KR20170062379A - Communication apparatus and communication method for continuously quantum key distribution - Google Patents

Abstract

The present invention provides a communication device, comprising: a synchronization signal detector for detecting a synchronization signal received from another communication device connected to the communication device, wherein the other communication device transmits a quantum signal generated from the first light source to the communication device and; And a second light source for generating a decoy signal to be added to the quantum signal to be transmitted to the other communication apparatus according to the detection result of the synchronization signal.

Description

Technical Field [0001] The present invention relates to a communication apparatus and communication method for continuous quantum cryptography key distribution,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of quantum cryptography and, more particularly, to a communication device and a communication method for continuous quantum key distribution (QKD) in a plug & play key distribution system. .

The QKD system is a system in which two communication devices, that is, a transmitting device (Alice) and a receiving device (Bob) distribute a quantum cryptographic key using photons as a communication medium. In such a QKD system, when an eavesdropper (Eve) tries to tap (e.g., tapping a photon in transit), returning the photons observed by Heisenberg's uncertainty principle to a pre-observed quantum state The statistical value of the received data detected by the receiving apparatus changes. Therefore, the receiving apparatus can detect the presence or absence of eavesdropping by detecting this change.

Among the QKD systems, the "Plug & Play" method is frequently used recently due to the advantage of automatically compensating for polarization drift during transmission. This " Plug & Play "QKD system (hereinafter referred to as a P & P QKD system) transmits two photon pulses that are temporally divided in time at the receiving apparatus and polarized orthogonally to the transmitting apparatus, Directional manner by rotating the direction of the photon pulse by 90 degrees and phase-modulating one of the two photon pulses temporally divided and sending it back to the receiving device.

At this time, when the intensity of the quantum signal transmitted to the transmitting apparatus is high, since the magnitude of the signal extracted from the photodetector of the transmitting apparatus is large, the transmitting apparatus transmits the timing information for phase modulation of the quantum signal And has the advantage that the Trojan Horse Attack by the eavesdropper can be monitored more easily, while the transmitting device has the advantage that the optical attenuator for lowering the light intensity of the quantum signal to a single photon level, and The P & P QKD system is difficult to perform continuous operation because it is difficult to miniaturize the transmission device because a storage line (delay line) for removing noise light generated due to high light intensity must be provided.

Alternatively, when the optical intensity of the quantum signal transmitted to the transmitting apparatus is low (for example, in the case of having a light intensity of a single photon level), since the transmitting apparatus does not need to include the optical attenuator and the storage line, And the P & P QKD system can perform continuous operation. On the other hand, since the size of the signal extracted from the photodetector is small due to low light intensity, it is difficult to obtain timing information using the photodetector And it is difficult to monitor Trojan horse attacks by eavesdroppers.

As described above, in the P & P QKD system, the degree to which the intensity of the photon signal (also referred to as a "quantum signal") transmitted from the receiving apparatus to the transmitting apparatus is determined depends on the performance, security, and size of the P & P QKD system. It is an important issue.

Zhao, Yi, et al. "Design of synchronous Plug & Play QKD-WDM-PON for efficient quantum communications." Lasers and Electro-Optics (CLEO), 2011 Conference on IEEE, 1-6, May, 2011.

It is an object of the present invention to provide a communication device of a P & P QKD system for continuously distributing a quantum cryptographic key by maintaining a light intensity of a quantum signal transmitted from a receiving device to a transmitting device at a low level.

It is an object of the present invention to provide a communication device of a new P & P QKD system which can maintain the performance and security of the system while maintaining the light intensity of the quantum signal at a low level.

According to a first aspect of the present invention, there is provided a communication device including a synchronization signal detector for detecting a synchronization signal received from another communication device connected to the communication device, To the communication device; And a second light source for generating a decoy signal to be added to the quantum signal to be transmitted to the other communication apparatus according to the detection result of the synchronization signal.

Preferably, the synchronization signal may correspond to a signal having a wavelength different from the quantum signal, a GPS signal, or a network time.

Preferably, the synchronization signal detector includes: a wavelength divider for dividing the quantum signal and the synchronization signal when the synchronization signal is a signal having a wavelength different from that of the quantum signal; And a photodetector for detecting a sync signal divided by the wavelength divider.

Preferably, the synchronization signal may have a higher light intensity than the quantum signal.

Preferably, the synchronization signal detector may include a time synchronization device for detecting the GPS signal or the network signal when the synchronization signal is a GPS signal or a network signal.

The apparatus may further include a phase modulator that receives the detection result of the synchronization signal by the photodetector and modulates the phase of the quantum signal in accordance with the detection result of the synchronization signal.

Preferably, the polarization controller may further include a polarization controller for controlling polarization of the decoy signal generated by the second light source.

Preferably, the polarization controller may set the polarization of the decoy signal to be the same as the polarization of the quantum signal or randomly.

Preferably, the apparatus further includes a Faraday mirror for generating a noise component orthogonal to the decoy signal generated by the light source, wherein the noise component may be transmitted to the other communication device together with the decoy signal.

The apparatus may further include a processing unit that adds the decoy signal generated by the second light source to at least a part of the quantum signals to be transmitted to the other communication apparatus based on the detection result of the synchronization signal.

Preferably, the light intensity of the quantum signal transmitted to the other communication device may be a light intensity of a single photon level.

According to a second aspect of the present invention, there is provided a communication method performed in a communication device, the method comprising: receiving a quantum signal and a synchronization signal generated from a first light source of the other communication device from another communication device connected to the communication device Receiving; Detecting a synchronization signal received from the other communication device; And generating a decoy signal to be added to the quantum signal to be transmitted from the second light source to the other communication apparatus, in accordance with the detection result of the synchronization signal.

Preferably, the step of detecting the synchronization signal includes: dividing the received quantum signal and the synchronization signal when the synchronization signal is a signal having a wavelength different from the quantum signal; And detecting the divided sync signal.

Preferably, the step of detecting the synchronization signal may include detecting the GPS signal or the network signal through the time synchronization device when the synchronization signal is a GPS signal or a network signal.

The method may further include modulating the phase of the quantum signal according to the detection result of the synchronization signal after the detection of the synchronization signal.

Advantageously, the step of generating the decoy signal includes selecting the polarization of the generated decoy signal, wherein the polarization of the decoy signal may be set to be the same as the polarization of the quantum signal or randomly.

Advantageously, the step of generating the decoy signal includes generating a noise component orthogonal to the generated decoy signal, wherein the noise component may be transmitted to the other communication device together with the decoy signal.

The method may further include adding the generated decoy signal to at least a part of the quantum signals transmitted to the other communication apparatus based on the detection result of the synchronization signal.

According to a third aspect of the present invention, there is provided a communication system including a communication device and another communication device connected to the communication device, wherein the communication device receives a quantum signal and a synchronization signal from the other communication device And to generate a decoy signal from the second light source to be added to the quantum signal to be transmitted to the other communication apparatus, wherein the other communication apparatus generates a quantum signal from the first light source, And to transmit a synchronization signal to the communication device.

As described above, according to the present invention, since the optical intensity of the quantum signal transmitted from the receiving apparatus to the transmitting apparatus can be maintained at a low level, the transmitting apparatus does not need to have the optical attenuator and the storage line, And the P & P QKD system can perform continuous operation.

Further, according to the present invention, it is possible to easily acquire timing information for phase modulation of a quantum signal and to monitor a Trojan horse attack by an eavesdropper, while maintaining a light intensity of a quantum signal at a low level, Performance and high level of security can be maintained.

In addition, according to the present invention, it is possible to prevent an intercept-resent attack by controlling polarization of a decoy signal for monitoring a Trojan horse attack by an eavesdropper.

1 is a configuration diagram showing a conventional communication system.
2 is a configuration diagram illustrating a communication system according to a preferred embodiment of the present invention.
3 is a configuration diagram illustrating a communication system according to an embodiment of the present invention.
4 is a configuration diagram illustrating a communication system according to an embodiment of the present invention.
5 is a configuration diagram illustrating a communication system according to an embodiment of the present invention.
6 is a configuration diagram illustrating a communication system according to an embodiment of the present invention.
7 is a configuration diagram illustrating a communication system according to an embodiment of the present invention.
8 is a diagram illustrating an example of how a decoy signal is added to a quantum signal according to an embodiment of the present invention.
FIG. 9 is a diagram illustrating a method of detecting an attack by an eavesdropper using a decoy signal according to an embodiment of the present invention. Referring to FIG.
10 is a flowchart showing a communication method performed in the communication apparatus of the communication system of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will be more apparent from the following detailed description taken in conjunction with the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification. "And / or" include each and every combination of one or more of the mentioned items.

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

Also, in each step, the identification code (e.g., a, b, c, etc.) is used for convenience of explanation, and the identification code does not describe the order of each step, Unless the order is described, it may happen differently from the stated order. That is, each step may occur in the same order as described, may be performed substantially concurrently, or may be performed in reverse order.

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. It is noted that the terms "comprises" and / or "comprising" used in the specification are intended to be inclusive in a manner similar to the components, steps, operations, and / Or additions.

Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Also, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

In the following description of the present invention, detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. The following terms are defined in consideration of the functions in the embodiments of the present invention, which may vary depending on the intention of the user, the intention or the custom of the operator. Therefore, the definition should be based on the contents throughout this specification.

1 is a configuration diagram showing a conventional communication system.

Referring to Fig. 1, the communication system includes a first communication device 10 which is a receiving device (so-called Bob) and a second communication device 20 which is a transmitting device (so-called Alice). The communication system referred to below corresponds to the Plug and Play quantum key distribution (P & P QKD) system.

In the communication system of Fig. 1, the first communication device 10 transmits a photon signal (hereinafter referred to as " quantum signal ") having a high light intensity to the second communication device 20. [ Since the first communication device 10 transmits a quantum signal having a high light intensity to the second communication device 20, the second communication device 20 uses the photodetector 22 to generate a quantum signal The timing information for modulating the phase of the signal can be obtained. However, since the first communication device 10 transmits a quantum signal having a high light intensity to the second communication device 20, the second communication device 20 can not detect the noise (" a storage line (SL) for removing noise light and a variable optical attenuator (VOA) 23 for reducing the intensity of a quantum signal to a single photon level. Therefore, it is difficult to miniaturize the second communication device 20 in the communication system of FIG. 1, and it is difficult for the communication system to perform continuous operation.

Hereinafter, the process of distributing the quantum cryptographic key by the communication system will be described with reference to FIG.

The first communication device 10 uses the first light source 11 to generate photon pulses with arbitrary polarization. The generated photon pulse P is transmitted to the beam splitter 13 through the optical circulator 12 and is divided into two photon pulses P1 and P2 by the beam splitter 13 do. One of the divided photon pulses P1 passes through a short path and passes through a Polarization Beam Splitter (PBS) 15 and the other P2 passes through a long path to a phase modulator (PM) 14 and passes through the polarization beam splitter 15. A pair of photon pulses P1 and P2 having the temporally divided and mutually orthogonal polarizations generated in this way are transmitted to the second communication device 20 via the quantum channel 30. [

Next, the second communication device 20 removes the noise light generated by the quantum signal of high brightness by temporally separating the noise and the quantum signal through the storage line SL. The second communication device 20 also reflects the received photon pulses P1 and P2 through a Faraday Mirror (FM) 25 to invert the traveling direction of the photon pulses and rotate the polarized light 90 degrees . The second communication device 20 then uses the optical attenuator 23 to attenuate the light intensity of the photon pulses P1 and P2 to a single photon level and use the phase modulator 24 to generate one of the photon pulses For example, P2), and then returns the photon pulses to the first communication device 10 via the quantum channel 30. [ At this time, the photodetector 22 of the second communication device 20 detects the photon pulses divided through the beam splitter 21 and provides the detection result to the phase modulator 24 as a timing signal. The phase modulator 24 generates a phase modulated photon pulse P2 'by modulating the phase of the photon pulse P2 at the timing at which the photon pulse P2 passes, based on the received timing signal.

Next, the first communication device 10 receives the photon pulses P1 and P2 'from the second communication device 20. Since the polarization of the received photon pulses P1 and P2 'is rotated by 90 degrees as compared with that at the time of transmission, the received photon pulses P1 and P2' pass through a path different from that at the time of transmission. That is, the photon pulse P1 goes through a long path, and the photon pulse P2 'goes through a short path. At this time, the phase modulator 14 modulates the phase of the photon pulse P1 at the timing at which the photon pulse P1 passes to generate a phase modulated photon pulse P1 '. Thereafter, the photon pulse P1 'phase-modulated by the first communication device 10 and the photon pulse P2' phase-modulated by the second communication device 20 interfere with each other, Is detected by the detectors (16, 17).

The communication system then communicates with the first communication device 10 and the second communication device 20 by performing a predefined cryptographic key distribution protocol (e.g., BB84: Bennett Brassard 84) based on the detection result of the single photon detector. So that the quantum cryptographic key can be shared.

As discussed, the communication system of FIG. 1 uses photon pulses with high light intensity, making it difficult to miniaturize the second communication device 20 and making it difficult for the P & P QKD system 10 to perform continuous operation.

2 is a configuration diagram illustrating a communication system according to a preferred embodiment of the present invention.

2, the configuration of the first communication device 100 is substantially the same as the configuration of the first communication device 10 of FIG. 1, 1 includes the first light source 110, the optical circulator 120, the optical splitter 130, the phase modulator 140, the polarization beam splitter 150 and the single photon detectors 160 and 170, The detailed description of the same or similar parts will be omitted.

The communication system of FIG. 2 is characterized in that, unlike the communication system of FIG. 1, the first communication device 100 transmits a quantum signal having a low light intensity to the second communication device 200. Here, the low light intensity of the quantum signal means that the quantum signal is transmitted from the first communication device 100 to the second communication device 200 and then from the second communication device 200 to the first communication device 100 Corresponds to the extent that the intensity of light when transmitted has a light intensity of a single photon level. Since the first communication device 100 transmits a quantum signal having a low light intensity to the second communication device 200, the second communication device 200 does not need to have a storage line for removing noise light , It is not necessary to provide an optical attenuator for lowering the light intensity of the quantum signal to a single photon level. Alternatively, the optical attenuator may be optionally provided. Therefore, the communication system of Fig. 2 can miniaturize the second communication device 200, and has the advantage that the communication system can perform continuous operation.

However, since the first communication device 100 transmits a quantum signal having a low light intensity to the second communication device 200, the second communication device 200 uses a photon detector to detect the quantum signal from the quantum signal itself The timing information for modulating the phase can not be obtained. Therefore, the communication system according to the present invention uses a synchronization signal so as to obtain timing information for modulating the phase of the quantum signal. The possible synchronization signals and accordingly the implementation of the communication device will be described in more detail below with reference to FIG. 3 and FIG.

Hereinafter, the process of distributing the quantum cryptographic key by the communication system will be described with reference to FIG.

2, the first communication device 100 further transmits a synchronization signal, which can be distinguished from the quantum signal, to the second communication device 200, and the second communication device 200 transmits a synchronization signal detector , And obtains timing information for modulating the phase of the quantum signal from the detected synchronization signal. Here, the synchronous signal detector may be implemented differently depending on the type of the synchronous signal.

Referring to Fig. 2, the communication system includes a first communication device 100, which is a receiving device Bob, and a second communication device 200, which is a transmitting device (Alice), similar to the communication system of Fig. At this time, the communication system may include a plurality of second communication devices 200.

First, the first communication device 100, similar to the first communication device 10 of FIG. 1, generates a photon pulse and generates a pair of photon pulses P 1, P 2 having temporally divided and orthogonal polarized light from the photon pulses, P2 and transmit it to the second communication device 200 as a quantum signal.

At this time, the first communication device 100 is configured to transmit a quantum signal from the second communication device 200 to the first communication device 100 at a lower light intensity than the first communication device 10 of FIG. 1 The intensity of light at a level corresponding to the light intensity of a single photon level) and transmit the quantum signal to the second communication device 200. [ Here, the quantum signal is temporally separated and comprises a sequence of photon pulse pairs consisting of a pair of photon pulses with orthogonal polarization. The first communication device 100 transmits a quantum signal having a lower light intensity to the second communication device 200 as compared with the first communication device 10 of FIG. Unlike the second communication device 20 of FIG. 1, it is not necessary to include a storage line for removing noise light and a light attenuator for optical attenuation.

The first communication device 100 may transmit a synchronization signal to the second communication device 200, unlike the first communication device 10 of FIG. Here, the synchronization signal means a signal for providing the second communication device 200 with timing information for modulating the phase of the quantum signal. In one embodiment, the first communication device 100 may transmit a quantum signal and a synchronization signal together on the same transmission channel 30 (e.g., a quantum channel). In another embodiment, the first communication device 100 can transmit a quantum signal over a first channel (e.g., a quantum channel) and transmit a second signal over a second channel (e.g., a data channel) Can be transmitted.

Next, like the second communication device 20 of FIG. 1, the second communication device 200 switches the traveling path of the received quantum signal, rotates the polarization direction by 90 degrees, modulates the phase of the quantum signal To the first communication device 100 again.

On the other hand, unlike the second communication device 20 of FIG. 1, the second communication device 200 receives both the quantum signal and the synchronization signal from the first communication device 100, Not shown in Figure 2). Here, the synchronous signal detector may be implemented in a different configuration depending on the type of the synchronous signal, which will be described in more detail with reference to FIGS. 3 and 4. FIG.

When the synchronization signal is detected by the synchronization signal detector in the second communication apparatus 200, the phase modulator 220 can use the detection result of the synchronization signal as the timing information to modulate the phase of the quantum signal. For example, the phase modulator 220 can phase-modulate the photon pulse P2 at the timing at which the photon pulse P2 passes, using the detection result of the synchronization signal.

Next, the second communication device 200 generates a decode signal (Active Decoy) through the second light source 240 and outputs a decode signal (Active Decoy) through a processing unit (not shown in FIG. 2) And transmits a quantum signal to which the decode signal (Active Decoy) is added to the first communication apparatus 100. [ At this time, the intensity of the decode signal (Active Decoy) may be substantially equal to the intensity of the quantum signal. 2, since the light intensity of the quantum signal received by the second communication apparatus 200 is low, the second communication apparatus 200 can be prevented from performing the Trojan horse attack by the eavesdropper (Eve) It is difficult to monitor. Therefore, the communication system of the present invention can easily detect the hacking by the eavesdropper while using a quantum signal having a low light intensity. The decoupling signal generated by the second light source 240 of the second communication device 200 Active Decoy) to the quantum signal.

In one embodiment, the second light source 240 may be coupled to the light splitter 210 and the processing unit may be a main processor of the second communication device 200 that controls the operation of each configuration of the second communication device 200 . In another embodiment, the processing unit is coupled to the first communication device 100 and the second communication device 200 to control the operation of the first communication device 100 and the second communication device 200, Protocol of the main server (or computer) that monitors the eavesdropping by the eavesdropper.

Hereinafter, with reference to FIGS. 8 and 9, a description will be given in detail of how a processing unit can add a decoy signal (Active Decoy) to a quantum signal and how a hacking attack can be monitored by adding a decoy signal (Active Decoy) .

As described above, the quantum signal can be made up of a sequence of a pair of photon pulses (" photon pulse pairs "). For example, as in the upper part of Fig. 8, the quantum signal may consist of a sequence of a first photon pulse pair to a fourth photon pulse pair. At this time, the photon pulses constituting the photon pulse pair are temporally separated and have orthogonal polarized light as described above.

The second communication apparatus 200 generates a decode signal (Active Decoy) using the second light source 240 and outputs a decode signal (Active Decoy) generated using the processing unit to a part of a photon pulse pair Lt; / RTI > of the 100 photon pulse pairs). For example, as in the bottom Decoy of Fig. 8, the processing unit may add a decode signal (Active Decoy) to the first photon pulse pair, the second photon pulse pair, and the fourth photon pulse pair. As such, the second communication device 200 can randomly select a photon pulse pair to which a decode signal (Active Decoy) is added, and can store information on the photon pulse pair in the memory.

The processing unit may add a decode signal (Active Decoy) to the photon pulse that is temporally preceding or temporally out of the photon pulses in the selected photon pulse pair. In one embodiment, the processing section can use the detection result of the synchronization signal as the timing information, and add a decode signal (Active Decoy) at the timing when the photon pulse temporally preceding or temporally trailing passes through the optical splitter 210 .

At this time, the processing unit can consistently add a decode signal (Active Decoy) to the photon pulse at any timing in accordance with a preset reference. For example, the processing unit may add a decode signal (Active Decoy) only to temporally preceding photon pulses among the photon pulses in the photon pulse pair, or add a decode signal (Active Decoy) only to temporally outward photon pulses. The quantized signal to which the decode signal (Active Decoy) is added is as shown in the (Signal + Decoy) in FIG.

Thereafter, the communication system can compare only the case where a decode signal (Active Decoy) is added to the quantum signal, and confirm the existence of the eavesdropper. For example, referring to FIG. 9, when there is no eavesdropper (Eve) at the top, a quantum signal to which a decode signal (Active Decoy) is added from the second communication device 200 to the first communication device 100 The first communication apparatus 100 receives the two-level signal including the quantum signal and the decode signal (Active Decoy) since the eavesdropping by the eavesdropper is not performed in this process. On the other hand, when there is the eavesdropper (Eve) at the bottom of Fig. 9, a signal by the eavesdropper Eve is added when the quantum signal is transmitted from the first communication device 100 to the second communication device 200 Two levels of signals are received at the second communication device 200. The second communication device 200 transmits a signal from the eavesdropper and a quantum signal to which a decoy signal (Active Decoy) is added to the first communication device 100, A signal transmitted to the base station 100 is transmitted at three levels including a quantum signal, a decode signal (Active Decoy), and an eavesdropper signal. Since the eavesdropping by the eavesdropper is performed in the process of transmitting the signal from the second communication device 200 to the first communication device 100, a signal of 1.5 (= 3/2) level is escaped by the eavesdropper, The signal received by the communication device 100 corresponds to a signal of 1.5 levels. That is, by adding the decode signal (Active Decoy) to the quantum signal, the level of the signal received by the first communication apparatus 100 becomes different when the eavesdropper Eve is present, (Eve) can be determined.

3 is a configuration diagram illustrating a communication system according to an embodiment of the present invention.

3, the communication system shown in FIG. 3 is based on the communication system shown in FIG. 2. In the case where the synchronization signal described in FIG. 2 is a signal having a wavelength different from that of the quantum signal, to be. The configuration described in FIG. 2 is not described in detail here.

3, the first communication device 100 may further include a third light source 180 and a wavelength divider 190, and the second communication device 200 may include a wavelength divider 310 and a photodetector (not shown) 320).

Preferably, the first communication device 100 generates and transmits a signal having a high light intensity with a wavelength (e.g., 1540 nm) different from the quantum signal (e.g., 1550 nm) to the second communication device 200, 2 communication apparatus 200 can obtain timing information for modulating the phase of the quantum signal from the corresponding signal. At this time, the light intensity of the signal may be higher than the light intensity of the quantum signal.

The first communication device 100 includes a wavelength splitter 190 for transmitting a signal generated from the third light source 180 to the second communication device 200 via the quantum channel 30. [ Here, the channel through which the corresponding signal is transmitted to the second communication apparatus 200 may be transmitted through a channel other than the quantum channel 30. [ Since the second communication apparatus 200 receives the quantum signals having different wavelengths from each other and the signal for acquiring the timing information, the second communication apparatus 200 includes the wavelength divider 310 to separate the signals.

Preferably, the second communication device 200 divides a signal for acquiring a quantum signal and timing information for each wavelength using a wavelength divider 310, and then the signal is input to a photodetector 320 (for example, a pin PD) And the quantum signal can be sent to a second path connected to the phase modulator 220 and the Faraday mirror 230. [ The photodetector 320 may detect the signal and send the detection result to the phase modulator 220. At this time, since the signal has a sufficiently high light intensity, unlike the quantum signal, it can be easily detected by the photodetector 320. The phase modulator 220 can modulate the phase of the quantum signal by using the detection result of the photodetector 320 as timing information. A concrete method of the phase modulator 220 can be described with reference to FIG. 2 have.

4 is a configuration diagram illustrating a communication system according to an embodiment of the present invention.

Referring to FIG. 4, the communication system shown in FIG. 4 is based on the communication system of FIG. 2, and is a possible embodiment of a synchronous signal detector when the synchronization signal described in FIG. 2 is a GPS signal or Network Time. The configuration described in FIG. 2 is not described in detail here.

Referring to FIG. 4, the second communication device 200 may further include a time synchronization device 330.

Preferably, the first communication device 100 may transmit a GPS signal or data for network time to the second communication device 200 and the second communication device 200 may transmit the GPS signal < RTI ID = 0.0 > Or network standard time can be detected. The time synchronization device 330 also sends the detected information to the phase modulator 220 and the phase modulator 220 can obtain timing information for modulating the phase of the quantum signal from the detected signal. That is, the phase modulator 220 can modulate the phase of the quantum signal by using the detection result of the time synchronization unit 330 as timing information, and a specific method for this is described with reference to FIG. 2 Can be referenced.

5 and 6 are block diagrams illustrating a communication system according to an embodiment of the present invention.

5 and 6, the communication system shown in FIGS. 5 and 6 is based on the communication system of FIG. 2 and is generated from the second light source 240 to prevent an intercept-resend attack And controlling the polarization of the decoded signal (Active Decoy). The configuration and method described in FIG. 2 are not described in detail here. 5 and 6 can also be applied to Figs. 3 and 4 based on the communication system of Fig.

Referring to FIG. 5, the second communication device 200 may further include a polarization controller 410. Here, the polarization controller 410 is not shown in the figure, but can be controlled in real time via the control unit.

In one embodiment, the second communication device 200 may set the polarity of the decode signal (Active Decoy) generated from the second light source 240 through the polarization controller 410 to be the same as the polarization of the quantum signal. This scheme can be applied to a case where the quantum signal transmitted from the first communication apparatus 100 is accurately known to the polarization of the quantum signal when the second communication apparatus 200 receives the quantum signal. That is, the second communication device 200 generates a decode signal (Active Decoy) through the second light source 240 and transmits the polarization of the generated decoy signal (Active Decoy) through the polarization controller 410 to the polarization of the quantum signal It is possible to insert the decode signal (Active Decoy) with the polarized light into the quantum signal through the processing section.

In another embodiment, the second communication device 200 transmits the polarization of the decode signal (Active Decoy) generated from the second light source 240 through the polarization controller 410 to the six polarizations H, V, D, A, R, and L). That is, the second communication device 200 generates a decode signal (Active Decoy) through the second light source 240 and arbitrarily sets the polarization of the generated decode signal (Active Decoy) through the polarization controller 410 , And a decode signal (Active Decoy) for which polarized light is set can be inserted into the quantum signal through the processing section. This method can also be performed through the light source box 420 shown in Fig. Here, the light source box 420 includes a second light source 240 having six polarizing plates. The polarized light of the decode signal (Active Decoy) is divided into six polarized lights (H, V, D, A, R, L).

Preferably, when the polarized light of the decode signal (Active Decoy) is set as above, the polarization information of the decode signal (Active Decoy) stored in the second communication apparatus 200 and the decode signal (Active Decoy) (Active decoy) detected by the first communication apparatus 100 after being transmitted from the first communication apparatus 100 to the first communication apparatus 100, the presence or absence of the eavesdropper, that is, the presence or absence of the blocking- Can be determined.

Preferably, the communication system can confirm the existence of the eavesdropper by comparing the measured detection rate with the predicted detection rate according to the polarization of the decoy signal (Active Decoy) with respect to the quantum signal into which the decode signal (Active Decoy) is inserted. Specifically, when a quantum signal into which the decode signal (Active Decoy) is inserted is transmitted to the first communication apparatus 100, the quantum signal is detected by the detector 160 or 170 according to the polarization information of the decode signal (Active Decoy) ). ≪ / RTI > That is, since a detector for detecting the corresponding signal can be determined according to the polarization information of the decode signal (Active Decoy), using the polarization information of the decode signal (Active Decoy) stored in the second communication device 200, 170 can be predicted with respect to the number of quantum signals detected. Here, when an eavesdropper takes the quantum signal transmitted from the second communication device 200 for eavesdropping and then transmits another quantum signal to the first communication device 100, Since the polarization information of the decode signal (Active Decoy) embedded in the quantum signal transmitted from the first communication device 100 is not known, the quantum signal having different polarization information is transmitted to the first communication device 100. That is, when there is an eavesdropper, a difference occurs between the number of detections in each detector and the actual number of detections in each detector using the polarization information of the decode signal (Active Decoy) stored in the second communication device 200 . Accordingly, the expected number of detections of each of the detectors 160 and 170 according to the polarization information of the decode signal (Active Decoy) stored in the second communication apparatus 200 and the number of detections of the detectors 160 and 170 in the first communication apparatus 100, The presence or absence of an eavesdropper can be determined by comparing the actual detection frequency detected through each of the detection devices.

7 is a configuration diagram illustrating a communication system according to an embodiment of the present invention.

7, the communication system shown in FIG. 7 is based on the communication system of FIG. 2, and includes a decode signal (Active Decoy) generated from the second light source 240 to prevent a blocking-retransmission attack and a noise component Is an embodiment for transmitting together. The configuration and method described in FIG. 2 are not described in detail here. The configuration disclosed in Fig. 7 can also be applied to Figs. 3 and 4 based on the communication system of Fig.

Referring to FIG. 7, the second communication device 200 may further include a light splitter 430 and a Faraday mirror 440. Preferably, in the second communication device 200, the quantum signal received from the first communication device 100 is divided into 50:50 through the beam splitter 210, and is transmitted to the Faraday mirror 440 of the divided quantum signal The progressive quantum signal is again divided by 1:99 through the beam splitter 430. Here, 99/100 of the quantized signals divided through the beam splitter 430 is changed by 180 degrees of polarization by the Faraday mirror 440 and reaches the beam splitter 210 through the beam splitter 430 again. The decode signal (Active Decoy) generated from the second light source 240 goes to the optical divider 210 only by the decode signal (Active Decoy) of 1/100 size by the optical divider 430. That is, in the optical splitter 210 of the second communication apparatus 200, the polarized light (90 °) and phase (phase difference) are transmitted through the Faraday mirror 230 and the phase modulator 220 among the quantum signals received from the first communication apparatus 100 (Hereinafter, referred to as a 'noise component') in which the polarized light is changed by 180 ° by the Faraday mirror 440 among the quantum signals received from the first communication apparatus 100 and the second quantum signal from the second light source 240 The generated Deco signal (Active Decoy) arrives.

Preferably, the embodiment shown in FIG. 7 further comprises a signal having polarization, such as the polarization of the quantum signal received from the first communication device 100 to the second communication device 200, back to the first communication device 100 A noise component orthogonal to the quantum signal transmitted by the first communication device 100 is generated by the Faraday mirror 440 and the decode signal (Active Decoy) is generated as a noise component orthogonal to the first And is transmitted to the communication device 100, so that the eavesdropper can not distinguish the decode signal (Active Decoy). In order for the eavesdropper to successfully attack, the time when the decode signal (Active Decoy) is used in the first communication device 100 and the second communication device 200, that is, the time point at which the decode signal (Active Decoy) However, according to the embodiment shown in FIG. 7, it is impossible to distinguish the noise component from the active decoy signal, so that the eavesdropper does not know when the decode signal (Active Decoy) is used.

For example, if there is no noise component, in the embodiment shown in FIG. 7, since the decode signal (Active Decoy) has arbitrary polarization information, if the eavesdropper has the same system as the first communication apparatus 100, The user can know when the decode signal (active decoy) is used due to the abnormal interference caused by the decode signal (active decoy). That is, the quantum signal transmitted to the second communication device 200 through the long path of the first communication device 100 is transmitted from the second communication device 200 to the first communication device 100 The quantum signal transmitted through the short path and transmitted to the second communication device 200 through the short path of the first communication device 100 is transmitted from the second communication device 200 to the first communication device 200 100, it passes through a long path, so that the point of time at which interference between both quantum signals occurs is constant. However, a decode signal (Active Decoy) having arbitrary polarization information can pass a long path when it is required to pass a short path in the first communication apparatus 100, or pass a short path The detection by the detectors 160 and 170 can be performed due to the abnormal interference caused by the decoy signal before or after the time when the interference between the normal quantum signals occurs. The eavesdropper can grasp the time point at which the decoy signal is inserted based on the time point at which the detection due to the abnormal interference due to the decoy signal occurs.

However, according to the embodiment shown in FIG. 7, since the noise component orthogonal to the quantum signal is always generated using the Faraday mirror 440, the first communication apparatus 100 can detect the interference before and after the normal interference occurs The interference by the noise component always occurs, and abnormal detection through the detectors 160 and 170 is always performed. Therefore, the eavesdropper can not distinguish whether the abnormal interference is due to the decoy signal or the noise component, and thus the point at which the decoy signal is inserted can not be grasped, so an attack by the eavesdropper can be prevented.

10 is a flowchart showing a communication method performed in the communication apparatus of the communication system of the present invention.

In FIG. 10, detailed description of the same or similar parts as those described in FIGS. 1 to 9 will be omitted.

Referring to FIG. 10, the second communication device 200 receives the quantum signal and the synchronization signal generated by the first light source 110 of the first communication device 100 (step S1010). Here, the quantum signal is temporally separated and comprises a sequence of photon pulse pairs consisting of a pair of photon pulses with orthogonal polarization, and the synchronization signal is variously implemented as a signal for obtaining timing information of phase modulation .

The second communication apparatus 200 detects the synchronization signal through the synchronization signal detector (step S1020). Here, the synchronous signal detector may be implemented differently depending on the type of the synchronous signal. Preferably, the information about the sync signal detected through the sync signal detector may be provided to at least one of the phase modulator 220, the second light source 240 and the processing unit.

The second communication apparatus 200 changes the traveling direction of the quantum signal using the Faraday mirror 230 and rotates the polarization of the quantum signal by 90 degrees and the phase modulator 220 acquires And modulates the phase of the quantum signal according to the timing information of one phase modulation (step S1030).

The second communication device 200 generates a decode signal (Active Decoy) using the second light source 240 (step S1040). In one embodiment, the light intensity of the decode signal (Active Decoy) may be substantially the same as the light intensity of the quantum signal. Also, the decode signal (Active Decoy) may be buried in a noise component orthogonal to the decode signal (Active Decoy) so that the polarization can be set through the polarization controller or the decode signal (Active Decoy) can not be distinguished.

The second communication apparatus 200 adds a decode signal (Active Decoy) to at least a part of the quantum signals based on the detection result of the synchronization signal (step S1050). In one embodiment, the second communication device 200 may add a decode signal (Active Decoy) to some photon pulse pairs in the quantum signal based on the detection result of the synchronization signal using the processing unit. At this time, the processing unit may add a decode signal (Active Decoy) to the photon pulse that is temporally preceding or temporally out of the photon pulses in the selected photon pulse pair. Further, the processor can consistently add a decode signal (Active Decoy) to the photon pulse at any timing in accordance with a preset reference.

The second communication apparatus 200 transmits the quantum signal whose phase is modulated and the decode signal (Active Decoy) is added to the first communication apparatus 100 again (step S1060).

In one embodiment, the first communication device 100 may receive the quantum signal from the second communication device 200 and detect the phase modulated quantum signal. More specifically, the first communication device 100 receives the photon pulses P1 and P2 'from the second communication device 200 and uses the phase modulator to convert the non-phase modulated photon pulses among the photon pulse pairs into phase Modulated and the fact that the photon pulse P1 'phase-modulated by the first communication device 100 and the photon pulse P2' phase-modulated by the second communication device 200 interfere with the plurality of single photon detectors Can be detected.

Next, the first communication device 100 and the second communication device 200 share a quantum cryptographic key. In one embodiment, the first communication device 100 and the second communication device 200 perform a predefined cryptographic key distribution protocol (e.g., BB84: Bennett Brassard 84) based on the detection results of a single photon detector, Cryptographic keys can be shared.

Such a quantum cryptographic key distribution method may be implemented in an application or may be implemented in the form of program instructions that can be executed through various computer components and recorded on a computer-readable recording medium. The computer-readable recording medium may include program instructions, data files, data structures, and the like, alone or in combination. Program instructions that are recorded on a computer-readable recording medium may be those that are specially designed and constructed for the present invention and are known and available to those skilled in the art of computer software.

Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks and magnetic tape, optical recording media such as CD-ROMs and DVDs, magneto-optical media such as floptical disks, media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those generated by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. A hardware device may be configured to operate as one or more software modules to perform processing in accordance with the present invention, and vice versa.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It should be understood that various modifications may be made by those skilled in the art without departing from the spirit and scope of the present invention.

In this specification, both the invention and the method invention are explained, and the description of both inventions can be supplemented as necessary.

100: first communication device
110: first light source 120: optical circulator
130: optical splitter 140: phase modulator
150: polarizing beam splitter 160, 170: single photon detector
200: second communication device
210: optical splitter 220: phase modulator
230: Faraday mirror 240: Second light source
310: Wavelength divider 320: Photodetector
330: Time synchronization device
410: polarization controller 420: light source box
430: optical splitter 440: Faraday mirror

Claims (19)

A communication device comprising:
And a synchronization signal detector for detecting a synchronization signal received from another communication device connected to the communication device, wherein the other communication device transmits a quantum signal generated from the first light source to the communication device; And
And a second light source for generating a decoy signal to be added to the quantum signal to be transmitted to the other communication apparatus in accordance with the detection result of the synchronization signal.
The method of claim 1,
A signal having a wavelength different from the quantum signal, a GPS signal, or a Network Standard Time.
3. The apparatus of claim 2, wherein the synchronization signal detector
When the synchronization signal is a signal having a wavelength different from that of the quantum signal,
A wavelength divider for dividing the quantum signal and the synchronization signal; And
And a photodetector for detecting a sync signal divided by the wavelength divider.
The method of claim 3,
Wherein the synchronization signal has a higher light intensity than the quantum signal.
3. The apparatus of claim 2, wherein the synchronization signal detector
And a time synchronization device for detecting the GPS signal or the network signal when the synchronization signal is a GPS signal or a network signal.
The method according to claim 1,
Further comprising a phase modulator for receiving the detection result of the synchronization signal by the photodetector and modulating the phase of the quantum signal in accordance with the detection result of the synchronization signal.
The method according to claim 1,
Further comprising a polarization controller for controlling polarization of the decoy signal generated by the second light source.
The apparatus of claim 7, wherein the polarization controller
Wherein the polarized light of the decoy signal is set to be the same as the polarization of the quantum signal or is set to be random.
The method according to claim 1,
Further comprising a Faraday mirror for generating a noise component orthogonal to the decoy signal generated by the light source, wherein the noise component is transmitted to the other communication device together with the decoy signal.
The method according to claim 1,
Further comprising a processing unit for adding the decoy signal generated by the second light source to at least a part of the quantum signals to be transmitted to the other communication apparatus based on the detection result of the synchronization signal.
The method according to claim 1,
Wherein the optical intensity of the quantum signal transmitted to the other communication device is a light intensity of a single photon level.
A communication method performed in a communication device,
Receiving a quantum signal and a synchronization signal generated from a first light source of the other communication apparatus from another communication apparatus connected to the communication apparatus;
Detecting a synchronization signal received from the other communication device; And
And generating a decoy signal to be added to the quantum signal to be transmitted from the second light source to the other communication apparatus, in accordance with the detection result of the synchronization signal.
13. The method of claim 12, wherein detecting the synchronization signal comprises:
When the synchronization signal is a signal having a wavelength different from that of the quantum signal,
Dividing the received quantum signal and the synchronization signal; And
And detecting the divided synchronization signal.
13. The method of claim 12, wherein detecting the synchronization signal comprises:
And detecting the GPS signal or the network signal through the time synchronization device when the synchronization signal is a GPS signal or a network signal.
13. The method of claim 12, further comprising: after detecting the sync signal
And modulating the phase of the quantum signal according to the detection result of the synchronization signal.
13. The method of claim 12, wherein generating the decoy signal comprises:
Selecting polarized light of the generated decoy signal,
Wherein the polarization of the decoy signal is set to be the same as the polarization of the quantum signal or randomly.
13. The method of claim 12, wherein generating the decoy signal comprises:
And generating a noise component orthogonal to the generated decoy signal, wherein the noise component is transmitted to the other communication device together with the decoy signal.
13. The method of claim 12,
Further comprising the step of adding the generated decoy signal to at least a part of the quantum signals transmitted to the other communication apparatus based on the detection result of the synchronizing signal.
A communication system comprising a communication device and another communication device connected to the communication device,
Wherein the communication device is configured to receive a quantum signal and a synchronization signal from the other communication device, detect the synchronization signal, and generate from the second light source a decoy signal to be added to the quantum signal to be transmitted to the other communication device,
Wherein the other communication device is configured to generate a quantum signal from the first light source and to transmit the quantum signal and the synchronization signal to the communication device.

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