Example usage for org.bouncycastle.math.ec ECFieldElement negate

Introduction

In this page you can find the example usage for org.bouncycastle.math.ec ECFieldElement negate.

Prototype

public abstract ECFieldElement negate();

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();

    if (yTilde == null) {
        throw new IllegalArgumentException("invalid point compression");
    }//from   w w w.  j a v  a 2  s. c  om

    // 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();

    if (yTilde == null) {
        throw new IllegalArgumentException("invalid point compression");
    }//from   w ww .ja va2s  .co m

    // 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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