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package org.spongycastle.math.ec;
import java.math.BigInteger;
/**
* Class implementing the NAF (Non-Adjacent Form) multiplication algorithm (right-to-left) using
* mixed coordinates.
*/
public class MixedNafR2LMultiplier extends AbstractECMultiplier
{
protected int additionCoord, doublingCoord;
/**
* By default, addition will be done in Jacobian coordinates, and doubling will be done in
* Modified Jacobian coordinates (independent of the original coordinate system of each point).
*/
public MixedNafR2LMultiplier()
{
this(ECCurve.COORD_JACOBIAN, ECCurve.COORD_JACOBIAN_MODIFIED);
}
public MixedNafR2LMultiplier(int additionCoord, int doublingCoord)
{
this.additionCoord = additionCoord;
this.doublingCoord = doublingCoord;
}
protected ECPoint multiplyPositive(ECPoint p, BigInteger k)
{
ECCurve curveOrig = p.getCurve();
ECCurve curveAdd = configureCurve(curveOrig, additionCoord);
ECCurve curveDouble = configureCurve(curveOrig, doublingCoord);
int[] naf = WNafUtil.generateCompactNaf(k);
ECPoint Ra = curveAdd.getInfinity();
ECPoint Td = curveDouble.importPoint(p);
int zeroes = 0;
for (int i = 0; i < naf.length; ++i)
{
int ni = naf[i];
int digit = ni >> 16;
zeroes += ni & 0xFFFF;
Td = Td.timesPow2(zeroes);
ECPoint Tj = curveAdd.importPoint(Td);
if (digit < 0)
{
Tj = Tj.negate();
}
Ra = Ra.add(Tj);
zeroes = 1;
}
return curveOrig.importPoint(Ra);
}
protected ECCurve configureCurve(ECCurve c, int coord)
{
if (c.getCoordinateSystem() == coord)
{
return c;
}
if (!c.supportsCoordinateSystem(coord))
{
throw new IllegalArgumentException("Coordinate system " + coord + " not supported by this curve");
}
return c.configure().setCoordinateSystem(coord).create();
}
}
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