Transmitting device, receiving device, quantum key distribution method, and quantum key distribution program for quantum key distribution system

1. A transmitting device for a quantum key distribution system, comprising:

an encoding unit configured to encode a train of optical pulses;

an intensity modulating unit configured to subject a train of encoded optical pulses to N types of intensity modulation having mutually different intensities, with different timings, where N is an integer which is not less than three; and

a first key distillation processing unit configured to generate an encryption key based on a data sequence obtained by removing data obtained from optical pulses having a specific modulation pattern from a data sequence used when the encoding unit and the intensity modulating unit carry out encoding and intensity modulation.

2. The transmitting device as claimed in claim 1 , wherein the first key distillation processing unit is configured to determine data to be removed among the train of optical pulses based on data obtained from a current optical pulse and data obtained from an M-th preceding or an M-th succeeding optical pulse preceding or succeeding the current optical pulse, where M is an integer which is not less than one.

3. The transmitting device as claimed in claim 1 , wherein the first key distillation processing unit includes a decoy pulse as the modulation pattern and is configured to dispose of data having large intensity fluctuation.

4. The transmitting device as claimed in claim 1 , wherein the first key distillation processing unit is configured to dispose of at least data having the largest intensity fluctuation due to a pattern effect.

5. The transmitting device as claimed in claim 1 ,

wherein the first key distillation processing unit comprises a first basis verification processing portion, a first pattern disposal processing portion, and a first encryption key generating portion,

wherein the first basis verification processing portion is configured to generate a first sifted key based on a basis which is given to the data sequence of the train of optical pulses,

wherein the first pattern disposal processing portion is configured to generate a second sifted key from the first sifted key based on a data sequence obtained by removing, from the data sequence of the train of optical pulses, data obtained from a train of optical pulses having the specific modulation pattern,

wherein the first encryption key generating portion is configured to generate the encryption key by calculating an error rate (QBER: Quantum Bit Error Rate) included in the second sifted key and by carrying out error correction and privacy amplification on the second sifted key based on the error rate.

6. A receiving device for a quantum key distribution system, comprising:

a decoding unit configured to receive, from a transmitting device, a train of optical pulses which has been encoded and subjected to N types of intensity modulation having mutually different intensities, with different timings, where N is an integer which is not less than three, the decoding unit producing a data sequence obtained by decoding the train of optical pulses; and

a second key distillation processing unit configured to generate an encryption key based on a data sequence obtained by removing data obtained from optical pulses having a specific modulation pattern from the data sequence obtained by the decoding.

7. The receiving device as claimed in claim 6 , wherein the second key distillation processing unit is configured to determine data to be removed among the train of optical pulses based on data obtained from a current optical pulse and data obtained from an M-th preceding or an M-th succeeding optical pulse preceding or succeeding the current optical pulse, where M is an integer which is not less than one.

8. The receiving device as claimed in claim 6 , wherein the second key distillation processing unit includes a decoy pulse as the modulation pattern and is configured to dispose of data having large intensity fluctuation.

9. The receiving device as claimed in claim 6 , wherein the second key distillation processing unit is configured to dispose of at least data having the largest intensity fluctuation due to a pattern effect.

10. The receiving device as claimed in claim 6 ,

wherein the second key distillation processing unit comprises a second basis verification processing portion, a second pattern disposal processing portion, and a second encryption key generating portion,

wherein the second basis verification processing portion is configured to generate a first sifted key by randomly selecting a basis which is given to the data sequence of the train of optical pulses,

wherein the second pattern disposal processing portion is configured to generate a second sifted key based on a data sequence obtained by removing, from the first sifted key, data obtained from a train of optical pulses having the specific modulation pattern,

wherein the second encryption key generating portion is configured to generate the encryption key by calculating an error rate (QBER: Quantum Bit Error Rate) included in the second sifted key and by carrying out error correction and privacy amplification on the second sifted key based on the error rate.

11. A quantum key distribution method comprising generating an encryption key based on a data sequence obtained by removing data obtained from optical pulses having a specific modulation pattern from a data sequence used when a train of optical pulses are subjected to encoding and N types of intensity modulation having mutually different intensities, where N is an integer which is not less than three.

12. The quantum key distribution method as claimed in claim 11 , comprising determining data to be removed among the train of optical pulses based on data obtained from a current optical pulse and data obtained from an M-th preceding or an M-th succeeding optical pulse preceding or succeeding the current optical pulse, where M is an integer which is not less than one.

13. The quantum key distribution method as claimed in claim 11 , comprising including a decoy pulse as the modulation pattern; and disposing of data having large intensity fluctuation.

14. The quantum key distribution method as claimed in claim 11 , comprising disposing of at least data having the largest intensity fluctuation due to a pattern effect.

15. The quantum key distribution method as claimed in claim 11 , comprising:

generating a first sifted key based on a basis which is given to the data sequence of the train of optical pulses;

generating a second sifted key from the first sifted key based on a data sequence obtained by removing, from the data sequence of the train of optical pulses, data obtained from a train of optical pulses having the specific modulation pattern; and

generating the encryption key by calculating an error rate (QBER: Quantum Bit Error Rate) included in the second sifted key and by carrying out error correction and privacy amplification on the second sifted key based on the error rate.

16. A quantum key distribution method comprising:

receiving, from a transmitting device, a train of optical pulses which has been encoded and subjected to N types of intensity modulation having mutually different intensities, with different timings, where N is an integer which is not less than three, to produce a data sequence obtained by decoding the train of optical pulses; and

generating an encryption key based on a data sequence obtained by removing data obtained from optical pulses having a specific modulation pattern from the data sequence obtained by the decoding.

17. The quantum key distribution method as claimed in claim 16 , comprising determining data to be removed among the train of optical pulses based on data obtained from a current optical pulse and data obtained from an M-th preceding or an M-th succeeding optical pulse preceding or succeeding the current optical pulse, where M is an integer which is not less than one.

18. The quantum key distribution method as claimed in claim 16 , comprising including a decoy pulse as the modulation pattern; and disposing of data having large intensity fluctuation.

19. The quantum key distribution method as claimed in claim 16 , comprising disposing of at least data having the largest intensity fluctuation due to a pattern effect.

20. The quantum key distribution method as claimed in claim 16 , comprising:

generating a first sifted key by randomly selecting a basis which is given to the data sequence of the train of optical pulses;

generating a second sifted key based on a data sequence obtained by removing, from the first sifted key, data obtained from a train of optical pulses having the specific modulation pattern; and

generating the encryption key by calculating an error rate (QBER: Quantum Bit Error Rate) included in the second sifted key and by carrying out error correction and privacy amplification on the second sifted key based on the error rate.

21. A non-transitory computer readable medium for storing a quantum key distribution program for making a computer function as:

means for generating an encryption key based on a data sequence obtained by removing data obtained from optical pulses having a specific modulation pattern from a data sequence used when a train of optical pulses are subjected to encoding and N types of intensity modulation having mutually different intensities, where N is an integer which is not less than three; and

means for determining data to be removed among the train of optical pulses based on data obtained from a current optical pulse and data obtained from an M-th preceding or an M-th succeeding optical pulse preceding or succeeding the current optical pulse, where M is an integer which is not less than one.

22. The non-transitory computer readable medium as claimed in claim 21 , the quantum key distribution program making the computer function as:

means for including a decoy pulse as the modulation pattern and disposing of data having large intensity fluctuation.

23. The non-transitory computer readable medium as claimed in claim 21 , the quantum key distribution program making the computer function as:

means for disposing of at least data having the largest intensity fluctuation due to a pattern effect.

24. The non-transitory computer readable medium as claimed in claim 21 , the quantum key distribution program making the computer function as:

means for generating a first sifted key based on a basis which is given to the data sequence of the train of optical pulses;

means for generating a second sifted key from the first sifted key based on a data sequence obtained by removing, from the data sequence of the train of optical pulses, data obtained from a train of optical pulses having the specific modulation pattern; and

means for generating the encryption key by calculating an error rate (QBER: Quantum Bit Error Rate) included in the second sifted key and by carrying out error correction and privacy amplification on the second sifted key based on the error rate.

25. A non-transitory computer readable medium for storing a quantum key distribution program for making a computer function as:

means for generating an encryption key based on a data sequence obtained by removing data obtained from optical pulses having a specific modulation pattern from a data sequence obtained by decoding a train of optical pulses which has been encoded and subjected to N types of intensity modulation having mutually different intensities, with different timings, where N is an integer which is not less than three; and

means for determining data to be removed among the train of optical pulses based on data obtained from a current optical pulse and data obtained from an M-th preceding or an M-th succeeding optical pulse preceding or succeeding the current optical pulse, where M is an integer which is not less than one.

26. The non-transitory computer readable medium as claimed in claim 25 , the quantum key distribution program making the computer function as:

means for including a decoy pulse as the modulation pattern and disposing of data having large intensity fluctuation.

27. The non-transitory computer readable medium as claimed in claim 25 , the quantum key distribution program making the computer function as:

means for disposing of at least data having the largest intensity fluctuation due to a pattern effect.

28. The non-transitory computer readable medium as claimed in claim 25 , the quantum key distribution program making the computer function as:

means for generating a first sifted key by randomly selecting a basis which is given to the data sequence of the train of optical pulses;

means for generating a second sifted key based on a data sequence obtained by removing, from the first sifted key, data obtained from a train of optical pulses having the specific modulation pattern; and

means for generating the encryption key by calculating an error rate (QBER: Quantum Bit Error Rate) included in the second sifted key and by carrying out error correction and privacy amplification on the second sifted key based on the error rate.

29. A quantum key distribution system comprising:

a transmitting device; and

a receiving device,

wherein the transmitting device comprises:

an encoding unit configured to encode a train of optical pulses;

an intensity modulating unit configured to subject a train of encoded optical pulses to N types of intensity modulation having mutually different intensities, with different timings, where N is an integer which is not less than three; and

a first key distillation processing unit configured to generate an encryption key based on a data sequence obtained by removing data obtained from optical pulses having a specific modulation pattern from a data sequence used when the encoding unit and the intensity modulating unit carry out encoding and intensity modulation,

wherein the receiving device comprises:

a decoding unit configured to receive, from a transmitting device, a train of optical pulses which has been encoded and subjected to N types of intensity modulation having mutually different intensities, with different timings, where N is an integer which is not less than three, the decoding unit producing a data sequence obtained by decoding the train of optical pulses; and

a second key distillation processing unit configured to generate an encryption key based on a data sequence obtained by removing data obtained from optical pulses having a specific modulation pattern from the data sequence obtained by the decoding.