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

Introduction

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

Prototype

public abstract ECFieldElement square();

Source Link

Usage

From source file:org.ScripterRon.BitcoinCore.ECKey.java

License:Apache License

/**
 * Decompress a compressed public key (x coordinate and low-bit of y-coordinate).
 *
 * @param       xBN                 X-coordinate
 * @param       yBit                Sign of Y-coordinate
 * @return                          Uncompressed public key
 *//*from   w w  w.j  av  a2  s  .  c  o m*/
private static ECPoint decompressKey(BigInteger xBN, boolean yBit) {
    SecP256K1Curve curve = (SecP256K1Curve) ecParams.getCurve();
    ECFieldElement x = curve.fromBigInteger(xBN);
    ECFieldElement alpha = x.multiply(x.square().add(curve.getA())).add(curve.getB());
    ECFieldElement beta = alpha.sqrt();
    if (beta == null)
        throw new IllegalArgumentException("Invalid point compression");
    ECPoint ecPoint;
    BigInteger nBeta = beta.toBigInteger();
    if (nBeta.testBit(0) == yBit) {
        ecPoint = curve.createPoint(x.toBigInteger(), nBeta);
    } else {
        ECFieldElement y = curve.fromBigInteger(curve.getQ().subtract(nBeta));
        ecPoint = curve.createPoint(x.toBigInteger(), y.toBigInteger());
    }
    return ecPoint;
}

---