JP2007221583A - Quantum cryptography key distribution unit, and method for detecting wiretapped key information - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve detection of complete interception wiretapping to a quantum correlation key distribution system which is robust to branch wiretapping but has been weak in complete interception wiretapping. <P>SOLUTION: A means for monitoring a simultaneous detection count to an incoming photon is newly provided without an interferometer. By the introduction of a new condition based on the above monitored output, the complete interception wiretapping is detected. Specifically, after receiving photons, presence or non-presence of the complete interception wiretapping is decided by mutually comparing photon detection times in photon detectors A0, B0 and at the interferometer output stage, and by calculating A0-B0 simultaneous photon detection counts and a simultaneous output detection count of the optical interferometer, and comparing therebetween. The principle of the above condition is that there is a difference between a pair of the probability of simultaneous detection of photons in the both receivers and the probability of simultaneous detection in the interferometer output, depending on a case of the photons having quantum correlation (genuine key information) or a case of the photons not having quantum correlation (false key information generated by a wiretapper). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a quantum cryptographic key distribution technique using a photon pair having a quantum correlation, and more particularly to a quantum cryptographic key distribution apparatus and a key information eavesdropping detection method based on a quantum cryptographic key distribution technique using time-entangled photons.

  In recent years, research on quantum cryptography communication in which safety is physically guaranteed by using light of one photon level has been advanced. The quantum cipher is for sharing a secret key for performing cipher communication between two distant communication devices, and is also called quantum key distribution. There are various types of quantum key distribution. Here, a quantum correlation secret key distribution system similar to the present invention will be described (Non-Patent Document 1).

  FIG. 5 shows a basic configuration of a conventional quantum correlation secret key distribution system. This system is a set of receivers (A, B) 41, 42 for generating secret keys at points separated from each other for the purpose of extending the delivery distance of photon pairs, which are information carriers for generating quantum encryption keys. The quantum correlation photon pair generator 11 is arranged at an intermediate position. The quantum correlation photon pair generator 11 has a pump light source 12 and an optical nonlinear medium 13, and has a quantum correlation by making the pump light generated by the pump light source 12 incident on the optical nonlinear medium 13 that causes an optical parametric process. A series of optical pulse trains (signal photons and idler photons) at regular time intervals are delivered to receivers A and B at an optical level that averages photon pairs less than 1 photon pair / pulse (eg, 0.1). In this delivery, a differential phase shift method is applied. The signal photon and idler photon are always generated in pairs in order to satisfy the energy conservation law. A pair of photons having such a correlation is called a quantum correlation photon pair.

The signal / idler pulse train output from the quantum correlation photon pair generator 11 reaches the receivers (A, B) 41, 42 via the transmission paths 31, 32, respectively. Each of the receivers (A, B) 41 and 42 has the same configuration, includes a one-pulse delay interferometer, and includes two photon detectors that detect an interference result that is an output of the interferometer. That is, each of the receivers A and B branches the received pulse train into two by an optical branching unit (C1, C3) 5 and adds a delay to one by an optical delay circuit (L _a , L _b ) 6. The signal is multiplexed again by the 2 × 2 optical coupler (C2, C4) 7. Photon detectors 8 and 9 are provided at two output ports of the multiplexing coupler (optical multiplexer) 7, respectively. Outputs of the photon detectors 8 and 9 are supplied to the information processing apparatus 10. The information processing apparatus 10 has a function for exchanging information between two receivers, and includes a general CPU, a memory, a communication device, and the like.

  In the above configuration, the delay time given to one by the optical branching / multiplexing circuits 5 and 7 is assumed to be equal to the time interval of the input pulse train. With this setting, the multiplexing coupler 7 combines the preceding and succeeding pulses in an overlapping manner. Due to this overlap, both interfere with each other, and a photon is detected by one of the two photon detectors 8 and 9 depending on the result of the interference. At this time, when both the receivers A and B detect photons, if the first photon detector A1 of one receiver A detects a photon due to the nature of the above-described quantum correlation photon pair, the other photons must be detected. If the first photon detector B1 of the receiver B detects a photon, and the second photon detector A2 of one receiver A detects a photon, the second photon detection of the other receiver B is always performed. Instrument B2 detects the photons. However, it is quite random whether the first photon detector A1 / B1 detects photons or the second photon detector A2 / B2 detects photons. Thus, since the photon pair has a quantum correlation, the receivers A and B obtain the same interference result for the same event, that is, among the photon detectors that each has, the photon detectors having the same setting simultaneously Result is detected.

  In general, the transmission distance of the signal transmission device is determined by the difference between the transmission power and the minimum reception sensitivity. Assuming that the photon pair generation efficiency of the quantum correlation photon pair generator is the same as the photon transmission efficiency of the previous transmitter incorporating the photon generation means, the transmission distance from the quantum correlation photon pair generator to the receiver is This is the same as the distance between the previous transmitter and receiver. Since the quantum correlation photon pair generator is located at the intermediate point between the receivers A and B, the distance between the receivers A and B is twice the distance between the previous transmitter and receiver, and the two parties sharing the secret key The distance between them can be made longer than before.

Using the above configuration, the receivers A and B obtain a secret key by the following procedure.
A) First, each of the receivers A and B detects a photon by the above reception configuration. At this time, the detected time and the detector are recorded by the information processing apparatus 10.
B) After receiving the required number of photons, each of the receivers A and B communicates only the time when the photons are detected (photon detection time) with each other via the information processing apparatus 10 and the normal transmission path 14 that is generally used. Send and receive.
C) The receivers A and B both detect a photon at the same time, and a predetermined rule (for example, the first photon detector A1 of the two photon detectors of each receiver). / B1 is a photon detected event bit “0”, the second photon detector A2 / B2 photon detected event is a bit “1” rule, the bit “0” or “1” numerical value is A key is generated according to bit information).

  Due to the nature of the quantum-correlated photon pair, the bits generated by both receivers A and B always match each other. Thus, the two receivers A and B can obtain the same bit string as a secret key.

  In this procedure, the information transmitted and received by the receivers A and B through the transmission line 14 is only the photon detection time, and the bit information is not output to the outside. Therefore, the bit information will not be eavesdropped by others. Also, since the light being transmitted is an average of less than one photon per pulse, an eavesdropper cannot obtain bit information by branching a part of the signal. This is because, since the photon is not divided into two, if the eavesdropper detects the photon by branching, the photon does not reach the receiver and does not become a bit string acquired by the two receivers.

Satoshi Inoue “Proposal for Differential Phase Quantum Key Distribution Using Quantum Correlated Photon Pairs” Proceedings of the 65th JSAP Scientific Meeting P1365 3P-ZF-9 Japan Society of Applied Physics September 1, 2004

  The conventional system as described above is safe against branch eavesdropping in the middle of the optical transmission lines 31 and 32, but is not compatible with an eavesdropping method (complete blocking eavesdropping method) that completely blocks the quantum correlation photon pair. There was a problem that safety could not be secured.

  Here, complete blocking means that the photons transmitted by the photon pair generator of the conventional device are completely blocked, and an eavesdropper generates new photons conforming to the differential phase shift method immediately before the receivers A and B. (An eavesdropper assumes that the phases of all photons have been grasped), and means that the generated photons are delivered to the receivers A and B and the detection times exchanged by the receivers A and B are wiretapped.

  The complete blocking wiretapping method will be described more specifically with reference to FIG. In FIG. 6, an eavesdropper (eavesdropper) A 61 connected in the middle of the optical transmission path 31, an eavesdropper (eavesdropper) B 62 connected in the middle of the optical transmission path 32, and an eavesdropping connected in the middle of the normal transmission path 14. It is assumed that the person (wiretap) C 63 cooperates to obtain a secret key. An eavesdropper A is located near the receiver A 41, and an eavesdropper B is located near the receiver B 42. First, eavesdroppers A and B block the quantum correlation photon pair pulse train sent to the receivers A and B, respectively. Then, the eavesdroppers A and B generate coherent optical pulse trains with the coherent light sources 64 and 65, and the phase modulators 66 and 67 modulate the phase of each pulse with 0 or π, and then to the receivers A and B. Send it in. At this time, it is assumed that the modulation phases given to each optical pulse by the eavesdroppers A and B are the same. Further, as shown in FIG. 7, each receiver A, B is intermittently sent a block (block) of continuous n pulses having the same time interval as the optical pulse train from the quantum correlation photon pair generator 11. To do.

  Each of the receivers A and B splits the transmitted light (false signal) into two by the optical branching / combining circuits 5 and 7 and causes the optical delay circuit (optical delay line) 6 to cause one pulse to cause interference. At this time, since the phase of each pulse is 0 or π as described above, the phase difference between the preceding and succeeding pulses is also 0 or π. If the phase difference between the preceding and following pulses is 0 as a result of the interference, the first photon detector A1 / B1 detects the photon, and if it is π, the second photon detector A2 / B2 detects the photon. Each receiver A, B informs the photon detection time after receiving the required predetermined number of photons, and the first photon detector A1, B1 uses the photon for the time slot in which both A, B detect the photon. If detected, bit "0", second photon detector A2. When B2 detects a photon, a bit is generated as bit “1”. Since both receivers A and B receive the light subjected to the same phase modulation, the bits obtained by both receivers A and B always match. Here, the eavesdropper C 63 eavesdrops on the photon detection time when the receivers A and B inform each other, and informs the eavesdroppers A and B of the time slot in which the bits are generated. Thereby, the eavesdroppers A and B can know the bits generated by the receivers A and B from the phase modulation data corresponding to the time slot.

  The present invention has been made in view of the above-mentioned problems to be solved in the conventional system, and its purpose is to check whether or not there is a complete interception wiretapping as described above, based on the conventional quantum correlation secret key distribution system. An object of the present invention is to provide a quantum key distribution device and a key information wiretapping detection method that can be detected.

  In order to achieve the above object, the present invention provides a photon pair generator for generating photon pairs having a quantum correlation at regular intervals, and two receivers each receiving the photons of the photon pair via an optical transmission line. Each of the receivers includes a direct photon detection unit that directly detects a photon, and a light splitting unit that splits the light into two by the optical branching unit. After giving a time delay equal to the generation interval of the pair, these branched lights are multiplexed by optical multiplexing means having two output terminals, and photons from the two output terminals of the optical multiplexing means are respectively photon detection means Exchanges the time information of the photon detection in the optical interference detection means with the optical interference detection means for detecting by the optical interference detection means, the optical branching means for stochastically branching the input light and outputting it to the direct photon detection means and the optical interference detection means, respectively. To do By using the bit information corresponding to the photon detection means that has detected the photons by the optical interference detection means, a bit string common to each other is generated as key information, and the detection result of the direct photon detection means and the optical interference detection means Quantum key generation means for determining the presence or absence of eavesdropping by calculating the photon simultaneous detection count and the interferometer output simultaneous detection count using the detection results of the two, and comparing the calculated values with respective predetermined values. It is characterized by comprising.

  Here, when the photon simultaneous detection count and the interferometer output simultaneous detection count do not coincide with each predetermined value, the quantum encryption key generating means determines that there is an eavesdropping, and discards the generated key information, Alternatively, the generation of the key information can be stopped.

  Further, when the photon coincidence detection count and the interferometer output coincidence detection count coincide with each other, the quantum cryptography key generation means determines that there is an eavesdropping and discards the generated key information or the key information The generation may be stopped.

  In order to achieve the above object, the present invention provides a photon pair generator for generating photon pairs having a quantum correlation at regular intervals, and two receivers each receiving the photons of the photon pair via an optical transmission line. In a key information eavesdropping detection method for detecting key information eavesdropping for a quantum cryptography key distribution device comprising: a procedure for stochastically branching input light; a direct photon detection procedure for directly detecting photons of branched light; The branched light is further branched, and after a time delay equal to the generation interval of the photon pair is given to the light passing between the one of the branched paths, the branched light is multiplexed by the optical multiplexing means, and the optical multiplexing is performed. Photon simultaneous detection count and interferometer output using optical interference detection procedure for detecting photons from two output terminals of wave means, detection result of direct photon detection procedure and detection result of optical interference detection procedure, respectively Simultaneous detection count Calculated by the calculated two values are compared to predetermined values for each, characterized in that it comprises a procedure for detecting the presence or absence of the key information eavesdropping.

  Here, in the procedure for detecting the key information wiretapping, when the photon simultaneous detection count and the interferometer output simultaneous detection count do not match the predetermined values, it is determined that there is wiretapping and the generated key information is discarded. Alternatively, the generation of key information may be stopped.

  Further, the procedure for detecting the key information eavesdropping determines that there is an eavesdropping when the photon simultaneous detection count and the interferometer output simultaneous detection count match, and discards the generated key information or The generation may be stopped.

  With the above configuration, according to the present invention, it is possible to provide a function of detecting the presence or absence of complete interception wiretapping in quantum secret key distribution using a quantum correlation photon pair.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows the configuration of a quantum key distribution system according to an embodiment of the present invention. This is basically the same as the conventional system of FIG. 5, but in each receiver (A, B) 141, 142, a third optical coupler (C5, C6) in which the input photons are provided immediately before the interferometer. The difference is that the branch is made probabilistically by 101 and the photon is directly detected by the third photon detector (A0, B0) 102. Since the other components are the same as those in FIG. 5, the same reference numerals are given to portions having the same functions, and redundant description thereof is omitted.

  The procedure for generating the secret key is the same as in the conventional system described with reference to FIG. 5, but the information processing device 110 of each receiver A and B records the photon detection time and detector after the output of the interferometer, respectively. The photon detection time at the third photon detector (A0, B0) 102 is also recorded.

  As the information processing apparatus 110, not only a dedicated apparatus but also a commercially available computer can be used. For example, as shown in FIG. 2, a processor (CPU) 201, a memory 202 for recording a photon detection time, a detector, and the like, a photon An analog / digital converter 203 for digitizing the output of the detectors 8, 9, 102, a line control unit (modem) 204 for exchanging information with other receivers via the transmission line 14, a bus 205, etc. Including. However, the configuration in FIG. 2 is merely an example, and other configurations can be applied to the information processing apparatus 110. For example, the analog-digital converter 203 may be included on the photon detector 8, 9, 102 side. The processor 201 performs a key generation process and various count processes necessary for detecting a complete interception eavesdropping described below and control of the entire apparatus in accordance with a built-in program.

  Then, the information processing device 110 of each receiver A, B receives the required predetermined number of photons, and after that, the photon detection count at the detectors A0, B0, the simultaneous detection count at both detectors A0, B0, Then, the complete interception wiretap shown in FIG. 6 is detected by comparing the simultaneous detection count at the interferometer output obtained from the detectors A1, B1, A2 and B2. The principle is described below.

First, simultaneous detection of a quantum correlation photon pair will be described. A photon pair having a quantum correlation is always generated as a pair. In the present invention, the light level of the photon pair pulse train is averaged and set to less than one pair per pulse, for example, 0.1 pair / pulse. When such a photon pair pulse train is directly received, photons are detected at a rate of once every 10 pulses, and nothing is detected in the remaining pulses. At this time, due to the nature of the quantum correlation, at one time (for example, the photon detector A), a photon is necessarily detected by the other (for example, the photon detector B) at the time position where the photon is detected (for example, (A in FIG. 3). )). Therefore, when the transmission light level is an average μ pair / pulse, the photon detection probability per pulse is μ, and the simultaneous detection probability is μ. When the transmission transmittance including the detection efficiency of the photon detector is α (<1), the probability of one photon reaching one (photon detector A or B) is α and both (photon detectors A and B). ) Reaches α ² , the photon detection probability = μα and the simultaneous detection probability = μα ² .

On the other hand, when two normal pulse light trains having an average μ photon / pulse are received independently by the two photon detectors A and B (see FIG. 3B), per pulse The probability of photon detection is μ, and the probability that both happen to be detected with a certain pulse (that is, the simultaneous detection probability) is simply multiplied to μ ² .

  The case where photons are directly received has been described above. Next, a case where photons are detected via an interferometer will be described.

When photons are detected via an interferometer as shown in FIG. 1 (or FIG. 5), the simultaneous detection characteristics are different from the simultaneous detection characteristics when the above photons are directly received. The simultaneous detection characteristics performed through the interferometer will be described with reference to FIG. For this explanation, it is assumed that receiver A 141 has detected a photon at a certain time t ′ ₃ . This photon is detected as a result of the interference of two pulses through the long and short paths of the interferometer. Therefore, the photon was present in either of these two pulses. However, it is not possible to specify which is the case. These two pulses are originally two pulses that are temporally adjacent. This _{t 2} pulses respectively, and _{t 3} pulses. (T _i is used in the sense of the time position of the photon pair generator output.) Then, by the nature of the quantum correlated photon pairs, in the pulse train to go to the receiver B 142, one of t ₂ pulse or t ₃ pulses Crab photons exist. It is not possible to specify which one is, but at least one of them has a photon. Since t ₂ pulse and t ₃ pulse both is exactly the same, the existence probability is one by 1/2. The receiver B 142 receives this pulse train via the interferometer (the optical branching circuit 5, the delay circuit 6, and the optical multiplexing circuit 7). At the interferometer output, as shown in FIG. 4, t ₂ pulses / t ₃ pulses are dispersed at times t ′ ₂ , t ′ ₃ , and t ′ ₄ . Therefore, the photon is detected at any one of these three times t ′ ₂ , t ′ ₃ , t ′ ₄ . However, it is uncertain and probabilistic at which time is detected.

When it is detected at time t _'3, it will be detected by the receiver A the same time, the simultaneous detection event. The probability that a photon was present in the t ₂ pulse or t ₃ pulse is 1/2, respectively, and this is branched into two by the interferometer, so the photon detection probability at t ′ ₂ is 1/2 × 1/2 = 1 / 4, the photon detection probability at t ′ ₃ is 1/4 + 1/4 = 1/2, and the photon detection probability at t ′ ₄ is 1/4. That is, the simultaneous detection probability is ½. This 1/2 is the probability that when receiver A detects a photon, it will be detected simultaneously with receiver B. Therefore, considering the probability μ that receiver A detects a photon, simultaneous detection probability = μ / 2, further consider the transmission transmittance α and simultaneous detection probability = μα ^2/2, and becomes. On the other hand, the simultaneous detection probability in the case of receiving normal pulse light is μ ² as in the case of direct detection even if an interferometer is present, as described above, since the photon detection events are independent of each other.

Utilizing the above characteristics relating to the simultaneous detection probability, the configuration of FIG. 1 according to the present invention can detect the presence / absence of complete interception wiretapping as described in the section of the prior art with reference to FIGS. In order to explain the principle, system parameters are described as follows.
μ: Photon pair generation level (average number of pairs per pulse) from the quantum correlation photon pair generator 11
N: number of pulses output from the quantum correlation photon pair generator 11
α: Transmission transmittance from the quantum correlation photon pair generator 11 to the photon detectors A and B,
N _b : Number of blocks sent by eavesdroppers A and B,
n: number of pulses in one block,
μ ′: Average number of photons per pulse in the block sent by eavesdroppers A and B.

  For simplicity, the branching ratio of the optical coupler (C5, C6) 101 is 1: 1, and the quantum correlation photon pair generator 11 to the photon detector (A1, B1, A2, B2, A0, B0) 8, 9 , 102 is commonly α.

When eavesdropping is not normal, the photon detection probability of the photon detector A0, B0 per pulse Myuarufa, simultaneous detection probability μα ^2/2 in the simultaneous detection probability Myuarufa ^2, also the interferometer output, since, in N pulses As seen, the photon detection count of the photon detectors A0 and B0 = Nμα, the photon detector A0-B0 simultaneous detection count = Nμα ² , and the interferometer output simultaneous detection count of the photon detectors A1, B1 / A2 and B2 = Nμα ² / 2.

On the other hand, in the case of complete interception eavesdropping, normal pulse light is input to the photon detector (A0, B0) 102, so that the photon detection probability of the photon detectors A0, B0 per pulse is μ ′, The simultaneous detection probability is μ ′ ² , and the simultaneous detection probability at the interferometer output is also μ ′ ² . Here, since it is assumed that the eavesdroppers A and B are immediately before the receivers A and B, the transmission transmittance at this time is set to 1. If there is a loss in the receiver including the detection efficiency of the photon detector, it may be included in μ ′. Since the light having the probability per pulse is n pulses × _Nb blocks, the photon detector A0. The photon detection count of B0 is N _b nμ ′, the photon detector A0-B0 simultaneous detection count is N _b nμ ′ ² , and the interferometer output simultaneous detection count of photon detectors A1, B1 / A2, B2 is N _b nμ ′ ^2. .

The eavesdroppers A and B must make sure that the operating state of the receiver does not change depending on the presence or absence of eavesdropping so that eavesdropping is not revealed. This can be expressed in terms of a photon detector A0. Conditions for the photon detection count of B0 to be unchanged Nμα = N _b nμ ′, (1)
Conditions for the simultaneous detection count of the photon detectors A0-B0 to be unchanged Nμα ² = N _b nμ ′ ² (2)
Photon detector A1, B1 / A2, conditions for simultaneous detection count in the interferometer output B2 is invariant _{^{Nμα 2/2 = N b nμ}} '2, (3)
These three conditions must be satisfied.

There are three equations to be satisfied in this way, whereas there are two parameters N _b n and μ ′ that can be manipulated by the eavesdroppers A and B (註: N _b and n are always integrated). Therefore, an eavesdropper cannot satisfy all the above three conditions. More specifically, since the conditions (2) and (3) cannot be satisfied at the same time, if parameters are set so that the eavesdroppers A and B satisfy the expressions (1) and (2), the expression ( If (3) is not satisfied and Expressions (1) and (3) are satisfied, Expression (2) is not satisfied. Thus, since it is impossible to generate false key information so as to satisfy the expressions (2) and (3) at the same time, the presence / absence of eavesdropping can be determined by comparing the two probabilities.

  Therefore, each of the information processing apparatuses 110 of the receivers A and B shown in FIG. 1 receives the required predetermined number of photons, and then receives the photon detectors A0. The photon detection times at B0 and the interferometer output stage (A1, B1 / A2, B2) are compared, the photon detectors A0-B0 simultaneous detection count, and the interferometers of the photon detectors A1, B1 / A2, B2 Calculate and compare output coincidence detection counts.

That is, when complete interception wiretapping is performed, as described in the equations (1) to (3), any of these counts is a predetermined value (a value when complete interception wiretap is not performed). Since they do not match, it is possible to determine that there is an eavesdropping action by detecting the mismatch. If it is determined that there is an eavesdropping action, the key information is discarded and the key generation is stopped.
As another method, as can be seen from the equations (2) and (3), when complete interception is not performed, the photon detector A0-B0 simultaneous detection count is Nμα ² , and the photon detectors A1, B1 / A2, the interferometer output simultaneous detection count of B2 is Nμα ^2/2, becomes, both count value becomes a mismatch in the case of completely blocking eavesdropping has taken place, the photon detector A0-B0 simultaneous detection count N _b nμ ′ ² , and the photon detectors A1, B1 / A2, and B2 have an interferometer output simultaneous detection count of N _b nμ ′ ² , and the two count values coincide with each other, so that the photon detector A0-B0 simultaneous detection count If the interferometer output simultaneous detection count matches, it can be determined that there is an eavesdropping action.

On the other hand, in the conventional system, since there is no means for monitoring the simultaneous detection count without using an interferometer for the transmitted photons, there are two conditions that the eavesdropper must satisfy, and the eavesdropper has two parameters (N By appropriately setting _b n, μ ′), it was possible to satisfy both of these conditions. For this reason, the conventional system is robust against branch eavesdropping, but is vulnerable to complete blocking eavesdropping. In order to solve this, in the present invention, a set of a probability of simultaneous detection of photons by both receivers A and B (photon simultaneous detection count) and a probability of simultaneous detection at the interferometer output (interferometer output simultaneous detection count) is , Sent when the photon has a quantum correlation (true key information) and when the photon does not have a quantum correlation (false key information generated by an eavesdropper) By newly providing a means for monitoring the simultaneous detection count for the photon without an interferometer, and bringing in a new condition based on this monitor output, the complete interception wiretap detection can be performed as described above.

(Other embodiments)
In the above, the preferred embodiment of the present invention has been described by way of example. However, the embodiment of the present invention is not limited to the above-described example, and the constituent members thereof are within the scope of the claims. Various modifications such as replacement, change, addition, increase / decrease in number, change in shape design, and the like are all included in the embodiment of the present invention.

It is a block diagram which shows the structure of the quantum correlation key distribution system of one Embodiment of this invention. It is a block diagram which shows the structural example of the information processing apparatus of FIG. It is a figure explaining the simultaneous detection of a photon, (A) is a case where it is a quantum correlation photon pair pulse train, (B) is an explanatory view showing the case of a normal pulse train. It is explanatory drawing which shows the simultaneous detection event when a photon is detected via the interferometer of each receiver of a quantum correlation key distribution system. It is a block diagram which shows the structure of the conventional quantum correlation key distribution system. It is a block diagram for demonstrating the complete interception wiretapping method. It is a wave form diagram which shows the transmission signal light of an eavesdropper in the complete interception wiretapping method.

Explanation of symbols

5 Optical branch circuit C1, C3 (Optical coupler)
6 Optical delay circuit La, Lb (optical delay line)
7 Optical multiplexing circuit C2, C4 (Optical coupler)
8 1st photon detector A1, B1
9 Second photon detector A2, B2
DESCRIPTION OF SYMBOLS 10 Information processing apparatus 11 Quantum correlation photon pair generator 12 Pump light source 13 Optical nonlinear medium 14 Normal transmission path 31, 32 Photon transmission path 41, 141 Receiver A
42,142 Receiver B
61 Eavesdropper A
62 Eavesdropper B
64,65 Coherent light source 66,67 Phase modulator 101 Optical branch circuit C5, C6 (optical coupler)
102 Third photon detectors A0, B0
DESCRIPTION OF SYMBOLS 110 Information processing apparatus 201 Processor 202 Memory 203 Analog / digital converter (A / D converter)
204 Line control unit 205 Bus 206 Terminal input / output control unit 207 Display and keyboard

Claims (6)

In a quantum key distribution device comprising a photon pair generator for generating photon pairs having a quantum correlation at regular intervals, and two receivers each receiving the photons of the photon pair via an optical transmission path,
Each receiver is
Direct photon detection means for directly detecting photons;
The light is branched into two by the optical branching means, and after giving a time delay equal to the generation interval of the photon pair to the light passing between the branched paths, the branched light is split by the optical multiplexing means having two output terminals. Optical interference detection means for multiplexing and detecting photons from two output terminals of the optical multiplexing means by respective photon detection means;
Light branching means for stochastically branching input light and outputting the light directly to the direct photon detection means and the light interference detection means,
By exchanging time information of photon detection in the optical interference detection means, using the bit information corresponding to the photon detection means that detected the photon in the optical interference detection means, a common bit string is generated as key information, And, using the detection result of the direct photon detection means and the detection result of the optical interference detection means, a photon simultaneous detection count and an interferometer output simultaneous detection count are calculated, and the calculated values are compared with respective predetermined values. And a quantum encryption key generating unit for determining whether or not there is an eavesdropping.   If the photon simultaneous detection count and the interferometer output simultaneous detection count do not match the predetermined values, the quantum encryption key generating means determines that there is an eavesdropping and discards the generated key information, or the key 2. The quantum key distribution apparatus according to claim 1, wherein the generation of information is stopped.   When the photon coincidence detection count and the interferometer output coincidence detection count coincide with each other, the quantum cryptography key generation unit determines that there is an eavesdropping and discards the generated key information or generates the key information. The quantum key distribution apparatus according to claim 1, wherein the quantum key distribution apparatus is stopped. A key for a quantum cryptography key distribution device comprising a photon pair generator for generating photon pairs having a quantum correlation at regular intervals, and two receivers each receiving the photons of the photon pair via an optical transmission line In the key information eavesdropping detection method for detecting information eavesdropping,
A procedure for stochastically branching the input light;
A direct photon detection procedure that directly detects the photons of the branched light;
The branched light is further branched, and after a time delay equal to the generation interval of the photon pair is given to the light passing between the one of the branched paths, the branched light is multiplexed by the optical multiplexing means, and the optical multiplexing is performed. A light interference detection procedure for respectively detecting photons from the two output terminals of the wave means;
Using the detection result of the direct photon detection procedure and the detection result of the optical interference detection procedure, a photon simultaneous detection count and an interferometer output simultaneous detection count are calculated, and the calculated values are compared with respective predetermined values. A key information eavesdropping detection method comprising: detecting the presence or absence of the key information eavesdropping.   The procedure for detecting the key information wiretapping is that if the photon simultaneous detection count and the interferometer output simultaneous detection count do not match the predetermined values, it is determined that there is wiretapping and the generated key information is discarded or the key 5. The key information eavesdropping detection method according to claim 4, wherein the generation of information is stopped. If the photon simultaneous detection count and the interferometer output simultaneous detection count match, the procedure for detecting the key information wiretapping determines that there is wiretapping and discards the generated key information or generates key information. The key information wiretapping detection method according to claim 4, wherein the key information wiretapping detection method is stopped.

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