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

Abstract

This disclosure provides a quantum key distribution device, a quantum key distribution method, and a program that can improve the security of quantum key distribution. [Solution] The quantum key distribution device according to the present disclosure comprises an optical modulation unit that modulates an optical signal and transmits the modulated optical signal, and a control unit that controls the modulation, wherein at a first timing, the control unit includes a plurality of optical modulation rules, each optical modulation rule defines an association between a first combination of a base type and an optical signal state and a second combination of a second bit value corresponding to the base type and a first bit value corresponding to the optical signal state, and the plurality of optical modulation rules control the modulation of the optical signal by the optical modulation unit based on a first optical modulation rule in a first correspondence relationship in which the associations are different from each other, and at a second timing different from the first timing, the control unit controls the modulation of the optical signal by the optical modulation unit based on a second optical modulation rule that is different from the first optical modulation rule among the plurality of optical modulation rules in the first correspondence relationship.

Description

Technical Field

[0001] The present disclosure relates to a quantum key distribution apparatus, a quantum key distribution method, and a program.

Background Art

[0002] In the field of optical communication, research is being conducted towards the practical application of quantum key distribution (QKD). A quantum key distribution system is a system that securely distributes a quantum key (common key) to two remote locations. In a quantum key distribution system, a transmitter (Alice) modulates an optical signal using, for example, key information and basis information, and transmits the modulated signal to a receiver (Bob) (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] ' By the way, as a threat assumed in a quantum key distribution system, there is a concern that information such as random numbers and quantum keys inside the transmitter may be estimated by measuring electromagnetic waves leaking from the electrical components of the transmitter (Alice) outside the transmitter (i.e., TEMPEST attack, side channel attack). Such a threat may reduce the security of quantum key distribution.

[0005] The purpose of this disclosure is to provide a quantum key distribution device, a quantum key distribution method, and a program that can improve the security of quantum key distribution. It should be noted that this purpose is only one of several purposes that the various embodiments disclosed herein seek to achieve. Other purposes or problems and novel features will be revealed in the description herein or in the accompanying drawings. [Means for solving the problem]

[0006] The quantum key distribution device according to this disclosure comprises an optical modulation unit that modulates an optical signal and transmits the modulated optical signal, and a control unit that controls the modulation, wherein the control unit includes a plurality of optical modulation rules at a first timing, each optical modulation rule defines an association between a first combination of a base type and an optical signal state and a second combination of a second bit value corresponding to the base type and a first bit value corresponding to the optical signal state, and the plurality of optical modulation rules control the modulation of the optical signal by the optical modulation unit based on a first optical modulation rule in a first correspondence relationship in which the associations are different from each other, and at a second timing different from the first timing, the control unit controls the modulation of the optical signal by the optical modulation unit based on a second optical modulation rule among the plurality of optical modulation rules in the first correspondence relationship that is different from the first optical modulation rule.

[0007] The quantum key distribution method according to the present disclosure is a method performed by a quantum key distribution device, which includes controlling the modulation of an optical signal by an optical modulation unit, wherein, at a first timing, the modulation of the optical signal is controlled based on a first optical modulation rule in a first correspondence relationship, where the plurality of optical modulation rules include a plurality of optical modulation rules, each optical modulation rule defines a correspondence between a first combination of a basis type and an optical signal state and a second combination of a second bit value corresponding to the basis type and a first bit value corresponding to the optical signal state, and the plurality of optical modulation rules have different correspondences from each other; and at a second timing different from the first timing, the modulation of the optical signal is controlled based on a second optical modulation rule from among the plurality of optical modulation rules in the first correspondence relationship, which is different from the first optical modulation rule.

[0008] The program relating to this disclosure causes a quantum key distribution device to perform a process that includes controlling the modulation of an optical signal by an optical modulation unit, and the control of the modulation includes, at a first timing, controlling the modulation of an optical signal based on a first optical modulation rule in a first correspondence relationship, where the plurality of optical modulation rules include a plurality of optical modulation rules, each optical modulation rule defines a correspondence between a first combination of a base type and an optical signal state and a second combination of a second bit value corresponding to the base type and a first bit value corresponding to the optical signal state, and the plurality of optical modulation rules have different correspondences from each other; and at a second timing different from the first timing, controlling the modulation of an optical signal based on a second optical modulation rule from the plurality of optical modulation rules in the first correspondence relationship that is different from the first optical modulation rule. [Effects of the Invention]

[0009] This disclosure provides a quantum key distribution device, a quantum key distribution method, and a program that can improve the security of quantum key distribution. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example of the system disclosed herein. [Figure 2] This is a block diagram showing an example of a quantum key distribution device in this disclosure. [Figure 3] A flowchart illustrating an example of the processing operation of the quantum key distribution device disclosed herein. [Figure 4] A block diagram showing another example of a quantum key distribution device in this disclosure. [Figure 5] This figure shows an example of the first correspondence in this disclosure. [Figure 6] A block diagram showing another example of a quantum key distribution device in this disclosure. [Figure 7] This figure shows an example of the second correspondence in this disclosure. [Figure 8] This diagram illustrates an example of synchronization for switching between target optical modulation rules. [Figure 9]This is a diagram showing an example configuration of a quantum key distribution device. [Modes for carrying out the invention]

[0011] The embodiments will be described below with reference to the drawings. In this disclosure, the drawings may be associated with one or more embodiments. Also, each element in the drawings may correspond to one or more embodiments. Furthermore, in the embodiments, the same or equivalent elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0012] <First Embodiment> <System Overview> Figure 1 shows an example of the system of this disclosure. In Figure 1, system 1 includes a quantum key distribution device 10 and a quantum key distribution device 20. Here, the quantum key distribution device 10 is the transmitter (Alice), and the quantum key distribution device 20 is the receiver (Bob).

[0013] A quantum key is distributed between quantum key distribution device 10 and quantum key distribution device 20. For example, the quantum key is distributed using the BB84 scheme.

[0014] For example, the quantum key distribution device 10 selects a random bit sequence (i.e., a key type) and a random basis. The quantum key distribution device 10 then modulates the optical signal into a signal state corresponding to the combination of bit value and selected basis, and transmits the modulated optical signal to the quantum key distribution device 20. The quantum key distribution device 20 selects a random basis, measures the received optical signal using the selected basis, and thereby obtains a bit value. The quantum key distribution device 10 and the quantum key distribution device 20 then share the patterns of their respective basis sets, and share the bit values ​​of the parts where the basis sets match as a shared key.

[0015] <Example of a quantum key distribution system configuration> FIG. 2 is a block diagram showing an example of the quantum key distribution apparatus of the present disclosure. In FIG. 2, the quantum key distribution apparatus 10 has a control unit (control device) 11 and an optical modulation unit 12. Here, the control unit (control device) 11 is described as being included in the quantum key distribution apparatus 10, but the control unit (control device) 11 may be a device independent of the quantum key distribution apparatus 10.

[0016] The optical modulation unit 12 modulates an optical signal and transmits the modulated optical signal. For example, the optical signal may be an optical pulse.

[0017] At a first timing, the control unit 11 controls the modulation of the optical signal by the optical modulation unit 12 based on a first optical modulation rule in a correspondence relationship (hereinafter sometimes referred to as the "first correspondence relationship"). This first correspondence relationship includes a plurality of "optical modulation rules". Each optical modulation rule defines the association between a first combination of a "basis type" and an "optical signal state" and a second combination of a value of a second bit corresponding to the basis type and a value of a first bit corresponding to the optical signal state. The plurality of optical modulation rules in the first correspondence relationship have different associations between the first combination and the second combination from each other.

[0018] At a second timing different from the first timing, the control unit 11 controls the modulation of the optical signal by the optical modulation unit 12 based on a second optical modulation rule different from the first optical modulation rule among the plurality of optical modulation rules in the above first correspondence relationship.

[0019] <Operation example of the quantum key distribution apparatus> FIG. 3 is a flowchart showing an example of the processing operation of the quantum key distribution apparatus of the present disclosure. In particular, here, an example of the processing operation of the control unit (control device) 11 will be described.

[0020] At a first timing, the control unit 11 controls the modulation of the optical signal by the optical modulation unit 12 based on the first optical modulation rule in the "first correspondence relationship" (step S11).

[0021] At the second timing, the control unit 11 controls the modulation of the optical signal by the optical modulation unit 12 based on the second optical modulation rule (step S12).

[0022] As described above, according to the first embodiment, in the quantum key distribution device 10, the control unit 11 controls the modulation of the optical signal by the optical modulation unit 12 at a first timing based on the first optical modulation rule in the "first correspondence relationship". This first correspondence relationship includes a plurality of "optical modulation rules". Each optical modulation rule defines a correspondence between a first combination of "basis type" and "optical signal state", and a second combination of the value of the second bit corresponding to the basis type and the value of the first bit corresponding to the optical signal state. The plurality of optical modulation rules in the first correspondence relationship have different correspondences between the first and second combinations. At a second timing different from the first timing, the control unit 11 controls the modulation of the optical signal by the optical modulation unit 12 based on a second optical modulation rule that is different from the first optical modulation rule among the plurality of optical modulation rules in the first correspondence relationship.

[0023] The configuration of this quantum key distribution device 10 allows the optical signal to be modulated based on a first optical modulation rule and a second optical modulation rule, the above-mentioned correspondences being different at the first and second timings. Therefore, the combination of "base type" and "optical signal state" corresponding to a predetermined 2 bits at the first timing can be made different from the combination of "base type" and "optical signal state" corresponding to the same predetermined 2 bits at the second timing. In other words, the 2 bits corresponding to a predetermined combination of "base type" and "optical signal state" at the first timing can be made different from the 2 bits corresponding to the same predetermined combination of "base type" and "optical signal state" at the second timing. Therefore, even if the state of electromagnetic waves corresponding to a predetermined combination of "base type" and "optical signal state" leaking from the electrical components of the quantum key distribution device 10 is measured, it is possible to prevent the corresponding 2-bit combination from being accurately estimated based on the measured state of electromagnetic waves. As a result, the security of quantum key distribution can be improved.

[0024] <Second Embodiment> Figure 4 is a block diagram showing another example of the quantum key distribution device of this disclosure. In Figure 4, the quantum key distribution device 30 includes a control unit (control device) 31 and an optical modulation unit 32. Here, the control unit (control device) 31 is described as being included in the quantum key distribution device 30, but the control unit (control device) 31 may be a device independent of the quantum key distribution device 30. Also, the basic configuration of the system of the second embodiment is the same as system 1 of the first embodiment, so please refer to Figure 1. That is, system 1 of the second embodiment has a quantum key distribution device 30 instead of a quantum key distribution device 10.

[0025] The optical modulation unit 32 modulates the optical signal and transmits the modulated optical signal, similar to the optical modulation unit 12.

[0026] The control unit 31, like the control unit 11, switches the target optical modulation rule (hereinafter sometimes referred to as the "first target optical modulation rule") from among the multiple optical modulation rules in the "first correspondence relationship". The "first target optical modulation rule" is an optical modulation rule set based on the first correspondence relationship. That is, the above first optical modulation rule is the first target optical modulation rule at the first timing. Also, the above second optical modulation rule is the first target optical modulation rule at the second timing.

[0027] The control unit 31 then controls the modulation of the optical signal by the optical modulation unit 32 based on the first target optical modulation rule, a second random bit value that specifies the base type to be used, and a first random bit value that specifies the optical signal state to be used. The second random bit value is the value of a bit included in the base type specification random bit sequence. The first random bit value is the value of a bit included in the key type random bit sequence.

[0028] Here, a specific example of the first correspondence relationship will be explained. Figure 5 is a diagram showing an example of the first correspondence relationship of this disclosure. In Figure 5, the first correspondence relationship is illustrated in table format. In Figure 5, RAND2 corresponds to the value of the second bit corresponding to the basis type described above. Also, RAND1 corresponds to the value of the first bit corresponding to the optical signal state described above. That is, RAND1 and RAND2 correspond to the "second combination" described above. Also, in Figure 5, "Y0", "Y1", "Z0", and "Z1" each correspond to the "first combination" of the basis type and the optical signal state described above. The correspondence table in Figure 5 holds multiple optical modulation rules (corresponding to multiple entries labeled "4 states" in Figure 5) in which the correspondence between the 2 bits "00", "10", "01", and "11" and the optical signal states "Y0", "Y1", "Z0", and "Z1" is different from each other. This correspondence table is shared between the control unit (control device) 31 and the quantum key distribution device 20.

[0029] The following are some possible combinations of base type and optical signal state, although they are not limited to these: (A) There are two types of bases: phase base and time base. For the phase base, there are two states for the optical signal: one where the phase difference between the two optical pulses of a double pulse is +90°, and another where the phase difference is -90°. For the time base, there are two states for the optical signal: one where only the leading optical pulse of a double pulse exists, and another where only the trailing optical pulse exists. For this modulation, for example, the technology disclosed in Patent Document 2 can be used. (B) There are two types of bases: linear bases and circular bases. For linear bases, there are two states for the optical signal: when the phase of the optical signal is 0° and when the phase of the optical signal is 90°. For circular bases, there are also two states for the optical signal: when the optical signal is clockwise and when the optical signal is counterclockwise.

[0030] In the following explanation, we will primarily use combinations of base type and optical signal state corresponding to (A) above. In this case, the optical signal is a pair of pulses (hereinafter sometimes referred to as a "pulse pair"). The optical modulation unit 32 performs phase modulation on the pulse pair when it is phase-based. When it is time-based, the optical modulation unit 32 performs intensity modulation on the pulse pair such that either the leading or trailing pulse has zero intensity.

[0031] The control unit 31 may periodically switch the first target optical modulation rule in synchronization with the quantum key distribution device 20. In this switching, the first target optical modulation rule may be selected from top to bottom among the multiple optical modulation rules in the corresponding table. Alternatively, if a random number synchronization method is used, the control unit 31 may receive a random number for selecting the first target optical modulation rule and select the optical modulation rule with an identification number corresponding to the remainder when this random number is divided by the number of optical modulation rules held in the corresponding table as the first target optical modulation rule. In this case, the quantum key distribution device 20 will similarly select the optical modulation rule with an identification number corresponding to the remainder when the random number for selecting the first target optical modulation rule is divided by the number of optical modulation rules held in the corresponding table as the first target optical modulation rule.

[0032] <Third Embodiment> Figure 6 is a block diagram showing another example of the quantum key distribution device of this disclosure. In Figure 6, the quantum key distribution device 40 includes a control unit (control device) 41, an optical modulation unit 42, an optical output unit 43, and an attenuator 44. Here, the control unit (control device) 41 is described as being included in the quantum key distribution device 40, but the control unit (control device) 41 may be a device independent of the quantum key distribution device 40. Also, the basic configuration of the system of the third embodiment is the same as system 1 of the first embodiment, so please refer to Figure 1. That is, system 1 of the third embodiment has a quantum key distribution device 40 instead of a quantum key distribution device 10.

[0033] The control unit 41, like the control unit 31, switches the "first target optical modulation rule" from among the multiple optical modulation rules in the "first correspondence relationship". The control unit 41 also switches the "second target optical modulation rule" from among the multiple optical intensity modulation rules in the correspondence relationship (hereinafter sometimes referred to as the "second correspondence relationship"). The "second correspondence relationship" includes multiple optical intensity modulation rules. Each optical intensity modulation rule defines the correspondence between an optical signal intensity candidate and the bit sequence corresponding to that intensity candidate. The multiple optical intensity modulation rules in the second correspondence relationship have different correspondences between the optical signal intensity candidates and the bit sequences corresponding to those intensity candidates.

[0034] Figure 7 shows an example of the second correspondence relationship of this disclosure. In Figure 7, RAND3 and RAND4 are bit sequences corresponding to intensity candidates. In Figure 7, "S" is a signal light carrying key seed data and corresponds to the intensity candidate "high". "D" is a decoy light and corresponds to the intensity candidate "weak". "V" means vacuum and means that the intensity is approximately zero. The correspondence table in Figure 7 holds multiple optical intensity modulation rules (corresponding to multiple entries labeled "Intensity" in Figure 7) where the correspondence between the 2 bits "00 (or 01)", "10", and "11" and the intensity candidates "S", "D", and "V" is different from each other. This correspondence table is shared between the control unit (control device) 31 and the quantum key distribution device 20. For this intensity modulation, for example, the technology disclosed in Patent Document 2 can be used.

[0035] Then, similar to the control unit 31, the control unit 41 controls the modulation of the optical signal by the optical modulation unit 32 based on the first target optical modulation rule, a second random bit value that specifies the base type of the target, and a first random bit value that specifies the optical signal state of the target.

[0036] Furthermore, the control unit 41 controls the optical modulation unit 42 so that, in the second target modulation rule, the intensity of the optical signal is modulated to an intensity corresponding to the specified bit sequence that specifies the optical signal intensity to be used.

[0037] The optical modulation unit 42 modulates the optical signal and transmits the modulated optical signal. For example, as shown in Figure 6, the optical modulation unit 42 includes a modulator 42A, an asymmetric interferometer 42B, and a modulator 42C.

[0038] The modulator 42A receives multiple optical pulses output from the optical output unit 43 at a predetermined period T. Then, the modulator 42A performs intensity modulation on each optical pulse according to the control based on the second modulation rule set by the control unit 41, and outputs the intensity-modulated optical pulses.

[0039] The asymmetric interferometer 42B forms a double pulse (pulse pair) from the optical pulse it receives from the modulator 42A. The asymmetric interferometer 42B has two optical waveguides with different optical path lengths. The optical pulse input to the asymmetric interferometer 42B is distributed to the two optical waveguides with different optical path lengths to become two pulses (pulse pair). These two pulses (pulse pair) are then output from the asymmetric interferometer 42B at different timings (for example, with a T / 2 time interval between them).

[0040] The modulator 42C performs phase modulation or intensity modulation on each pulse pair output from the asymmetric interferometer 42B, in accordance with the control by the control unit 41 based on the first target modulation rule. The modulator 42C outputs the modulated pulse pair to the attenuator 44.

[0041] The attenuator 44 attenuates the light intensity of the optical pulse output from the modulator 42C to a single-photon level before transmission.

[0042] <Fourth Embodiment> The fourth embodiment relates to the synchronization of switching of the optical modulation rules to be used. This technique for switching synchronization is applicable to any of the systems 1 of the first to third embodiments. Here, we will explain the case where this technique for switching synchronization is applied to the system 1 of the third embodiment, with reference to Figures 1 and 6.

[0043] In the third embodiment, the quantum key distribution device 40 and the quantum key distribution device 20 of System 1 share a bit string (hereinafter sometimes referred to as the "quantum cryptographic key bit string") as a shared key using the sharing method described in the first to third embodiments.

[0044] The control unit 41 of the quantum key distribution device 40 switches between the first target optical modulation rule and the second target optical modulation rule based on a switching rule with the quantum key distribution device 20. The "switching rule" is a rule that checks whether each of the multiple partial bit sequences matches the "desired bit sequence pattern" in a predetermined order, and switches the target optical modulation rule at the timing when a partial bit sequence that matches the desired bit sequence pattern appears. The above multiple partial bit sequences are obtained by dividing the quantum cryptographic key bit sequence shared between the quantum key distribution device 40 and the quantum key distribution device 20 into predetermined bit sequence lengths.

[0045] Figure 8 illustrates an example of synchronization for switching between target optical modulation rules. The quantum key distribution device 40 and the quantum key distribution device 20 each hold a "desired bit sequence pattern" in advance to determine the switching timing. In Figure 8, the "desired bit sequence pattern" is shown as a 4-bit "1111".

[0046] When a quantum cryptographic key bit sequence is shared between the quantum key distribution device 40 and the quantum key distribution device 20, the control unit 41 divides the quantum cryptographic key bit sequence into predetermined bit sequences of length (in this case, 4 bits, the same length as the desired bit sequence pattern) to identify multiple sub-bit sequences. Then, at each switching determination cycle, the control unit 41 checks whether each sub-bit sequence matches the "desired bit sequence pattern" in a predetermined order (for example, from the beginning of the quantum cryptographic key bit sequence). The control unit 41 then switches the target optical modulation rule when a sub-bit sequence matching the desired bit sequence pattern appears. That is, in the example in Figure 8, the control unit 41 switches the target optical modulation rule when a sub-bit sequence "1111" matching the desired bit sequence pattern "1111" appears. Note that the quantum key distribution device 20 also switches the target optical modulation rule in the same way as the quantum key distribution device 40.

[0047] By switching the target optical modulation rule as described above, it is possible to increase the randomness of the update timing while utilizing the information held by the existing quantum key distribution device.

[0048] <Other Embodiments> Figure 9 shows an example configuration of a quantum key distribution device. In Figure 9, the quantum key distribution device 100 includes a processor 101, a memory 102, a communication circuit 103, and an optical output circuit 104. The processor 101 may be, for example, a microprocessor, an MPU (Micro Processing Unit), or a CPU (Central Processing Unit). The processor 101 may include multiple processors. The memory 102 is composed of a combination of volatile memory and non-volatile memory. The memory 102 may include storage located away from the processor 101. In this case, the processor 101 may access the memory 102 via an I(Input) / O(Output) interface, which is not shown.

[0049] The quantum key distribution devices 10, 20, 30, and 40 of the first to fourth embodiments can each have the configuration shown in Figure 9. The control units (control devices) 11, 31, and 41 of the quantum key distribution devices 10, 20, 30, and 40 of the first to fourth embodiments may be implemented by a processor 101 reading and executing a program stored in memory 102. In other words, the quantum key distribution devices 10, 20, 30, and 40 of the first to fourth embodiments can be implemented in software. The optical modulation units 12, 32, and 42 and the attenuator 44 are implemented by a communication circuit 103. The optical output unit 43 is implemented by an optical output circuit 104. The program can be stored using various types of non-transitory computer-readable medium and supplied to the quantum key distribution devices 10, 20, 30, and 40. Examples of non-transitory computer-readable media include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives) and magneto-optical recording media (e.g., magneto-optical disks). Furthermore, examples of non-transitory computer-readable media include CD-ROMs (Read Only Memory), CD-Rs, and CD-R / Ws. Additionally, examples of non-transitory computer-readable media include semiconductor memory. Semiconductor memory includes, for example, mask ROMs, PROMs (Programmable ROMs), EPROMs (Erasable PROMs), flash ROMs, and RAMs (Random Access Memory). Programs may also be supplied to quantum key distribution devices 10, 20, 30, and 40 by various types of transient computer-readable media. Examples of transient computer-readable media include electrical signals, optical signals, and electromagnetic waves. Transitory computer-readable media can supply programs to quantum key distribution devices 10, 20, 30, and 40 via wired communication channels such as electric wires and optical fibers, or via wireless communication channels.

[0050] Alternatively, the control units (control devices) 11, 31, and 41 of the quantum key distribution devices 10, 20, 30, and 40 of the first to fourth embodiments may each be implemented with dedicated hardware. Furthermore, some or all of the components of each device may be implemented by general-purpose or dedicated circuits, processors, etc., or combinations thereof. These may be configured by a single chip or by multiple chips connected via a bus. Some or all of the components of each device may be implemented by a combination of the above-mentioned circuits, etc., and programs. In addition, a CPU (Central Processing Unit), GPU (Graphics Processing Unit), FPGA (field-programmable gate array), quantum processor (quantum computer control chip), etc. can be used as the processor.

[0051] Although the present invention has been described above with reference to embodiments, the present invention is not limited thereto. Various modifications to the structure and details of the present invention can be made within the scope of the invention as can be understood by those skilled in the art. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0052] Each drawing is merely illustrative to illustrate one or more embodiments. Each drawing may be associated with one or more other embodiments rather than with only one specific embodiment. As those skilled in the art will understand, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings, for example, to create embodiments not explicitly shown or described. Not all features or steps shown in any one drawing to illustrate an exemplary embodiment are necessarily required, and some features or steps may be omitted. The order of steps shown in any of the drawings may be changed as appropriate.

[0053] Some or all of the above embodiments may also be described as follows, but are not limited to the following: (Note 1) An optical modulation unit modulates an optical signal and transmits the modulated optical signal, A control unit that controls the modulation, It is equipped with, The control unit, At the first timing, the optical modulation unit controls the modulation of the optical signal based on a first optical modulation rule in a first correspondence relationship in which the above correspondences differ from one another. At a second timing different from the first timing, the modulation of the optical signal by the optical modulation unit is controlled based on a second optical modulation rule that is different from the first optical modulation rule among a plurality of optical modulation rules of the first correspondence relationship. Quantum key distribution device. (Note 2) The control unit controls the modulation of the optical signal by the optical modulation unit based on a first target optical modulation rule set based on the first correspondence, a second random bit value specifying the base type of the target, and a first random bit value specifying the optical signal state of the target. The quantum key distribution device described in Appendix 1. (Note 3) The control unit switches the first target optical modulation rule from among the multiple optical modulation rules of the first correspondence relationship. The quantum key distribution device described in Appendix 2. (Note 4) The control unit includes a plurality of optical intensity modulation rules, each optical intensity modulation rule defines an association between an intensity candidate of an optical signal and a bit sequence corresponding to the intensity candidate, and the plurality of optical intensity modulation rules switch a second target modulation rule from among the plurality of optical intensity modulation rules in a second correspondence relationship where the associations differ from each other, and controls the optical modulation unit to modulate the intensity of the optical signal to an intensity corresponding to a specified bit sequence that specifies the optical signal intensity to be used in the second target modulation rule. A quantum key distribution device as described in Appendix 2 or 3. (Note 5) The second random bit value is the value of a bit included in the base type-specified random bit sequence, The aforementioned first random bit value is the value of a bit included in the key seed random bit sequence. A quantum key distribution device as described in Appendix 2 or 3. (Note 6) The control unit switches the first target optical modulation rule based on the switching rule between it and the receiving device of the transmitted optical signal. The switching rule is a rule that, when the quantum cryptographic key bit sequence shared with the receiving device is divided into a plurality of sub-bit sequences of predetermined bit sequences, and it is checked whether each sub-bit sequence matches a desired bit sequence pattern in a predetermined order, the first target optical modulation rule is switched at the timing when a sub-bit sequence matching the desired bit sequence pattern appears. The quantum key distribution device described in Appendix 3. (Note 7) The control unit periodically switches the first target optical modulation rule in synchronization with the receiving device of the modulated optical signal. The quantum key distribution device described in Appendix 3. (Note 8) A method performed by a quantum key distribution device, Controlling the modulation of optical signals by the optical modulation unit, Includes, The control of the aforementioned modulation means that In the first timing, the optical modulation is controlled based on a first optical modulation rule in a first correspondence relationship, where the multiple optical modulation rules include a plurality of optical modulation rules, each optical modulation rule defining a correspondence between a first combination of a base type and an optical signal state and a second combination of a second bit value corresponding to the base type and a first bit value corresponding to the optical signal state, and the plurality of optical modulation rules have different correspondences from each other. In a second timing different from the first timing, the modulation of the optical signal is controlled based on a second optical modulation rule, which is different from the first optical modulation rule among the multiple optical modulation rules of the first correspondence, including, Quantum key distribution method. (Note 9) Controlling the modulation includes controlling the modulation of the optical signal by the optical modulation unit based on a first target optical modulation rule set based on the first correspondence, a second random bit value specifying the base type of the target, and a first random bit value specifying the optical signal state of the target. The quantum key distribution method described in Appendix 8. (Note 10) Controlling the modulation includes switching the first target optical modulation rule from among the multiple optical modulation rules of the first correspondence relationship. The quantum key distribution method described in Appendix 9. (Note 11) Controlling the modulation includes a plurality of optical intensity modulation rules, each optical intensity modulation rule defining an association between an intensity candidate of an optical signal and a bit sequence corresponding to the intensity candidate, the plurality of optical intensity modulation rules switching a second target modulation rule from among the plurality of optical intensity modulation rules having a second correspondence relationship in which the associations differ from each other, and controlling the optical modulation unit so that the intensity of the optical signal is modulated in the second target modulation rule to an intensity corresponding to a specified bit sequence that specifies the optical signal intensity to be used. The quantum key distribution method described in Appendix 9 or 10. (Note 12) The second random bit value is the value of a bit included in the base type-specified random bit sequence, The aforementioned first random bit value is the value of a bit included in the key seed random bit sequence. The quantum key distribution method described in Appendix 9 or 10. (Note 13) Controlling the modulation includes switching the first target optical modulation rule based on a switching rule with the receiving device of the modulated optical signal, The switching rule is a rule that, when the quantum cryptographic key bit sequence shared with the receiving device is divided into a plurality of sub-bit sequences of predetermined bit sequences, and it is checked whether each sub-bit sequence matches a desired bit sequence pattern in a predetermined order, the first target optical modulation rule is switched at the timing when a sub-bit sequence matching the desired bit sequence pattern appears. The quantum key distribution method described in Appendix 10. (Note 14) Controlling the modulation includes periodically switching the first target optical modulation rule in synchronous manner with the receiving device of the modulated optical signal. The quantum key distribution method described in Appendix 10. (Note 15) The quantum key distribution device is made to perform a process that includes controlling the modulation of the optical signal by the optical modulation unit. The control of the aforementioned modulation means that In the first timing, the optical modulation is controlled based on a first optical modulation rule in a first correspondence relationship, where the multiple optical modulation rules include a plurality of optical modulation rules, each optical modulation rule defining a correspondence between a first combination of a base type and an optical signal state and a second combination of a second bit value corresponding to the base type and a first bit value corresponding to the optical signal state, and the plurality of optical modulation rules have different correspondences from each other. In a second timing different from the first timing, the modulation of the optical signal is controlled based on a second optical modulation rule, which is different from the first optical modulation rule among the multiple optical modulation rules of the first correspondence, including, program. (Note 16) Controlling the modulation includes controlling the modulation of the optical signal by the optical modulation unit based on a first target optical modulation rule set based on the first correspondence, a second random bit value specifying the base type of the target, and a first random bit value specifying the optical signal state of the target. The program described in Appendix 15. (Note 17) Controlling the modulation includes switching the first target optical modulation rule from among the multiple optical modulation rules of the first correspondence relationship. The program described in Appendix 16. (Note 18) Controlling the modulation includes a plurality of optical intensity modulation rules, each optical intensity modulation rule defining an association between an intensity candidate of an optical signal and a bit sequence corresponding to the intensity candidate, the plurality of optical intensity modulation rules switching a second target modulation rule from among the plurality of optical intensity modulation rules having a second correspondence relationship in which the associations differ from each other, and controlling the optical modulation unit so that the intensity of the optical signal is modulated in the second target modulation rule to an intensity corresponding to a specified bit sequence that specifies the optical signal intensity to be used. The program described in Appendix 16 or 17. (Note 19) The second random bit value is the value of a bit included in the base type-specified random bit sequence, The aforementioned first random bit value is the value of a bit included in the key seed random bit sequence. The program described in Appendix 16 or 17. (Note 20) Controlling the modulation includes switching the first target optical modulation rule based on a switching rule with the receiving device of the modulated optical signal, The switching rule is a rule that, when the quantum cryptographic key bit sequence shared with the receiving device is divided into a plurality of sub-bit sequences of predetermined bit sequences, and it is checked whether each sub-bit sequence matches a desired bit sequence pattern in a predetermined order, the first target optical modulation rule is switched at the timing when a sub-bit sequence matching the desired bit sequence pattern appears. The program described in Appendix 17. (Note 21) Controlling the modulation includes periodically switching the first target optical modulation rule in synchronous manner with the receiving device of the modulated optical signal. The program described in Appendix 17. [Explanation of Symbols]

[0054] 1 System 10 Quantum key distribution device 11 Control Unit (Control Device) 12 Optical Modulation Section 20 Quantum key distribution device 30 Quantum key distribution device 31 Control Unit (Control Device) 32 Optical Modulation Section 40 Quantum key distribution device 41 Control Unit (Control Device) 42 Optical Modulation Section 42A modulator 42B Asymmetric Interferometer 42C modulator 43 Optical output section 44 Attenuator

Claims

1. An optical modulation unit modulates an optical signal and transmits the modulated optical signal, A control unit that controls the modulation, It is equipped with, The control unit, At the first timing, the optical modulation unit controls the modulation of the optical signal based on a first optical modulation rule in a first correspondence relationship in which the above correspondences differ from one another. At a second timing different from the first timing, the modulation of the optical signal by the optical modulation unit is controlled based on a second optical modulation rule that is different from the first optical modulation rule among the plurality of optical modulation rules of the first correspondence relationship. Quantum key distribution device.

2. The control unit controls the modulation of the optical signal by the optical modulation unit based on a first target optical modulation rule set based on the first correspondence, a second random bit value specifying the base type of the target, and a first random bit value specifying the optical signal state of the target. The quantum key distribution device according to claim 1.

3. The control unit switches the first target optical modulation rule from among the multiple optical modulation rules of the first correspondence relationship. The quantum key distribution device according to claim 2.

4. The control unit includes a plurality of optical intensity modulation rules, each optical intensity modulation rule defines an association between an intensity candidate of an optical signal and a bit sequence corresponding to the intensity candidate, and the plurality of optical intensity modulation rules switch a second target modulation rule from among the plurality of optical intensity modulation rules in a second correspondence relationship where the associations differ from each other, and controls the optical modulation unit to modulate the intensity of the optical signal to an intensity corresponding to a specified bit sequence that specifies the optical signal intensity to be used in the second target modulation rule. The quantum key distribution device according to claim 2 or 3.

5. The second random bit value is the value of a bit included in the base type-specified random bit sequence, The first random bit value is the value of a bit included in the key seed random bit sequence. The quantum key distribution device according to claim 2 or 3.

6. The control unit switches the first target optical modulation rule based on the switching rule between the receiving device and the transmitted optical signal. The switching rule is a rule that, when the quantum cryptographic key bit sequence shared with the receiving device is divided into a plurality of sub-bit sequences of predetermined bit sequences, and it is checked whether each sub-bit sequence matches a desired bit sequence pattern in a predetermined order, the first target optical modulation rule is switched at the timing when a sub-bit sequence matching the desired bit sequence pattern appears. The quantum key distribution device according to claim 3.

7. The control unit periodically switches the first target optical modulation rule in synchronization with the receiving device of the modulated optical signal. The quantum key distribution device according to claim 3.

8. A method performed by a quantum key distribution device, Controlling the modulation of optical signals by the optical modulation unit, Includes, The control of the aforementioned modulation means that In the first timing, the modulation of the optical signal is controlled based on a first optical modulation rule in a first correspondence relationship, where the multiple optical modulation rules include a plurality of optical modulation rules, each optical modulation rule defines a correspondence between a first combination of a base type and an optical signal state and a second combination of a second bit value corresponding to the base type and a first bit value corresponding to the optical signal state, and the plurality of optical modulation rules have different correspondences from each other. At a second timing different from the first timing, the modulation of the optical signal is controlled based on a second optical modulation rule, which is different from the first optical modulation rule among the multiple optical modulation rules of the first correspondence, including, Quantum key distribution method.

9. The quantum key distribution device is made to perform a process that includes controlling the modulation of the optical signal by the optical modulation unit. The control of the aforementioned modulation means that In the first timing, the modulation of the optical signal is controlled based on a first optical modulation rule in a first correspondence relationship, where the multiple optical modulation rules include a plurality of optical modulation rules, each optical modulation rule defines a correspondence between a first combination of a base type and an optical signal state and a second combination of a second bit value corresponding to the base type and a first bit value corresponding to the optical signal state, and the plurality of optical modulation rules have different correspondences from each other. At a second timing different from the first timing, the modulation of the optical signal is controlled based on a second optical modulation rule, which is different from the first optical modulation rule among the multiple optical modulation rules of the first correspondence, including, program.

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