A QKD post-processing method based on BP decoding

Abstract

The present invention discloses a QKD post-processing method based on BP decoding, which is used in a QKD system. The QKD system includes N pairs of transmitters and receivers, where N≥1, and the method includes the following steps: S1: obtaining the original quantum key; S2: performing key screening; S3: performing parameter estimation to obtain a quantum bit error rate; S4: judging whether the quantum bit error rate is lower than a preset bit error rate threshold; S5: performing error negotiation on the remaining post-screening quantum keys using a polarization code combined with BP decoding, so that the transmitter and the receiver obtain a consistent quantum key string; S6: obtaining the final quantum key. The present invention discloses a QKD post-processing method based on BP decoding, which accelerates the decoding time by introducing a BP decoding algorithm in the error negotiation process of QKD post-processing, solves the problem of unsatisfactory decoding performance of the polarization code in the SC decoding algorithm when the code length is short or medium, thereby improving the error negotiation efficiency, and is widely used in QKD systems and quantum networks.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum secure communication and quantum network, and in particular to a QKD post-processing method based on BP decoding. Background Art

[0002] Quantum Key Distribution (QKD) is the most mature and widely used in the field of quantum secure communication, and its security is based on the laws of physics.

[0003] A complete QKD process consists of two steps: (1) preparation, distribution and measurement of quantum states; (2) post-processing. In practice, due to channel attenuation, noise, and the limitations of detection technology, the key obtained through quantum channel transmission is not completely secure. In order to further improve security, the legitimate communicating parties need to post-process part of the key.

[0004] At present, some QKD post-processing solutions will use polarization codes in the error negotiation process. Although the encoding and decoding algorithms of polarization codes have relatively low complexity, and according to the polarization characteristics of polarization codes, when the code length of polarization codes tends to infinity, the channel is almost completely polarized, so its performance is superior on long codes; however, in the case of medium and short code lengths, due to incomplete channel polarization, the SC decoding performance of polarization codes is lacking, and it is impossible to achieve the same superior performance as in the long code case, resulting in insufficient efficiency of error negotiation. Summary of the invention

[0005] In order to solve the problem that the error negotiation efficiency of the current polarization code is not high enough when the code length is medium or short, the present invention provides a QKD post-processing method based on BP decoding.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A QKD post-processing method based on BP decoding is used in a QKD system, wherein the QKD system includes N pairs of transmitting ends and receiving ends, where N≥1, and the method includes the following steps:

[0008] S1: The sender and receiver each obtain a string of original quantum keys of equal length after information transmission;

[0009] S2: The sender and the receiver perform key screening based on the original quantum key and obtain the screened quantum keys of equal length respectively;

[0010] S3: The sending end and the receiving end randomly select some of the sieved quantum keys for parameter estimation to obtain the quantum bit error rate;

[0011] S4: determining whether the quantum bit error rate is lower than a preset bit error rate threshold;

[0012] If yes, execute step S5;

[0013] If not, return to step S1;

[0014] S5: Use polarization codes combined with BP decoding to perform error negotiation on the remaining post-screening quantum keys, so that the sender and receiver obtain a consistent quantum key string;

[0015] S6: Use the hash function to compress the quantum key string to obtain the final quantum key.

[0016] In the above scheme, the BP decoding algorithm is introduced in the error negotiation process of QKD post-processing to accelerate the decoding time, solve the problem of unsatisfactory decoding performance of the SC decoding algorithm for polar codes in medium and short code lengths, and thus improve the error negotiation efficiency.

[0017] Preferably, in step S1, the transmitting end and the receiving end transmit information through a quantum channel.

[0018] Preferably, step S2 is specifically as follows: the receiving end first announces the moment when the quantum is detected, and then the sending end and the receiving end perform basis vector comparison and time comparison, discard the key bits at the moment when the quantum is not received by the receiving end, and retain the available key as the screened quantum key according to the actually selected quantum key distribution protocol.

[0019] Preferably, in step S3, the transmitting end and the receiving end respectively randomly select 50% of the sieved quantum keys for parameter estimation.

[0020] Preferably, in step S3, the randomly selected post-sieving quantum key is made public via a classical channel.

[0021] Preferably, in step S3, the estimated parameters include transmission rate and noise.

[0022] Preferably, in step S5, polar code construction is performed by using a genetic algorithm combined with BP decoding, including the following steps:

[0023] S51: Generate codeword structures under different signal-to-noise ratio conditions as initial populations;

[0024] S52: Calculate the fitness of each individual in the population, and select the individuals to be inherited according to the fitness; wherein the fitness is the bit error rate obtained by BP decoding statistics;

[0025] S53: Perform mutation and crossover operations on the individuals selected to be inherited, generate mutation and crossover offspring, and obtain a new population;

[0026] S54: repeat steps S32 to S33 until the maximum number of evolution times is reached;

[0027] S55: Select an optimal solution from the output codeword set to obtain an optimal codeword structure.

[0028] Preferably, the BP decoding process is as follows:

[0029] Assuming that the polar code length is N, according to the factor graph including N(m+1) nodes, the information L propagated from the right and the information R propagated from the left are used to complete the information update of each processing unit. The formula is as follows:

[0030]

[0031] Among them, m represents the number of factor graph stages, i represents the number of factor graph layers, j represents the number of factor graph nodes, and t represents the decoding position;

[0032] Until the calculation of L values ​​of all leftmost nodes is completed, the decoding decision is made according to the following formula:

[0033]

[0034] Wherein, T represents the maximum number of code words.

[0035] Preferably, in step S31, a Gaussian approximation construction algorithm is used to generate codeword structures under different signal-to-noise ratio conditions.

[0036] Preferably, in step S32, the individuals retained for inheritance are selected according to the truncation selection method.

[0037] Beneficial technical effects of the present invention:

[0038] The present invention provides a QKD post-processing method based on BP decoding, which accelerates the decoding time by introducing the BP decoding algorithm in the error negotiation process of QKD post-processing, solves the problem of unsatisfactory decoding performance of the SC decoding algorithm of polar codes in medium and short code lengths, thereby improving the error negotiation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the framework of the QKD post-processing process in the present invention;

[0040] Figure 2 It is a flow chart of the implementation steps of the technical solution of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments, but the scope of protection claimed in the present invention is not limited to the following specific embodiments.

[0042] Example 1

[0043] like Figure 1-2 As shown, a QKD post-processing method based on BP decoding is used in a QKD system, wherein the QKD system includes N pairs of transmitting ends and receiving ends, where N≥1, and the method includes the following steps:

[0044] S1: The sender and receiver each obtain a string of original quantum keys of equal length after information transmission;

[0045] S2: The sender and the receiver perform key screening based on the original quantum key and obtain the screened quantum keys of equal length respectively;

[0046] In actual implementation, information transmission and key screening are realized by the key screening units at the sending and receiving ends;

[0047] S3: The sending end and the receiving end randomly select some of the sieved quantum keys for parameter estimation to obtain the quantum bit error rate;

[0048] In actual implementation, the parameter estimation of the post-screening quantum key is realized through the parameter estimation units at the transmitting end and the receiving end;

[0049] S4: determining whether the quantum bit error rate is lower than a preset bit error rate threshold;

[0050] If yes, execute step S5;

[0051] If not, return to step S1;

[0052] S5: Use polarization codes combined with BP decoding to perform error negotiation on the remaining post-screening quantum keys, so that the sender and receiver obtain a consistent quantum key string;

[0053] In actual implementation, error negotiation is performed on the remaining post-screening quantum key through error negotiation units at the transmitting end and the receiving end;

[0054] S6: Use the hash function to compress the quantum key string to obtain the final quantum key;

[0055] In actual implementation, the quantum key string is compressed using a hash function through the confidentiality enhancement units at the sending and receiving ends to obtain the final quantum key.

[0056] In the specific implementation process, the BP decoding algorithm is introduced in the error negotiation process of QKD post-processing to accelerate the decoding time and solve the problem of unsatisfactory decoding performance of the SC decoding algorithm for polar codes in medium and short code lengths, thereby improving the error negotiation efficiency.

[0057] Example 2

[0058] A QKD post-processing method based on BP decoding comprises the following steps:

[0059] S1: The sender and receiver each obtain a string of original quantum keys of equal length after information transmission;

[0060] More specifically, in step S1, the transmitting end and the receiving end transmit information through a quantum channel.

[0061] S2: The sender and the receiver perform key screening based on the original quantum key and obtain the screened quantum keys of equal length respectively;

[0062] More specifically, step S2 is as follows: the receiving end first announces the moment when the quantum is detected, and then the sending end and the receiving end perform basis vector comparison and time comparison, discard the key bits at the moment when the quantum is not received by the receiving end, and retain the available key as the screened quantum key according to the actually selected quantum key distribution protocol.

[0063] S3: The sending end and the receiving end randomly select some of the sieved quantum keys for parameter estimation to obtain the quantum bit error rate;

[0064] More specifically, in step S3, the transmitting end and the receiving end respectively randomly select 50% of the sieved quantum keys for parameter estimation.

[0065] More specifically, in step S3, a randomly selected post-sieving quantum key is made public via a classical channel.

[0066] More specifically, in step S3, the estimated parameters include transmission rate and noise.

[0067] In the specific implementation process, the sender and the receiver use public information to count the parameters of the quantum transmission channel, and estimate the upper limit of the amount of information that a potential eavesdropper may know based on the statistical parameters, so as to decide whether to continue communication.

[0068] S4: determining whether the quantum bit error rate is lower than a preset bit error rate threshold;

[0069] If yes, execute step S5;

[0070] If not, return to step S1;

[0071] S5: Use polarization codes combined with BP decoding to perform error negotiation on the remaining post-screening quantum keys, so that the sender and receiver obtain a consistent quantum key string;

[0072] In the specific implementation process, error correction technology is used in the error negotiation process to eliminate the difference in the quantum key after screening. The error correction part is implemented using polarization code, including the encoding construction and decoding of polarization code. Among them, the polarization code encoding is optimized and constructed by genetic algorithm.

[0073] More specifically, in step S5, polar code construction is performed by using a genetic algorithm combined with BP decoding, including the following steps:

[0074] S51: Generate codeword structures under different signal-to-noise ratio conditions as initial populations;

[0075] S52: Calculate the fitness of each individual in the population, and select the individuals to be inherited according to the fitness; wherein the fitness is the bit error rate obtained by BP decoding statistics;

[0076] S53: Perform mutation and crossover operations on the individuals selected to be inherited, generate mutation and crossover offspring, and obtain a new population;

[0077] S54: repeating steps S32 to S33 until the maximum number of evolution times is reached or a preset condition is met;

[0078] S55: Select an optimal solution from the output codeword set to obtain an optimal codeword structure.

[0079] In the specific implementation process, by improving the calculation of the fitness function of the genetic algorithm during the construction of polarization codes, the BP decoding algorithm is introduced to accelerate the decoding time, thereby optimizing the error correction code construction algorithm for error negotiation in QKD post-processing, accelerating the running time and efficiency of the construction algorithm, and improving the efficiency of the codeword as a whole.

[0080] More specifically, the BP decoding process is as follows:

[0081] Assuming that the polar code length is N and the information bit length is K, according to the factor graph including N(m+1) nodes, the information L propagated from the right and the information R propagated from the left are used to complete the information update of each processing unit. The formula is as follows:

[0082]

[0083] Among them, m represents the number of factor graph stages, i represents the number of factor graph layers, j represents the number of factor graph nodes, and t represents the decoding position;

[0084] g(x,y)=sign(x)sign(y)min(x,y);

[0085] Until the calculation of L values ​​of all leftmost nodes is completed, the decoding decision is made according to the following formula:

[0086]

[0087] Wherein, T represents the maximum number of code words.

[0088] More specifically, in step S31, a Gaussian approximation construction algorithm is used to generate codeword structures under different signal-to-noise ratio conditions.

[0089] More specifically, in step S32, individuals remaining to be inherited are selected according to the truncation selection method.

[0090] S6: Use the hash function to compress the quantum key string to obtain the final quantum key.

[0091] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs may also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the invention should also fall within the scope of protection of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A QKD post-processing method based on BP decoding, used in a QKD system, wherein the QKD system comprises N pairs of transmitting ends and receiving ends, N≥1, characterized in that: The method comprises the following steps: S1: The sender and receiver each obtain a string of original quantum keys of equal length after information transmission; S2: The sender and the receiver perform key screening based on the original quantum key to obtain the screened quantum keys of equal length. S3: The sending end and the receiving end randomly select some of the sieved quantum keys for parameter estimation to obtain the quantum bit error rate; S4: determining whether the quantum bit error rate is lower than a preset bit error rate threshold; If yes, execute step S5; If not, return to step S1; S5: Use polarization codes combined with BP decoding to perform error negotiation on the remaining post-screening quantum keys, so that the sender and receiver obtain a consistent quantum key string; S6: Use the hash function to compress the quantum key string to obtain the final quantum key.

2. A QKD post-processing method based on BP decoding according to claim 1, characterized in that: In step S1, the sending end and the receiving end transmit information through a quantum channel.

3. A QKD post-processing method based on BP decoding according to claim 1, characterized in that: Step S2 is specifically as follows: the receiving end first announces the moment when the quantum is detected, and then the sending end and the receiving end perform basis vector comparison and time comparison, discard the key bits at the moment when the quantum is not received by the receiving end, and retain the available key as the screened quantum key according to the actually selected quantum key distribution protocol.

4. A QKD post-processing method based on BP decoding according to claim 1, characterized in that: In step S3, the transmitting end and the receiving end respectively randomly select 50% of the sieved quantum keys for parameter estimation.

5. A QKD post-processing method based on BP decoding according to claim 1 or 4, characterized in that: In step S3, the randomly selected post-sieving quantum key is made public via a classical channel.

6. A QKD post-processing method based on BP decoding according to claim 1, characterized in that: In step S3, the estimated parameters include transmission rate and noise.

7. A QKD post-processing method based on BP decoding according to claim 1, characterized in that: In step S5, polar code construction is performed by using a genetic algorithm combined with BP decoding, including the following steps: S51: Generate codeword structures under different signal-to-noise ratio conditions as initial populations; S52: Calculate the fitness of each individual in the population, and select the individuals to be inherited according to the fitness; wherein the fitness is the bit error rate obtained by BP decoding statistics; S53: Perform mutation and crossover operations on the individuals selected to be inherited, generate mutation and crossover offspring, and obtain a new population; S54: repeat steps S32 to S33 until the maximum number of evolution times is reached; S55: Select an optimal solution from the output codeword set to obtain an optimal codeword structure.

8. A QKD post-processing method based on BP decoding according to claim 1 or 7, characterized in that: The BP decoding process is as follows: Assuming that the polar code length is N, according to the factor graph including N(m+1) nodes, the information L propagated from the right and the information R propagated from the left are used to complete the information update of each processing unit. The formula is as follows: Among them, m represents the number of factor graph stages, i represents the number of factor graph layers, j represents the number of factor graph nodes, and t represents the decoding position; Until the calculation of L values ​​of all leftmost nodes is completed, the decoding decision is made according to the following formula: Wherein, T represents the maximum number of code words.

9. A QKD post-processing method based on BP decoding according to claim 7, characterized in that: In step S31, a Gaussian approximation construction algorithm is used to generate codeword structures under different signal-to-noise ratio conditions.

10. A QKD post-processing method based on BP decoding according to claim 7, characterized in that: In step S32, individuals remaining for inheritance are selected according to the truncation selection method.

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