コード例 #1
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;

            SecP224R1FieldElement X1 = (SecP224R1FieldElement)this.RawXCoord, Y1 = (SecP224R1FieldElement)this.RawYCoord;
            SecP224R1FieldElement X2 = (SecP224R1FieldElement)b.RawXCoord, Y2 = (SecP224R1FieldElement)b.RawYCoord;

            SecP224R1FieldElement Z1 = (SecP224R1FieldElement)this.RawZCoords[0];
            SecP224R1FieldElement Z2 = (SecP224R1FieldElement)b.RawZCoords[0];

            uint c;

            uint[] tt1 = Nat224.CreateExt();
            uint[] t2  = Nat224.Create();
            uint[] t3  = Nat224.Create();
            uint[] t4  = Nat224.Create();

            bool Z1IsOne = Z1.IsOne;

            uint[] U2, S2;
            if (Z1IsOne)
            {
                U2 = X2.x;
                S2 = Y2.x;
            }
            else
            {
                S2 = t3;
                SecP224R1Field.Square(Z1.x, S2);

                U2 = t2;
                SecP224R1Field.Multiply(S2, X2.x, U2);

                SecP224R1Field.Multiply(S2, Z1.x, S2);
                SecP224R1Field.Multiply(S2, Y2.x, S2);
            }

            bool Z2IsOne = Z2.IsOne;

            uint[] U1, S1;
            if (Z2IsOne)
            {
                U1 = X1.x;
                S1 = Y1.x;
            }
            else
            {
                S1 = t4;
                SecP224R1Field.Square(Z2.x, S1);

                U1 = tt1;
                SecP224R1Field.Multiply(S1, X1.x, U1);

                SecP224R1Field.Multiply(S1, Z2.x, S1);
                SecP224R1Field.Multiply(S1, Y1.x, S1);
            }

            uint[] H = Nat224.Create();
            SecP224R1Field.Subtract(U1, U2, H);

            uint[] R = t2;
            SecP224R1Field.Subtract(S1, S2, R);

            // Check if b == this or b == -this
            if (Nat224.IsZero(H))
            {
                if (Nat224.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 = t3;
            SecP224R1Field.Square(H, HSquared);

            uint[] G = Nat224.Create();
            SecP224R1Field.Multiply(HSquared, H, G);

            uint[] V = t3;
            SecP224R1Field.Multiply(HSquared, U1, V);

            SecP224R1Field.Negate(G, G);
            Nat224.Mul(S1, G, tt1);

            c = Nat224.AddBothTo(V, V, G);
            SecP224R1Field.Reduce32(c, G);

            SecP224R1FieldElement X3 = new SecP224R1FieldElement(t4);

            SecP224R1Field.Square(R, X3.x);
            SecP224R1Field.Subtract(X3.x, G, X3.x);

            SecP224R1FieldElement Y3 = new SecP224R1FieldElement(G);

            SecP224R1Field.Subtract(V, X3.x, Y3.x);
            SecP224R1Field.MultiplyAddToExt(Y3.x, R, tt1);
            SecP224R1Field.Reduce(tt1, Y3.x);

            SecP224R1FieldElement Z3 = new SecP224R1FieldElement(H);

            if (!Z1IsOne)
            {
                SecP224R1Field.Multiply(Z3.x, Z1.x, Z3.x);
            }
            if (!Z2IsOne)
            {
                SecP224R1Field.Multiply(Z3.x, Z2.x, Z3.x);
            }

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

            return(new SecP224R1Point(curve, X3, Y3, zs, IsCompressed));
        }