source 2007 Hisil--Carter--Dawson compute A = X1^2 compute B = Y1(X1+Y1) compute C = A + B compute D = Z1(Z1+X1) compute E = A + D compute F = C(X1-Y1) compute G = E(Z1-X1) compute Z3 = F Z1 compute Y3 = -(F+G)X1 compute X3 = G Y1