コード例 #1
0
  public ECFieldElement getYCoord() {
    ECFieldElement X = x, L = y;

    if (this.isInfinity() || X.isZero()) {
      return L;
    }

    // Y is actually Lambda (X + Y/X) here; convert to affine value on the fly
    ECFieldElement Y = L.add(X).multiply(X);

    ECFieldElement Z = zs[0];
    if (!Z.isOne()) {
      Y = Y.divide(Z);
    }

    return Y;
  }
コード例 #2
0
  public ECPoint add(ECPoint b) {
    if (this.isInfinity()) {
      return b;
    }
    if (b.isInfinity()) {
      return this;
    }

    ECCurve curve = this.getCurve();

    ECFieldElement X1 = this.x;
    ECFieldElement X2 = b.getRawXCoord();

    if (X1.isZero()) {
      if (X2.isZero()) {
        return curve.getInfinity();
      }

      return b.add(this);
    }

    ECFieldElement L1 = this.y, Z1 = this.zs[0];
    ECFieldElement L2 = b.getRawYCoord(), Z2 = b.getZCoord(0);

    boolean Z1IsOne = Z1.isOne();
    ECFieldElement U2 = X2, S2 = L2;
    if (!Z1IsOne) {
      U2 = U2.multiply(Z1);
      S2 = S2.multiply(Z1);
    }

    boolean Z2IsOne = Z2.isOne();
    ECFieldElement U1 = X1, S1 = L1;
    if (!Z2IsOne) {
      U1 = U1.multiply(Z2);
      S1 = S1.multiply(Z2);
    }

    ECFieldElement A = S1.add(S2);
    ECFieldElement B = U1.add(U2);

    if (B.isZero()) {
      if (A.isZero()) {
        return twice();
      }

      return curve.getInfinity();
    }

    ECFieldElement X3, L3, Z3;
    if (X2.isZero()) {
      // TODO This can probably be optimized quite a bit
      ECPoint p = this.normalize();
      X1 = p.getXCoord();
      ECFieldElement Y1 = p.getYCoord();

      ECFieldElement Y2 = L2;
      ECFieldElement L = Y1.add(Y2).divide(X1);

      //            X3 = L.square().add(L).add(X1).add(curve.getA());
      X3 = L.square().add(L).add(X1);
      if (X3.isZero()) {
        //                return new SecT283K1Point(curve, X3, curve.getB().sqrt(),
        // this.withCompression);
        return new SecT283K1Point(curve, X3, curve.getB(), this.withCompression);
      }

      ECFieldElement Y3 = L.multiply(X1.add(X3)).add(X3).add(Y1);
      L3 = Y3.divide(X3).add(X3);
      Z3 = curve.fromBigInteger(ECConstants.ONE);
    } else {
      B = B.square();

      ECFieldElement AU1 = A.multiply(U1);
      ECFieldElement AU2 = A.multiply(U2);

      X3 = AU1.multiply(AU2);
      if (X3.isZero()) {
        //                return new SecT283K1Point(curve, X3, curve.getB().sqrt(),
        // this.withCompression);
        return new SecT283K1Point(curve, X3, curve.getB(), this.withCompression);
      }

      ECFieldElement ABZ2 = A.multiply(B);
      if (!Z2IsOne) {
        ABZ2 = ABZ2.multiply(Z2);
      }

      L3 = AU2.add(B).squarePlusProduct(ABZ2, L1.add(Z1));

      Z3 = ABZ2;
      if (!Z1IsOne) {
        Z3 = Z3.multiply(Z1);
      }
    }

    return new SecT283K1Point(curve, X3, L3, new ECFieldElement[] {Z3}, this.withCompression);
  }