Patent ID: 7639808

Claim:
An elliptic curve cryptosystem apparatus performing an elliptic curve cryptosystem process comprising: a coordinate transforming unit for transforming coordinates (X:Y:Z) of a point P on an elliptic curve over a finite field GF(p^m) to coordinates (r 1 )×(X−s 1 ):r 2 ×(Y−s 2 ):r 3 ×(Z−s 3 )) (where p is a prime number, m is an integer not less than 1, r 1 , r 2 and r 3 are integers not less than 1 and not larger than (p−1), s 1 , s 2 and s 3 are integers not less than 0 and not larger than (p−1), and a code “^” represents power); and a scalar multiplication operating unit for performing scalar multiplication on the point on the elliptic curve transformed by said coordinate transforming unit; at least any one of the parameters s 1 , s 2 and s 3 having a value other than 0.