KR102134347B1 - Method for quantum key distribution - Google Patents

Abstract

The present invention is a quantum key distribution method in a communication system having a first communication device and a second communication device, wherein the optical signals generated from the first communication device are sequentially transmitted to the second communication device, and the second communication device The first quantum signal and the second quantum signal are sequentially generated by encoding a random amount of phase information corresponding to the corresponding digital bit in order to change to a single photon level and transmit the “0” or “1” digital bits. 1 transmitting to a communication device; The first communication device randomly modulates the first quantum signal and the second quantum signal by selecting one of four phase information amounts, and matches the paths of the two signals to measure through different detectors according to the reinforcement or destructive interference of the signals. step; The second communication device may transmit base information used when sending the quantum signals to the first communication device; And the first communication device provides a quantum key distribution method comprising the step of using the same data as the basis information received from the second communication device and the base information used when measuring itself.

Description

Quantum key distribution method {METHOD FOR QUANTUM KEY DISTRIBUTION}

The present invention relates to a quantum key distribution technique, and more particularly, to a quantum key distribution method using four phases in phase modulation in a receiving device.

Recently, as communication security has become a problem due to events such as large-scale personal information leakage, the demand for a secure encryption system is gradually increasing. Commonly used cryptographic systems are not systems that use physical phenomena, but systems that use a low probability of hacking when using mathematical difficulties. Therefore, there is a problem that the probability of analyzing the encrypted information by hacking the encryption system from the outside still exists.

On the other hand, quantum cryptography (quantum cryptography) is based on the uncertainty of quantum mechanics, a single photon that exhibits a quantum effect is a cryptosystem developed in view of the fact that replication is impossible, and the subjects of communication use the same secret key. They are safely divided using both, and the key is used to encrypt or decrypt the information. Theoretically, since the characteristics of the photon change when attempting to hack from the outside, it is possible to implement a cryptographic system that cannot be hacked, which cannot obtain the original secret key or information from the outside.

Specifically, the Quantum Key Distribution (QKD) system is a system in which two communication devices, that is, a transmitting device (Alice) and a receiving device (Bob), use a photon as a communication medium to distribute a quantum cryptographic key. In this QKD system, when the eavesdropper (Eve) attempts to eavesdrop (e.g., tapping a photon in transit), returning the observed photon to the quantum state before being observed by Heisenberg's uncertainty principle Since it is impossible, a change occurs in the statistical value of the received data detected by the receiving device. Therefore, the reception apparatus can detect the presence or absence of wiretapping by detecting this change.

However, even in such a quantum cryptography system, it may actually be possible to hack due to defects or incompleteness of a measuring device used in the quantum cryptography system. Accordingly, although research on a measurement-device-independent quantum key distribution (MDI QKD) independent of a measurement device capable of distributing a secret key regardless of a measurement device is actively conducted, MDI QKD generates a key It has the disadvantage of very low speed.

Korean Patent Publication No. 10-2016-0070032

An object of the present invention is to secure a key generation rate above a certain level while ensuring stability in quantum key distribution.

Another object of the present invention is to perform quantum key distribution by using not only 0 and π/2 but also π and 3π/2, which are used in phase modulation.

A first aspect of the present invention for achieving the above object, in a quantum key distribution method in a communication system having a first communication device and a second communication device, the optical signal generated from the first communication device to the second communication device Sequentially transmitted, and the second communication device encodes a random amount of phase information corresponding to the digital bit in order to change them to a single photon level and transmit "0" or "1" digital bits, respectively. And sequentially generating and transmitting a second quantum signal to the first communication device; The first communication device randomly modulates the first quantum signal and the second quantum signal by selecting one of four phase information amounts, and matches the paths of the two signals to measure through different detectors according to the reinforcement or destructive interference of the signals. step; The second communication device may transmit base information used when sending the quantum signals to the first communication device; And the first communication device provides a quantum key distribution method comprising the step of using the same data as the basis information received from the second communication device and the base information used when measuring itself.

Preferably, in the first communication device, when the basis information is the same, the bit information of the quantum signal detected by the first detector is used in the same manner by further using the detector information from which the measurement result is detected, and the second detector detects The bit information of the quantum signal is used inverted.

Here, if the base information is the same, 0 and π phases are defined as the basis '0', π/2, and 3π/2 phases as the basis '1', and the amount of phase information is 0 and π. /2, 3π/2, or 2π.

Meanwhile, one of the phase information amounts 0 and π/2 is transmitted by transmitting the “0” digital bit, and one of the phase information amounts π and 3π/2 is transmitted by transmitting the “1” digital bit.

As described above, according to the present invention, it is possible to introduce a method in which π, 3π/2 can be additionally used in addition to 0 and π/2 as the phase modulation amount used for phase modulation in the receiving device.

According to this method, since the quantum keys are independently distributed to the output of the detector, even if the eavesdroppers know the detection state of the detector, the key value distributed between the transmitting device and the receiving device is not known unless the transmitter and receiver know the phase modulation state. It is unknown, and thus it has an effect of improving security while maintaining the speed of key generation.

1 is a block diagram showing a quantum key distribution system according to a preferred embodiment of the present invention.
2 and 3 are exemplary views for explaining a quantum key distribution method according to an embodiment.
4 is a flowchart illustrating a quantum key distribution method according to an embodiment.

Hereinafter, advantages and features of the present invention, and methods for achieving them will be clarified with reference to embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only the present embodiments allow the disclosure of the present invention to be complete, and the general knowledge in the technical field to which the present invention pertains. It is provided to fully inform the holder of the scope of the invention, and the invention is only defined by the scope of the claims. The same reference numerals refer to the same components throughout the specification. “And/or” includes each and every combination of one or more of the items mentioned.

Although the first, second, etc. are used to describe various elements, components and/or sections, it goes without saying that these elements, components and/or sections are not limited by these terms. These terms are only used to distinguish one element, component or section from another element, component or section. Accordingly, it goes without saying that the first element, the first component or the first section mentioned below may be the second element, the second component or the second section within the technical spirit of the present invention.

In addition, in each step, an identification code (for example, a, b, c, etc.) is used for convenience of description, and the identification code does not describe the order of each step, and each step is clearly specified in context. Unless you specify the order, it may happen differently from the order specified. That is, each step may occur in the same order as specified, or may be performed substantially simultaneously, or in the reverse order.

The terminology used herein is for describing the embodiments and is not intended to limit the present invention. In the present specification, the singular form also includes the plural form unless otherwise specified in the phrase. As used herein, “comprises” and/or “comprising” refers to the components, steps, operations and/or elements mentioned above, the presence of one or more other components, steps, operations and/or elements. Or do not exclude additions.

Unless otherwise defined, all terms (including technical and scientific terms) used in the present specification may be used as meanings commonly understood by those skilled in the art to which the present invention pertains. In addition, terms defined in the commonly used dictionary are not ideally or excessively interpreted unless specifically defined.

In addition, in describing embodiments of the present invention, when it is determined that a detailed description of known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, terms to be described later are terms defined in consideration of functions in an embodiment of the present invention, which may vary according to a user's or operator's intention or practice. Therefore, the definition should be made based on the contents throughout this specification.

1 is a block diagram showing a quantum key distribution system according to a preferred embodiment of the present invention.

Referring to FIG. 1, the quantum key distribution system includes a first communication device 100 as a receiving device (so-called Bob) and a second communication device 200 as a transmitting device (so-called Alice). Preferably, the first communication device 100 and the second communication device 200 may be connected through a quantum channel (QC) and a classic channel, and a signal is transmitted and received through the quantum channel, and data through the classic channel Can be transmitted and received. The quantum key distribution system mentioned below is applicable not only to a plug and play quantum key distribution (P&P QKD) system, but also to a unidirectional quantum key distribution system.

The first communication device 100 includes a light source 110, an optical circulator 120, an optical splitter 130, a phase modulator 140, a polarization controller 150, a polarization beam splitter 160, and a single photon detector ( 170 and 180).

Preferably, the light source 110 generates a photon pulse (hereinafter, referred to as “light signal”) having an arbitrary polarization, and may correspond to a laser, and the light signal generated by the light source 110 is an optical circulator. It is transmitted to the optical splitter (BS) 130 through 120. The optical splitter 130 divides the optical signal into two optical signals, and the divided two optical signals are temporally separated and have orthogonal polarizations, respectively, and the corresponding optical signals are quantum channels (Quantum). Channel (QC) is transmitted to the second communication device 200. Therefore, when the optical signal generated by the first communication device 100 is transmitted to the second communication device, it is divided into two and transmitted through two optical signals separated in time.

The second communication device 200 includes an optical splitter 210, an optical detector 220, a variable optical attenuator (VOA) 230, a storage line (SL), a phase modulator 240, and Faraday Includes mirror 250.

Preferably, the second communication device 200 receives two optical signals sequentially separated from the first communication device 100. When one optical signal is described, the photo detector 220 may obtain timing information for modulating the phase of the quantum signal from the received optical signal. In addition, a storage line (SL) removes noise generated by an optical signal received from the first communication device 100, and a variable optical attenuator (VOA) 230 is optical. The light intensity of the signal is reduced to a single photon level to become a quantum signal. In the present specification, an optical signal is generated from the light source 110 of the first communication device 100, and the signal is transmitted to the second communication device 200 to pass through the optical attenuator 230, thereby reducing the intensity to a single photon level. In this case, it is called a quantum signal.

The second communication device 200 reflects the received quantum signal through a Faraday Mirror (FM) 250, inverting the direction of the quantum signal, rotating polarization 90 degrees, and rotating the phase modulator 240. Phase modulation is performed on one of the quantum signals using the quantum signal and then transmitted to the first communication device 100 through the quantum channel.

Next, the first communication device 100 receives the quantum signals from the second communication device 200, and since the polarization of the received quantum signals is rotated 90 degrees compared to the transmission, the received quantum signals are transmitted You will pass a different path than the city. That is, a quantum signal that has passed a long path with a delay line during transmission passes through a short path after being received from the second communication device 200, and a quantum signal that has passed a short path during transmission is transmitted from the second communication device 200. After receiving, it will go through a long path. At this time, the phase modulator 140 modulates the phase of the quantum signal whose phase is not modulated in the second communication device 200 among the two quantum signals. The quantum signals phase-modulated by the first communication device 100 and the quantum signals phase-modulated by the second communication device 200 reach the optical splitter 130 to interfere with each other, and the interference results are a plurality of single It is detected by the photon detectors 160 and 170.

Thereafter, the first communication device 100 and the second communication device 200 perform quantum key distribution based on the detection results of the single photon detectors 160 and 170.

Hereinafter, the phase modulation performed in the first communication device 100 and the second communication device 200 and the quantum key distribution method performed based on the first communication device 100 and the second communication device 200 will be described in more detail with reference to FIGS. 2 and 3. Detailed descriptions of the same or similar parts to those described above will be omitted.

The optical signal generated by the light source 110 is divided into two optical signals by the optical splitter 130, and then passes through the first path with the delay line DL and the second path with the phase modulator 140. do. Here, it is assumed that the optical signal generated by the light source 110 has vertical polarization, and the polarization beam splitter 160 passes vertical polarization.

First, referring to FIG. 2, an optical signal passing through a second path having a phase modulator 140 corresponding to a short path is transmitted to the second communication device 200 through a quantum channel. The optical signal transmitted to the second communication device 200 is reversed by the Faraday mirror 250 and the polarization is rotated 90 degrees to have horizontal polarization. The quantum signal in which the traveling direction is inverted and has horizontal polarization by the Faraday mirror 250 reaches the phase modulator 240, and any of 0, π/2, π, and 3π/2 by the phase modulator 240 The phase is modulated by one of. Here, the phase modulated by the phase modulator 240 (that is, the amount of phase modulation) is not communicated later, and only the base information is communicated. Phase and base are distinct. When the phase is first described, it is used to modulate the digital bit '0' and '1' information to a characteristic that can be transmitted by photons. Normally, in quantum cryptography, phase 0 or π/2 is used to represent digital bit '0'. Modulate. Π or 3π/2 is used to represent the digital bit '1'. That is, there can be two ways to express one digital bit. The basis is information that shows which of the two methods can be used. Usually, in quantum cryptography, the phase of 0 and π is called the phase belonging to the basis '0', and the phase of π/2 and 3π/2 is basis '1. Promise that it belongs to'and use it.

As described above, the first communication device 100 receiving only the'base' information from the second communication device 200 later does not know whether digital information '0' or '1' has been sent, so the amount of phase modulation is random. Select to perform phase modulation.

Likewise, according to the phase modulation amount, which basis is used as promised (in the quantum code, the 0, π phase is usually called the phase belonging to the base '0', and the π/2, 3π/2 phase is the phase belonging to the base '1'. (Promised that) will be decided. Thereafter, the protocol for distributing the quantum cryptographic key is performed by transmitting and receiving information by communication only about which basis is used, without communicating about the four phase modulation amounts. There is no way to extract digital information '0' or '1' information because eavesdroppers cannot specifically know the amount of phase information using only the base information exchanged in communication.

Meanwhile, a quantum signal whose phase is modulated by the phase modulator 240 is transmitted to the first communication device 100 through a quantum channel (QC), and the quantum signal received by the first communication device 100 is a polarization beam splitter Without passing through 160, the first path is passed. As the quantum signal passes through the first path, the polarization is rotated 90 degrees by the polarization controller 150 to have vertical polarization, and then reaches the optical splitter 130.

Next, referring to FIG. 3, the quantum signal passing through the first path after the quantum signal is divided by the optical splitter 130 is used, and the quantum signal has a delay line DL corresponding to a long path The polarization is rotated 90 degrees by the polarization controller 150 provided in the first path while passing through the first path to have horizontal polarization. The quantum signal passing through the first path is transmitted to the second communication device 200, the quantum signal transmitted to the second communication device 200 is reversed by the Faraday mirror 250, the polarization is rotated 90 degrees It has vertical polarization. The direction of travel reversed by the Faraday mirror 250 and the quantum signal having horizontal polarization passes through the phase modulator 240 and is transmitted to the first communication device 100. Here, the phase modulator 240 is to selectively modulate the phase of the two quantum signals received from the first communication device 100, one of the two quantum signals according to the timing information obtained from the photo detector 220 The phase is modulated only with respect to the quantum signal of. Preferably, the phase can be modulated only with respect to the quantum signal that has reached the phase modulator 240 first in time through the second path in the first communication device 100. That is, the phase of the quantum signal described with reference to FIG. 2 is modulated by the phase modulator 240, and the phase of the quantum signal described with reference to FIG. 3 is not modulated by the phase modulator 240.

Since the quantum signal received by the first communication device 100 has vertical polarization, the polarization beam splitter 160 passes through the second path, and the phase is modulated by the phase modulator 140 provided in the second path. do. Preferably, the phase modulator 140 modulates the phase of the quantum signal to any one of 0, π/2, π, and 3π/2. In addition, it is as described above that a corresponding base exists in the arbitrary modulated phase information. Information about this base is recorded in a control unit (not shown in the drawing) provided in the first communication device 100. The quantum signal whose phase is modulated while passing through the second path reaches the optical splitter 130.

Since the lengths of the paths through which the two quantum signals have been described with reference to FIGS. 2 and 3 are the same, the two quantum signals are overlapped in the optical splitter 130, and the constructive interference or cancelation interference is caused by the relative phase difference between the two quantum signals Causes Here, when constructive interference occurs in the path to the first detector 170, the signal is detected by the first detector 170, and when offset interference occurs in the same path, constructive interference in the path to the second detector 180 As this occurs, it is detected by the second detector 180, and information on the detector that detected the signal is recorded in the control unit of the first communication device 100. That is, the control unit of the first communication device 100 has a basis (eg, 0 and π phases are the basis '0', π/2, 3π/2 used in the phase modulator 140 of the first communication device 100). The phase is the base '1') and detector information (eg, a first detector or a second detector) that detects a quantum signal is recorded.

Preferably, according to information about the base used by the phase modulator 240 of the second communication device 200, the base used by the phase modulator 140 of the first communication device 100, and the detector detecting the quantum signal 1 The quantum signal measurement results in the communication device 100 are shown in [Table 1] below.

Information 2nd communication device / 1st communication device 0 π/2 π 3π/2 0 0 First detector
(0) Second detector
(0) π/2 First detector
(0) Second detector
(0) One π Second detector
(One) First detector
(One) 3π/2 Second detector
(One) First detector
(One)

Referring to [Table 1], in the second communication device 200, a base corresponding to 0 or π/2 is used to represent information corresponding to 0, and π or 3π is used to represent information corresponding to 1. It is assumed that the basis corresponding to /2 is used. It is used as information only when the basis used in the second communication device 200 and the basis used in the first communication device 200 are the same. In addition, when constructive interference is seen based on the path through which the quantum signal goes to the first detector 170, it is detected by the first detector 170, and based on the path through which the quantum signal goes to the first detector 170. When it is viewed, the interference is detected by the second detector 180. When the first communication device 100 is measured using 0, π/2, the bit of the detector is left unchanged, and the measurement result is detected only when the first communication device 100 is measured using π, 3π/2. Bit information of 1 and detector 2 is changed.

Referring to Table 1, the detector bits are the same for the two left columns (0, π/2), and the detector bits are the opposite for the two right columns (π, 3π/2). Generally, detector 1 is bit '0' and 2 is bit '1'. In Table 1,'-' means that there is a probability that both can be detected, so it is not used for the operation of dividing the secret key later.

According to the above-described method, when both the quantum signal transmission and reception are completed, the second communication device 200 does not transmit the phase information amount, but sends the base information used when sending the quantum signal to the first communication device 100. Then, the first communication device 100 compares the basis information used when measuring with the basis information transmitted from the second communication device 200 and determines that only the information measured at the same time as the basis is valid information. In this case, if there are no errors in the system, the measurement results always appear as shown in [Table 1], but errors may occur due to hardware system problems. This appears as QBER. QBER directly exchanges some of the valid information exchanged with each other to check how many percent an error occurs, and the information exchanged with each other to calculate QBER is discarded.

According to the quantum key distribution method according to the present invention, the detector information and the measurement result are the same even though the detector information that detects the quantum signal, that is, whether it is detected by the first detector or the second detector is known to the wiretap. Since it does not, information on the quantum key cannot be exposed, and in addition, the key generation speed is also excellent compared to the conventional BB84 protocol and MDI (Measurement Device Independent) method.

4 is an exemplary diagram for describing a quantum key distribution method according to an embodiment.

In FIG. 4, detailed descriptions of the same or similar contents to those described in FIGS. 1 to 3 are omitted.

Referring to FIG. 4, in a quantum key distribution method in a communication system having a first communication device 100 and a second communication device 200, overlapping movements of two paths from the first communication device 100 are performed. Quantum signals are sequentially received (S100). The second communication device 200 receives these optical signals and changes them to a single photon level, respectively, thereby generating a first quantum signal and a second quantum signal. Then, in order to transmit the "0" or "1" digital bits to each of the first and second quantum signals, the amount of random phase information corresponding to the digital bits is encoded and transmitted to the first communication device 100 (S110) ).

Next, the first communication device 100 modulates the first quantum signal and the second quantum signal by randomly selecting and modulating one of four phase information amounts, and matching the paths of the two signals, thereby causing the quantum signals to reinforce or cancel interference. To enable (S120). When the constructive interference occurs when viewed based on the path to the first detector 170, the first detector 170 is configured to be detected, and when the interference is generated based on the path to the first detector 170. Is configured to measure through a second detector.

Next, the second communication device 200 transmits the base information used when sending the quantum signals to the first communication device (S130).

The first communication device 100 uses the same data as the basis information used when measuring by itself and the basis information received from the second communication device (S140). In this case, when the base information is the same, the first communication device 100 additionally uses the detector information for which the measurement result is detected, and the bit information of the quantum signal detected by the first detector is used identically, and the second detector The bit information of the detected quantum signal is used inverted. Since the detailed method is as described above, the description is omitted.

Meanwhile, the quantum key distribution method according to an embodiment of the present invention may also be embodied as computer readable codes on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data readable by a computer system is stored.

For example, a computer-readable recording medium includes ROM, RAM, CD-ROM, magnetic tape, hard disk, floppy disk, removable storage device, and non-volatile memory (Flash Memory). , Optical data storage devices.

Although the preferred embodiment of the quantum key distribution method according to the present invention described above has been described, the present invention is not limited thereto, and can be implemented by various modifications within the scope of the claims and detailed description of the invention and the accompanying drawings. And this also belongs to the present invention.

100: first communication device
110: light source 120: light circulator
130: optical splitter 140: phase modulator
150: polarization controller 160: polarization beam splitter
200: second communication device
210: optical splitter 230: optical attenuator
240: phase modulator 250: Faraday mirror

Claims (6)

In the quantum key distribution method in a communication system having a first communication device and a second communication device,
Optical signals generated from the first communication device are sequentially transmitted to a second communication device, and the second communication device converts them to a single photon level and transmits the "0" or "1" digital bits, respectively. Encoding a random amount of phase information corresponding to and sequentially generating a first quantum signal and a second quantum signal, respectively, and transmitting the first quantum signal to the first communication device;
The first communication device modulates the first quantum signal and the second quantum signal by randomly selecting and modulating one of four phase information amounts and matching the paths of the two signals to measure through different detectors according to the reinforcement or destructive interference of signals. To do;
The second communication device transmitting base information used when sending the quantum signals to the first communication device; And
The first communication device is provided with the step of using the same data as the basis information received from the second communication device and the basis information used when measuring itself,
When the basis information is the same, the first communication device further uses detector information from which the measurement result is detected, and when the phase information amount of the first communication device is 0 or π/2, the bit information of the detected quantum signal is the same. When the phase information amount of the first communication device is π or 3π/2, the bit information of the detected quantum signal is inverted and used.
delete According to claim 1,
The method of quantum key distribution is characterized in that the base information is the same when the 0 and π phases are defined as the basis '0', π/2, and 3π/2 phases as the basis '1'.
According to claim 1,
The phase information amount is a quantum key distribution method, characterized in that one of 0, π/2, 3π/2, 2π.
According to claim 1,
Characterized in that the transmission of the "0" digital bit to transmit one of the phase information amount 0, π/2, and transmitting the "1" digital bit to transmit one of the phase information amount 3π/2, 2π Key distribution method.
According to claim 1,
The quantum key distribution method is a quantum key distribution method used in a plug and play quantum key distribution (P&P QKD) system or a unidirectional quantum key distribution system.

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