Particularly, when p is a prime number not less than 5, the elliptic curve E over the prime field GF(p) is a set obtained by adding a point ??? called the point at infinity to a set of points (x, y) satisfying the following equation: E:Y???2=x???3+a???x+b Incidentally, the point at infinity ??? is also referred to as 0. a, b, x and y are elements of GF(p).