org.bouncycastle.math.ec.endo.EndoUtil Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of bcprov-ext-debug-jdk18on Show documentation

The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for Java 1.8 and later with debug enabled.

The newest version!

package org.bouncycastle.math.ec.endo;

import java.math.BigInteger;

import org.bouncycastle.math.ec.ECConstants;
import org.bouncycastle.math.ec.ECCurve;
import org.bouncycastle.math.ec.ECPoint;
import org.bouncycastle.math.ec.PreCompCallback;
import org.bouncycastle.math.ec.PreCompInfo;

public abstract class EndoUtil
{
    public static final String PRECOMP_NAME = "bc_endo";

    public static BigInteger[] decomposeScalar(ScalarSplitParameters p, BigInteger k)
    {
        int bits = p.getBits();
        BigInteger b1 = calculateB(k, p.getG1(), bits);
        BigInteger b2 = calculateB(k, p.getG2(), bits);

        BigInteger a = k.subtract((b1.multiply(p.getV1A())).add(b2.multiply(p.getV2A())));
        BigInteger b = (b1.multiply(p.getV1B())).add(b2.multiply(p.getV2B())).negate();

        return new BigInteger[]{ a, b };
    }

    public static ECPoint mapPoint(final ECEndomorphism endomorphism, final ECPoint p)
    {
        final ECCurve c = p.getCurve();

        EndoPreCompInfo precomp = (EndoPreCompInfo)c.precompute(p, PRECOMP_NAME, new PreCompCallback()
        {
            public PreCompInfo precompute(PreCompInfo existing)
            {
                EndoPreCompInfo existingEndo = (existing instanceof EndoPreCompInfo) ? (EndoPreCompInfo)existing : null;

                if (checkExisting(existingEndo, endomorphism))
                {
                    return existingEndo;
                }

                ECPoint mappedPoint = endomorphism.getPointMap().map(p);

                EndoPreCompInfo result = new EndoPreCompInfo();
                result.setEndomorphism(endomorphism);
                result.setMappedPoint(mappedPoint);
                return result;
            }

            private boolean checkExisting(EndoPreCompInfo existingEndo, ECEndomorphism endomorphism)
            {
                return null != existingEndo
                    && existingEndo.getEndomorphism() == endomorphism
                    && existingEndo.getMappedPoint() != null;
            }
        });

        return precomp.getMappedPoint();
    }

    private static BigInteger calculateB(BigInteger k, BigInteger g, int t)
    {
        boolean negative = (g.signum() < 0);
        BigInteger b = k.multiply(g.abs());
        boolean extra = b.testBit(t - 1);
        b = b.shiftRight(t);
        if (extra)
        {
            b = b.add(ECConstants.ONE);
        }
        return negative ? b.negate() : b;
    }
}