JP7003007B2 - Quantum cryptography communication equipment, quantum cryptography communication system, quantum cryptography communication method and program - Google Patents

Description

Embodiments of the present invention relate to a quantum cryptographic communication device, a quantum cryptographic communication system, a quantum cryptographic communication method and a program.

The LDPC (Low Density Parity Check) code is attracting attention as an error correction code having an error correction capability very close to the Shannon limit, which is the theoretical limit value of the information transmission rate. Therefore, in the fields of communication and storage systems, studies such as implementing an LDPC decoder as hardware are being actively conducted.

“High speed and adaptive error correction for megabit / straight quantum key distribution”, A.I. R. Dixon et al, Scientific Reports 4, 2014 "Continuous operation of high bit rate quantum key distribution", A.I. R. Dixon et al, APPLIED PHYSICS LETERS 96, 161102 (2010) “Stability of high bit rate quantum key distribution on instant fiber”, A.I. R. Dixon et al, OPTICS EXPRESS 16339 Vol. 20, No. 15 (2012) “Efficient decoy-state quantum key distribution with quantified security”, M.D. Lucamarini et al, Optics Express Vol. 21, Issue 21, 2013

However, with the conventional technique, it is difficult to set the setting information of the error correction process more appropriately. An object to be solved by the present invention is to provide a quantum cryptographic communication device, a quantum cryptographic communication system, a quantum cryptographic communication method and a program capable of more appropriately setting the setting information of error correction processing.

The quantum cryptography communication device of the embodiment includes an estimation unit, a margin calculation unit, and a setting unit. The estimation unit estimates the estimation error rate of the shift key data. The margin calculation unit is based on the estimated error rate and the estimated error distribution showing the distribution of the probability that the estimated error a indicating the difference between the true value of the error rate of the shift key data and the estimated error rate occurs . A margin is calculated that indicates the rate at which the estimated error rate is estimated to be larger . The setting unit sets the setting information of the error correction processing of the shift key data based on the estimated error rate and the margin.

The figure which shows the example of the apparatus configuration of the quantum cryptography communication system of embodiment. The figure which shows the example of the functional structure of the quantum cryptography communication system of embodiment. The figure which shows the example of the functional structure of the error correction processing part of an embodiment. The figure which shows the example of the functional structure of the analysis part of embodiment. The figure which shows the example of the estimation error rate region of an embodiment. The figure which shows the example of the estimation error distribution of the estimation error rate region-3 of an embodiment. The figure which shows the value of the probability of the estimation error distribution of FIG. The flowchart which shows the example of the calculation method of the estimation error distribution of an embodiment. The flowchart which shows the example of the calculation method of the margin of an embodiment. The figure which shows the example of the distribution of the error rate in the estimation error rate region-3 of an embodiment. The figure which shows the example of the compression rate data table in the estimation error rate area-3 of an embodiment. The figure which shows the example of the expected value of the compression rate for every candidate value of the margin of an embodiment. The figure which shows the example of the estimation error distribution of an embodiment. The figure which shows the example of the efficiency property of an embodiment. The figure which shows the example (when σ = 1) of the expected value of the compression rate of an embodiment. The figure which shows the example (in the case of σ = 1.25) of the expected value of the compression rate of an embodiment. The figure which shows the example (when σ = 1.5) of the expected value of the compression rate of an embodiment. The figure which shows the example of the optimum value of the margin of an embodiment (in the case of σ = 1). The figure which shows the example of the optimum value of the margin of an embodiment (in the case of σ = 1.25). The figure which shows the example of the optimum value of the margin of an embodiment (in the case of σ = 1.5). The figure which shows the example of the hardware composition of the main part of the transmitting device and the receiving device of an embodiment.

When performing error correction processing, it is necessary to appropriately set setting information such as the coding rate. For example, a method of estimating the error rate of the quantum channel and setting the setting information from the estimated value and the margin of the estimation error with respect to the estimated value can be considered.

Refer to the attached drawings below for details of the quantum cryptography communication device, the quantum cryptography communication system, the quantum cryptography communication method, and the embodiment of the program, which can optimally control the margin for setting the setting information of the error correction processing. To explain to.

[Example of device configuration]
FIG. 1 is a diagram showing an example of a device configuration of the quantum cryptography communication system 100 of the embodiment. The quantum cryptographic communication system 100 of the embodiment includes two quantum cryptographic communication devices (transmitting device 10 and receiving device 20). The transmitting device 10 continuously transmits photons indicating qubits to the receiving device 20. In the embodiment, for convenience of explanation, the device on the side of transmitting photons is referred to as a transmitting device 10, but the transmitting device 10 may have a function of receiving photons. Similarly, the receiving device 20 may have a function of transmitting photons.

The transmitting device 10 and the receiving device 20 use the quantum key data to transmit and receive encrypted data. The details of the method of generating the quantum key data will be described with reference to FIG.

[Example of functional configuration]
FIG. 2 is a diagram showing an example of the functional configuration of the quantum cryptography communication system 100 of the embodiment. The quantum cryptography communication system 100 of the embodiment includes a transmission device 10 and a reception device 20.

The transmitting device 10 and the receiving device 20 are connected to each other via the quantum communication path 1. The quantum channel 1 is an optical fiber that transmits and receives photons indicating qubits. Since the quantum channel 1 transmits and receives very weak light called one photon, it is easily affected by disturbance.

Further, the transmitting device 10 and the receiving device 20 are connected via the classical communication path 2. The classical channel 2 transmits and receives control information for generating quantum key data 105 (205). The classical communication path 2 may be wired or wireless, or may be realized by combining wired and wireless.

The transmission device 10 includes a transmission unit 11, a shifting processing unit 12, an error correction processing unit 13, and a confidentiality enhancement processing unit 14.

The receiving device 20 includes a receiving unit 21, a shifting processing unit 22, an error correction processing unit 23, and a confidentiality enhancing processing unit 24.

The transmission unit 11 transmits a single photon to the reception unit 21 via the quantum (cryptographic) communication path 1. Then, the transmission unit 11 inputs the transmission photon data 101 to the shifting processing unit 12. When the receiving unit 21 receives a single photon from the transmitting device 10, the receiving photon data 201 is input to the shifting processing unit 22.

The shifting processing unit 12 selects data that can be used for the quantum key data 105 based on the control information communicated via the classical communication path 2, and generates the shift key data 103. Similarly, the shifting processing unit 22 selects data that can be used for the quantum key data 205 based on the control information communicated via the classical communication path 2, and generates the shift key data 203.

When the error correction processing unit 13 receives the shift key data 103 from the shifting processing unit 12, it generates a syndrome corresponding to the shift key data 103, and also generates the shift key data 103 as the correction key data 104 as it is. .. Similarly, when the error correction processing unit 23 receives the shift key data 203 from the shifting processing unit 22, the error correction processing unit 23 corrects the error included in the shift key data 203 to generate the correction key data 204.

Finally, when the confidentiality enhancement processing unit 14 receives the correction key data 104 from the error correction processing unit 13, the confidentiality enhancement processing for generating the quantum key data 105 is performed by compressing the correction key data 104. The security of the quantum key data 105 can be enhanced by the confidentiality enhancement processing performed by the confidentiality enhancement processing unit 14. Similarly, when the confidentiality enhancement processing unit 24 receives the correction key data 204 from the error correction processing unit 23, the confidentiality enhancement processing unit 24 performs the confidentiality enhancement processing to generate the quantum key data 205 by compressing the correction key data 204. The security of the quantum key data 205 can be enhanced by the confidentiality enhancement processing performed by the confidentiality enhancement processing unit 24.

Note that the error correction processing units 13 and 23 and the confidentiality enhancement processing units 14 and 24 transmit and receive control information necessary for processing via the classical communication path 2, similarly to the shifting processing units 12 and 22 described above. ..

FIG. 3 is a diagram showing an example of the functional configuration of the error correction processing units 13 and 23 of the embodiment. The error correction processing unit 13 of the receiving device 20 of the embodiment includes an inspection matrix generation unit 131 and a syndrome generation unit 132. The error correction processing unit 23 of the transmission device 20 of the embodiment includes an estimation unit 231, a setting unit 232, an inspection matrix generation unit 233, a decoding unit 234, an analysis unit 235, and a margin calculation unit 236.

First, the error correction processing unit 13 of the receiving device 20 takes out a part of the shift key data 103, generates the partial shift key data 106, and transfers the partial shift key data 106 to the estimation unit 231 via the classical channel 2. Send.

On the other hand, the error correction processing unit 23 of the transmission device 20 takes out a part of the shift key data 203, generates the partial shift key data 206, and inputs the partial shift key data 206 to the estimation unit 231. The estimation unit 231 compares the partial shift key data 106 with the partial shift key data 206, and estimates the estimated error rate 207 (estimated value of the error rate) of the quantum channel 1.

The setting unit 232 sets the setting information (for example, the coding rate 210) corresponding to the setting error rate and the setting error rate based on the margin for the estimation error of the error rate and the estimated error rate. The relational expression between the setting error rate, the estimated error rate, and the margin is setting error rate = estimated error rate × (1 + margin), and when the estimated error rate is 4% and the margin is 20%, the setting error rate. Is 4.8%. The setting unit 232 inputs the coding rate 210 to the inspection matrix generation unit 233 and transmits it to the inspection matrix generation unit 131 via the classical channel 2.

The check matrix generation unit 233 generates a check matrix 211 corresponding to the coding rate, and inputs the check matrix 211 to the decoding unit 234.

On the other hand, the inspection matrix generation unit 131 of the transmission device 10 generates the inspection matrix 107 corresponding to the coding rate received from the transmission device 20 via the classical communication path 2. The syndrome generation unit 132 uses the check matrix 107 to generate a syndrome 108 corresponding to the shift key data 103, and transmits the syndrome 108 to the decoding unit 234 via the classical channel 2.

The decoding unit 234 generates the correction key data 212 by correcting the error of the shift key data 203 by using the syndrome 108 and the check matrix 211, and the correction key data 212 is sent to the confidentiality enhancement processing unit 24. input. Further, in the transmission device 10, the error correction processing unit 13 inputs the shift key data 103 as the correction key data 104 into the confidentiality enhancement processing unit 14.

Further, the decoding unit 234 inputs the correction information 213 to the analysis unit 235. The correction information 213 includes the correction key data 212 and the correction result 216 (see FIG. 4). The correction result 216 is data indicating whether or not the error correction was successful.

When the analysis unit 235 receives the shift key data 203 from the shifting processing unit 22, the estimation error rate 207 is received from the estimation unit 231, the correction information 213 is received from the decoding unit 234, and the margin 209 is received from the margin calculation unit 236. The estimated error distribution 208 is analyzed. The details of the analysis process of the estimated error distribution 208 will be described later.

The margin calculation unit 236 calculates the optimum value of the margin 209 by using the estimation error distribution 208 according to the update timing of the margin, and updates the margin 209. The above is a series of flows of the error correction processing units 13 and 23.

FIG. 4 is a diagram showing an example of the functional configuration of the analysis unit 235 of the embodiment. The analysis unit 235 of the embodiment includes a true value calculation unit 2351, an estimation error calculation unit 2352, and an estimation error distribution calculation unit 2353.

First, when the true value calculation unit 2351 receives the shift key data 203 and the correction key data 212, the shift key data 203 and the correction key data 212 are compared, and the true value (actual error rate) of the error rate is obtained. calculate. Next, the estimation error calculation unit 2352 calculates the estimation error based on the difference between the true value of the error rate and the estimation error rate. Then, the estimation error distribution calculation unit 2353 calculates the estimation error distribution 208 from the margin 209, the true value 214 of the error rate, the estimation error 215, and the correction result 216. The estimation error is calculated by the estimation error = (true value of error rate-estimated error rate) / estimation error rate.

Next, the calculation method of the estimation error distribution 208 in the estimation error distribution calculation unit 2353 will be described, but before that, the data structure and terms of the estimation error distribution 208 of the embodiment will be described. The estimation error distribution 208 of the embodiment is calculated for each interval (estimation error rate region) of the estimation error rate 207 of the shift key data 203 (see FIG. 5).

FIG. 5 is a diagram showing an example of an estimated error rate region of the embodiment. In the example of FIG. 5, the estimation error distribution 208 is the estimation error distribution 208 of the estimation error rate region-1, the estimation error distribution 208 of the estimation error rate region-2, the estimation error distribution 208 of the estimation error rate region-3, and the estimation error. It is divided into an estimated error distribution 208 in the rate region-4 and an estimated error distribution 208 in the estimated error rate region-5. Here, the reference value of the error rate is a value (representative value) used when calculating the compression rate of the confidentiality enhancing process in each estimated error rate region.

Next, the estimation error distribution 208 of each estimation error rate region will be described. As a specific example, an example of the estimation error distribution 208 in the estimation error rate region-3 is shown in FIGS. 6 and 7.

FIG. 6 is a diagram showing an example of the estimation error distribution 208 of the estimation error rate region-3 of the embodiment. FIG. 7 is a diagram showing the value of the probability of the estimation error distribution 208 of FIG.

When the estimation error (a) is negative, it indicates that the true value of the error rate is smaller than the estimation error rate. For example, when the estimated error rate is 4% and the estimation error is −20%, the true value of the error rate is 3.2% (= 4% × (100% + (-20%))).

On the contrary, when the estimation error (a) is positive, it indicates that the true value of the error rate is larger than the estimation error rate. For example, when the estimated error rate is 4% and the estimated error is + 20%, the true value of the error rate is 4.8% (= 4% × (100% + 20%)). In the examples of FIGS. 6 and 7, the estimation error is divided into regions of every 5%, and the probability of occurrence of the estimation error is obtained for each estimation error section.

The estimation error distribution 208 of the embodiment includes an estimation error region A and an estimation error region B. The estimation error region A indicates the entire estimation error interval in which the estimation error is equal to or less than the margin 209 before the update (the margin 209 calculated by the previous margin calculation process and currently set). The estimation error region B shows the entire estimation error interval in which the estimation error exceeds the margin 209 before the update. In the example of FIG. 6, the margin 209 before update in the estimated error rate region-3 is C = 10%, where C is the size of the margin 209. Therefore, the estimation error region A is the entire estimation error interval in which the estimation error is C (= 10)% or less, and the estimation error region B is the entire estimation error interval in which the estimation error exceeds C (= 10)%.

The estimation error region A is a region in which the estimation error is smaller than the margin 209 before updating, and the setting error rate is larger than the true value of the error rate. In other words, it can be said that this is an area where error correction processing is successful. The estimated error distribution in this region can be calculated from the estimated error (difference between the true value of the error rate and the estimated error rate) when the error correction processing is successful.

On the other hand, in the estimation error region B, the estimation error is a region larger than the margin 209 before updating, and the setting error rate is a region smaller than the true value of the error rate. That is, it can be said that the estimation error area B is an area in which the error correction process always fails, so that the true value of the error rate cannot be obtained. Therefore, unlike the estimation error region A, the estimation error in the estimation error region B cannot be calculated accurately, so the following two items (α) and (β) are assumed.

(Α) The sum D of the probabilities of the estimation error region B is equal to the error correction failure probability when the margin 209 is set to C%.

Since it can be said that the estimation error area B is an area in which the error correction processing always fails, the sum of the probabilities of the estimation error area B has a property equal to the error correction failure probability when the margin 209 is set to a certain value. .. In the case of the example of FIG. 6, the value C of the margin 209 is 10%. Therefore, the error correction failure probability when the margin 209 is set to C% is the probability of the estimation error interval (5.8289%) in which the estimation error a is 10% <a≤15%, and the estimation error a is 15% <a≤. It is the sum (about 7.666606%) of the probability of the estimation error section of 20% (1.695023%) and the probability of the estimation error section of 20% <a (0.142144%). Therefore, the total D of the probabilities of the estimation error region B is about 7.66660%. The error correction failure probability when the margin 209 is set to C% can be calculated from the correction result 216.

(Β) The value of the margin 209 is C%, the sum of the probabilities of the estimation error region B is D%, the sum of the probabilities of the estimation error of −C% or less in the estimation error region A is E%, and the sum of the probabilities is E%. When the probability of the estimation error section where the estimation error a is −F% <a ≦ −G% is H%, the probability I of the estimation error section where the estimation error a in the estimation error region B is G% <a ≦ F% is , I = H × (D / E).

Item (β) is premised on the assumption that the way of changing the probability in the estimation error area B is the same as the way of changing the estimation error area A by −C% or more. For example, when the value C of the margin 209 is 10%, the estimation error region B has a value in which the estimation error a exceeds 10%. Estimated error a is 10% <a ≤ 15% probability of estimation error interval, estimation error a is 15% <a ≤ 20% probability of estimation error interval, and estimation error a is 20% <a The way in which the error interval probability changes is that the estimation error a is -15% <a− ≦ 10% in the estimation error region A, and the estimation error a is -20% <a− ≦. It means that the probability of the estimation error interval of 15% and the estimation error a are equal to the change of the probability of the estimation error interval of a− ≦ 20%. In the case of the example of FIG. 6, the value C of the margin 209 is 10%. The sum D of the probabilities of the estimation error region B is about 7.66660%. The total E of the probabilities of the estimation error interval with the estimation error of -10% or less in the estimation error region A is about 10.29181%, and the estimation error a in the estimation error region B is -15% <a≤10%. The probability H of the estimation error interval is 7.825385%. Therefore, the probability I of the estimation error interval in which the estimation error a of the estimation error region B is 10 (= G)% <a≤15 (= F)% is 7.825385 × (7.66606 / 10.29181) ≈5. It will be 8.8289%. Other estimation error intervals in the estimation error region B can be obtained in the same manner.

<Example of calculation method of estimated error distribution>
FIG. 8 is a flowchart showing an example of the calculation method of the estimation error distribution 208 of the embodiment. First, the estimation error distribution calculation unit 2353 determines the estimation error rate region from the estimation error rate 207 (step S1). The method for determining the estimated error rate region follows, for example, FIG.

Next, the estimation error distribution calculation unit 2353 calculates the error correction failure probability when the margin before update is set in the estimation error rate region determined by the process of step S1 (step S2).

Next, the estimation error distribution calculation unit 2353 calculates the estimation error distribution of the estimation error region A (step S3), and finally calculates the estimation error distribution of the estimation error region B (step S4). The estimation error distribution of the estimation error region A may be calculated based on the estimation error output from the estimation error calculation unit 2352. The procedure for calculating the estimated error distribution in the estimated error region B is as follows. The definitions of the alphabets C to I are the same as the above definitions.

(1) The error correction failure probability when the margin (C%) before update is set is read, and this value is set as the sum total D of the probabilities of the estimation error region B.
(2) Obtain the sum E of the probabilities that the estimation error is −C% or less in the estimation error region A.
(3) According to the above item (β), the probability of each estimated interval in the estimation error region B is calculated.

<Example of margin calculation method>
FIG. 9 is a flowchart showing an example of the calculation method of the margin 209 of the embodiment. First, the margin calculation unit 236 calculates the error rate distribution in the estimated error rate region using the estimated error distribution in the estimated error rate region (see FIG. 5) to be the margin calculation target (step S11). The details of the calculation method of the error rate distribution in the estimated error rate region will be described later.

Next, the margin calculation unit 236 refers to a compression rate data table showing the compression rate of the confidentiality enhancement process when the candidate value of the margin 209 is set in each error rate region of the error rate distribution (step S12). .. The details of the compression rate data table will be described later.

Next, the margin calculation unit 236 calculates the expected value of the compression rate when the candidate value of the margin 209 is set in each error rate region of the error rate distribution (step S13), and the expected value of the compression rate. The candidate value of the margin 209 that maximizes is selected as the margin 209 in the error rate region (step S14). The above is an example of the calculation method of the margin 209.

Next, a method of calculating the margin 209 will be described with specific numerical values. The case where the setting of the estimated error rate region is shown in FIG. 5 and the optimum value of the margin 209 of the estimated error rate region-3 is obtained will be described. The estimation error distribution of the estimation error rate region-3 is shown in FIGS. 6 and 7, and the candidate values of the margin 209 are 0%, 5%, 10%, 15%, and 20%.

First, the margin calculation unit 236 obtains the distribution of the error rate in the estimated error rate region-3 from the estimated error distribution in the estimated error rate region-3. Specifically, the margin calculation unit 236 calculates the error rate Q from the reference value 4% of the error rate in the estimation error rate region-3 and the estimation error a. For example, for an estimation error interval in which the estimation error a is -5% <a≤0%, the error rate Q is 3.8% <Q≤4%, and the estimation error a is 0% <a≤5%. For the interval, the error rate Q is 4% <Q≤4.2%, and for the estimation error interval where the estimation error a is 5% <a≤10%, the error rate is 4.2% <Q≤4.4. It shall be less than%. The other estimation error intervals are converted in the same manner. The margin calculation unit 236 also determines a representative value of the error rate in each error rate interval. The representative value shall be a value within the range of each error rate interval. As a result of the conversion, the distribution of the error rate is as shown in FIG.

FIG. 10 is a diagram showing an example of the distribution of the error rate in the estimated error rate region-3 of the embodiment. The error rate distribution shown in FIG. 10 is equal to the actual error rate distribution when the error rate of the quantum channel 1 is estimated to be 4%.

Next, the margin calculation unit 236 refers to the compression rate of the confidentiality enhancement processing when each candidate value of the margin 209 is used. The compression ratio is (data length of the quantum key output per confidentiality enhancement process / data length of the correction key input per confidentiality enhancement process), and the correction capability of the error correction method. And in accordance with Non-Patent Document 4, it is obtained in advance. The value of the compression rate is stored in the compression rate data table in the margin calculation unit 236.

FIG. 11 is a diagram showing an example of a compression rate data table in the estimation error rate region-3 of the embodiment. The representative value of the error rate in the compression rate data table of FIG. 11 corresponds to the error rate of the shift key data 203 of the receiving device 20. The compression rate data table of FIG. 11 shows the compression rate when the margin 209 is changed from 0% to 20% in 5% increments. The correctable error rate is the maximum value of the error rate that can be corrected by the error correction process. For example, if the margin is 0%, the correctable error rate is 4%, if the margin is 5%, the correctable error rate is 4.2%, and if the margin is 10%, the correctable error rate is 4.4%. When the margin is 15%, the correctable error rate is 4.6%, and when the margin is 20%, the correctable error rate is 4.8%.

For example, when the correctable error rate is 4.0% and the representative value of the error rate is 3.8% (the error rate of the shift key data 203 is 3.8%), the above-mentioned setting error rate is 4. Error correction processing is performed using the check matrix with the coding rate corresponding to 0%. Then, in the confidentiality enhancement process, the correction key data 204 is compressed to 0.24765, so that the quantum key data 205 is generated.

Further, for example, when the correctable error rate is 4.0% and the representative value of the error rate is 4.2% (the error rate of the shift key data 203 is 4.2%), the above-mentioned setting error rate is 4. Error correction processing is performed using a code rate check matrix corresponding to 0.0%. In this case, since the error correction processing unit 23 fails to correct the error, the correction key data 212 is not transmitted to the confidentiality enhancement processing unit 24, and the quantum key data 205 is not generated. Therefore, if the correctable error rate is 4.0% and the representative value of the error rate is 4.2% (the error rate of the shift key data 203 is 4.2%), it becomes 0 (correction failure). ..

Next, the margin calculation unit 236 calculates the expected value of the compression rate when each candidate value of the margin 209 is used. In the case of this example (estimated error rate region-3), the expected value of the compression rate of each candidate value of the margin 209 is calculated using the error rate distribution shown in FIG. 10 and the compression rate table shown in FIG. do.

First, when the margin calculation unit 236 obtains the expected value of the compression rate when the margin 209 is set to 0%, the probability corresponding to the representative value of each error rate in FIG. 10 and the margin in FIG. 11 are 0%. Multiply the compression rate corresponding to the representative value of each error rate in the case. For example, the probability (0.19083%) when the representative value of the error rate in FIG. 10 is 3.2%, and 0 when the margin in FIG. 11 is 0% and the representative value of the error rate is 3.2%. Multiply with 27933.

The margin calculation unit 236 calculates the expected value of the compression rate at each candidate value of the margin 209 by adding all the values multiplied by the representative value of each error rate. For example, the error rate distribution shown in FIG. 10 and the expected value of the compression rate when the margin 209 is 0% calculated using the compression rate table shown in FIG. 11 are 0.130765409.

FIG. 12 is a diagram showing an example of an expected value of the compression rate for each candidate value of the margin 209 of the embodiment. The margin calculation unit 236 calculates the expected value of the compression rate of each candidate value of the margin 209, and then selects the candidate value of the margin 209 at which the expected value becomes the maximum value as the update value of the margin 209. In the case of the example of FIG. 12, when the margin 209 is 15%, the expected value of the compression rate is the maximum, so that the update value of the margin 209 of the error rate estimation region-3 is 15%.

The margin calculation unit 236 calculates the updated value of the above margin 209 in the total estimated error rate region, and updates the margin 209 in the total estimated error rate region.

Here, the relationship between the variation in the estimation error distribution and the size of the margin 209 will be described.

FIG. 13 is a diagram showing an example of the estimation error distribution of the embodiment. For example, if the estimation error distribution has a large variation (in FIG. 13, the standard deviation σ becomes large) and the margin 209 is set small (for example, set to 0%), the error correction failure probability becomes very large. As a result, the quantum key generation speed decreases. Therefore, when the variation in the estimation error distribution is large, the margin 209 needs to be larger than when the variation in the estimation error distribution is small.

On the contrary, when the variation of the estimation error distribution is small (in FIG. 13, the standard deviation σ is small), the error correction failure probability is small even if the margin is made smaller than that when the variation of the estimation error distribution is large. Therefore, the quantum key generation speed can be optimized by making the margin setting amount variable according to the variation in the estimation error distribution.

Further, when the compression rate of the quantum key data 205 is calculated based on Non-Patent Document 4, the larger the error rate of the quantum communication path 1, the greater the influence of the transmission data length of the syndrome 108 on the compression rate.

FIG. 14 is a diagram showing an example of efficiency characteristics of the embodiment. In the example of FIG. 14, the efficiency characteristics of the compression rate at each error rate are shown. The graph of FIG. 14 is calculated based on Non-Patent Document 4.

The horizontal axis of FIG. 14 is efficacy, which is the syndrome data length used in the actual error correction when the code-theoretical minimum value (minimum value based on the Shannon limit) of the syndrome data length required for error correction is 1. That is, the larger the efficiency, the larger the syndrome data length used in the actual error correction.

The vertical axis of FIG. 14 is the compression rate, but each error rate is standardized to the compression rate when the efficiency is 1. As can be seen from FIG. 14, as the efficiency increases, the compression rate decreases, and the amount of quantum key data 205 generated at one time decreases. This is because the amount of data flowing on the classical channel 2 increases as the efficiency increases. It can also be seen that the higher the error rate, the higher the rate of decrease in the compression rate when the efficiency increases.

Regarding the relationship between the margin 209 and the efficiency, the larger the margin 209, the larger the communication amount of the syndrome 108 as a result, and therefore the larger the efficiency. Therefore, the higher the error rate, the larger the decrease in the compression rate due to the increase in the margin, so the margin must be set small. By changing the margin according to the error rate as in the present embodiment, the generation speed of the quantum key data 205 can be optimized.

FIG. 15A is a diagram showing an example of an expected value of the compression rate of the embodiment (when σ = 1). FIG. 15B is a diagram showing an example of an expected value of the compression rate of the embodiment (in the case of σ = 1.25). FIG. 15C is a diagram showing an example of an expected value of the compression rate of the embodiment (in the case of σ = 1.5). FIG. 16A is a diagram showing an example (when σ = 1) of the optimum value of the margin 209 of the embodiment. FIG. 16B is a diagram showing an example of the optimum value of the margin 209 of the embodiment (in the case of σ = 1.25). FIG. 16C is a diagram showing an example of the optimum value of the margin 209 of the embodiment (when σ = 1.5).

As can be seen from FIGS. 16A to 16C, in the case of all standard deviations σ, the larger the error rate, the smaller the optimum value of the margin 209. Further, in most cases, the larger the standard deviation σ of the estimation error distribution, the larger the optimum value of the margin 209.

The parameter setting example including the estimation error rate region described above is an example, and may be changed in any way. Further, the update timing of the margin 209 may be arbitrary. For example, the margin 209 may be recalculated when sufficient new data is accumulated to update the margin 209. Also, for example, the margin 209 may be updated (regularly) every time a predetermined time elapses. If the number of samples used in the calculation of the estimated error rate distribution is very small, the initial value of the margin 209 when the quantum cryptography communication operation is started is used as the margin instead of the margin 209 obtained by the margin calculation unit 236. It may be used as an update value of 209.

Finally, an example of the hardware configuration of the transmitting device 10 and the receiving device 20 of the embodiment will be described.

[Example of hardware configuration]
FIG. 17 is a diagram showing an example of the configuration of the main parts of the transmitting device 10 and the receiving device 20 of the embodiment. The transmitting device 10 and the receiving device 20 of the embodiment include a control device 301, a main storage device 302, an auxiliary storage device 303, a display device 304, an input device 305, a quantum communication IF (Interface) 306, and a classical communication IF 307.

The control device 301, the main storage device 302, the auxiliary storage device 303, the display device 304, the input device 305, the quantum communication IF 306, and the classical communication IF 307 are connected via the bus 310.

The control device 301 executes the program read from the auxiliary storage device 303 to the main storage device 302. The main storage device 302 is a memory such as a ROM (Read Only Memory) and a RAM (Random Access Memory). The auxiliary storage device 303 is an HDD (Hard Disk Drive), a memory card, or the like.

The display device 304 displays the status of the transmitting device 10 and the receiving device 20 and the like. The input device 305 accepts input from the user.

The quantum communication IF 306 is an interface for connecting to the quantum communication path 1. The classical communication IF 307 is an interface for connecting to the classical communication path 2.

The program executed by the transmitting device 10 and the receiving device 20 of the embodiment is a file in an installable format or an executable format, such as a CD-ROM, a memory card, a CD-R, and a DVD (Digital Versaille Disc). It is stored on a computer-readable storage medium and provided as a computer program product.

Further, the program executed by the transmitting device 10 and the receiving device 20 of the embodiment may be stored on a computer connected to a network such as the Internet and provided by downloading via the network.

Further, the program executed by the transmitting device 10 and the receiving device 20 of the embodiment may be configured to be provided via a network such as the Internet without being downloaded.

Further, the program executed by the transmitting device 10 and the receiving device 20 of the embodiment may be configured to be provided by incorporating it into a ROM or the like in advance.

The program executed by the transmitting device 10 and the receiving device 20 of the embodiment has a module configuration including functions that can be realized by the program among the functional configurations of the transmitting device 10 and the receiving device 20 of the embodiment.

The function realized by the program is loaded into the main storage device 302 by the control device 301 reading the program from the storage medium such as the auxiliary storage device 303 and executing the program. That is, the function realized by the program is generated on the main storage device 302.

A part or all of the functions of the transmitting device 10 and the receiving device 20 of the embodiment may be realized by hardware such as an IC (Integrated Circuit). The IC is, for example, a processor that executes dedicated processing.

Further, when each function is realized by using a plurality of processors, each processor may realize one of each function, or may realize two or more of each function.

Further, the operation mode of the transmission device 10 and the reception device 20 of the embodiment may be arbitrary. The transmitting device 10 and the receiving device 20 of the embodiment may be operated as devices constituting a cloud system on a network, for example.

As described above, in the receiving device 20 (quantum cryptography communication device) of the embodiment, the estimation unit 231 estimates the estimation error rate 207 of the shift key data 203. The margin calculation unit 236 calculates the margin 209 of the estimated error rate 207 based on the estimated error rate 207. Then, the setting unit 232 sets the setting information (for example, the coding rate 210) of the error correction processing of the shift key data 203 based on the estimated error rate 207 and the margin 209. Thereby, according to the receiving device 20 of the embodiment, the setting information of the error correction processing can be set more appropriately.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

10 Transmitter 11 Transmitter 12 Shifting processing unit 13 Error correction processing unit 14 Confidentiality enhancement processing unit 20 Receiver 21 Receiver unit 22 Shifting processing unit 23 Error correction processing unit 24 Confidentiality enhancement processing unit 100 Quantum cryptography communication system 131 Inspection matrix generation unit 132 Syndrome generation unit 231 Estimating unit 232 Setting unit 233 Inspection matrix generation unit 234 Decoding unit 235 Analysis unit 236 Margin calculation unit 301 Control device 302 Main memory device 303 Auxiliary storage device 304 Display device 305 Input device 306 Quantum communication IF
307 Classic communication IF
310 Bus 2351 True value calculation unit 2352 Estimated error calculation unit 2353 Estimated error distribution calculation unit

Claims (9)

An estimation unit that estimates the estimation error rate of shift key data,
The estimated error rate is calculated based on the estimated error rate and the estimated error distribution showing the distribution of the probability that the estimated error a indicating the difference between the true value of the error rate of the shift key data and the estimated error rate is generated. A margin calculation unit that calculates a margin that indicates a larger estimation rate ,
A setting unit for setting setting information for error correction processing of the shift key data based on the estimated error rate and the margin.
Quantum cryptographic communication device equipped with. The margin calculation unit updates the margin for each interval of the estimation error rate of the shift key data.
The quantum cryptography communication device according to claim 1. The margin calculation unit uses the compression rate of the confidentiality enhancement processing according to the error rate determined for each candidate value of the margin and the estimated error distribution, and the compression is performed for each candidate value of the margin. The margin is calculated by calculating the expected value of the rate and selecting the candidate value of the margin that maximizes the expected value.
The quantum cryptography communication device according to claim 1 . The margin calculation unit updates the margin by calculating the margin at a predetermined timing, and when the value of the margin before the update is C%, the estimation error a is estimated to be a ≦ C%. The estimation error distribution is calculated by dividing the error region A and the estimation error region B in which the estimation error a is C% <a.
The quantum cryptography communication device according to claim 1 . When the sum of the probabilities of the estimation error region B is D%, D is equal to the error correction failure probability when the margin is C%.
The quantum cryptography communication device according to claim 4 . The sum of the probabilities of the estimation error interval in which the estimation error a is a ≦ −C% or less in the estimation error region A is E%, and the estimation error a in the estimation error region A is −F% <a ≦ −G%. When the probability of the error interval is H%, the probability I of the estimation error interval in which the estimation error a in the estimation error region B is G% <a≤F% is calculated by I = H × (D / E).
The quantum cryptography communication device according to claim 4 . It is a quantum cryptographic communication system in which a transmitting device and a receiving device are connected via a quantum communication path.
The receiving device is
An estimation unit that estimates the estimation error rate of shift key data,
The estimated error rate is calculated based on the estimated error rate and the estimated error distribution showing the distribution of the probability that the estimated error a indicating the difference between the true value of the error rate of the shift key data and the estimated error rate is generated. A margin calculation unit that calculates a margin that indicates a larger estimation rate ,
A setting unit for setting setting information for error correction processing of the shift key data based on the estimated error rate and the margin.
Quantum cryptographic communication system. Steps to estimate the estimation error rate of shift key data,
The estimated error rate is calculated based on the estimated error rate and the estimated error distribution showing the distribution of the probability that the estimated error a indicating the difference between the true value of the error rate of the shift key data and the estimated error rate a occurs. Steps to calculate the margin, which indicates the higher estimated percentage, and
A step of setting setting information for error correction processing of the shift key data based on the estimated error rate and the margin, and
Quantum cryptography communication method including. Computer,
An estimation unit that estimates the estimation error rate of shift key data,
The estimated error rate is calculated based on the estimated error rate and the estimated error distribution showing the distribution of the probability that the estimated error a indicating the difference between the true value of the error rate of the shift key data and the estimated error rate is generated. A margin calculation unit that calculates a margin that indicates a larger estimation rate ,
A setting unit that sets setting information for error correction processing of the shift key data based on the estimated error rate and the margin.
A program to function as.

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