ref: a065270fd74fff6a19dc5178d8829d3122226225
dir: /sys/src/libauthsrv/edwards.mp/
# Edwards curve arithmetic edwards_add(p,a,d, X1,Y1,Z1,T1, X2,Y2,Z2,T2, X3,Y3,Z3,T3) mod(p) { A = X1*X2; B = Y1*Y2; C = d*T1*T2; D = Z1*Z2; E = (X1+Y1)*(X2+Y2); E = E - A - B; F = D - C; G = D + C; H = B - a*A; X3 = E*F; Y3 = G*H; Z3 = F*G; T3 = E*H; } edwards_sel(s, X1,Y1,Z1,T1, X2,Y2,Z2,T2, X3,Y3,Z3,T3){ X3 = s != 0 ? X1 : X2; Y3 = s != 0 ? Y1 : Y2; Z3 = s != 0 ? Z1 : Z2; T3 = s != 0 ? T1 : T2; } edwards_new(x,y,z,t, X,Y,Z,T) { X = x; Y = y; Z = z; T = t; } edwards_scale(p,a,d, s, X1,Y1,Z1,T1, X3,Y3,Z3,T3) { X2,Y2,Z2,T2 = edwards_new(X1,Y1,Z1,T1); X4,Y4,Z4,T4 = edwards_new( 0, 1, 1, 0); X3,Y3,Z3,T3 = edwards_sel(s % 2, X2,Y2,Z2,T2, X4,Y4,Z4,T4); k = s >> 1; j = p >> 1; while(j != 0){ X2,Y2,Z2,T2 = edwards_add(p,a,d, X2,Y2,Z2,T2, X2,Y2,Z2,T2); X4,Y4,Z4,T4 = edwards_add(p,a,d, X2,Y2,Z2,T2, X3,Y3,Z3,T3); X3,Y3,Z3,T3 = edwards_sel(k % 2, X4,Y4,Z4,T4, X3,Y3,Z3,T3); k = k >> 1; j = j >> 1; } }