Example usage for org.bouncycastle.math.ec ECCurve fromBigInteger

Introduction

In this page you can find the example usage for org.bouncycastle.math.ec ECCurve fromBigInteger.

Prototype

public abstract ECFieldElement fromBigInteger(BigInteger x);

Source Link

Usage

From source file:com.github.horrorho.inflatabledonkey.crypto.ec.ECPointsCompact.java

License:Open Source License

public static BigInteger y(ECCurve curve, BigInteger x) {
    // Andrey Jivsov https://www.ietf.org/archive/id/draft-jivsov-ecc-compact-05.txt.
    ECFieldElement X = curve.fromBigInteger(x);
    ECFieldElement rhs = X.square().add(curve.getA()).multiply(X).add(curve.getB());

    // y' = sqrt( C(x) ), where y'>0
    ECFieldElement yTilde = rhs.sqrt();//from ww w .  j a va 2s  .com

    if (yTilde == null) {
        throw new IllegalArgumentException("invalid point compression");
    }

    // y = min(y',p-y')
    BigInteger yT = yTilde.toBigInteger();
    BigInteger yTn = yTilde.negate().toBigInteger();
    BigInteger y = yT.compareTo(yTn) == -1 ? yT : yTn;

    return y;
}

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From source file:com.github.horrorho.inflatabledonkey.crypto.ec.ECPointsCompact.java

License:Open Source License

@Deprecated
public static ECPoint decompressFPPoint(ECCurve curve, BigInteger X) {
    // See Andrey Jivsov https://www.ietf.org/archive/id/draft-jivsov-ecc-compact-05.txt.
    ECFieldElement x = curve.fromBigInteger(X);
    ECFieldElement rhs = x.square().add(curve.getA()).multiply(x).add(curve.getB());

    // y' = sqrt( C(x) ), where y'>0
    ECFieldElement yTilde = rhs.sqrt();//from  ww w . java 2  s  .  c  om

    if (yTilde == null) {
        throw new IllegalArgumentException("invalid point compression");
    }

    // y = min(y',p-y')
    BigInteger yT = yTilde.toBigInteger();
    BigInteger yTn = yTilde.negate().toBigInteger();
    BigInteger y = yT.compareTo(yTn) == -1 ? yT : yTn;

    // Q=(x,y) is the canonical representation of the point
    ECPoint Q = curve.createPoint(X, y);

    return Q;
}

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From source file:org.jmrtd.Util.java

License:Open Source License

/**
 * This just solves the curve equation for y.
 *
 * @param affineX the x coord of a point on the curve
 * @param params EC parameters for curve over Fp
 * @return the corresponding y coord//from  w  w w . j  a v a2s .co m
 */
public static BigInteger computeAffineY(BigInteger affineX, ECParameterSpec params) {
    ECCurve bcCurve = toBouncyCastleECCurve(params);
    ECFieldElement a = bcCurve.getA();
    ECFieldElement b = bcCurve.getB();
    ECFieldElement x = bcCurve.fromBigInteger(affineX);
    ECFieldElement y = x.multiply(x).add(a).multiply(x).add(b).sqrt();
    return y.toBigInteger();
}

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From source file:service.ACService.java

License:Open Source License

private static ECPoint reconstructPoint(ECCurve c, BigInteger i, boolean negate) {
    ECFieldElement x = c.fromBigInteger(i);
    ECFieldElement y = x.multiply(x).multiply(x).add(c.getA().multiply(x)).add(c.getB()).sqrt();
    if (negate) {
        return c.createPoint(x.toBigInteger(), y.toBigInteger().negate(), false);
    } else {//from   www . j a v  a  2s .  c om
        return c.createPoint(x.toBigInteger(), y.toBigInteger(), false);
    }
}

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