Patent ID: 8239680

Claim:
A secret communication method for efficiently communicating information between a device at a sender side and a device at a receiver side, each at remote locations, using correlated initial random numbers X and Y respectively held at the sender and the receiver sides, the method comprising: (a) estimating an error ratio between the initial random numbers X and Y, stored in initial random number storage units of the devices at the sender and the receiver sides under the situation that the information can be leaked to the third party, the estimating performed by an error estimation unit provided in the device at the sender side or the device at the receiver side; (b) estimating an upper limit of an eavesdropped information amount by an eavesdropped information amount estimation unit provided in the device at the sender side or the device at the receiver side; (c) step of determining, at the device of the sender side, an error correction code based on the estimated value of the error ratio, an encryption function corresponding to the error correction code by an encryption function determination unit, and determining at the device at the receiver side, an error correction decoding function g, and a decryption auxiliary variable by an error correction code decoding function determination unit, respectively; (d) uniquely determining a confidentiality increase matrix C based on the estimated upper limit value of the eavesdropped information amount and an encoding ratio of the error correction code, by confidentiality increase matrix generation units provided in the devices at the sender and the receiver sides; (e) uniquely generating a ciphertext Z from transmission information M to be sent to the device at the receiver side using the encryption function, the initial random number X, and the confidentiality increase matrix C by an encryption unit provided in the device at the sender side; (f) transmitting the ciphertext Z from a transmission unit at the device at the sender side to a reception unit at the device at the receiver side via a public communication path; and (g) decrypting the ciphertext Z to a transmission text M B using the initial random number Y, the confidentiality increase matrix C, the decryption auxiliary variable, and the error correction decoding function by an encryption decoding unit and an error correction decoding unit provided in the device at the receiver side.