JP2015012311A - Quantum cryptography apparatus and wiretapping prevention method used for quantum cryptography apparatus - Google Patents

Abstract

The present invention relates to a configuration that does not require an increase in the number of photodetectors to be used and does not require a random number generator, so that measurement data other than the phase of probe light is not wiretapped. .
An eavesdropper is configured to include auxiliary light sources (16, 25) that emit auxiliary light that is not related to an optical signal to be encrypted, and an eavesdropper enters probe light via a transmission path (30) to eavesdrop. When acquiring measurement data for use, the probe light and the auxiliary light emitted from the auxiliary light source are mixed to provide an eavesdropping prevention function that uses the measurement data as the data value of the auxiliary light. A quantum cryptography device having resistance against a channel attack is realized.
[Selection] Figure 1

Description

  The present invention relates to a quantum cryptography device having resistance against a side channel attack by an eavesdropper and an eavesdropping prevention method used for the quantum cryptography device.

  When quantum key distribution (QKD) is performed, a secret key can be securely shared between two parties performing communication. Here, “safely” means that no limit is imposed on the attacker's ability (unconditional safety), and that the ability to prove such safety using the principle of quantum mechanics is the largest in QKD. This is an advantage.

  However, as a premise of the proof, an eavesdropper can use a quantum communication channel (communication channel for transmitting and receiving quantum bits (usually weak coherent light)) that connects the sender and the receiver's quantum cryptography device, and a public communication channel (public information). The communication path with an authentication function for transmitting and receiving the message can be attacked, but the quantum cryptography apparatus cannot be accessed.

  On the other hand, there is a cryptanalysis technique called a side channel attack. This analysis is not based on decryption using only messages and ciphertext, but also by considering the behavior of the cryptographic device, for example, information such as the calculation time for encryption, the electromagnetic wave radiated from the device, and the power consumption. It is a technique to do.

  As described above, the security proof of quantum cryptography assumes that an eavesdropper cannot access the device. However, in practice, an eavesdropper cannot access the device, and many side channel attacks against the quantum cryptography device have been studied. Therefore, when actually creating a quantum cryptography device, it should be implemented so as to be resistant to these side channel attacks so as to satisfy the assumptions imposed at the time of security proof.

  One of the side channel attacks on the quantum cryptography apparatus described above is Trojan horse attack. In this attack, probe light is incident on the quantum cryptography apparatus from the outside via the quantum communication path, and the information of the apparatus, in particular, the transmission / reception base of the sender / receiver is eavesdropped. As conventional countermeasures against this attack, a method that does not actively select a base (for example, refer to Patent Document 1), or a method that further changes the state of probe light carrying the base information (for example, Non-Patent Document 1). Etc.) have been proposed.

Japanese Patent No. 5146682

N. Gisin, S.M. Fasel, B.B. Kraus, H.C. Zbinden, and G.G. Ribbon Phys. Rev. A 73, 023320 (2006)

However, the prior art has the following problems.
In Patent Document 1, instead of actively performing base selection, a larger number of detectors must be used as the photodetectors of the reception-side quantum cryptography device than in the conventional method (normally two). However, in Patent Document 1, there are four). In Non-Patent Document 1, it is necessary to additionally use a random number generator in order to perform random modulation on the probe light.

  The present invention has been made in order to solve the above-described problems, and it is not necessary to increase the number of photodetectors to be used, and does not require a random number generator, and measures other than the phase of the probe light. An object of the present invention is to obtain a quantum cryptography device having an eavesdropping preventing function for preventing information on the quantum cryptography device from being eavesdropped on data, and an eavesdropping prevention method used for the quantum cryptography device.

  A quantum cryptography device according to the present invention is a quantum cryptography device having resistance against side channel attacks by an eavesdropper, and includes an auxiliary light source that emits auxiliary light that is not related to an optical signal to be encrypted. However, when probe light is incident through the transmission line and measurement data for eavesdropping is to be acquired, the measurement data is converted to auxiliary light data by mixing the probe light with the auxiliary light emitted from the auxiliary light source. It has an eavesdropping prevention function as a value.

  The wiretapping prevention method used in the quantum cryptography device according to the present invention includes an auxiliary light source that has resistance against a side channel attack by an eavesdropper and emits auxiliary light that is unrelated to the optical signal to be encrypted. An eavesdropping prevention method used in a quantum cryptography device that emits probe light and an auxiliary light source when an eavesdropper enters probe light through a transmission line and attempts to acquire measurement data for eavesdropping. By mixing with auxiliary light, there is an eavesdropping prevention step in which the measurement data becomes the data value of the auxiliary light.

  According to the present invention, using the auxiliary light source newly prepared by the transmitter / receiver, the measurement data value of the eavesdropper is used as the light data value not used for key sharing output from the auxiliary light source. Eliminates the need to increase the number of photodetectors and does not require a random number generator, and has an eavesdropping prevention function that prevents information on the quantum cryptography device from being eavesdropped on measurement data other than the phase of the probe light. The quantum cryptography device and the wiretapping prevention method used for the quantum cryptography device can be obtained.

It is a block diagram of the quantum cryptography apparatus in Embodiment 1 of this invention. It is explanatory drawing of the eavesdropping prevention function which the transmission side quantum cryptography apparatus in Embodiment 1 of this invention has. It is explanatory drawing of the eavesdropping prevention function which the receiving side quantum cryptography apparatus in Embodiment 1 of this invention has.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a quantum cryptography device and an eavesdropping prevention method used in the quantum cryptography device of the invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a quantum cryptography apparatus according to Embodiment 1 of the present invention. The quantum cryptography apparatus according to the first embodiment is roughly composed of three parts: a transmission-side quantum cryptography apparatus 10, a reception-side quantum cryptography apparatus 20, and a transmission path 30 that connects the two apparatuses.

  The transmission-side quantum cryptography device 10 includes a laser light source (LD) 11, a transmission-side PLC (Planer Light wave Circuit) 12, a transmission-side phase modulator (PM) 13, an optical attenuator (ATT) 14, an optical fiber coupler 15, And an auxiliary light source (Source) 16. The reception-side quantum cryptography apparatus 20 includes an optical fiber coupler 21, a reception-side phase adjuster (PM) 22, a reception-side PLC 23, a photon detector 24, and an auxiliary light source (Source) 25. An optical fiber is used for the transmission line 30.

Hereinafter, an eavesdropping preventing operation in each of the transmission-side quantum cryptography device 10 and the reception-side quantum cryptography device 20 will be described.
First, an eavesdropping prevention function in the transmission-side quantum cryptography device 10 will be described.
<Description of transmitting side quantum cryptography device>
In the transmission-side quantum cryptography device 10, first, pulsed light (signal light) is emitted from the laser light source 11 and enters the transmission-side PLC 12. This transmission side PLC 12 is an asymmetric Mach-Zehnder interferometer (interferometer configured with two inputs, two outputs, and two paths Long arm and Short arm having different lengths). , Internally divided into two pulses.

  Each signal light pulse propagates through a long arm and a short arm, and is further divided into two, and a duplex signal light pulse separated in time from the output ports 1 and 2 of the PLC is output.

  Here, it is necessary to keep the temperature inside the transmission side PLC 12 constant by using a Peltier element or the like. This corresponds to keeping the delay amount between the above-mentioned two light pulses constant. Note that the dual light pulse output from the output port 2 of the transmission side PLC 12 is not used thereafter.

  Next, the duplex signal light pulse output from the output port 1 enters the transmission-side phase modulator 13. In the transmission-side phase modulator 13, a relative phase difference is added between the duplex signal light pulses. As the phase difference amount φA to be given, for example, any one of (−π / 2, 0, π / 2, π) is selected at random.

  This phase φA is key information used for key sharing and base information on the transmitting side. Thereafter, the double signal light pulse with the relative phase difference φA is attenuated by the optical attenuator 14 to the intensity of light per pulse to a single photon level.

  The light intensity of the duplex signal light pulse only needs to be at a single photon level when output from the transmission-side quantum cryptography apparatus 10. Therefore, the dimming operation may be performed, for example, immediately after the light is output from the laser light source 11 or immediately after the output port 1 of the transmission side PLC 12.

  The dimmed duplex signal light pulse then enters the input port 1 of the optical fiber coupler 15, and is finally output from the output port 1 and enters the transmission line 30. It should be noted that the duplex signal light pulse output from the output port 2 of the optical fiber coupler 15 is not used thereafter.

  FIG. 2 is an explanatory diagram of an eavesdropping prevention function of the transmission-side quantum cryptography apparatus 10 according to the first embodiment of the present invention. Here, from the viewpoint of an eavesdropper performing Trojan horse attack, the object is to obtain the operation information of the quantum cryptography device, particularly the phase φA described above. For this purpose, the eavesdropper first enters probe light into the transmission-side quantum cryptography device 10 via the transmission path 30 connected to the quantum cryptography device (corresponding to step S21 in FIG. 2). Then, the probe light passes through the inside of the transmission-side quantum cryptography apparatus 10, is reflected at each optical component connection point or the like (corresponding to step S22 in FIG. 2), and returns to the transmission path 30 again.

  Since the probe light passes through the inside of the transmission-side quantum cryptography device 10, it reflects the state of the device, and the eavesdropper obtains device information by measuring the returned probe light. . In particular, the probe light is transmitted during the time that the transmission-side phase modulator 13 in the transmission-side quantum cryptography apparatus 10 maintains any setting of (−π / 2, 0, π / 2, π). When passing through the side phase modulator 13, information of φA is carried on the probe light. That is, the eavesdropper can obtain the key used for key sharing selected by the sender (transmission-side quantum cryptography apparatus 10) and information related to the base.

  Return the story to the sender's perspective. From the sender's point of view, the eavesdropper does not want to know his / her selected key and base information. Therefore, in the first embodiment, in order to change the probe light state of the eavesdropper, particularly the phase state, the transmitting-side quantum cryptography apparatus 10 uses light that is not used for key sharing. Therefore, in the transmission-side quantum cryptography apparatus 10, a light source for emitting light that is not used for key sharing (that is, auxiliary light unrelated to the optical signal to be encrypted) is provided as the auxiliary light source 16, and the auxiliary light source 16 Is connected to the input port 2 of the optical fiber coupler 15 described above. As the light emitted from the auxiliary light source 16, CW (Continuous Wave) light and temporally random pulse light can be considered.

  In either case, the auxiliary light source 16 is driven so that it does not overlap in time with the signal light pulse of the sender when entering the transmission line 30 from the optical fiber coupler 15. Further, it is assumed that the intensity of the optical signal emitted from the auxiliary light source 16 is approximately the same as or higher than the reflected light of the probe light from the eavesdropper. The phase of the light from the auxiliary light source 16 may be changed randomly, but may not be changed. If it is not changed randomly, a random number generator is unnecessary.

  As described above, by operating the transmission-side quantum cryptography device 10, the probe light of the eavesdropper is mixed with the light from the auxiliary light source 16 and enters the transmission line 30 at the same timing (step S23 in FIG. 2). Equivalent). Thus, by mixing the probe light from the eavesdropper and the light from the auxiliary light source 16, the measurement data value of the eavesdropper can be the light data value of the auxiliary light source 16 prepared by the sender. The operation of the measurement data by the auxiliary light source 16 can be applied to the other measurement data in addition to the phase, thereby preventing information leakage of the transmission-side quantum cryptography apparatus 10 including the key and the base information. .

Next, an eavesdropping prevention function in the reception-side quantum cryptography device 20 will be described.
<Description of receiving-side quantum cryptography device>
In the reception-side quantum cryptography device 20, first, the double light pulse output from the transmission path 30 enters the input port 1 of the optical fiber coupler 21 and is output from the output port 1. An auxiliary light source 25 is connected to the output port 2 of the optical fiber coupler 21 as in the receiving side. The operation of the auxiliary light source 25 will be described later.

  Next, the double light pulse is input to the reception-side phase modulator 22. The reception-side phase modulator 22 adds a relative phase difference between the two series of optical pulses in the same manner as performed on the transmission side. As the phase difference amount φB to be given, for example, any one of (0, π / 2) is selected at random. This phase φB is the basis information of the receiver.

  Next, the double light pulse output from the reception-side phase modulator 22 enters the input port 1 of the reception-side PLC 23. In the reception side PLC 23, each of the duplex light pulses is divided into two pulses, and propagates through the long arm and the short arm, and then is output to the output port 1 and the output port 2, as in the transmission side PLC 12.

  At this time, similarly to the transmission side PLC 12, the temperature inside the reception side PLC 23 is also kept constant and is set to a temperature setting that causes a delay of the same amount as the delay amount between the two optical pulses generated in the transmission side PLC 12. Thus, the front pulse among the pulses propagated through the long arm and the rear pulse among the pulses propagated through the short arm interfere with each other, and are output as a triplet light pulse. Of these triplex light pulses, the middle pulse is data that is the basis of the shared secret key.

  Whether the interfering optical pulse (the middle pulse of the triplet optical pulse) is output from the output port 1 or the output port 2 depends on the phase difference amount φA added by the transmission-side phase modulator 13 and the reception. It changes depending on the combination of the phase difference amount φB added by the side phase modulator 22.

  Finally, in order to detect the middle pulse among the triplet light pulses output from the receiving side PLC 23 with the photon detector 24, the photon detector 24 is driven and detected at the timing when the pulse is incident. The sender / receiver shares a secret key based on the detected pulse data.

  Here, as considered in the transmission-side quantum cryptography device 10, the Trojan horse attack for the reception-side quantum cryptography device 20 is considered. FIG. 3 is an explanatory diagram of an eavesdropping prevention function of the reception-side quantum cryptography apparatus 20 according to Embodiment 1 of the present invention.

  The purpose of the eavesdropper is to obtain the operation information of the receiving-side quantum cryptography device 20, particularly the phase φB described above. For this purpose, the eavesdropper enters probe light into the reception-side quantum cryptography device 20 via the transmission path 30 connected to the quantum cryptography device (corresponding to step S31 in FIG. 3). The incident probe light passes through the inside of the reception-side quantum cryptography device 20, is reflected at each optical component connection point or the like (corresponding to step S32 in FIG. 3), and returns to the transmission path 30 again.

  Since the probe light passes through the inside of the reception-side quantum cryptography device 20, it reflects the state of the device, and the eavesdropper obtains device information by measuring the returned probe light. . In particular, the probe light is received during the time in which the reception-side phase modulator 22 in the reception-side quantum cryptography device 20 maintains one of the modulation (0, π / 2) settings for the duplex signal light pulse. When passing through the side phase modulator 22, information of φB is carried on the probe light. That is, the eavesdropper can obtain information related to the base used for key sharing selected by the receiver (reception-side quantum cryptography apparatus 20).

  In order to prevent leakage of the base information, the receiver uses light that is not used for key sharing, like the sender. Light that is not used for key sharing is made incident by the auxiliary light source 25 connected to the output port 2 of the optical fiber coupler 21 described above. As the light emitted from the auxiliary light source 25, CW light and temporally random pulse light can be considered.

  It is assumed that the light intensity is comparable to or higher than the reflected light of the probe light from the eavesdropper. The phase of the light from the auxiliary light source 25 may be randomly changed, but may not be changed. If it is not changed randomly, a random number generator is unnecessary. Light that is not used for key sharing is output from the input ports 1 and 2, but the light output from the input port 2 is not used thereafter.

  As described above, by operating the reception-side quantum cryptography device 20, the probe light of the eavesdropper is mixed with the light from the auxiliary light source 25 and enters the transmission line 30 at the same timing (step S33 in FIG. 3). Equivalent). Similar to the transmission side, the probe light from the eavesdropper and the light from the auxiliary light source 25 are mixed, so that the measurement data value of the eavesdropper can be the light data value of the auxiliary light source 25 prepared by the receiver. it can. The operation of the measurement data by the auxiliary light source 25 can be applied to the other measurement data in addition to the phase, thereby preventing information leakage of the reception-side quantum cryptography device 20 including the key and the base information. .

  As described above, according to the first embodiment, the following effects can be obtained. In the conventional method, information leakage (wiretapping) of the quantum cryptography device is prevented by randomly changing the phase of the probe light. On the other hand, in the present invention, the transmitter / receiver achieves the above-mentioned object by mixing light from a newly prepared auxiliary light source. The advantage of the present invention is that the state of the probe light can be changed in other measurement data in addition to the phase, the number of photodetectors to be used need not be increased, and a random number generator is not required. In the point.

  DESCRIPTION OF SYMBOLS 10 Transmission side quantum cryptography apparatus, 11 Laser light source (LD), 12 Transmission side PLC, 13 Transmission side phase modulator (transmission side PM), 14 Optical attenuator, 15 Optical fiber coupler, 16 Auxiliary light source (transmission side auxiliary light source), 20 reception side quantum cryptography device, 21 optical fiber coupler, 22 reception side phase modulator (reception side PM), 23 reception side PLC, 24 photon detector, 25 auxiliary light source (reception side auxiliary light source), 30 transmission path.

Claims (10)

A quantum cryptography device having resistance to side channel attacks by an eavesdropper,
An auxiliary light source that emits auxiliary light that is unrelated to the optical signal to be encrypted is configured,
When the eavesdropper enters probe light through a transmission path and tries to acquire measurement data for eavesdropping, by mixing the probe light and the auxiliary light emitted from the auxiliary light source, A quantum cryptography device having an eavesdropping prevention function in which measurement data is a data value of the auxiliary light. The quantum cryptography device according to claim 1,
The auxiliary light source is a transmission-side auxiliary light source provided in the transmission-side quantum cryptography device among the transmission-side quantum cryptography device and the reception-side quantum cryptography device connected via the transmission path,
The transmission-side quantum cryptography device drives the transmission-side auxiliary light source to emit the auxiliary light so as not to overlap in time with the timing of emitting the encrypted optical signal. The quantum cryptography device according to claim 2,
The transmission-side auxiliary light source emits the auxiliary light as temporally random pulsed light. The quantum cryptography device according to claim 2,
The transmission-side auxiliary light source emits the auxiliary light as CW light. The quantum cryptography device according to claim 2,
The transmission side auxiliary light source emits the auxiliary light so as to have a light intensity equal to or higher than the reflected light by the probe light. The quantum cryptography device according to claim 1,
The auxiliary light source is a reception-side auxiliary light source provided in the reception-side quantum cryptography device among the transmission-side quantum cryptography device and the reception-side quantum cryptography device connected via the transmission path,
The reception-side quantum cryptography device drives the reception-side auxiliary light source to emit the auxiliary light. The quantum cryptography device according to claim 6,
The reception side auxiliary light source emits the auxiliary light as temporally random pulsed light. The quantum cryptography device according to claim 6,
The reception side auxiliary light source emits the auxiliary light as CW light. The quantum cryptography device according to claim 6,
The quantum cryptography apparatus, wherein the reception side auxiliary light source emits the auxiliary light so as to have a light intensity equal to or higher than that of the reflected light by the probe light. An eavesdropping prevention method used in a quantum cryptography device that includes an auxiliary light source that has resistance against a side channel attack by an eavesdropper and emits auxiliary light that is not related to an optical signal to be encrypted.
When the eavesdropper enters probe light through a transmission path and tries to acquire measurement data for eavesdropping, by mixing the probe light and the auxiliary light emitted from the auxiliary light source, An eavesdropping prevention method used in a quantum cryptography apparatus, comprising an eavesdropping prevention step in which measurement data is a data value of the auxiliary light.

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