| 摘要 |
PROBLEM TO BE SOLVED: To provide a cipher processing method in which, even when a cipher processing progress is leaked by power analysis, secret information is not leaked in itself and moreover a cipher processing can be executed at high speed in order to solve the problem that there is possibility that the secret information is restored from the cipher processing progress by an attacking method called as power analysis of a DPA (demand possibility area) or the like in the cipher processing in which secret information in an elliptic curve cipher is used. SOLUTION: This method is a cipher processing method in which the dependency relationship between the cipher processing progress and the secret information is cut off. Especially, the method is a scalar-fold calculating method in which a scalar multiplication calculating progress is not depended on the value of bits with respect to a scalar value being the secret information. That is, when the scalar value is to be calculated in the elliptic curve cipher and scalar multiplication points are to be calculated from points on an elliptic curve, the value of bits of the scalar value is judged and operations on the elliptic curve are executed fixed times and in a fixed order without depending on the value of bits which are judged.
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