source 2002 Izu--Takagi "A fast parallel elliptic curve multiplication resistant against side channel attacks", formula (8) compute X5 = Z1 ((X2 X3 - a Z2 Z3)^2 - 4 b Z2 Z3(X2 Z3 + X3 Z2)) compute Z5 = X1 (X2 Z3 - X3 Z2)^2