source 2007(?) Kim--Kim "A New Method for Speeding Up Arithmetic on Elliptic Curves over Binary Fields" compute A = X1^2 compute B = Y1^2 compute Z3 = ZZ1 A compute ZZ3 = Z3^2 compute X3 = A^2 + a6 ZZ1^2 compute Y3 = B (B + X3 + Z3) + a6 ZZ3 + ZZ3