US Patent 7434898 Computer system, computer program, and addition method

A computer system that makes it difficult to analyze the content of a calculation. In the computer system, a power operation unit performs the following operations using the input data “a” and “b”: ga=ga mod n, gb=gb mod n. Next, in the computer system, a multiplication unit performs the following calculation using ga and gb: gab=ga×gb mod n. Next, in the computer system, a discrete logarithm calculation unit calculates ci mod pi−1 to satisfy gab=gci mod pi (i=1, 2, 3, . . . , k). Next, in the computer system, a CRT unit calculates “c” to satisfy ci=c mod pi−1 (i=1, 2, 3, . . . , k) using the Chinese remainder theorem CRT.