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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.jcajce.provider.asymmetric.util;

import java.math.BigInteger;
import java.security.spec.ECField;
import java.security.spec.ECFieldF2m;
import java.security.spec.ECFieldFp;
import java.security.spec.ECParameterSpec;
import java.security.spec.ECPoint;
import java.security.spec.EllipticCurve;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;

import org.spongycastle.asn1.x9.ECNamedCurveTable;
import org.spongycastle.asn1.x9.X9ECParameters;
import org.spongycastle.crypto.ec.CustomNamedCurves;
import org.spongycastle.jce.spec.ECNamedCurveParameterSpec;
import org.spongycastle.jce.spec.ECNamedCurveSpec;
import org.spongycastle.math.ec.ECAlgorithms;
import org.spongycastle.math.ec.ECCurve;

public class EC5Util
{
    private static Map customCurves = new HashMap();

    static
    {
        Enumeration e = CustomNamedCurves.getNames();
        while (e.hasMoreElements())
        {
            String name = (String)e.nextElement();

            X9ECParameters curveParams = ECNamedCurveTable.getByName(name);
            if (curveParams != null)  // there may not be a regular curve, may just be a custom curve.
            {
                customCurves.put(curveParams.getCurve(), CustomNamedCurves.getByName(name).getCurve());
            }
        }
    }

    public static EllipticCurve convertCurve(
        ECCurve curve, 
        byte[]  seed)
    {
        // TODO: the Sun EC implementation doesn't currently handle the seed properly
        // so at the moment it's set to null. Should probably look at making this configurable
        if (ECAlgorithms.isFpCurve(curve))
        {
            return new EllipticCurve(new ECFieldFp(curve.getField().getCharacteristic()), curve.getA().toBigInteger(), curve.getB().toBigInteger(), null);
        }
        else
        {
            ECCurve.F2m curveF2m = (ECCurve.F2m)curve;
            int ks[];
            
            if (curveF2m.isTrinomial())
            {
                ks = new int[] { curveF2m.getK1() };
                
                return new EllipticCurve(new ECFieldF2m(curveF2m.getM(), ks), curve.getA().toBigInteger(), curve.getB().toBigInteger(), null);
            }
            else
            {
                ks = new int[] { curveF2m.getK3(), curveF2m.getK2(), curveF2m.getK1() };
                
                return new EllipticCurve(new ECFieldF2m(curveF2m.getM(), ks), curve.getA().toBigInteger(), curve.getB().toBigInteger(), null);
            } 
        }
    }

    public static ECCurve convertCurve(
        EllipticCurve ec)
    {
        ECField field = ec.getField();
        BigInteger a = ec.getA();
        BigInteger b = ec.getB();

        if (field instanceof ECFieldFp)
        {
            ECCurve.Fp curve = new ECCurve.Fp(((ECFieldFp)field).getP(), a, b);

            if (customCurves.containsKey(curve))
            {
                return (ECCurve)customCurves.get(curve);
            }

            return curve;
        }
        else
        {
            ECFieldF2m fieldF2m = (ECFieldF2m)field;
            int m = fieldF2m.getM();
            int ks[] = ECUtil.convertMidTerms(fieldF2m.getMidTermsOfReductionPolynomial());
            return new ECCurve.F2m(m, ks[0], ks[1], ks[2], a, b); 
        }
    }

    public static ECParameterSpec convertSpec(
        EllipticCurve ellipticCurve,
        org.spongycastle.jce.spec.ECParameterSpec spec)
    {
        if (spec instanceof ECNamedCurveParameterSpec)
        {
            return new ECNamedCurveSpec(
                ((ECNamedCurveParameterSpec)spec).getName(),
                ellipticCurve,
                new ECPoint(
                    spec.getG().getAffineXCoord().toBigInteger(),
                    spec.getG().getAffineYCoord().toBigInteger()),
                spec.getN(),
                spec.getH());
        }
        else
        {
            return new ECParameterSpec(
                ellipticCurve,
                new ECPoint(
                    spec.getG().getAffineXCoord().toBigInteger(),
                    spec.getG().getAffineYCoord().toBigInteger()),
                spec.getN(),
                spec.getH().intValue());
        }
    }

    public static org.spongycastle.jce.spec.ECParameterSpec convertSpec(
        ECParameterSpec ecSpec,
        boolean withCompression)
    {
        ECCurve curve = convertCurve(ecSpec.getCurve());

        return new org.spongycastle.jce.spec.ECParameterSpec(
            curve,
            convertPoint(curve, ecSpec.getGenerator(), withCompression),
            ecSpec.getOrder(),
            BigInteger.valueOf(ecSpec.getCofactor()),
            ecSpec.getCurve().getSeed());
    }

    public static org.spongycastle.math.ec.ECPoint convertPoint(
        ECParameterSpec ecSpec,
        ECPoint point,
        boolean withCompression)
    {
        return convertPoint(convertCurve(ecSpec.getCurve()), point, withCompression);
    }

    public static org.spongycastle.math.ec.ECPoint convertPoint(
        ECCurve curve,
        ECPoint point,
        boolean withCompression)
    {
        return curve.createPoint(point.getAffineX(), point.getAffineY(), withCompression);
    }
}