WO2006006232A1

WO2006006232A1 - Quantum encryption key delivery system

Info

Publication number: WO2006006232A1
Application number: PCT/JP2004/009931
Authority: WO
Inventors: Jun'ichi Abe; Katsuhiro Shimizu
Original assignee: Mitsubishi Denki Kabushiki Kaisha
Priority date: 2004-07-12
Filing date: 2004-07-12
Publication date: 2006-01-19
Also published as: JPWO2006006232A1

Abstract

A quantum encryption key delivery system wherein three or more users can easily and safely share a quantum encryption key and wherein a plurality of users can share a photon generator. There are provided transmitting means (1) comprising photon generating means (4) and modulating means (5); two or more receiving means (2a,2b,2c) comprising demodulating means (7a,7b,7c) connected to the respective ones of two or more transmission paths (3a,3b,3c) connected to the transmitting means (1). It is arranged that pulses transmitted to each transmission path do not include two or more photons. Modulation system information selected by the transmitting means is exchanged between the transmitting means and at least one of the receiving means. Demodulation system information selected by the receiving means and information indicative of whether a photon arrives are exchanged between the receiving means. When all the receiving means receive photons, and all the demodulation systems selected by the receiving means coincide with the modulation system selected by the transmitting means, the quantum encryption key is shared.

Description

Specification

Quantum 喑 key distribution system

Technical field

The present invention relates to a quantum encryption key distribution system, and more particularly to a quantum encryption key distribution system for sharing a quantum encryption key among three or more users. Background art

An encryption key distribution system is a system whose purpose is to share a random bit string (encryption key) between transmission / reception means. In recent years, quantum key distribution technology that can deliver a safe and secure cryptographic key, regardless of the computational capability of the attacker, has attracted attention.

[0003] As a conventional technique related to quantum key distribution, a quantum key distribution technique using a single photon light source known as a BB84 method is widely known (for example, Non-Patent Documents 1 and 2). ). The quantum key distribution technology disclosed in these documents uses the uncertainty (randomness) of the quantum signal bits to avoid eavesdropping by an eavesdropper (sender) and receiving means ( The key can be shared with the recipient.

[0004] In quantum cryptography communication, which is the basis of quantum cryptography key distribution technology, photons (photons) are used as a communication means, and 1-bit information is generated by 1 photon so that quantum effects such as the uncertainty principle occur. Is transmitted. At this time, if the eavesdropper selects an arbitrary basis without knowing the quantum state such as the polarization and phase, and measures the photon, the quantum state changes. Therefore, the receiver can recognize whether or not the transmission data has been wiretapped by confirming the change in the quantum state of the photon. In other words, the quantum key distribution technique according to the prior art has a characteristic that the quantum key sharing and the eavesdropper detection are physically guaranteed.

[0005] Non-Patent Document 1: CH Bennett, and G. Brassard, ： Quantum Cryptogra phy: Public Key Distribution and Coin Tossing, In Proceedings of I EEE Conference on Computers, System and signal Processing, Ban galore, India, pp. 175 -179 (DEC. 1984). Patent Document 2: CH Bennett, “Quantum Cryptography Using Any Two Nonorthogonal States,” Phys. Rev. Lett. 68, 3121 (1992). Disclosure of the Invention

Problems to be solved by the invention

[0006] However, in the BB84 system disclosed in Non-Patent Documents 1 and 2 above, the sender is

There is a problem that a complicated and expensive photon generator must be provided because it is necessary to accurately transmit a minute optical signal of less than 1 photon per pulse.

[0007] Further, the BB84 system has a problem in that each user who uses the system must have a photon generator.

Furthermore, the BB84 system provides a mechanism for sharing a quantum encryption key between two parties, but there is a problem that it is difficult to share an encryption key between three or more parties.

[0008] In view of such a situation, the present invention enables three or more users to share a quantum encryption key easily and securely, and sharing a photon generator among a plurality of users or a plurality of systems. It is an object of the present invention to provide a quantum key distribution system that enables the above. Means for solving the problem

[0009] The quantum cryptography key distribution system that is effective in the present invention has a photon generating means and two or more selectable modulation systems in the quantum cryptography key distribution system for sharing the quantum cryptography key. A transmission means comprising a modulation means, two or more transmission paths connected to the transmission means, and two or more selectable demodulation systems connected to each of the two or more transmission paths. Two or more receiving means including a demodulating means, and the pulse sent to each transmission path is controlled so that two or more photons are not included, and the transmitting means and the 2 The modulation system information selected by the transmission unit is exchanged with at least one of the above reception units, and the demodulation system information selected by each of the two or more reception units and photon arrival information are exchanged. Presence / absence information is All of the two or more receiving means receive the photons, and all of the demodulation systems selected by each of the two or more receiving means and the modulation system selected by the transmitting means are exchanged between the two. And the quantum encryption key is shared when the two match.

[0010] According to the present invention, a pulse transmitted to each transmission path includes two or more photons. The modulation system information selected by the transmission means is exchanged between the transmission means and at least one of the two or more reception means, and each of the two or more reception means is selected. Demodulated system information and presence / absence information of photon are exchanged between the receiving means, all of the two or more receiving means receive the photons, and each of the two or more receiving means is selected. When all of the demodulated systems match the modulation system selected by the transmitting means, the quantum encryption key is shared between two or more receiving means.

The invention's effect

[0011] According to the quantum key distribution system according to the present invention, all of the two or more receiving units receive the photons, and each of the two or more receiving units selects all of the demodulation systems and the transmission system. Since the quantum encryption key is shared when the modulation system selected by the transmission means matches, the ability to easily and safely share the quantum encryption key among three or more users including the sender If you can S, you will have the effect.

Brief Description of Drawings

FIG. 1 is a conceptual diagram showing a configuration of a quantum key distribution system according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a configuration of a quantum key distribution system according to a second embodiment of the present invention.

FIG. 3 is a conceptual diagram showing a configuration of a quantum key distribution system according to a third embodiment of the present invention.

FIG. 4 is a conceptual diagram showing a configuration of a quantum key distribution system according to a fourth embodiment of the present invention.

FIG. 5 is a conceptual diagram showing the configuration of the quantum key distribution system according to the fifth embodiment of the present invention.

FIG. 6 is a conceptual diagram showing a configuration example of a quantum key distribution system according to the prior art using the BB84 method.

FIG. 7 is a diagram showing a configuration example when a phase modulator is used for each of the modulation means 5 and the demodulation means 7 of the quantum key distribution system shown in FIG.

Explanation of symbols [0013] 1 Transmission means

2, 2a, 2b, 2c, 2d, 2e receiving means

3a, 3b, 3c is route

4 Photon generator

5 Modulation means

6a, 6b Signal processing means

7 Demodulation means

8 Light receiving means

9 Information exchange means

10 Error rate detection means

11, 11a, l ib Demultiplexing means

12a, 12b, 12c Variable attenuator

13a, 13b phase modulator

14a, 14b multiplexing means

BEST MODE FOR CARRYING OUT THE INVENTION

[0014] Exemplary embodiments of a quantum key distribution system according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments.

[0015] Embodiment 1.

First, the quantum key distribution system according to the first exemplary embodiment of the present invention will be described. FIG. 1 is a conceptual diagram showing a configuration of the quantum key distribution system according to the first exemplary embodiment of the present invention. The quantum cryptography key distribution system of this embodiment includes a transmission means 1 used on the transmission side, three transmission lines 3a, 3b, 3c connected to the transmission means 1, and a transmission line on the reception side. Receiving means 2a, 2b, 2c connected thereto. The transmitting means 1 has a photon generator 4, a modulating means 5, and a demultiplexing means 11, and each receiving means has a demodulating means 7 and a light receiving means 8. Here, as the modulation means 5 and the demodulation means 7, a phase modulator, a polarization modulator, or the like can be used. As the photon generator 4, for example, a light source such as a laser diode is generally used. The transmission wavelength is suitable for transmission line 3. Any wavelength can be used. As the branching means 11, for example, a light power bra or the like can be used. As the transmission lines 3a, 3b, and 3c, various optical signal transmission lines such as a single mode optical fiber and a dispersion shifted optical fiber can be used. Also, the transmission line need not be wired, but may be a wireless transmission line such as spatial transmission.

Next, in order to facilitate understanding of the quantum cryptography key distribution system that can be used in the present invention described above, the quantum cryptography key distribution system that is effective in the prior art using the BB84 system is taken as an example. The operation will be described.

[0017] FIG. 6 is a conceptual diagram showing a configuration example of a quantum cryptography key distribution system using the BB84 method and working on the prior art. In the figure, the transmission means 1 includes a photon generator 4, a modulation means 5, and a signal processing means 6a. Here, description will be made assuming that a phase modulator is used as the modulation means 5. In transmission means 1, either [0, π] system or [π / 2, 3 π Ζ2] system phase modulation system is selected for each pulse, and a signal of “0” or “1” is transmitted on transmission line 3 Sent to. In signal transmission, two modulation systems are used, and only one photon is used per pulse. On the other hand, the receiving means 2 includes a demodulating means 7, a light receiving means 8, and a signal processing means 6b. In the receiving means 2, a received pulse is observed using an arbitrary demodulation system, and it is determined whether it is "0", "1", or "no photon". Further, in the transmission means 1 and the reception means 2, the selected modulation / demodulation system information and the presence / absence information of the arrival of the pulse are exchanged by the information exchange means 9 such as a public line that may be intercepted. In a lossy transmission line, many pulses result in “no photons.” Only when the photon is received by the receiving means 2 and the system matches between the transmission and reception, the bit string is shared between the two. The shared bit string is used as a quantum encryption key after error detection and error correction by the error rate detection means 10.

FIG. 7 is a diagram showing a configuration example when a phase modulator is used for each of the modulating means 5 and the demodulating means 7 of the quantum key distribution system shown in FIG. In the figure, the modulation means 5 is constituted by a demultiplexing means l la, a phase modulator 13a, and a multiplexing means 14a, and the demodulation means 7 is constituted by a demultiplexing means l lb, a phase modulator 13b, and a multiplexing means 14b. Is done. When the transmission means 1 selects the [0, π] system (“π” measurement system), the phase modulator 13a generates a phase modulation amount “0” for the signal “0”. Generates phase modulation amount “π” for signal “1” The When the transmission means 1 selects the [π / 2, 3π / 2] system ("π / 2" measurement system), the phase modulator 13a uses the phase modulation amount "π / 2" for the signal "0". Generates a phase modulation amount “3π / 2” for signal '. On the other hand, when the receiving means 2 selects the [0, π] system (“π” measurement system) as the demodulator, the phase modulator 13b generates the phase modulation amount “0”, and [π / 2, When the 3π / 2] system (“π / 2” measurement system) is selected, the phase modulator 13b generates a phase modulation amount “π / 2”. The light receiving means 8 can detect a correct signal only when the transmitting means 1 and the receiving means 2 select the same modulation / demodulation system.

[0019] Like the above-described processing, 1 foot per pulse is used, and since it is not used, in order to eavesdrop on the signal sent to the communication path, the eavesdropper once extracts and observes the photon, and then I have to return Huotong to the communication channel again. However, due to the uncertainty principle of quantum mechanics, observation cannot be performed without disturbing the quantum state of photon, so if there is an eavesdropper in the above protocol, an error will occur with a probability of 1Z4 on the receiving side. Become. For example, when [0, π] system signal “0” is transmitted from transmission means 1, it is the probability that an eavesdropper selects the [π / 2, 3 π / 2] system, which is received at that time. The polarization direction observed by means 2 changes to [π / 2, 3π / 2]. On the other hand, when the signal in the polarization direction is observed in the [0, π] system, which is the same measurement system used in the transmission means 1, in the receiving means 2, the signal "0" and the signal "1" Since “and” are observed with equal probability, the probability that the receiving means 2 observes the signal “0” transmitted by the transmitting device 1 as the signal “Τ” is 1/4.

[0020] If the number of check bits m is made sufficiently large, the error rate always approaches 25% according to the law of large numbers, so the probability that wiretapping cannot be detected can be made small enough to be ignored. If the number of selectable modulation / demodulation systems is 3 or more, the number of check bits m required to prevent eavesdropping can be reduced. Thus, the presence of an eavesdropper can always be detected by performing error detection between the transmission side and the reception side. This BB84 system has a significant meaning that the sharing of the quantum key and the detection of an eavesdropper are physically guaranteed by quantum mechanical complementarity, which is the principle of quantum mechanics.

Next, returning to FIG. 1, the operation of the quantum cryptographic key distribution system of this embodiment will be described in the case where a phase modulator is used as the modulation means 5. In transmission means 1, either [0, π] system or [π / 2, 3 π Ζ2] system is selected for each pulse. The same signal is transmitted almost simultaneously to the three transmission lines 3a, 3b, and 3c. What is important here is that the number of photons per pulse is controlled to be 1 or less in any transmission path. In the receiving means 2a, 2b, and 2c, the received pulse is independently observed in an arbitrary demodulation system, and it is determined whether it is “0”, “1”, or “without photon”. The receiving means 2a, 2b, and 2c exchange the selected demodulation system information with the presence / absence information of the pulse, and the information is not the measurement result information measured by each receiving means. Even if it is done, the security of quantum key sharing is not compromised, so it can be sent and received using a public line.

[0022] Only when all of the receiving means 2a, 2b, and 2c receive photons and the receiving systems selected by the three parties match the modulation system of the transmitting means, the bit strings are shared among the three parties. . The shared bit string of the receiving means is used as a quantum encryption key between the three parties after error detection and error correction are performed as necessary. The feature is that the three parties sharing the quantum encryption key do not need to have a photon generator.

At this time, the transmission means 1 does not necessarily need to know the demodulation system selected by the reception means 2a, 2b, 2c. Further, the transmission means 1 does not necessarily need to exchange the selected modulation / demodulation system information with all the reception means 2a, 2b, 2c. That is, any one of the receiving means 2a, 2b, 2c may know the modulation system information of the transmitting means 1. Further, the transmission means 1 does not need to know the quantum encryption key shared by the reception means 2a, 2b, 2c.

[0024] Although FIG. 1 shows an example in which the number of receiving means is three, the number of receiving means may be two or four or more.

[0025] In addition, the number of receiving means increases because bit information is shared between receiving means only when all receiving means receive photons and all receiving means adopt the same demodulation system. As a result, the quantum key sharing speed decreases. However, the quantum encryption key sharing rate is independent of the information transmission rate, and in many cases, the quantum encryption key sharing rate is not so important as long as it is above a certain level.

[0026] As described above, according to the quantum key distribution system of this embodiment, control is performed so that two or more photons are not included in a pulse transmitted to each transmission path, and transmission is performed. Means for transmitting between the means and at least one of the two or more receiving means Is exchanged, and the demodulation system information selected by each of the two or more receiving means and the presence / absence information of photon are exchanged between the receiving means, and all of the two or more receiving means are When all of the demodulation systems selected by each of the two or more receiving means and the modulation system selected by the transmitting means coincide with each other, the quantum encryption key is shared. Therefore, multiple users including the sender can share the quantum encryption key easily and securely.

Embodiment 2.

FIG. 2 is a conceptual diagram showing a configuration of the quantum key distribution system according to the second exemplary embodiment of the present invention. The difference between the quantum cryptographic key distribution system shown in FIG. 1 and FIG. 1 is that variable attenuators 12a, 12b, and 12c are provided at the three outputs of the demultiplexing means 11. Other configurations are the same as or equivalent to those of the first embodiment, and these portions are denoted by the same reference numerals.

[0028] As described above, in the quantum key distribution system, it is important to control so that the number of photons per pulse is 1 or less. Therefore, in the quantum key distribution system shown in Fig. 2, the variable attenuator is set to 12a, 12b, 12c so that the optical signal power transmitted to transmission lines 3a, 3b, 3c does not exceed 1 photon per SI pulse. Are controlled using each. In addition, noise on the transmission path affects the results measured by the receiving means 2a, 2b, and 2c and the transmission result on the transmission side, so variable attenuation is applied to each of the transmission paths 3a, 3b, and 3c. 12a, 12b, and 12c are inserted into the equipment, and the attenuation can be controlled according to the transmission path characteristics of each transmission path. Note that the variable attenuators 12a, 12b, and 12c may be configured to use, for example, a feedback circuit that monitors light intensity and the like.

[0029] As described above, according to the quantum key distribution system of this embodiment, since it is configured such that a variable attenuator is further provided in two or more transmission paths connected to the transmission means. Therefore, the number of photons per pulse of the optical signal transmitted to each transmission line can be controlled so as not to exceed 1, and the quantum encryption key can be shared reliably and stably.

[0030] Embodiment 3.

FIG. 3 is a schematic diagram showing the configuration of the quantum key distribution system according to the third embodiment of the present invention. It is a mere idea. The difference between the quantum key distribution system shown in FIG. 1 and FIG. 1 is that transmission means 1 and reception means 2 are provided with respective signal processing means 6a and 6b, and a part of transmission means 1 and reception means 2 ( In the example of FIG. 3, the receiving means 2c) is provided with an error rate detecting means 10 that shares its function. Other configurations are the same as or equivalent to those of the first embodiment, and these portions are denoted by the same reference numerals.

In the quantum key distribution system shown in FIG. 3, an error between transmission and reception is detected by the error rate detection means 10. By detecting an error between the transmission means and the reception means, it is possible to share the quantum encryption key while reliably detecting the presence of an eavesdropper based on the same principle as that of the conventional technology such as the BB84 method. However, the major difference from the prior art is that error detection only needs to be performed by the transmission means and a part of the reception means. Since it is not necessary for the transmitting means to know the demodulation system selected by all the receiving means, the transmitting means need not know the quantum encryption key shared by the receiving means.

[0032] It should be noted that all receiving means can perform error detection with the transmitting means, but it is not essential that all receiving means perform error detection with the transmitting means. Moreover, it does not prevent the receiving means from performing error detection.

[0033] As described above, according to the quantum key distribution system of this embodiment, all of the two or more receiving means receive the photons, and each of the two or more receiving means has selected the demodulation. Since the error rate of the bit string shared between the transmission means and two or more receivers is detected only when all the systems match the modulation system selected by the transmission means, eavesdropping Quantum encryption keys can be shared while reliably detecting the presence of a person.

[0034] Embodiment 4.

FIG. 4 is a schematic diagram showing a configuration of the quantum key distribution system according to the fourth embodiment of the present invention. The difference between the quantum key distribution system shown in FIG. 3 and FIG. 3 is that the receiving means 2a, 2b, 2c are provided with respective signal processing means 6b_l, 6b_2, 6b_3, and only the receiving means 2a, 2b, 2c (the transmitting means is (Not used) is equipped with error rate detection means 10 that share its functions. Other configurations are the same as or equivalent to those of the third embodiment, and these portions are denoted by the same reference numerals.

In the quantum cryptographic key distribution system shown in FIG. 4, the transmission means 1 transmits transmission modulation system information. Do not receive any information such as demodulated information or photon reception from the receiving means. In addition, by detecting errors between receiving means, it is possible to detect the presence of an eavesdropper with the same principle as that of the prior art such as the BB84 method, while quantizing with a receiver using three or more receiving means. The encryption key can be shared. However, unlike the prior art, it is sufficient to perform error detection only between the receiving means, without the need for the transmitting means to know the demodulation system of the receiving means. Further, the transmission means may not know the quantum encryption key shared by the reception means. Because of these characteristics, the sender using the transmission means does not have to be an absolutely reliable target. If such a feature is used, for example, a quantum encryption key can be shared only by an arbitrary receiver using a quantum communication channel provided by a third party.

[0036] As described above, according to the quantum key distribution system of this embodiment, all of the two or more receiving units receive the photons, and each of the two or more receiving units selects the demodulation. The error rate of the bit string shared with two or more receivers is detected only when all of the systems match the modulation system selected by the transmission means. In addition, since it is not necessary for the transmitting means to know the quantum key shared by the receiving means, the quantum encryption key can be shared only by an arbitrary receiver.

[0037] Embodiment 5.

FIG. 5 is a conceptual diagram showing a configuration of the quantum key distribution system according to the fifth exemplary embodiment of the present invention. The difference between the quantum key distribution system shown in FIG. 1 and FIG. 1 is that the number of receiving means is increased. Other configurations are the same as or equivalent to those of the third embodiment, and these portions are denoted by the same reference numerals.

In the quantum key distribution system shown in FIG. 5, the demodulation system information mutually selected by the receiving means 2a, 2b, and 2c and the presence / absence information on the arrival of the pulse are exchanged, and the quantum information is exchanged between these three parties. The encryption key is shared. At substantially the same time, the receiving means 2d and 2e also exchange the demodulated system information selected with each other and the presence / absence information of the arrival of the pulse, and the quantum encryption key is shared between these two parties. However, as is clear from the principle of quantum communication already described above, even if the receiving means 2a, 2b, 2c and the receiving means 2d, 2e receive the optical pulse transmitted by the same transmitting means 1, the receiving means The quantum encryption key shared by 2a, 2b, and 2c and the quantum encryption key shared by the receiving means 2d and 2e can be different from each other. Therefore, the same transmission means sends By using optical pulses, multiple groups can share a quantum encryption key almost simultaneously.

[0039] Further, according to the powerful configuration, the optical pulse transmitted by the transmission means having the photon generator can be shared by a plurality of users and a plurality of systems, so that the construction of the system is inexpensive and easy. Arise.

In the system of FIG. 5 as well, the presence of an eavesdropper can be ensured by performing error detection for each group, as in the quantum key distribution system of Embodiment 3 shown in FIG. Detecting force S is positive.

[0041] As described above, according to the quantum key distribution system of this embodiment, the photon generating means is shared by a plurality of quantum encryption key distribution systems. This makes it possible to share photon generators, making the system configuration cheap and simple.

Industrial applicability

As described above, the quantum cryptography key distribution system according to the present invention is useful for sharing quantum cryptography keys among a plurality of users or a plurality of systems, and in particular, an object that can be absolutely trusted by a sender. This is suitable as a quantum key distribution system that can flexibly respond to various needs, such as when it is difficult to share a quantum encryption key for each of a plurality of user groups.

Claims

The scope of the claims

[1] In a quantum key distribution system for sharing a quantum key,

Transmitting means comprising photon generating means and modulation means having two or more selectable modulation systems;

Two or more transmission lines connected to the transmission means;

Two or more receiving means connected to each of the two or more transmission paths and including a demodulating means having two or more selectable demodulation systems;

With

The pulses sent to each transmission line are controlled so as not to contain two or more photons,

Modulation system information selected by the transmission means is exchanged between the transmission means and at least one reception means of the two or more reception means,

The demodulation system information selected by each of the two or more receiving means and the presence / absence information of photon are exchanged between the receiving means,

When all of the two or more receiving means receive the photons, and all of the demodulation systems selected by each of the two or more receiving means and the modulation system selected by the transmitting means match. A quantum key distribution system, wherein the quantum encryption key is shared.

[2] The quantum cryptography key 酉 according to claim 1, further comprising a variable attenuator inserted between the transmission unit and two or more transmission paths connected to the transmission unit. Self-sending system.

[3] All of the two or more receiving means receive photons, and all of the demodulation systems selected by each of the two or more receiving means and the modulation system selected by the transmitting means are Only when it does, the transmission means and the two or more recipients share a bit string, and further comprise an error rate detection means for detecting an error rate of the shared bit string. Item 2. The quantum key distribution system according to item 1.

[4] All of the two or more receiving means receive photons, and all of the demodulation systems selected by each of the two or more receiving means and the modulation system selected by the transmitting means are Only if it does, share the bit string with the two or more recipients, and the error rate of the shared bit string 2. The quantum encryption key distribution system according to claim 1, further comprising error rate detection means for detecting.

5. The quantum key distribution system according to claim 1, wherein the photon generating means is shared by a plurality of quantum key distribution systems.

6. The quantum key distribution system according to claim 1, wherein a phase modulator is used as the modulation system and the demodulation system.

7. The quantum key distribution system according to claim 1, wherein a polarization modulator is used as the modulation system and the demodulation system.