Patent ID: 7587654

Claim:
A quantum key distributing method of correcting an error of reception data with probability information obtained as a result of measurement of a photon on a quantum communication path to estimate original transmission data and using a result of the estimation as shared information, the quantum key distributing method comprising: first error-correction-information notifying including a transmission-side communication apparatus notifying a reception-side communication apparatus of said first error correction information generated based on a second parity check matrix and the transmission data, via a public communication path, the second parity check matrix, which is identical in both of the communication apparatuses, corresponding to a specific coding rate within a desired range, and being extracted from a first parity check matrix that is identical in both of the communication apparatuses, and is optimized at a coding rate in the desired range; first error correcting including the reception-side communication apparatus correcting an error of the reception data based on the first error correction information; second error-correction-information notifying including the transmission-side communication apparatus notifying the reception-side communication apparatus of additional second error correction information generated based on a third parity check matrix and the transmission data, via the public communication path, the third parity check matrix, which is identical in both of the communication apparatuses, corresponding to a coding rate lower than a last coding rate, and being extracted, when the error of the reception data is not completely corrected, from the first parity check matrix such that last error correction information becomes a part of information at a time of next error correction; second error correcting including the reception-side communication apparatus correcting the error of the reception data based on the first error correction information and the second error correction information; and encryption-key generating including, when the error of the reception data is completely corrected at the first error correcting or when the error is completely corrected by repeatedly executing the second check-matrix generating, the second error-correction-information notifying, and the second error correcting, discarding a part of shared information according to an amount of opened error correction information; and setting a result of the discarding as an encryption key.