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Spongy Castle is a package-rename (org.bouncycastle.* to org.spongycastle.*) of Bouncy Castle intended for the Android platform. Android unfortunately ships with a stripped-down version of Bouncy Castle, which prevents easy upgrades - Spongy Castle overcomes this and provides a full, up-to-date version of the Bouncy Castle cryptographic libs.

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package org.spongycastle.math.ec;

import java.math.BigInteger;

public abstract class AbstractECMultiplier implements ECMultiplier
{
    public ECPoint multiply(ECPoint p, BigInteger k)
    {
        int sign = k.signum();
        if (sign == 0 || p.isInfinity())
        {
            return p.getCurve().getInfinity();
        }

        ECPoint positive = multiplyPositive(p, k.abs());
        ECPoint result = sign > 0 ? positive : positive.negate();

        /*
         * Although the various multipliers ought not to produce invalid output under normal
         * circumstances, a final check here is advised to guard against fault attacks.
         */
        return ECAlgorithms.validatePoint(result);
    }

    protected abstract ECPoint multiplyPositive(ECPoint p, BigInteger k);
}