation unit 111 generates multiple weak light beams. The modulation unit 112 phase-modulates each of the multiple weak light beams generated by the light generation unit 111 using a randomly selected transmission bit and transmission basis in the transmitter 11. For example, a random number generated by a random number generation unit (not shown) is used as the bit value of the transmission bit. The multiple weak light beams phase-modulated by the modulation 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, so their explanation is omitted.

[0034] In the encryption key distribution system 1 according to this embodiment, 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, according to the load status of the receiver 12. As a result, the encryption key distribution system 1 can generate an encryption key shared by both the transmitter 11 and the receiver 12 without increasing the processing load of the receiver 12.

[0035] <Details of the encryption key distribution system according to Embodiment 1> Figure 3 is a block diagram showing the details of the cryptographic key distribution system 1 according to Embodiment 1 as the cryptographic key distribution system 2. The cryptographic key distribution system 2 comprises a transmitter 21, a receiver 22, a quantum communication channel 13, and a classical communication channel 24. The transmitter 21 and receiver 22 correspond to the transmitter 11 and receiver 12 in the cryptographic key distribution system 1.

[0036] Compared to transmitter 11, transmitter 21 further includes a control unit 213 in addition to the light generation unit 111 and modulation unit 112. Compared to receiver 12, receiver 22 further includes a control unit 226 in addition to the modulation unit 121, extraction unit 123, and adjustment unit 125. Control units 213 and 226 are configured to communicate via classical communication channel 24. Below, we will mainly describe the differences between cryptographic key distribution system 2 and cryptographic key distribution system 1.

[0037] Figure 4 shows the distribution of multiple bit information detected by the detection unit 122. In other words, Figure 4 shows the distribution of multiple bit information after base matching by the receiver 22. For simplification, Figure 4 only shows the distribution of bit information around the real axis, where the base value is "X," among the multiple bit information detected by the detection unit 122. However, basically the same phenomenon occurs for the distribution of bit information around the imaginary axis, where the base value is "Y."

[0038] In the upper example of Figure 4, the horizontal axis represents the real axis and the vertical axis represents the imaginary axis. In the upper example of Figure 4, the color becomes darker as the distribution of bit information increases, and lighter as the distribution of bit information decreases. In the lower example of Figure 4, the horizontal axis represents the value of the amplitude component of the bit information (amplitude of the difference signal mentioned above) on the real axis, and the vertical axis represents the probability that bit information is detected.

[0039] As shown in Figure 4, weak light (bit information) that has been phase-modulated based on a transmitted bit with a bit value of "0" is distributed such that the average value is located on the positive side of the real axis because the phase modulation amount is 0 degrees. On the other hand, weak light (bit information) that has been phase-modulated based on a transmitted bit with a bit value of "1" is distributed such that the average value is located on the negative side of the real axis because the phase modulation amount is 180 degrees. Here, with very weak light, especially very weak light that is so weak that it overlaps with weak light that has a phase difference of 180 degrees, it may not be possible to detect the correct bit value due to quantum fluctuations.

[0040] Therefore, in the cryptographic key distribution system 2, as shown in Figure 5, a threshold P is set in the receiver 22, which is 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 mean. 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 mean. For such a distribution of bit information, a negative threshold P- is set. The absolute values ​​of thresholds P+ and P- are both threshold P. The extraction unit 123 then extracts bit information with an amplitude component greater than or equal to threshold P from among the multiple bit information (i.e., bit information after basis matching) detected by the detection unit 122, and discards bit information with an amplitude component less than threshold P.

[0041] Furthermore, in the cryptographic key distribution system 2, as shown in Figures 6 and 7, the receiver 22 adjusts the threshold P according to the load status of the receiver 22 (more specifically, the load status of the processor that performs predetermined processing in the receiver 22).

[0042] For example, the adjustment unit 125 has a monitoring unit 124 that directly monitors the load status of the receiver 12, and adjusts the threshold P based on the monitoring results from the monitoring unit 124. In this case, the adjustment unit 125 increases the threshold P as the processing load of the receiver 12 increases (see Figure 6). As a result, the bit values ​​extracted by the extraction unit 123 are limited to more reliable bit values, the error rate between transmitted bits and received bits decreases, and as a result, the processing load of the receiver 12 is reduced. Also, the adjustment unit 125 decreases the threshold P as the processing load of the receiver 12 decreases (see Figure 7). As a result, the number of bit values ​​extracted by the extraction unit 123 increases, the number of bit values ​​used to generate the encryption key increases, and as a result, the amount of key generated increases.

[0043] Furthermore, the monitoring unit 124 is not limited to directly monitoring the load status of the receiver 12, but may also monitor the load status of the receiver 12 indirectly or auxiliaryly. For example, the adjustment unit 125 may adjust the threshold P according to the temperature and vibration of the quantum communication channel 13, which is an optical fiber, as monitored by the monitoring unit 124. The temperature and vibration of the quantum communication channel 13 are detected, for example, by a temperature sensor or a vibration sensor. In addition, the monitoring by the monitoring unit 124 may be an operation to monitor whether the load status is within a certain range, in which case the adjustment of the threshold P by the adjustment unit 125 may be an operation to adjust to an appropriate threshold P for that load status based on calculations performed in advance.

[0044] For example, the adjustment unit 125 may determine that the processing load on the receiver 12 increases as the temperature of the quantum communication channel 13 rises, and increase the threshold P, or determine that the processing load on the receiver 12 decreases as the temperature of the quantum communication channel 13 falls, and decrease the threshold P. Alternatively, the adjustment unit 125 may determine that the processing load on the receiver 12 increases as the oscillation of the quantum communication channel 13 increases, and increase the threshold P, or determine that the processing load on the receiver 12 decreases as the oscillation of the quantum communication channel 13 decreases, and decrease the threshold P.

[0045] The control units 213 and 226 exchange information necessary for generating an encryption key via the classical communication channel 24. For example, the control units 213 and 226 exchange synchronization signals to operate the transmitter 21 and receiver 22 in synchronous order. The control units 213 and 226 also exchange identification information to associate multiple weak lights transmitted from the transmitter 21 with multiple weak lights received by the receiver 22.

[0046] Furthermore, the control units 213 and 226 perform error correction processing after base matching and post-selection. Specifically, if the error rate between the bit sequence (key information) extracted by the transmitter 21 and the bit sequence (key information) extracted by the receiver 22 is less than a predetermined rate, the control units 213 and 226 perform processing to reconcile the mismatched parts between the bit sequence extracted by the transmitter 21 and the bit sequence extracted by the receiver 22. If the error rate is above the predetermined rate, the process returns to the photon generation by the transmitter 21 because it is not suitable for generating an encryption key.

[0047] Subsequently, control unit 213 and control unit 226 each perform confidentiality enhancement processing on the error-corrected bit sequence to individually generate cryptographic keys (i.e., shared cryptographic keys) whose bit sequences match each other.

[0048] Thus, in the cryptographic key distribution system 2 according to this embodiment, 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, according to the load status of the receiver 22. As a result, the cryptographic key distribution system 2 can generate cryptographic keys shared by the transmitter 21 and the receiver 22 without increasing the processing load of the receiver 22.

[0049] Furthermore, this disclosure can be implemented by having a CPU execute a computer program on part or all of the cryptographic key distribution system or the receiver provided therein.

[0050] Specifically, the program described above includes a set of instructions (or software code) for causing the computer to perform one or more of the functions described in the embodiments when loaded into the computer. The program may be stored in a non-temporary computer-readable medium or a physical storage medium. Examples, but not limited to, include RAM (Random-Access Memory), ROM (Read-Only Memory), flash memory, SSD (Solid-State Drive), or other memory technologies, CD-ROM, DVD (Digital Versatile Disc), Blu-ray® disc, or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage, or other magnetic storage devices. The program may be transmitted over a temporary computer-readable medium or a communication medium. Examples, but not limited to, include temporary computer-readable medium or a communication medium that includes electrically, optically, acoustically, or otherwise propagating signals.

[0051] Although the embodiments of this disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to those described above, and various design changes are possible without departing from the gist of this disclosure.

[0052] Furthermore, some or all of the above embodiments may also be described as follows, but are not limited to the following.

[0053] (Note 1) In the cryptographic key distribution system, A first modulation unit phase-modulates a reference light using a randomly assigned receiving basis corresponding to a randomly assigned transmitting basis for each of several weak light signals transmitted from a transmitter and received via a quantum communication channel. A detection unit detects multiple bits of information from each of the multiple weak lights that are interfered with by the reference light having a receiving basis whose basis value matches that of the transmitting basis, by interfering the multiple weak lights with the reference light having a phase-modulated first modulation unit. An extraction unit extracts a plurality of bit pieces of information having amplitude components greater than or equal to a threshold from among the plurality of bit pieces of information detected by the detection unit, A monitoring unit that monitors the load status of the receiver, which is the unit itself, An adjustment unit adjusts the threshold according to the load status of the receiver monitored by the monitoring unit, A receiver equipped with the following features.

[0054] (Note 2) The adjustment unit increases the threshold as the processing load on the receiver increases, and decreases the threshold as the processing load on the receiver decreases. The receiver described in Appendix 1.

[0055] (Note 3) The load status of the receiver is determined based on the temperature of the quantum communication channel. The receiver described in Appendix 1.

[0056] (Note 4) The adjustment unit increases the threshold as the temperature of the quantum communication channel increases, and decreases the threshold as the temperature of the quantum communication channel decreases. The receiver described in Appendix 3.

[0057] (Note 5) The load status of the receiver is determined based on the vibration status of the quantum communication channel. The receiver described in Appendix 1.

[0058] (Note 6) The adjustment unit increases the threshold as the vibration of the quantum communication channel increases, and decreases the threshold as the vibration of the quantum communication channel decreases. The receiver described in Appendix 5.

[0059] (Note 7) The aforementioned transmitter and, The receiver described in Appendix 1, A quantum communication channel is provided between the transmitter and the receiver, Equipped with, The aforementioned transmitter is The photogenerating unit that generates the plurality of weak lights, A second modulation unit that modulates each of the aforementioned multiple weak lights one by one using randomly selected bit information and a transmission basis in the transmitter, and transmits them to the receiver via the quantum communication channel. Having, Cryptographic key distribution system.

[0060] (Note 8) The aforementioned transmitter is The first control unit further comprises a first cryptographic key that generates a first cryptographic key using at least a portion of the bit information contained in each of the multiple weak lights phase-modulated by the second modulation unit, to which a transmit basis matching the base value of the receive basis assigned in the receiver is assigned. The aforementioned receiver is The system further includes a second control unit that generates a second cryptographic key using at least a portion of the multiple bit information extracted by the extraction unit, The encryption key distribution system described in Appendix 7.

[0061] (Note 9) The aforementioned quantum communication channel is an optical fiber. The cryptographic key distribution system described in Appendix 7 or 8.

[0062] (Note 10) The reference light is phase-modulated using a randomly assigned receiving basis corresponding to a randomly assigned transmitting basis for each of the multiple weak lights transmitted from the transmitter and received via the quantum communication channel. By interfering the aforementioned plurality of weak lights with the phase-modulated reference light, multiple bits of information are detected from each of the plurality of weak lights that are interfered with by the reference light of the receiving basis, whose basis value matches that of the transmitting basis. From the multiple bit information detected, multiple bit information having amplitude components above a threshold is extracted. The receiver, which is the device itself, monitors the load status. The threshold is adjusted according to the load status of the receiver being monitored. The control method for the receiver.

[0063] (Note 11) A process of phase-modulating a reference light using a randomly assigned receiving basis corresponding to a randomly assigned transmitting basis for each of the multiple weak light signals transmitted from the transmitter and received via the quantum communication channel, A process for detecting multiple bits of information from each of the multiple weak lights that are interfered with by the reference light of a receiving basis whose base value matches that of the transmitting basis, by interfering the multiple weak lights with the phase-modulated reference light. A process to extract multiple bit pieces of information from the detected multiple bit pieces of information that have amplitude components above a threshold, The process involves monitoring the load status of the receiver, which is the device itself. A process to adjust the threshold according to the load status of the receiver being monitored, A control program that instructs a computer to execute a command.

[0064] (Note 12) Transmitter and, Receiver and A quantum communication channel is provided between the transmitter and the receiver, Equipped with, The aforementioned transmitter is A light-generating unit that generates multiple weak lights, A first modulation unit that modulates each of the aforementioned multiple weak lights one by one using randomly selected bit information and a transmission basis in the transmitter, and transmits them to the receiver via the quantum communication channel. It has, The aforementioned receiver is A second modulation unit phase-modulates a reference light using a randomly assigned receiving basis in the receiver, corresponding to a randomly assigned transmitting basis in each of the plurality of weak lights transmitted from the transmitter and received via the quantum communication channel. A detection unit detects multiple bits of information from each of the multiple weak lights that are interfered with by the reference light having a receiving basis whose basis value matches that of the transmitting basis, by interfering the multiple weak lights with the reference light having a phase-modulated basis by the second modulation unit. An extraction unit extracts a plurality of bit pieces of information having amplitude components greater than or equal to a threshold from among the plurality of bit pieces of information detected by the detection unit, A monitoring unit that monitors the load status of the receiver, which is the unit itself, An adjustment unit adjusts the threshold according to the load status of the receiver monitored by the monitoring unit, Having, Cryptographic key distribution system.

[0065] (Note 13) The adjustment unit increases the threshold as the processing load on the receiver increases, and decreases the threshold as the processing load on the receiver decreases. The encryption key distribution system described in Appendix 12.

[0066] (Note 14) The load status of the receiver is determined based on the temperature of the quantum communication channel. The encryption key distribution system described in Appendix 12.

[0067] (Note 15) The adjustment unit increases the threshold as the temperature of the quantum communication channel increases, and decreases the threshold as the temperature of the quantum communication channel decreases. The encryption key distribution system described in Appendix 14.

[0068] (Note 16) The load status of the receiver is determined based on the vibration status of the quantum communication channel. The encryption key distribution system described in Appendix 12.

[0069] (Note 17) The adjustment unit increases the threshold as the vibration of the quantum communication channel increases, and decreases the threshold as the vibration of the quantum communication channel decreases. The encryption key distribution system described in Appendix 16.

[0070] (Note 18) The aforementioned transmitter is The first control unit further comprises a first cryptographic key that generates a first cryptographic key using at least a portion of the bit information contained in each of the multiple weak lights phase-modulated by the first modulation unit, to which a transmit basis matching the base value of the receive basis assigned in the receiver is assigned. The aforementioned receiver is The system further includes a second control unit that generates a second cryptographic key using at least a portion of the multiple bit information extracted by the extraction unit, The encryption key distribution system described in Appendix 12.

[0071] (Note 19) The aforementioned quantum communication channel is an optical fiber. The encryption key distribution system described in any one of the appendices 12 to 18. [Explanation of symbols]

[0072] 1. Cryptographic Key Distribution System 2. Cryptographic Key Distribution System 11 Transmitter 12 receivers 13 Quantum communication channels 21 Transmitter 22 Receivers 24 Classical Communication Channels 111 Light generation part 112 Modulation section 121 Modulation section 122 Detection unit 123 Extraction part 124 Monitoring Department 125 Adjustment section 213 Control Unit 226 Control Unit

Claims

1. In the cryptographic key distribution system, A first modulation unit phase-modulates a reference light using a first and second receiving basis value, which is randomly assigned to correspond to a first and second transmission basis value, which is randomly assigned to each of the multiple weak lights transmitted from the transmitter and received via the quantum communication channel. A detection unit detects multiple bits of information from each of the multiple weak lights that are interfered with by the reference light having a receiving basis whose basis value matches that of the transmitting basis, by interfering the multiple weak lights with the reference light having a phase-modulated first modulation unit. An extraction unit extracts a plurality of bit pieces of information having amplitude components greater than or equal to a threshold from among the plurality of bit pieces of information detected by the detection unit, A monitoring unit that monitors the load status of the receiver, which is the unit itself, An adjustment unit adjusts the threshold according to the load status of the receiver monitored by the monitoring unit, A receiver equipped with the following features.

2. The adjustment unit increases the threshold as the processing load on the receiver increases, and decreases the threshold as the processing load on the receiver decreases. The receiver according to claim 1.

3. The load status of the receiver is determined based on the temperature of the quantum communication channel. The receiver according to claim 1.

4. The adjustment unit increases the threshold as the temperature of the quantum communication channel increases, and decreases the threshold as the temperature of the quantum communication channel decreases. The receiver according to claim 3.

5. The load status of the receiver is determined based on the vibration status of the quantum communication channel. The receiver according to claim 1.

6. The adjustment unit increases the threshold as the vibration of the quantum communication channel increases, and decreases the threshold as the vibration of the quantum communication channel decreases. The receiver according to claim 5.

7. The aforementioned transmitter and, The receiver according to claim 1, A quantum communication channel is provided between the transmitter and the receiver, Equipped with, The aforementioned transmitter is The photogenerating unit that generates the plurality of weak lights, A second modulation unit that modulates each of the aforementioned multiple weak lights one by one using randomly selected bit information and a transmission basis in the transmitter, and transmits them to the receiver via the quantum communication channel. Having, Cryptographic key distribution system.

8. The aforementioned transmitter is The first control unit further comprises a first cryptographic key that generates a first cryptographic key using at least a portion of the bit information contained in each of the multiple weak lights phase-modulated by the second modulation unit, to which a transmit basis matching the base value of the receive basis assigned in the receiver is assigned. The aforementioned receiver is The system further includes a second control unit that generates a second cryptographic key using at least a portion of the multiple bit information extracted by the extraction unit, The cryptographic key distribution system according to claim 7.

9. The reference light is phase-modulated using the first and second receiving basis values, which are randomly assigned to each of the multiple weak light signals transmitted from the transmitter and received via the quantum communication channel, corresponding to the first and second transmission basis values, which are randomly assigned to each of the multiple weak light signals transmitted from the transmitter and received via the quantum communication channel. By interfering the aforementioned plurality of weak lights with the phase-modulated reference light, multiple bits of information are detected from each of the plurality of weak lights that are interfered with by the reference light of the receiving basis, whose basis value matches that of the transmitting basis. From the multiple bit information detected, multiple bit information having amplitude components above a threshold is extracted. The receiver, which is the device itself, monitors the load status. The threshold is adjusted according to the load status of the receiver being monitored. The control method for the receiver.

10. A process of phase-modulating a reference light using randomly assigned first and second basis values, which are the receiving basis values, corresponding to the first and second basis values, which are the transmitting basis values, randomly assigned to each of the multiple weak light signals transmitted from the transmitter and received via the quantum communication channel, A process for detecting multiple bits of information from each of the multiple weak lights that are interfered with by the reference light of a receiving basis whose base value matches that of the transmitting basis, by interfering the multiple weak lights with the phase-modulated reference light. A process to extract multiple bit pieces of information from the detected multiple bit pieces of information that have amplitude components above a threshold, The process involves monitoring the load status of the receiver, which is the device itself. A process to adjust the threshold according to the load status of the receiver being monitored, A control program that instructs a computer to execute a command.

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