예제 #1
0
        protected virtual Curve25519Point TwiceJacobianModified(bool calculateW)
        {
            Curve25519FieldElement X1 = (Curve25519FieldElement)this.RawXCoord, Y1 = (Curve25519FieldElement)this.RawYCoord,
                                   Z1 = (Curve25519FieldElement)this.RawZCoords[0], W1 = GetJacobianModifiedW();

            uint c;

            uint[] M    = Nat256.Create();
            Curve25519Field.Square(X1.x, M);
            c  = Nat256.AddBothTo(M, M, M);
            c += Nat256.AddTo(W1.x, M);
            Curve25519Field.Reduce27(c, M);

            uint[] _2Y1 = Nat256.Create();
            Curve25519Field.Twice(Y1.x, _2Y1);

            uint[] _2Y1Squared = Nat256.Create();
            Curve25519Field.Multiply(_2Y1, Y1.x, _2Y1Squared);

            uint[] S    = Nat256.Create();
            Curve25519Field.Multiply(_2Y1Squared, X1.x, S);
            Curve25519Field.Twice(S, S);

            uint[] _8T = Nat256.Create();
            Curve25519Field.Square(_2Y1Squared, _8T);
            Curve25519Field.Twice(_8T, _8T);

            Curve25519FieldElement X3 = new Curve25519FieldElement(_2Y1Squared);

            Curve25519Field.Square(M, X3.x);
            Curve25519Field.Subtract(X3.x, S, X3.x);
            Curve25519Field.Subtract(X3.x, S, X3.x);

            Curve25519FieldElement Y3 = new Curve25519FieldElement(S);

            Curve25519Field.Subtract(S, X3.x, Y3.x);
            Curve25519Field.Multiply(Y3.x, M, Y3.x);
            Curve25519Field.Subtract(Y3.x, _8T, Y3.x);

            Curve25519FieldElement Z3 = new Curve25519FieldElement(_2Y1);

            if (!Nat256.IsOne(Z1.x))
            {
                Curve25519Field.Multiply(Z3.x, Z1.x, Z3.x);
            }

            Curve25519FieldElement W3 = null;

            if (calculateW)
            {
                W3 = new Curve25519FieldElement(_8T);
                Curve25519Field.Multiply(W3.x, W1.x, W3.x);
                Curve25519Field.Twice(W3.x, W3.x);
            }

            return(new Curve25519Point(this.Curve, X3, Y3, new ECFieldElement[] { Z3, W3 }, IsCompressed));
        }
예제 #2
0
        public override ECPoint Add(ECPoint b)
        {
            if (this.IsInfinity)
            {
                return(b);
            }
            if (b.IsInfinity)
            {
                return(this);
            }
            if (this == b)
            {
                return(Twice());
            }

            ECCurve curve = this.Curve;

            Curve25519FieldElement X1 = (Curve25519FieldElement)this.RawXCoord, Y1 = (Curve25519FieldElement)this.RawYCoord,
                                   Z1 = (Curve25519FieldElement)this.RawZCoords[0];
            Curve25519FieldElement X2 = (Curve25519FieldElement)b.RawXCoord, Y2 = (Curve25519FieldElement)b.RawYCoord,
                                   Z2 = (Curve25519FieldElement)b.RawZCoords[0];

            uint c;

            uint[] tt1 = Nat256.CreateExt();
            uint[] t2  = Nat256.Create();
            uint[] t3  = Nat256.Create();
            uint[] t4  = Nat256.Create();

            bool Z1IsOne = Z1.IsOne;

            uint[] U2, S2;
            if (Z1IsOne)
            {
                U2 = X2.x;
                S2 = Y2.x;
            }
            else
            {
                S2 = t3;
                Curve25519Field.Square(Z1.x, S2);

                U2 = t2;
                Curve25519Field.Multiply(S2, X2.x, U2);

                Curve25519Field.Multiply(S2, Z1.x, S2);
                Curve25519Field.Multiply(S2, Y2.x, S2);
            }

            bool Z2IsOne = Z2.IsOne;

            uint[] U1, S1;
            if (Z2IsOne)
            {
                U1 = X1.x;
                S1 = Y1.x;
            }
            else
            {
                S1 = t4;
                Curve25519Field.Square(Z2.x, S1);

                U1 = tt1;
                Curve25519Field.Multiply(S1, X1.x, U1);

                Curve25519Field.Multiply(S1, Z2.x, S1);
                Curve25519Field.Multiply(S1, Y1.x, S1);
            }

            uint[] H = Nat256.Create();
            Curve25519Field.Subtract(U1, U2, H);

            uint[] R = t2;
            Curve25519Field.Subtract(S1, S2, R);

            // Check if b == this or b == -this
            if (Nat256.IsZero(H))
            {
                if (Nat256.IsZero(R))
                {
                    // this == b, i.e. this must be doubled
                    return(this.Twice());
                }

                // this == -b, i.e. the result is the point at infinity
                return(curve.Infinity);
            }

            uint[] HSquared = Nat256.Create();
            Curve25519Field.Square(H, HSquared);

            uint[] G = Nat256.Create();
            Curve25519Field.Multiply(HSquared, H, G);

            uint[] V = t3;
            Curve25519Field.Multiply(HSquared, U1, V);

            Curve25519Field.Negate(G, G);
            Nat256.Mul(S1, G, tt1);

            c = Nat256.AddBothTo(V, V, G);
            Curve25519Field.Reduce27(c, G);

            Curve25519FieldElement X3 = new Curve25519FieldElement(t4);

            Curve25519Field.Square(R, X3.x);
            Curve25519Field.Subtract(X3.x, G, X3.x);

            Curve25519FieldElement Y3 = new Curve25519FieldElement(G);

            Curve25519Field.Subtract(V, X3.x, Y3.x);
            Curve25519Field.MultiplyAddToExt(Y3.x, R, tt1);
            Curve25519Field.Reduce(tt1, Y3.x);

            Curve25519FieldElement Z3 = new Curve25519FieldElement(H);

            if (!Z1IsOne)
            {
                Curve25519Field.Multiply(Z3.x, Z1.x, Z3.x);
            }
            if (!Z2IsOne)
            {
                Curve25519Field.Multiply(Z3.x, Z2.x, Z3.x);
            }

            uint[] Z3Squared = (Z1IsOne && Z2IsOne) ? HSquared : null;

            // TODO If the result will only be used in a subsequent addition, we don't need W3
            Curve25519FieldElement W3 = CalculateJacobianModifiedW((Curve25519FieldElement)Z3, Z3Squared);

            ECFieldElement[] zs = new ECFieldElement[] { Z3, W3 };

            return(new Curve25519Point(curve, X3, Y3, zs, IsCompressed));
        }