Quantum key delivery system and quantum key delivery method

Abstract

To provide a quantum key delivery system capable of detecting wiretapping without utilizing a bit error rate, and a quantum key delivery method.SOLUTION: In a quantum key delivery system, a transmitter system comprises a transmission signal generation device for transmitting to a receiver system a transmission signal in which a decoy pulse is inserted at random in a signal pulse of which a phase of each pulse is 0 or π, and a decoy pulse information transmission device for generating a second signal relating to the decoy pulse and transmitting the second signal to the receiver system based on a first signal relating to a time slot on which photon detection is performed. The receiver system comprises a transmission signal detection device for performing the photon detection in response to a phase of the transmission signal, to which a delay time is given, and a simultaneous photon detection rate verification device for verifying a simultaneous photon detection rate in a time slot, in which the signal pulse and the decoy pulse interfere, in response to receiving the second signal.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a quantum key distribution system and a quantum key distribution method, and more particularly to a differential phase shift quantum key distribution system and a quantum key distribution method. [Background technology]

[0002] Research and development is underway on quantum cryptography or quantum key distribution (hereinafter referred to as QKD) as a system for securely supplying two parties engaged in cryptographic communication with a common secret key for encrypting / decrypting communication data. Several methods are known for QKD systems, one of which is a method called differential phase shift (hereinafter referred to as DPS) (see, for example, Non-Patent Document 1).

[0003] Fig. 1 is a diagram showing a schematic configuration of a conventional DPS-based QKD system 100. As shown in Fig. 1, the conventional QKD system 100 includes a sender system 110 that transmits a transmission signal and a receiver system 120 that receives the transmission signal. Furthermore, the sender system 110 includes a coherent pulsed light source 111, a phase modulator 112, and an attenuator 113, and the receiver system 120 includes a delayed Mach-Zehnder interferometer 121, a first photon detector 122a, and a second photon detector 122b.

[0004] Phase modulator 112 phase-modulates the transmission signal of the coherent pulse train output from coherent pulse light source 111 so that the phase of each pulse becomes 0 or π. Attenuator 113 attenuates the transmission signal so that the average number of photons in each pulse becomes less than 1 per pulse.

[0005] The delayed Mach-Zehnder interferometer 121 imparts a delay time to the transmission signal equal to the pulse time interval of the pulse train of the received transmission signal. The delayed Mach-Zehnder interferometer 121 is configured so that the propagation phase difference due to this delay is an integer multiple of 2π. The first photon detector 122a and the second photon detector 122b each perform photon detection on the transmission signal output from the delayed Mach-Zehnder interferometer 121. When a photon detection occurs, the first photon detector 122a and the second photon detector 122b each generate a signal containing information about the time in that time slot and transmit the signal to the sender system 110.

[0006] In a QKD system 100 having such a configuration, a weak coherent pulse train, in which each pulse has a phase of 0 or π, is transmitted as a transmission signal from a sender system 110. When this transmission signal is received by a receiver system 120, a delayed Mach-Zehnder interferometer 121 causes two adjacent pulses in the transmission signal to overlap. As a result of this interference, if the phase difference between the two pulses is 0, photons of the transmission signal are detected by a first photon detector 122a, and if the phase difference is π, photons of the transmission signal are detected by a second photon detector 122b. However, because the transmission signal is a weak pulse train to begin with, as described above, photon detection by the first photon detector 122a or the second photon detector 122b is rare and random.

[0007] FIG. 2 is a flow chart illustrating a QKD method 200 using the DPS-based QKD system 100 according to the prior art. As shown in FIG. 2, the prior art QKD method 200 includes the steps of: a sender system 110 generating a transmission signal of a weak coherent pulse train, each pulse having a phase of 0 or π, and transmitting the transmission signal to a receiver system 120 (S201); in response to receiving the transmission signal, the receiver system 120 generating a signal including information about the time slot in which the photon was detected (the signal including information about the time in which the photon was detected) and transmitting the signal to the sender system 110 (S202); based on the signal including information about the time slot in which the photon was detected, the sender system 110 generating a bit value on the sender system 110 side of the signal, where the phase difference between the two pulses that caused the photon detection is 0, or a bit value of π (S203); and a receiver system 120 generating a bit value on the receiver system 120 side of the signal, where the phase difference between the two pulses that caused the photon detection is 0, or a bit value of π, or a bit value of 0 if the detector that detected the photon is the first photon detector 122a, or a bit value of 1 if the detector that detected the photon is the second photon detector 122b (S204). The bit value thus generated is matched between the sender system 110 and the receiver system 120, and becomes the secret key bit.

[0008] The security of the secret key bits shared by the QKD method 200 is ensured by the fact that the transmission signal is a weak coherent pulse train. For example, consider a scenario in which an eavesdropper extracts a portion of the transmission signal and attempts to measure the phase difference between the pulses in the transmission signal to obtain information about the secret key bits. In such a case, because the average number of photons in the transmission signal in the QKD system 100 is very small, the eavesdropper cannot know all of the phase differences, but only a portion of them. The two pulses from which the eavesdropper has determined the phase difference may not necessarily be the same as the two pulses used by the receiver system 120 to generate the secret key bits through photon detection. Therefore, the eavesdropper cannot obtain all of the secret key bits from this measurement. While the eavesdropper's measured pulses and the receiver system 120's photon-detected pulses may coincide by chance, the probability of this occurring can be quantitatively estimated from the photon count statistics of the coherent light. By eliminating the overlapping pulses using a data compression technique called privacy amplification, a sufficiently secure secret key can be obtained.

[0009] Another eavesdropping method is known as an intercept-resend attack, in which an eavesdropper interrupts the transmission path, measures the transmitted signal, and then resends a fake signal based on the measurement results to the receiver system 120. If an eavesdropper who performs this intercept-resend attack can resend a fake signal so that the reception result at the receiver system 120 is the same as when there was no eavesdropping, it is possible to obtain information about the secret key bits without the eavesdropper noticing the eavesdropping.

[0010] However, for a weak coherent pulse train, such a spoofed signal cannot be retransmitted, and as mentioned above, an eavesdropper rarely obtains a measurement result. Therefore, the spoofed signal retransmitted by an eavesdropper to the receiver system 120 is two pulses with the measured phase difference. When such a signal is input to the delayed Mach-Zehnder interferometer 121 of the receiver system 120, photons can be detected in three time slots at the output of the delayed Mach-Zehnder interferometer 121: the time slot in which the first pulse is output via the short path, the time slot in which the first pulse that has traversed the long path and the second pulse that has traversed the short path are output, and the time slot in which the second pulse is output via the long path. Among these, photon detections at both end slots are randomly detected by the two detectors (the first photon detector 122a or the second photon detector 122b) because there is no interference. The bit value generated by the receiver system 120 from this photon detection event will then be different from the bit value generated by the sender system 110.

[0011] Therefore, the QKD method 200 using the QKD system 100 may further include the steps of: after generating the secret key bits, the sender system 110 and the receiver system 120 compare some of the secret key bits as test bits; if there is a bit value mismatch (bit error), determining that eavesdropping has occurred. The bit error rate caused by this eavesdropping can be quantitatively estimated. Conversely, the probability of eavesdropping can be quantitatively estimated from the bit error rate. Therefore, the bits used as the test bits are discarded, and the amount of information that may have been eavesdropped is deleted from the generated secret key by privacy amplification. This ultimately results in a secure secret key.

[0012] However, in reality, bit errors may occur due to factors other than eavesdropping, such as noise from the photon detectors (first photon detector 122a and second photon detector 122b), so privacy amplification is performed assuming the worst case scenario, assuming that all bit errors are due to eavesdropping. [Prior art documents] [Non-patent literature]

[0013] [Non-Patent Document 1] K. Inoue, E. Waks, and Y. Yamamoto, “Differential phase shift quantum key distribution using coherent light”, Physical Review A, vol. 68, 022317, (2003) Summary of the Invention [Problem to be solved by the invention]

[0014] In the above-described conventional QKD system 100 and QKD method 200, the amount of eavesdropping is estimated from the bit error rate of the generated private key bits, and the amount is removed by privacy amplification to share a secure private key. In this conventional technology, when performing privacy amplification, the original bit error rate included in the system is also considered to be due to eavesdropping, and the number of private key bits is reduced. Therefore, in a system with a high bit error rate, the amount of reduction due to privacy amplification is large, which poses a problem of reduced effective private key generation efficiency. [Means for solving the problem]

[0015] The present invention has been made in view of the above-mentioned problems, and its object is to provide a QKD system and a QKD method that are capable of detecting eavesdropping without using the bit error rate.

[0016] In order to achieve the above object, the present invention provides a quantum key distribution system, comprising: a sender system comprising: a transmission signal generator that generates a transmission signal in which a decoy pulse with a phase of π / 2 and an amplitude equal to or greater than that of the signal pulse is randomly inserted into a signal pulse of a weak coherent pulse train, each pulse having a phase of 0 or π, and transmits the transmission signal to a receiver system; and a decoy pulse information transmitter that generates a second signal containing information about the decoy pulse based on a first signal transmitted from the receiver system, the second signal containing information about a time slot in which a photon was detected, and transmits the second signal to the receiver system. The receiver system comprises: a transmission signal detector that receives the transmission signal transmitted by the sender system, applies a delay to the transmission signal, and then performs photon detection according to the phase of the transmission signal; and a simultaneous photon detection rate verification device that is configured to verify, in response to receiving the second signal, a simultaneous photon detection rate in a time slot in which the signal pulse and the decoy pulse interfere in the transmission signal, and to discard the private key if the verification determines that eavesdropping has occurred. [Effects of the Invention]

[0017] The QKD system and method of the present invention can detect eavesdropping from simultaneous photon detection events, whereas conventional techniques detect eavesdropping from bit error rates. This eliminates the need to reduce the private key by regarding the bit error rate inherent in the system as being due to eavesdropping, and enables more effective private key generation efficiency than conventional techniques. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a DPS-based QKD system 100 according to the prior art. [Figure 2] 2 is a flowchart illustrating a QKD method 200 using a DPS-based QKD system 100 according to the prior art. [Figure 3] 1 is a diagram showing a schematic configuration of a QKD system 300 according to the present invention. [Figure 4] 4 is a flow chart illustrating a QKD method 400 performed using the QKD system 300 according to the present invention. [Figure 5] 1 is a diagram showing a schematic configuration of a QKD system 500 according to the present invention. [Figure 6] 6 is a flow chart illustrating a QKD method 600 performed using the QKD system 300 in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Various embodiments of the present disclosure will be described in detail below with reference to the drawings. The same or similar reference numerals indicate the same or similar elements, and redundant description may be omitted. Numerical values ​​are for illustrative purposes only and are not intended to limit the technical scope of the present disclosure. The following description is an example, and some configurations may be omitted or modified, or additional configurations may be added, as long as they do not deviate from the gist of one embodiment of the present invention.

[0020] (QKD system configuration) Fig. 3 is a diagram showing a schematic configuration of a QKD system 300 according to the present invention. As shown in Fig. 3, the QKD system 300 according to the present invention includes a sender system 310 and a receiver system 320. The sender system 310 includes a transmission signal generator 311 that generates a transmission signal in which random decoy pulses are inserted into signal pulses of a weak coherent pulse train, each pulse having a phase difference of 0 or π, and transmits the transmission signal to the receiver system 320, and a decoy pulse information transmitter 312 that generates a second signal 330 including information about the decoy pulse based on a first signal including information about the time slot in which a photon transmitted from the receiver system 320 was detected, and transmits the second signal 330 to the receiver system 320. On the other hand, the receiver system 320 includes a transmission signal detection device 321 configured to receive the transmission signal sent by the sender system 310, impart a delay time to the transmission signal, and then perform photon detection according to the phase of the transmission signal, and a simultaneous photon detection rate verification device 322 configured to verify the simultaneous photon detection rate in the time slot in which the signal pulse and the decoy pulse in the transmission signal interfere in response to receiving the second signal 330 including information about the decoy pulse described above, and to discard the private key if the verification determines that eavesdropping has occurred.

[0021] In the above configuration, the transmission signal generator 311 may have the same configuration as the sender system 110 shown in Fig. 1. However, as described above, the transmission signal generated and transmitted by the transmission signal generator 311 is a signal in which random decoy pulses are inserted into the signal pulses of a weak coherent pulse train, each pulse having a phase of 0 or π. Meanwhile, the transmission signal detector 321 may have the same configuration as the receiver system 120 shown in Fig. 1. In other words, the QKD system 300 according to the present invention includes a sender system 310 in which a decoy pulse information transmitter 312 is additionally installed in the sender system 110 configured to generate a transmission signal in which random decoy pulses are inserted into the weak coherent pulse train, and a receiver system 320 in which a coincidence photon detection rate verification device 322 is additionally installed in the receiver system 120.

[0022] (QKD method) 4 is a flowchart showing a QKD method 400 executed using a QKD system 300 according to the present invention. As shown in FIG. 4, the QKD method 400 according to the present invention includes the steps of: generating a transmission signal by a sender system 310 in which decoy pulses are randomly inserted into signal pulses of a weak coherent pulse train, each pulse having a phase of 0 or π, and transmitting the transmission signal to a receiver system 120 (S401); generating a first signal by a receiver system 320 in response to receiving the transmission signal, the first signal including information about the time slot in which the photon was detected, and transmitting the first signal to the sender system 310 (S402); and based on the first signal, the sender system 310 generates a bit value of "0" if the phase difference between the two pulses that caused the photon detection is 0, or a bit value of "1" if the phase difference is π, and if the phase difference between the two pulses that caused the photon detection is ±π / 2 (i.e., if the transmission signal in which the photon was detected is an interference wave in which the signal pulse and the decoy pulse overlap), including information about the decoy pulse to notify this. The method includes generating a second signal 330 and transmitting it to the receiver system 320 S403; generating a bit value on the receiver system 320 side by the receiver system 320 of a bit "0" if the detector that detected the photon is the first photon detector 122a, or a bit "1" if the detector that detected the photon is the second photon detector 122b S404, and not generating a bit value from photon detection in which the phase difference between two pulses in the detected transmission signal is ±π / 2 S405; verifying by the receiver system 320, in response to receiving the second signal 330, the coincidence photon detection rate (probability that a photon is detected by both the first photon detector 122a and the second photon detector 122b) in a time slot in which the signal pulse and the decoy pulse in the transmission signal interfere S405; and determining whether eavesdropping has occurred by the receiver system 320 based on the verification result of the coincidence photon detection rate, and discarding the private key if eavesdropping has occurred S406.

[0023] In S401, the sender system 310 transmits a transmission signal in which decoy pulses are randomly inserted into signal pulses of a weak coherent signal pulse train with a phase of 0 or π to the receiver system 320. The phase of this decoy pulse is π / 2, the amplitude is equal to or greater than the amplitude of the signal pulse, and the insertion position is unknown to the outside.

[0024] When such a transmission signal is received by the receiver system 320, a transmission signal to which a delay time is added is output by the delay Mach-Zehnder interferometer 121 in the receiver system 320. Here, when the signal pulse and the decoy pulse overlap, the probability of a photon being detected by each detector (corresponding to the first photon detector 122a or the second photon detector 122b) in the receiver system 320 is expressed as follows: (μ s +μ d ) / 4. However, μ s and μ d are the average photon numbers of the signal pulse and the decoy pulse, respectively, in the transmitted signal input to the receiver system 320. The QKD method 400 of the present invention utilizes the photon detection properties of this transmitted signal to detect eavesdropping.

[0025] In S402, after the receiver system 320 receives the transmission signal, the receiver system 320 generates and transmits a first signal containing information about the time slot in which the photon was detected to the sender system 310. The first signal contains information about the time in that time slot when the photon detection occurred, similar to S202 in the prior art QKD method 200.

[0026] In S403, based on the received first signal, the sender system 310 generates a bit value on the sender system 310 side of the signal if the phase difference between the two pulses that caused the photon detection is 0, or a bit value of 1 if the phase difference is π. Furthermore, in S403, the sender system 310 transmits a second signal 330 containing information about the decoy pulse to the receiver system 320 if the phase difference between the two pulses is ±π / 2. The QKD system according to the present invention differs from prior art QKD systems in that it includes transmitting this second signal 330 to the receiver system 320.

[0027] In S404, the receiver system 320 generates a bit value on its side. At this time, the receiver system 320 generates a bit "0" if the detector that detected the photon is the first photon detector 122a, and generates a bit "1" if the detector is the second photon detector 122b. However, the receiver system 320 is configured not to generate a bit value from photon detection where the phase difference between two pulses in the detected transmission signal is ±π / 2.

[0028] In S405, in response to receiving the second signal 330 including information about the decoy pulse transmitted from the sender system 310, the receiver system 320 verifies the coincidence photon detection rate in the time slot where the signal pulse and the decoy pulse interfere. Here, the coincidence photon detection rate refers to the probability that a photon is detected by both the first photon detector 122a and the second photon detector 122b in any time slot (e.g., the time slot where the signal pulse and the decoy pulse interfere, the time slot where the signal pulse interferes, etc.).

[0029] In S406, the receiver system 320 determines whether eavesdropping has occurred based on the verification result of the coincidence photon detection rate, and if it is determined that eavesdropping has occurred, the receiver system 320 discards the private key. As a method for determining whether eavesdropping has occurred, for example, the coincidence photon detection rate in the time slot where the signal pulse and the decoy pulse interfere with each other is determined to be the same as the above (μ s +μ d ) / 4×(μ s +μd If the value is smaller than a predetermined value determined based on the probability obtained by 1 / 4, it is determined that eavesdropping has occurred.

[0030] (Principle of eavesdropping detection) The following describes in detail the principles of eavesdropping detection using the QKD system 300 and the QKD method 400. In the following description, the eavesdropping method is assumed to be the intercept-resend attack described above, as an example.

[0031] As mentioned above, in an intercept-resend attack, an eavesdropper interrupts the transmission path and measures the transmitted signal using the same receiving system as the receiver. When the QKD system 300 and QKD method 400 according to the present invention are used, the photon detection probability of each detector when the signal pulse and decoy pulse interfere is (μ s +μ d ) / 4. Therefore, the probability that only the first photon detector 122a detects a photon is (μ s +μ d ) / 4×{1-(μ s +μ d ) / 4}, and the probability that only the second photon detector 122b detects a photon is {1-(μ s +μ d ) / 4}×(μ s +μ d ) / 4, the probability that both the first photon detector 122a and the second photon detector 122b detect a photon is (μ s +μ d ) / 4×(μ s +μ d ) / 4. However, as described above, the transmission signal received by the receiver system 320 is essentially a weak coherent optical pulse, and therefore in many cases photons will be detected by only one of the first photon detector 122a or the second photon detector 122b.

[0032] If a photon is detected by only the first photon detector 122a or the second photon detector 122b, an eavesdropper cannot distinguish whether it is due to interference between a decoy pulse and a signal pulse or interference between signal pulses. In this case, the eavesdropper will consider most of the transmitted signal to be signal pulses and interference between the signal pulses, and will retransmit two pulses with a phase difference of 0 or π as a fake signal to the receiver system 320, depending on which detector detected the photon.

[0033] When the receiver system 320 receives the retransmitted decoy signal, the decoy signal is two pulses with a phase difference of 0 or π, and therefore photons are detected by only one of the first photon detector 122a or the second photon detector 122b. On the other hand, when there is no eavesdropping, the signal pulse and the decoy pulse should interfere with each other, and therefore photon detection may occur at both the first photon detector 122a and the second photon detector 122b. The probability that photon detection occurs at both detectors is, as described above, (μ s +μ d ) / 4×(μ s +μ d ) / 4. Therefore, in response to receiving the second signal 330 transmitted from the sender system 310, the receiver system 320 verifies the probability (simultaneous photon detection rate) that photons are detected by both the first photon detector 122a and the second photon detector 122b in the time slot where the signal pulse and the decoy pulse interfere, thereby making it possible to determine whether eavesdropping has occurred.

[0034] The receiver system 320 determines whether to discard the private key based on the determination of whether eavesdropping has occurred, as shown in S406 of the QKD method 400. If it determines that eavesdropping has occurred (for example, the coincidence photon detection rate is less than a predetermined value), it decides to discard the private key. In this way, it is possible to finally distribute a secure private key.

[0035] As described above, the QKD system 300 and QKD method 400 of the present invention can detect eavesdropping from coincidence photon detection events, whereas the prior art QKD system 100 and QKD method 200 detect eavesdropping from bit error rates. Therefore, there is an advantage that it is not necessary to reduce the secret key by regarding the bit error rate inherent in the system as being due to eavesdropping.

[0036] (additional components) However, actual photon detectors (first photon detector 122a and second photon detector 122b) may malfunction and output a photon detection signal even when no photons are input, a malfunction known as dark counting. Therefore, even if a retransmitted transmission signal with a phase difference of 0 / π is received, it may be recorded as a simultaneous detection due to dark counting, which may hinder eavesdropping detection.

[0037] Therefore, the receiver system of the QKD system according to the present invention may further include a coincidence photon detection rate comparison device 501, which compares the coincidence photon detection rate in the interference slot between signal pulses with the coincidence photon detection rate in the interference slot between the signal pulse and the decoy pulse, as in QKD system 500 shown in Fig. 5. In addition, the QKD method according to the present invention may further include comparing S407 the coincidence photon detection rate in the interference slot between the signal pulses with the coincidence photon detection rate in the interference slot between the signal pulse and the decoy pulse, as in QKD method 600 shown in Fig. 6. Since coincidence photon detection by dark counting also occurs in the interference slot between signal pulses, by examining the difference between the two in this way, it is possible to accurately detect whether eavesdropping has occurred.

[0038] It should be noted that the QKD methods 400, 600 according to the present invention do not have to be performed in the order shown in this specification and in Figures 4 and 6, but may be performed in any order, or some steps may be performed in parallel. [Industrial Applicability]

[0039] As described above, the quantum key distribution system and quantum key distribution method according to the present invention can detect eavesdropping from simultaneous photon detection events, thereby eliminating the need to reduce the secret key by regarding the bit error rate inherent in the system as being due to eavesdropping. Such a quantum key distribution system and quantum key distribution method are expected to be put into practical use as a system that more safely supplies a common secret key for encrypting / decrypting communication data to two parties engaged in encrypted communication. [Explanation of symbols]

[0040] 100 QKD Systems 110 Sender System 111 Coherent Pulse Light Source 112 Phase Modulator 113 Attenuator 120 Receiver System 121 Delayed Mach-Zehnder Interferometer 122a First photon detector 122b Second photon detector 200 QKD method 300 QKD systems 310 Sender System 311 Transmission signal generator 312 Decoy Pulse Information Transmitter 320 Receiver System 321 Transmission Signal Detector 322 simultaneous photon detection rate verification device 330 Second Signal 400 QKD method 500 QKD systems 501 Simultaneous Photon Detection Rate Comparison Device 520 Receiver System 600 QKD method

Claims

1. 1. A quantum key distribution system including a sender system and a receiver system, The sender system includes: a transmission signal generator that generates a transmission signal in which a decoy pulse having a phase of π / 2 and an amplitude equal to or greater than the amplitude of a signal pulse is randomly inserted into a signal pulse of a weak coherent pulse train, each pulse having a phase of 0 or π, and transmits the transmission signal to the receiver system; a decoy pulse information transmitting device that generates a second signal including information about a decoy pulse based on a first signal including information about a time slot in which a photon is detected and that is transmitted from the receiver system, and transmits the second signal to the receiver system; Equipped with The recipient system a transmission signal detection device configured to receive the transmission signal transmitted by the sender system, impart a delay time to the transmission signal, and then perform photon detection according to the phase of the transmission signal; a coincidence photon detection rate verification device configured to verify a coincidence photon detection rate in a time slot in which the signal pulse and the decoy pulse in the transmission signal interfere in response to receiving the second signal, and to discard a private key if it is determined as a result of the verification that eavesdropping has occurred; Equipped with Quantum key distribution system.

2. 2. The quantum key distribution system of claim 1, wherein the receiver system further comprises a coincidence photon detection rate comparison device that compares a coincidence photon detection rate in a time slot in which interference between the signal pulses is detected with a coincidence photon detection rate in a time slot in which interference between the signal pulse and the decoy pulse is detected.

3. 1. A quantum key distribution method, comprising: A transmitter system transmits to a receiver system a transmission signal in which a decoy pulse having a phase of π / 2 and an amplitude equal to or greater than the amplitude of a signal pulse is randomly inserted into a signal pulse of a weak coherent pulse train, each pulse having a phase of 0 or π; generating and transmitting, from the receiver system in response to receiving the transmission signal, a first signal including information regarding a time slot in which a photon was detected to the sender system; generating, by the sender system, a second signal containing information about a bit value or a decoy pulse on the sender side based on the first signal; generating a bit "0" if the phase difference between the two pulses that caused the detection of said photon is 0; generating a bit "1" if the phase difference between the two pulses that caused the detection of said photon is π; If the phase difference between the two pulses is ±π / 2, generating the second signal and transmitting the second signal to the receiver system. and generating, by the recipient system, a recipient-side bit value; generating a bit "0" if the detector that detected the photon is the first photon detector; generating a bit "1" if the detector that detected the photon is the second photon detector; A bit value is not generated from photon detection in which the phase difference between two pulses in the detected transmission signal is ±π / 2. and In response to receiving the second signal, verifying, by the receiver system, a coincidence photon detection rate in a time slot in which the signal pulse and the decoy pulse in the transmission signal interfere; The receiver system determines whether eavesdropping has occurred based on the verification result of the coincidence photon detection rate in the time slot where the signal pulse and the decoy pulse interfere, and discards the private key if it is determined that eavesdropping has occurred; A quantum key distribution method comprising:

4. 4. The quantum key distribution method of claim 3, further comprising: comparing a coincidence photon detection rate in a time slot in which interference between the signal pulses is detected with a coincidence photon detection rate in a time slot in which interference between the signal pulse and the decoy pulse is detected.

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